CA1201366A - Centrifugally cast tube of spheroidal graphite cast- iron and its method of manufacture - Google Patents
Centrifugally cast tube of spheroidal graphite cast- iron and its method of manufactureInfo
- Publication number
- CA1201366A CA1201366A CA000422457A CA422457A CA1201366A CA 1201366 A CA1201366 A CA 1201366A CA 000422457 A CA000422457 A CA 000422457A CA 422457 A CA422457 A CA 422457A CA 1201366 A CA1201366 A CA 1201366A
- Authority
- CA
- Canada
- Prior art keywords
- iron
- tube
- cast
- mould
- chill
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000034 method Methods 0.000 title claims abstract description 21
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 10
- 229910001141 Ductile iron Inorganic materials 0.000 title claims description 17
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 21
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 14
- 238000005507 spraying Methods 0.000 claims abstract description 14
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 9
- 229910052742 iron Inorganic materials 0.000 claims abstract description 8
- 229910001018 Cast iron Inorganic materials 0.000 claims description 29
- 238000001816 cooling Methods 0.000 claims description 20
- 239000000203 mixture Substances 0.000 claims description 17
- 239000011248 coating agent Substances 0.000 claims description 15
- 238000000576 coating method Methods 0.000 claims description 15
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 10
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 8
- 229910052799 carbon Inorganic materials 0.000 claims description 7
- 229910052802 copper Inorganic materials 0.000 claims description 7
- 239000010949 copper Substances 0.000 claims description 7
- 229910052748 manganese Inorganic materials 0.000 claims description 7
- 239000011572 manganese Substances 0.000 claims description 7
- 229910052759 nickel Inorganic materials 0.000 claims description 7
- 229910052710 silicon Inorganic materials 0.000 claims description 6
- 239000010703 silicon Substances 0.000 claims description 6
- 239000005864 Sulphur Substances 0.000 claims description 5
- 229910052749 magnesium Inorganic materials 0.000 claims description 5
- 239000011777 magnesium Substances 0.000 claims description 5
- 229910052698 phosphorus Inorganic materials 0.000 claims description 5
- 239000011574 phosphorus Substances 0.000 claims description 5
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 4
- 239000000440 bentonite Substances 0.000 claims description 4
- 229910000278 bentonite Inorganic materials 0.000 claims description 4
- SVPXDRXYRYOSEX-UHFFFAOYSA-N bentoquatam Chemical compound O.O=[Si]=O.O=[Al]O[Al]=O SVPXDRXYRYOSEX-UHFFFAOYSA-N 0.000 claims description 4
- 239000000377 silicon dioxide Substances 0.000 claims description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 3
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 3
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 3
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 3
- 239000010439 graphite Substances 0.000 abstract description 6
- 229910002804 graphite Inorganic materials 0.000 abstract description 6
- 238000012423 maintenance Methods 0.000 abstract 1
- 238000007669 thermal treatment Methods 0.000 description 18
- 238000009750 centrifugal casting Methods 0.000 description 11
- 238000005266 casting Methods 0.000 description 10
- 239000007921 spray Substances 0.000 description 10
- 238000011282 treatment Methods 0.000 description 8
- 238000010438 heat treatment Methods 0.000 description 6
- 239000010451 perlite Substances 0.000 description 6
- 235000019362 perlite Nutrition 0.000 description 6
- 238000000137 annealing Methods 0.000 description 4
- 238000000605 extraction Methods 0.000 description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000005755 formation reaction Methods 0.000 description 3
- 238000001000 micrograph Methods 0.000 description 3
- 230000001105 regulatory effect Effects 0.000 description 3
- 229910000859 α-Fe Inorganic materials 0.000 description 3
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 2
- 238000005119 centrifugation Methods 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 239000011733 molybdenum Substances 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 241000370685 Arge Species 0.000 description 1
- 240000004160 Capsicum annuum Species 0.000 description 1
- 241000985694 Polypodiopsida Species 0.000 description 1
- 206010037660 Pyrexia Diseases 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 230000001174 ascending effect Effects 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 229910001563 bainite Inorganic materials 0.000 description 1
- 239000011083 cement mortar Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000008646 thermal stress Effects 0.000 description 1
- 238000011144 upstream manufacturing Methods 0.000 description 1
- 239000002966 varnish Substances 0.000 description 1
Landscapes
- Heat Treatment Of Articles (AREA)
Abstract
"Centrifugally cast tube of spheroidal graphite east-iron and its method of manufacture."
ABRIDGEMENT
The cast tube (T) is subjected internally in a chill-mould (1) to the uniform spraying of water from 1000°C
approximately to 350°C approximately. Then it is extracted from the chill-mould and in a furnace is sub-jected to isothermal bainitisation maintenance, after which it is cooled in the atmosphere to ambient tempera-ture. Without it being necessary to add expensive chilling elements, one thus obtains lightened tubes having very good mechanical properties and the ovalisa-tion of which remains acceptable.
Figure 2.
ABRIDGEMENT
The cast tube (T) is subjected internally in a chill-mould (1) to the uniform spraying of water from 1000°C
approximately to 350°C approximately. Then it is extracted from the chill-mould and in a furnace is sub-jected to isothermal bainitisation maintenance, after which it is cooled in the atmosphere to ambient tempera-ture. Without it being necessary to add expensive chilling elements, one thus obtains lightened tubes having very good mechanical properties and the ovalisa-tion of which remains acceptable.
Figure 2.
Description
3~ 3~i The present invention relates to the manufacture of tubes from spheroidal graphite cast-iron by centrifugal casting and more particularly to a thermal treatment following the centrifugal casting intended to gi~e the centrifuged tube a structure mi~ki n~ it lighter.
After centrifugal castin~ and thermal treatment, tubes - that is to say cylindrical pipes of constant thickness - made from spheroidal graphite cast-iron at present have a ferritic structure which has two ad~an-tages: on the one hand, this structure gives them goodmechanical characteristics (elastic resilience and ductility), on the other hand, this ferritic structure is easily obtained by thermal treatment after centrifugal casting, either in a chill-mould provided internally with a thick coating of a pulverulent mixture of silica and bentonite in suspension in water (a so called "wet-spray"
coating) or in a chill-mould without such a coating.
In the case of the presence of a "wet-spray"
coating on the chill-mould, the tube is extracted from itB
chill-mould and rapidl~ introduced into a furnace before it has cooled too much then is sub~ect to a thermal tr~at-ment kno~rn as "maint~;n;n~ ferritisation" at a temperature of the order of 750C, for a period of time of the order of 20 to 25 minutes, then it is left to cool naturally.
If there is no "wet-spray" coating on the chill-mould, 1he pipe is extracted from its casting mould and ,f~
is introduced rapidly into a furnace where it is subjected to ~raphitisation annealing at a temperature of the order of 950C for a period of time of the order o~ 20 to 25 minutes, then to maintaining ferritisation at a tempera-ture of the order of 750C for a period of time of theorder of 15 to 20 minutes.
The Applicant has tackled the problem of obt~in;ng economically cast-iron tubes produced by centrifugal casting, which are lighter than current tubes, without any appreciable loss of mechanical features.
The Applicant has sought to achieve this result by giving the tube of spheroidal graphite cast-iron a bainitic structure 7 instead of the customary ferritic struct~re, which bainitic structure has a tensile strength and characteristic of elongation as well as a characteristic of resilience equal to or ~reater than those of the ferritic structure.
The bainitic structure of the spheroidal cast-iron has already been studied for cast-iron parts cast i~ a chill-mould, in particular for mechanical parts o~ motor vehicles, as described for example in French Patent ~oO
1 056 330, on account of the good mechanical character-istics conferred by a structure of this t~pe.
In an article of the journal "Hommes et Fonderie"
(Men and the Foundry) No. 84 of April 1978, a thermal treatment for obtaining this bainitic structure is ~ ~f3~ 3~
described. The thermal treatment described is that of so called "chilling by stages" which makes it possible to lead to the bainitic structure by passing through austenitisation by successive stages of cooling at different speeds, of which one is chilling, starting with the hot part, as it has been cast. This treatment has the advantage of not requiring initial heating for austenitisation.
Howevex, according to the technique described in this article, in view of the low aptitude for chilling of spheroidal graphite cast-iron, not only is it necessary to have very close checking of the carbon, silicon and manganese contents of the cast-iron, but also, if one wishes to treat relatively thick parts, it is necessary to add expensive alloying elements such as molybdenum, which even in small quantities are particu-larly effective for increasing the aptitude for chilling of cast-iron to a sufficient extent, in order that the chilling by stages prevents the formation of perlite and leads to the formation of bainite~
On the contrary, the Applicant has tackled the problem of obt~;n'ng centrifugally cast tu~es of bainitic cast-iron containin~ sphcroidal graphite without the addition of special substances, which are expensive even in smali quantities, such as molybdenu~.
~o this end, the invention relates to a centrifu-gally cast tube of spheroidal graphite cast-iron, characterised in that the cast-iron has the following composition by weight:
carbon : 2.5 - 4.0/~
silicon : 2 - 4.~0 manganese : 0.1 - 0.6%
nickel : 0 - 3.5%
copper : 0 - 11%
magnesium: 0 - 0.5%
sulphur : 0.01~/c m~ r phosphorus : 0. 06k ~i ml~r - the remainder being iron, this cast-iron having a bainitic structure.
In order to produce a tube of this type, according to the invention, one begins with a spheroidal graphite cast-iron having the above mentioned composition~ this cast-iron is cast in a centrifugal chill-mould provided with a refractory lining and cooled externally by water, the centrifugally cast tube is left to cool in the chill-mould to a temperature of the order of 800 - 1000C
in order to acquire an austenitic structure, then 7 still in the chill-mould, it is cooled vigorously and uniformly over its entire length by spraying wacer or a mixtlIre of air and water onto its inner wall~ to a ternperature ol approximately 250 - 400C, in order to give it an austenitic or bainitic structure, then the ~,f3~ ~6 tube is removed from the chill-mould and placed inside a furnace kept at a temperature of between 250 and 450C
for the purpose of creating or maint~;n;n@ a bainitic structure and the tube is removed from the furnace in order to allow it to cool in the air.
Experience shows that the tube according to the invention has a substantially reduced unit weight and a substantially increased working pressure, at the cost of higher ovalisation under the actual weight of the tube, but which remains within acceptable limits.
The irvention is described hereafter in more detail with reference to the accompanying drawings, which show only one embodiment thereof. In these drawings:
Figure 1 is a partial diagrammatic view in longitudinal section of a machine for the centrifugal casting of cast-iron tubes, equipped with a spray device ~or carrying out the method according to the invention, the machine being in the position at the end of casting;
Fi~ure 2 is a view similar to figure 1 of the machine during the stage of spraying the tube in the chill-mould of the method according to the invention;
Figure 3 is a cross-sectional view on line 3-3 of figure 2;
Figure 4 is a diagrammatic cross-sectional view showing ~z~
the stage of maint~;n;ng bainitisation, i~side a furnaee, of the method of the invention;
Figures 5 and 6 are comparative diagrams of the thermal treatment of the method of the invention (eurves drawn in full line) with respeet to known prior thermal treatments, respectively for obtaining a bainitic s-tructure with austenitisation heating and for obt~ining a ferritic structure i.n the conventional manufae-ture of centrifugally produced cast-iron tubes 9 these curves corresponding to tubes having a nom,nal diameter of 1600 mm;
Figures 7 and 8 are micrographs of a wall structure of tubes eentrifugally cast from spheroidal graphite cast-iron, respectively with a bainitie structure enlarged 1000 times and with a ferrito-perlitic structure enlarged 100 times.
According to the embodiment of figures 1 to 3~ the invention is applied to the manufacture of tubes ~rom spheroidal graphite cast-iron by centrifugal casting.
The method according to the invention consists of starting with a composi-tion of spheroidal graphite east-iron which is as follows, with percentages by weight:
- carbon : 2.5 - 4.C% and in particular 3.6%
silicon : 2 - /~.0/~ and in particular 2.4,~
manganese : 0.1 - 0.6% and in ~l~rticular 0.5%
.3~ 3~
nickel : 0 - 3 . 5% and in particular 0.~/o copper : 0 - 11% and in particular 0. 5/c magnesium : O - 0. 5% and in particular 0.03%
sulphur : 0.01% maximum phosphorus : 0.06% maximum the remainder being iron.
Thi.s composition of cast-iron has been modified with respect to that which normally serves for the manufacture of pipes from spheroidal graphite cast-iron with a ferri.to-perlitic structure due to the addition of the elements Ni and Cu, which ~ere not present and preferably by the addition of an appreciable amount of M~, basic cast-iron normally cont~ining only 001 ~ On~/O~ The elements Ni, Cu, Mn have the property of improving the capacity of the cast-iron for chilling.
This composition of spheroidal graphite cast-iron is cast by centrifugation in a centrifugal casting machine illustrated diagrammatically in figures 1 to 3.
This machine essentially comprises a carriage A
which is able to move longitudinally by virtue of a jack B. This carriage A supports a metal centrifugal casting chill-mould 1, on an approximately horizontal axis X-~, through the intermediary o rollers C whereof at least one is driven by a motor M. The chill-mould 1 provides a cylindrical casting cavity of the same di&meter from one end to the other, with a view to obtaining a tube T
~'~r~ 3~
of constant diameter and wall thickness o~er its entire len~th, thus without any socket. For example, the tube has a length of six to eight metres for an inner diameter which may range from 60 mm to 2000 mm depending on the centrifugal casting machine and the chill-mould 1 used.
As is kno~m, the machine is provided with a device for the external cooling of the chill-mould 1. The latter may be ramps for sprayin~ water, distributed around the chill-mould 1, inside a casing or bodyworX
enclosing this chill-mould, or even a ~acXet with water circulating from one end of the chill-mould to the other and outside the latter, in a closed circuitO ~or the purpose of simplification, the device for cooling the outside of the chill-mould 1, whatever this device and since it is known per se, has not been illustratedO
Moreover, in view of the ~act that the invention applies preferably, but not exclusively, to the manufac-ture of large diameter cast-iron tubes, i.e. dia eters greater than 700 mm and which may ever. reach 2000 mm, a human silhouette S has been shown beside the machine, on t~e right in figure 1, in order to illustrate the considerable diameter of the chill~mould 1 in which the tube T is to be cast.
Althou~h, for reasons given hereafter, it is for large diameters that the method of the invention is most adv.~tageous, this method can also be applied to the ., . . ~.. ;.
_ 1G -manufacture of cast-iron tubes of small and average diameters, i.e. of diameters comprised between approxi-mately 50 and 600 mm.
A runner E provided upstream of a chute G supplied with molten cast-iron by atilting ladle H is able to penetrate inside the chill-mould 1, roughly parallel to its axis X-X.
The arrangement of the runner E and of its chute G
is mounted to overhan~ on a carriage 2 able to move transversely with respect to the axis X-X, i.e. in an enQ direction with respect to the plane of figure 1.
The transverse carriage 2 also supports in an over-h~n~;n~ manner a long rigid conduit or ramp 3 for spraying water, which is connected to a suppl~ of pressurized water (not shown). The rigid conduit 3 has a length corresponding to that of the runner ~, thus of the chill-mould 1 and is also approximately parallel to the axis X-X of the chill-mould 1. It is mounted on the transverse carriage 2 staggered with respect to the runner E by a transverse dist~nce such that due to a transverse movement of the carriage 2, when the runner E is inside the chill-mould 1~ the rigid conduit 3 is outside ~ld vice versa.
~he riKi~ conduit or ramp 3 is provided over its entire length with pairs of twin nozzles 4 for spraying water. 'rhe Jets of the nozzles 4, which are arranged ., opposite each other in pairs~ have adjustable sections and are regulated in order that each provides a suitable flow of water depending on the thickness of the tube, which is substantially constant over the entire length of the tube T. The means for regulating the sections of the jets from the nozzles 4, which are known per se, are not shown.
Before each casting operation, the chill-mould 1 is provided with a refractory coating 1a, the so called "wet-spray" coating, i.e. a mixture of silica po~der and bentonite in suspension in water. ~or example~this coating has a thickness of between 0.05 and 0.8 mm. The constituents of this coating mixture are in the following proportions: 500 - 3000 grams of silica powder having a grain size of between 40 and 100 microns and 10 - 40 grams of bentonite per litre of water. The members for spraying this coating, which are known per se~ have not bee~ shown.
Ik should be noted that in figure 1, in ~hich the runner E is partly located inside the chill-mould 13 part of the conduit 3 comprising nozzles 4 is not visible, since this conduit is retracted laterallyO It is necessary to consider figure 2 in order to see the conduit 3 ~rith all its nozzles 4 introduced inside the chill-mould 1 in the spraying position. The runner E is thus in a position retracted laterally, in front of the pl~ne of figure 2 and has been shown only p~rtly, for the sake of clarity of the drawing. This is clear in figure 3.
By means of this installation, one proceeds with the casting of a tube T by centrifugation, by introducing into the chill-mbuld the runner E9 then by pouring cast-iron through this runner whilst extracting it progress-ively from the chill-mould. According to the invention7 one pours into the centrifugal casting chill-mould 1 only a quantity of cast-iron which is able to produce a centrifuged tube whereof the thickness is much less than the customary thicXness, taking into account the dic~meter (see hereafter the table of numerical values).
'~hen the casting of the tube T is completed, the latter is subjected to the following thermal treatment, which consists of chilling in stages carried out partly inside the centrifugal chill-mould 1 and partly in a maint~ining furnace~ with a view to obtaining and mai~-t~;ning a bainitic structure, thus preventing the forma-tion of perlite~
In a first stage of this thermal treatment (figures 5 and 6, cur~e dra~m in full line) the tube T is left inside the centrifugal chill-mould 1 in order to subject it to bainitisation chilling, passing through austeniti-sation, ~rithout heating, thus bene~ing from the heat of casting. One thus obtains a tube ~Jhich has been centri-fuged and has solidified and is still at a temperatureof the order of 1150C (after passing from the point a to -. .. 'h,~ c~ u~ r _~ .,!r.~, the point b on the curve drawn in full line in figures 5 and 6).
Owing to the fact that the chill-mould 1 is cooled externally and that the tube T is allowed to rotate about itself, the latter cools slo~ly from a to _ and from b to c, i.e. from 1300C to 1150C and from 1150C
to 1000C in a virtually homogeneous manner. In the vicinity of the point c of the curve drawn in full line in figures 5 and 6 and even below this point, for example to 800C, one notes a slight temperature differ-ence between the inner wall and the outer wall, less tha~
20C, it is this tube T with a homogeneous temperature which is thus austenitised, i.e. with an austenitic structure at the point c, without the application of heat, but by cooling which occurs after casting inside the chill-mould 1.
~ rom this homogeneous state as regards temperature andaustenitic structure, the thermal treatment of chilling or rapid cooling is carried out inside the centrifugal chill-mould by means of the spray ramp 3 and the spray nozzles 4, by spraying water or a mixture of air and water.
~ o this end, immediately after casting, the runner is retracted laterally due to a movement of the carriage ~, the spray ramp 3 comprising nozzles 4 is introduced completely into the centrifugal chill-mould 1 and one ~ ~3~ 3~i proceeds with spraying of the cavity of the tube T which has just been cast, whilst continuing 'o rotate the chill-mould 1. Naturally, the spray rate, which is theoretically constant over the entire length of the centrifuged tube, may be adjusted locally, if local irregularities in temperature o~ the chill-mould 1 are ascertained~ although one seeks to keep the external cooling of the latter constant and uniform.
By proceeding in this way, the tube T is cooled homogeneously. This stage of chilling is represented by the section c - d in the curves dra~m in full line in figures 5 and 6. The temperature of the tube T thus drops in several mi~utes from approximately 1000C (or less, for example 800C) to approximately 350C.
The water sprayed is vaporized inside the rotating pipe and discharged in a suitable manner by means which are not illustrated.
In fact, the temperature at the end of chilling is between 250C and 450C. In this temperature range which is located either slightly above or slightly below the value of 350C marked on the curves of figures 5 a~d 6, the tube T has sufficient rigidity so that there is no longer any danger of ovalisation outside the centri-fugal chill-mould. Owing to the chilling c - d, the tube has also obtained a structure which is free from perlite. In the curves of figures 5 and 6, the region corresponding to perlite is situated on the right of this curve~ at a certain distance from the portion c - d.
The second stage of thermal treatment consists of maint~;n;n~ the temperature in order to consolidate or fix the bainitic structure (maint~in;n~ bainitisation).
For this, subsequent to the preceding stage of rapid cooling or chilling, the tube T is extracted from the centrifugal chill-mould, either by stopping the rotation of the latter, or by continuing to rotate it during the extraction, depending on the extractor device available.
As shown in figure 4, the tube T removed from the mould is introduced into a tunnel furnace 5 comprising heating nozzles 6, of known type, regulated in order to keep the pipe at a constant temperature of between 250 and 450C, for example at 350C~ for 5 to 120 minutes (portion d -e of the Gh;11;n~ curve of fig~res 5 and 6), this main-t~;n;ng time being approximately the same for all diameters of tubes, to within 10 minutes.
The time for maintaining the temperature is intended to obtain a homogeneous bainitic structure producing the optimum mechanical characteristics mentioned hereafter.
The tube T is supported in the furnace 5 by a conveyor chain 7, which may be of a type simultaneously ensuring the rotation of the tube about its own axis.
25The last stage of the thermal treatmcnt consists of rapid cooling in the atmosphere: upon the expiry of the 3~
period of maintaining bainitisation, the tube T is removed from the maint~inin~ furnace 5 and left to cool in the atmosphere according to the portion e - f of the curves drawn in full line in figures 5 and 6, ~hich produces rapid cooling, in approximately 12 minutes, virtually do~n to ambient temperature. Chilling of the tube in stages is represented by the portions c - d - e - f of the cooling curve drawn in full line.
~igures 5 and 6 illustrate the advantages of the thermal treatment according to the invention, illustrated by the curves drawn in full line, with respect to previous known treatments, represented by the curves drawn in broken line. It can be seen that a considerable saving of time is achieved, but this is not the only advantage.
As sho~m by the curve dra~m in broken line in figure 5, the conventional treatment for obtaining a bainitic structure of a part cast in a static manner (which is thus not a centrifugally cast tube) comprises a portion h - .i - k - 1 similar to the portion c - d ~ e - f of the method of the invention, but staggered in time by approximately 1 to 2 hours owing to the two previous stages 0-~for austenitisation heating, which may last from 20 minutes to 2 hours depending on the applications and ~ - h for maint~; n; ng austenitisation at a temperature of approximately 1000C, more generally between ~00 and 1000C, ~he previous kno~m treatment thus requires the application of heat i~ order to bring the treated parts to the austenitisation temperature instead of treating the parts in the mould, immediately after their casting.
It is thus clear that the method of the inventio~, by economising on heating for austenitisation, provides a considerable saving of energy with respect to a treatment of this type.
In figure 6, the thermal treatment of the invention is compared ~ith the previous technique of thermal ferritisation treatment (annealing). The previous thermal treatment (curve drawn in broken line) has the portion a - b - c in common with the curve of the invention drawn in full line. Then, the remainder of the curve c - m - n - ~ - Q is substantially di~ferent from the curve c - d - e - f of the method of the invention. In the process of ferritisation~ the tube is left inside its centrifugal chill-mould according to the curve a - b - c - m: this corresponds to cooling at a moderate speed, owing to the external cooling of the centrifugal chill-mould and of the natural internal cooling of the centrifuged tube. The austenitic struc-ture fGrms from a to c. Beyond c, this structure is not maintained, but cooling continues up to m, at which point one proceeds with the extraction from the chill-mould of the tube which has cooled sufficiently to 3~ 3~;
prevent substantial ovalisation. This is followed b~
somewhat slower cooling ir~ air until the tube is intro-duced into an annealing furnace for ferritisation at a temperature of the order of 750C. As can be seen, the application of heat is ncessary1 inside the annealing furnace, in order to obtain the ferritic structure, according to the ascending part m - n of the curve, as well as for maint~in;n~ the temperature according to the portion n - p. This application of heat is substantially greater tha~ that which is necessary for maint~;n;ng bainitisation according to the portion d - e of the curve drawn in full line, in the mainta;n;ng furnace 5 and this is all the more since the temperature for main-t?;n;n~ bainitisation is much lower (approximately 350C) than the temperature for maint~;n;n~ ferritisation (approximately 750C). In particular7 it will be noted that the temperature for maint~n;n~ baini~satio~ is sufficientlg low for the extraction of the tube at this temperature to cause no problems and it is not necessary to re-heat this tube at the time of its introduction into the furnace 5~ Consequently, with respect to the prior art for the thermal treatment of ferritisation for centrifuged cast-iron tubes, the method of the invention also allo~ls an appreciable saving of energ~.
On account of the rotation of the tube whilst it is still inside the centrifugal chill-mould, i~e. during the ~3~
sta~es of thermal treatme~t represented by the portions a - b - c - d of the curves drawn in full line in figures 5 and 6, thus during natural cooling and during c~ ;ng by spraying, cooling of the pipe is homogeneous~
The bainitic structure makes it possible to reduce the wall thickness and thus the unit weight of the tubes OR account of its good mechanical properties. This substantial reduction of thickness is also advantageous as regards the homogeneity of cooling during the stages a - b - c - d and in particular for the aptitude for chilling: it ensures the efficiency of this chilling according to the stage c - d of the thermal treatment curve, throughout the entire thickness of t~e centrifu-gally cast tube, without it being necessary to add to the composition of the cast-iron, expensive metal elements having a chilling effect, i.e. facilitating chilling, such as molybdenum. In other words~ the substantial reduction in thickness of centrifuged cast~
iron tubes provides an appreciable saving as regards the composition of the cast-iron.
It has also been sho~m that the austenitisation and bainitisation treatment according to stages b - c -d of t~e thermal treatment curve of the tube l' inside the centrifugal chill-mould prevents any deformation Or the tube, thus any ovalisation whilst it is at a high te,-nperature. In fact, the centrifugal chill-mould, 3~
~ 20 -serving as a support for the tube, preserves its perfectly cylindrical shape and this is despite the appreciable reduction of thickness which increases its tendency to-wards ovalisatio~. This tendency towards ovalisation would cause serious problems if the tube were extracted from the centrifugal chill-mould at a higher temperature, for e~ample above 500C.
Carrying out the thermal treatment according to the invention and more particularly the stage of spraying or atomizing water inside the cavity of the tube according to the portion c - d is particularly simple and economi-cal with respect to a conventional hardening treatment in a bath of salt, which would also necessitate trans-portation of the tube from its chill-mould whilst it is still hot and handling to immerse the tube in a bath of salt. ~he method of the invention makes it possible to save on this handling and at the same time to prevent the danger of ovalisation which it involves.
~he apprecia'ole saving of time mentioned above makes it possible to increase the rates of manufacture of centrifugally cast tubes from spheroidal graphite cast-iron having a bainitic structure. Spraying the inside of the centrifugally cast pipe during the chilli~g sta~e reduces the residence time of the centrifugally cast tube in the centrifugal chill-mould~ This is show~
by comparing the two curves of figure 6, in which the ~2~
extraction of the tube from the chill-mould is loca'ced at the point m in the prior art whereas it is located at the point d, 5 to 10 minutes previously, i~ the method of the invention.
~or the centrifugal chill-mould this advantageously results in an appreciable reduction in the thermal stresses, since the heat to be discharged is approxi-mately ~0 to 4~o less with respect to the prior art for the manufacture of tubes from cast-iron having a ferritic structure, owing to the discharge of heat through the spray water and the reduction in the quantity of cast-iron poured inside the chill-mould. Consequently, the life expectancy of the centrifugal chill-mould~ which are the largest and most expensive parts of the centrifu-gal casting equipment, should be extended considerablywith respect to the prior art.
Finally, the tube of the invention cast centrifugally from spheroidal graphite cast-iron having a bainitic structure, despite its substantial reduction of thickness, which causes lightening facilitating its handling~
preserves mechanical characteristics substantially equiva-lent to those of previous ferritic tubes at the cost of greater sensitivity to ovalisation, however this sensi-tivity remaining tolerable owing to the fact that the tube
After centrifugal castin~ and thermal treatment, tubes - that is to say cylindrical pipes of constant thickness - made from spheroidal graphite cast-iron at present have a ferritic structure which has two ad~an-tages: on the one hand, this structure gives them goodmechanical characteristics (elastic resilience and ductility), on the other hand, this ferritic structure is easily obtained by thermal treatment after centrifugal casting, either in a chill-mould provided internally with a thick coating of a pulverulent mixture of silica and bentonite in suspension in water (a so called "wet-spray"
coating) or in a chill-mould without such a coating.
In the case of the presence of a "wet-spray"
coating on the chill-mould, the tube is extracted from itB
chill-mould and rapidl~ introduced into a furnace before it has cooled too much then is sub~ect to a thermal tr~at-ment kno~rn as "maint~;n;n~ ferritisation" at a temperature of the order of 750C, for a period of time of the order of 20 to 25 minutes, then it is left to cool naturally.
If there is no "wet-spray" coating on the chill-mould, 1he pipe is extracted from its casting mould and ,f~
is introduced rapidly into a furnace where it is subjected to ~raphitisation annealing at a temperature of the order of 950C for a period of time of the order o~ 20 to 25 minutes, then to maintaining ferritisation at a tempera-ture of the order of 750C for a period of time of theorder of 15 to 20 minutes.
The Applicant has tackled the problem of obt~in;ng economically cast-iron tubes produced by centrifugal casting, which are lighter than current tubes, without any appreciable loss of mechanical features.
The Applicant has sought to achieve this result by giving the tube of spheroidal graphite cast-iron a bainitic structure 7 instead of the customary ferritic struct~re, which bainitic structure has a tensile strength and characteristic of elongation as well as a characteristic of resilience equal to or ~reater than those of the ferritic structure.
The bainitic structure of the spheroidal cast-iron has already been studied for cast-iron parts cast i~ a chill-mould, in particular for mechanical parts o~ motor vehicles, as described for example in French Patent ~oO
1 056 330, on account of the good mechanical character-istics conferred by a structure of this t~pe.
In an article of the journal "Hommes et Fonderie"
(Men and the Foundry) No. 84 of April 1978, a thermal treatment for obtaining this bainitic structure is ~ ~f3~ 3~
described. The thermal treatment described is that of so called "chilling by stages" which makes it possible to lead to the bainitic structure by passing through austenitisation by successive stages of cooling at different speeds, of which one is chilling, starting with the hot part, as it has been cast. This treatment has the advantage of not requiring initial heating for austenitisation.
Howevex, according to the technique described in this article, in view of the low aptitude for chilling of spheroidal graphite cast-iron, not only is it necessary to have very close checking of the carbon, silicon and manganese contents of the cast-iron, but also, if one wishes to treat relatively thick parts, it is necessary to add expensive alloying elements such as molybdenum, which even in small quantities are particu-larly effective for increasing the aptitude for chilling of cast-iron to a sufficient extent, in order that the chilling by stages prevents the formation of perlite and leads to the formation of bainite~
On the contrary, the Applicant has tackled the problem of obt~;n'ng centrifugally cast tu~es of bainitic cast-iron containin~ sphcroidal graphite without the addition of special substances, which are expensive even in smali quantities, such as molybdenu~.
~o this end, the invention relates to a centrifu-gally cast tube of spheroidal graphite cast-iron, characterised in that the cast-iron has the following composition by weight:
carbon : 2.5 - 4.0/~
silicon : 2 - 4.~0 manganese : 0.1 - 0.6%
nickel : 0 - 3.5%
copper : 0 - 11%
magnesium: 0 - 0.5%
sulphur : 0.01~/c m~ r phosphorus : 0. 06k ~i ml~r - the remainder being iron, this cast-iron having a bainitic structure.
In order to produce a tube of this type, according to the invention, one begins with a spheroidal graphite cast-iron having the above mentioned composition~ this cast-iron is cast in a centrifugal chill-mould provided with a refractory lining and cooled externally by water, the centrifugally cast tube is left to cool in the chill-mould to a temperature of the order of 800 - 1000C
in order to acquire an austenitic structure, then 7 still in the chill-mould, it is cooled vigorously and uniformly over its entire length by spraying wacer or a mixtlIre of air and water onto its inner wall~ to a ternperature ol approximately 250 - 400C, in order to give it an austenitic or bainitic structure, then the ~,f3~ ~6 tube is removed from the chill-mould and placed inside a furnace kept at a temperature of between 250 and 450C
for the purpose of creating or maint~;n;n@ a bainitic structure and the tube is removed from the furnace in order to allow it to cool in the air.
Experience shows that the tube according to the invention has a substantially reduced unit weight and a substantially increased working pressure, at the cost of higher ovalisation under the actual weight of the tube, but which remains within acceptable limits.
The irvention is described hereafter in more detail with reference to the accompanying drawings, which show only one embodiment thereof. In these drawings:
Figure 1 is a partial diagrammatic view in longitudinal section of a machine for the centrifugal casting of cast-iron tubes, equipped with a spray device ~or carrying out the method according to the invention, the machine being in the position at the end of casting;
Fi~ure 2 is a view similar to figure 1 of the machine during the stage of spraying the tube in the chill-mould of the method according to the invention;
Figure 3 is a cross-sectional view on line 3-3 of figure 2;
Figure 4 is a diagrammatic cross-sectional view showing ~z~
the stage of maint~;n;ng bainitisation, i~side a furnaee, of the method of the invention;
Figures 5 and 6 are comparative diagrams of the thermal treatment of the method of the invention (eurves drawn in full line) with respeet to known prior thermal treatments, respectively for obtaining a bainitic s-tructure with austenitisation heating and for obt~ining a ferritic structure i.n the conventional manufae-ture of centrifugally produced cast-iron tubes 9 these curves corresponding to tubes having a nom,nal diameter of 1600 mm;
Figures 7 and 8 are micrographs of a wall structure of tubes eentrifugally cast from spheroidal graphite cast-iron, respectively with a bainitie structure enlarged 1000 times and with a ferrito-perlitic structure enlarged 100 times.
According to the embodiment of figures 1 to 3~ the invention is applied to the manufacture of tubes ~rom spheroidal graphite cast-iron by centrifugal casting.
The method according to the invention consists of starting with a composi-tion of spheroidal graphite east-iron which is as follows, with percentages by weight:
- carbon : 2.5 - 4.C% and in particular 3.6%
silicon : 2 - /~.0/~ and in particular 2.4,~
manganese : 0.1 - 0.6% and in ~l~rticular 0.5%
.3~ 3~
nickel : 0 - 3 . 5% and in particular 0.~/o copper : 0 - 11% and in particular 0. 5/c magnesium : O - 0. 5% and in particular 0.03%
sulphur : 0.01% maximum phosphorus : 0.06% maximum the remainder being iron.
Thi.s composition of cast-iron has been modified with respect to that which normally serves for the manufacture of pipes from spheroidal graphite cast-iron with a ferri.to-perlitic structure due to the addition of the elements Ni and Cu, which ~ere not present and preferably by the addition of an appreciable amount of M~, basic cast-iron normally cont~ining only 001 ~ On~/O~ The elements Ni, Cu, Mn have the property of improving the capacity of the cast-iron for chilling.
This composition of spheroidal graphite cast-iron is cast by centrifugation in a centrifugal casting machine illustrated diagrammatically in figures 1 to 3.
This machine essentially comprises a carriage A
which is able to move longitudinally by virtue of a jack B. This carriage A supports a metal centrifugal casting chill-mould 1, on an approximately horizontal axis X-~, through the intermediary o rollers C whereof at least one is driven by a motor M. The chill-mould 1 provides a cylindrical casting cavity of the same di&meter from one end to the other, with a view to obtaining a tube T
~'~r~ 3~
of constant diameter and wall thickness o~er its entire len~th, thus without any socket. For example, the tube has a length of six to eight metres for an inner diameter which may range from 60 mm to 2000 mm depending on the centrifugal casting machine and the chill-mould 1 used.
As is kno~m, the machine is provided with a device for the external cooling of the chill-mould 1. The latter may be ramps for sprayin~ water, distributed around the chill-mould 1, inside a casing or bodyworX
enclosing this chill-mould, or even a ~acXet with water circulating from one end of the chill-mould to the other and outside the latter, in a closed circuitO ~or the purpose of simplification, the device for cooling the outside of the chill-mould 1, whatever this device and since it is known per se, has not been illustratedO
Moreover, in view of the ~act that the invention applies preferably, but not exclusively, to the manufac-ture of large diameter cast-iron tubes, i.e. dia eters greater than 700 mm and which may ever. reach 2000 mm, a human silhouette S has been shown beside the machine, on t~e right in figure 1, in order to illustrate the considerable diameter of the chill~mould 1 in which the tube T is to be cast.
Althou~h, for reasons given hereafter, it is for large diameters that the method of the invention is most adv.~tageous, this method can also be applied to the ., . . ~.. ;.
_ 1G -manufacture of cast-iron tubes of small and average diameters, i.e. of diameters comprised between approxi-mately 50 and 600 mm.
A runner E provided upstream of a chute G supplied with molten cast-iron by atilting ladle H is able to penetrate inside the chill-mould 1, roughly parallel to its axis X-X.
The arrangement of the runner E and of its chute G
is mounted to overhan~ on a carriage 2 able to move transversely with respect to the axis X-X, i.e. in an enQ direction with respect to the plane of figure 1.
The transverse carriage 2 also supports in an over-h~n~;n~ manner a long rigid conduit or ramp 3 for spraying water, which is connected to a suppl~ of pressurized water (not shown). The rigid conduit 3 has a length corresponding to that of the runner ~, thus of the chill-mould 1 and is also approximately parallel to the axis X-X of the chill-mould 1. It is mounted on the transverse carriage 2 staggered with respect to the runner E by a transverse dist~nce such that due to a transverse movement of the carriage 2, when the runner E is inside the chill-mould 1~ the rigid conduit 3 is outside ~ld vice versa.
~he riKi~ conduit or ramp 3 is provided over its entire length with pairs of twin nozzles 4 for spraying water. 'rhe Jets of the nozzles 4, which are arranged ., opposite each other in pairs~ have adjustable sections and are regulated in order that each provides a suitable flow of water depending on the thickness of the tube, which is substantially constant over the entire length of the tube T. The means for regulating the sections of the jets from the nozzles 4, which are known per se, are not shown.
Before each casting operation, the chill-mould 1 is provided with a refractory coating 1a, the so called "wet-spray" coating, i.e. a mixture of silica po~der and bentonite in suspension in water. ~or example~this coating has a thickness of between 0.05 and 0.8 mm. The constituents of this coating mixture are in the following proportions: 500 - 3000 grams of silica powder having a grain size of between 40 and 100 microns and 10 - 40 grams of bentonite per litre of water. The members for spraying this coating, which are known per se~ have not bee~ shown.
Ik should be noted that in figure 1, in ~hich the runner E is partly located inside the chill-mould 13 part of the conduit 3 comprising nozzles 4 is not visible, since this conduit is retracted laterallyO It is necessary to consider figure 2 in order to see the conduit 3 ~rith all its nozzles 4 introduced inside the chill-mould 1 in the spraying position. The runner E is thus in a position retracted laterally, in front of the pl~ne of figure 2 and has been shown only p~rtly, for the sake of clarity of the drawing. This is clear in figure 3.
By means of this installation, one proceeds with the casting of a tube T by centrifugation, by introducing into the chill-mbuld the runner E9 then by pouring cast-iron through this runner whilst extracting it progress-ively from the chill-mould. According to the invention7 one pours into the centrifugal casting chill-mould 1 only a quantity of cast-iron which is able to produce a centrifuged tube whereof the thickness is much less than the customary thicXness, taking into account the dic~meter (see hereafter the table of numerical values).
'~hen the casting of the tube T is completed, the latter is subjected to the following thermal treatment, which consists of chilling in stages carried out partly inside the centrifugal chill-mould 1 and partly in a maint~ining furnace~ with a view to obtaining and mai~-t~;ning a bainitic structure, thus preventing the forma-tion of perlite~
In a first stage of this thermal treatment (figures 5 and 6, cur~e dra~m in full line) the tube T is left inside the centrifugal chill-mould 1 in order to subject it to bainitisation chilling, passing through austeniti-sation, ~rithout heating, thus bene~ing from the heat of casting. One thus obtains a tube ~Jhich has been centri-fuged and has solidified and is still at a temperatureof the order of 1150C (after passing from the point a to -. .. 'h,~ c~ u~ r _~ .,!r.~, the point b on the curve drawn in full line in figures 5 and 6).
Owing to the fact that the chill-mould 1 is cooled externally and that the tube T is allowed to rotate about itself, the latter cools slo~ly from a to _ and from b to c, i.e. from 1300C to 1150C and from 1150C
to 1000C in a virtually homogeneous manner. In the vicinity of the point c of the curve drawn in full line in figures 5 and 6 and even below this point, for example to 800C, one notes a slight temperature differ-ence between the inner wall and the outer wall, less tha~
20C, it is this tube T with a homogeneous temperature which is thus austenitised, i.e. with an austenitic structure at the point c, without the application of heat, but by cooling which occurs after casting inside the chill-mould 1.
~ rom this homogeneous state as regards temperature andaustenitic structure, the thermal treatment of chilling or rapid cooling is carried out inside the centrifugal chill-mould by means of the spray ramp 3 and the spray nozzles 4, by spraying water or a mixture of air and water.
~ o this end, immediately after casting, the runner is retracted laterally due to a movement of the carriage ~, the spray ramp 3 comprising nozzles 4 is introduced completely into the centrifugal chill-mould 1 and one ~ ~3~ 3~i proceeds with spraying of the cavity of the tube T which has just been cast, whilst continuing 'o rotate the chill-mould 1. Naturally, the spray rate, which is theoretically constant over the entire length of the centrifuged tube, may be adjusted locally, if local irregularities in temperature o~ the chill-mould 1 are ascertained~ although one seeks to keep the external cooling of the latter constant and uniform.
By proceeding in this way, the tube T is cooled homogeneously. This stage of chilling is represented by the section c - d in the curves dra~m in full line in figures 5 and 6. The temperature of the tube T thus drops in several mi~utes from approximately 1000C (or less, for example 800C) to approximately 350C.
The water sprayed is vaporized inside the rotating pipe and discharged in a suitable manner by means which are not illustrated.
In fact, the temperature at the end of chilling is between 250C and 450C. In this temperature range which is located either slightly above or slightly below the value of 350C marked on the curves of figures 5 a~d 6, the tube T has sufficient rigidity so that there is no longer any danger of ovalisation outside the centri-fugal chill-mould. Owing to the chilling c - d, the tube has also obtained a structure which is free from perlite. In the curves of figures 5 and 6, the region corresponding to perlite is situated on the right of this curve~ at a certain distance from the portion c - d.
The second stage of thermal treatment consists of maint~;n;n~ the temperature in order to consolidate or fix the bainitic structure (maint~in;n~ bainitisation).
For this, subsequent to the preceding stage of rapid cooling or chilling, the tube T is extracted from the centrifugal chill-mould, either by stopping the rotation of the latter, or by continuing to rotate it during the extraction, depending on the extractor device available.
As shown in figure 4, the tube T removed from the mould is introduced into a tunnel furnace 5 comprising heating nozzles 6, of known type, regulated in order to keep the pipe at a constant temperature of between 250 and 450C, for example at 350C~ for 5 to 120 minutes (portion d -e of the Gh;11;n~ curve of fig~res 5 and 6), this main-t~;n;ng time being approximately the same for all diameters of tubes, to within 10 minutes.
The time for maintaining the temperature is intended to obtain a homogeneous bainitic structure producing the optimum mechanical characteristics mentioned hereafter.
The tube T is supported in the furnace 5 by a conveyor chain 7, which may be of a type simultaneously ensuring the rotation of the tube about its own axis.
25The last stage of the thermal treatmcnt consists of rapid cooling in the atmosphere: upon the expiry of the 3~
period of maintaining bainitisation, the tube T is removed from the maint~inin~ furnace 5 and left to cool in the atmosphere according to the portion e - f of the curves drawn in full line in figures 5 and 6, ~hich produces rapid cooling, in approximately 12 minutes, virtually do~n to ambient temperature. Chilling of the tube in stages is represented by the portions c - d - e - f of the cooling curve drawn in full line.
~igures 5 and 6 illustrate the advantages of the thermal treatment according to the invention, illustrated by the curves drawn in full line, with respect to previous known treatments, represented by the curves drawn in broken line. It can be seen that a considerable saving of time is achieved, but this is not the only advantage.
As sho~m by the curve dra~m in broken line in figure 5, the conventional treatment for obtaining a bainitic structure of a part cast in a static manner (which is thus not a centrifugally cast tube) comprises a portion h - .i - k - 1 similar to the portion c - d ~ e - f of the method of the invention, but staggered in time by approximately 1 to 2 hours owing to the two previous stages 0-~for austenitisation heating, which may last from 20 minutes to 2 hours depending on the applications and ~ - h for maint~; n; ng austenitisation at a temperature of approximately 1000C, more generally between ~00 and 1000C, ~he previous kno~m treatment thus requires the application of heat i~ order to bring the treated parts to the austenitisation temperature instead of treating the parts in the mould, immediately after their casting.
It is thus clear that the method of the inventio~, by economising on heating for austenitisation, provides a considerable saving of energy with respect to a treatment of this type.
In figure 6, the thermal treatment of the invention is compared ~ith the previous technique of thermal ferritisation treatment (annealing). The previous thermal treatment (curve drawn in broken line) has the portion a - b - c in common with the curve of the invention drawn in full line. Then, the remainder of the curve c - m - n - ~ - Q is substantially di~ferent from the curve c - d - e - f of the method of the invention. In the process of ferritisation~ the tube is left inside its centrifugal chill-mould according to the curve a - b - c - m: this corresponds to cooling at a moderate speed, owing to the external cooling of the centrifugal chill-mould and of the natural internal cooling of the centrifuged tube. The austenitic struc-ture fGrms from a to c. Beyond c, this structure is not maintained, but cooling continues up to m, at which point one proceeds with the extraction from the chill-mould of the tube which has cooled sufficiently to 3~ 3~;
prevent substantial ovalisation. This is followed b~
somewhat slower cooling ir~ air until the tube is intro-duced into an annealing furnace for ferritisation at a temperature of the order of 750C. As can be seen, the application of heat is ncessary1 inside the annealing furnace, in order to obtain the ferritic structure, according to the ascending part m - n of the curve, as well as for maint~in;n~ the temperature according to the portion n - p. This application of heat is substantially greater tha~ that which is necessary for maint~;n;ng bainitisation according to the portion d - e of the curve drawn in full line, in the mainta;n;ng furnace 5 and this is all the more since the temperature for main-t?;n;n~ bainitisation is much lower (approximately 350C) than the temperature for maint~;n;n~ ferritisation (approximately 750C). In particular7 it will be noted that the temperature for maint~n;n~ baini~satio~ is sufficientlg low for the extraction of the tube at this temperature to cause no problems and it is not necessary to re-heat this tube at the time of its introduction into the furnace 5~ Consequently, with respect to the prior art for the thermal treatment of ferritisation for centrifuged cast-iron tubes, the method of the invention also allo~ls an appreciable saving of energ~.
On account of the rotation of the tube whilst it is still inside the centrifugal chill-mould, i~e. during the ~3~
sta~es of thermal treatme~t represented by the portions a - b - c - d of the curves drawn in full line in figures 5 and 6, thus during natural cooling and during c~ ;ng by spraying, cooling of the pipe is homogeneous~
The bainitic structure makes it possible to reduce the wall thickness and thus the unit weight of the tubes OR account of its good mechanical properties. This substantial reduction of thickness is also advantageous as regards the homogeneity of cooling during the stages a - b - c - d and in particular for the aptitude for chilling: it ensures the efficiency of this chilling according to the stage c - d of the thermal treatment curve, throughout the entire thickness of t~e centrifu-gally cast tube, without it being necessary to add to the composition of the cast-iron, expensive metal elements having a chilling effect, i.e. facilitating chilling, such as molybdenum. In other words~ the substantial reduction in thickness of centrifuged cast~
iron tubes provides an appreciable saving as regards the composition of the cast-iron.
It has also been sho~m that the austenitisation and bainitisation treatment according to stages b - c -d of t~e thermal treatment curve of the tube l' inside the centrifugal chill-mould prevents any deformation Or the tube, thus any ovalisation whilst it is at a high te,-nperature. In fact, the centrifugal chill-mould, 3~
~ 20 -serving as a support for the tube, preserves its perfectly cylindrical shape and this is despite the appreciable reduction of thickness which increases its tendency to-wards ovalisatio~. This tendency towards ovalisation would cause serious problems if the tube were extracted from the centrifugal chill-mould at a higher temperature, for e~ample above 500C.
Carrying out the thermal treatment according to the invention and more particularly the stage of spraying or atomizing water inside the cavity of the tube according to the portion c - d is particularly simple and economi-cal with respect to a conventional hardening treatment in a bath of salt, which would also necessitate trans-portation of the tube from its chill-mould whilst it is still hot and handling to immerse the tube in a bath of salt. ~he method of the invention makes it possible to save on this handling and at the same time to prevent the danger of ovalisation which it involves.
~he apprecia'ole saving of time mentioned above makes it possible to increase the rates of manufacture of centrifugally cast tubes from spheroidal graphite cast-iron having a bainitic structure. Spraying the inside of the centrifugally cast pipe during the chilli~g sta~e reduces the residence time of the centrifugally cast tube in the centrifugal chill-mould~ This is show~
by comparing the two curves of figure 6, in which the ~2~
extraction of the tube from the chill-mould is loca'ced at the point m in the prior art whereas it is located at the point d, 5 to 10 minutes previously, i~ the method of the invention.
~or the centrifugal chill-mould this advantageously results in an appreciable reduction in the thermal stresses, since the heat to be discharged is approxi-mately ~0 to 4~o less with respect to the prior art for the manufacture of tubes from cast-iron having a ferritic structure, owing to the discharge of heat through the spray water and the reduction in the quantity of cast-iron poured inside the chill-mould. Consequently, the life expectancy of the centrifugal chill-mould~ which are the largest and most expensive parts of the centrifu-gal casting equipment, should be extended considerablywith respect to the prior art.
Finally, the tube of the invention cast centrifugally from spheroidal graphite cast-iron having a bainitic structure, despite its substantial reduction of thickness, which causes lightening facilitating its handling~
preserves mechanical characteristics substantially equiva-lent to those of previous ferritic tubes at the cost of greater sensitivity to ovalisation, however this sensi-tivity remaining tolerable owing to the fact that the tube
2~ is not handled when it is at the high temperature prone to ovalisation.
_. .... . -~'~,Jj~ 3 As regards the mechanical characteristics of the tube according to the invention, the following table gives numerical examples of dimensions, weights, guaranteed working pressure and ovalisation for tubes intended to be buried at a depth of ~ metres and for large diameter pipes, i.e. greater than 700 mm nominal diameter. The ~alues relatlng to the bainitic tube of the invention are compared with those of the prior art relating to a ferritic tube and a lightened ferritic tube. In thi~
table, the coefficient K, defined by the international standard ISO 2531, characterises the thicX~ess of the tube according to the formula: e = K (0.5 + 0.001 D.N~) in which:
e = thickness of the tube wall in mm DN = nom~nal diameter.
- ~arge ~iameter Tubes -Depth of covering provided = 4 metres Nominal Prior firt ferritic and Prior art lightened Invention Diameter perlitic tube ferritic tube Bainitic Tube (K - 9) (with coating) ~ lightened~ coated wall mean Working Ovali- wall mean Ovali- wall mean '.lorking Ovali-thick- weight pressure sation thick- weight PS sation thick- weight pressure satio~
ness kg/m Ps under ness kg/m bars under ness kg/m Ps unàer mm own mm bars own uarsweight weight ~ei~ht (%~ (%) ~c ~
800 11.5211 28.50.09 8 147.8 23 0.22 5.9 109.3 29 0.56 11000 13.2303 28 0.13 9.7 223.1 23.2 0028 6.8 156.~ 28.7 Q.74 ;~
1200 15.0412 27.5 11.3 311~3 23 7.9 218.2 28.5 0.90 `~
1400 16.8536 2703 13.0 417.2 2302 9.0 189.6 28~5 1.05 1600 ~8~5677 26.9 14.5 531 23 10.0 367.2 28.4 l.21 1800 20.~833 26.5 -3 16.2 666.6 23 0.5111.1 458 28.3 1~36 2000 22.11006 26.30.34 17.8 813 23 ~.5612.3 ~3-3 28 1~47 i~ general, centrifugal inner coating of cement mortar and outer coating of black varnish~
~'~JJ~
The above table shows that the saving o~ unit weight which the invention makes it possible to obtain is much gretater the greater the diameter of the tube.
By way of comparison and to the advantage of the tube having a bainitic structure of the invention, the mechanical characteristics obtained are as follows:
- elastic limit 55 to 75 daN/mm~ (instead of appr~ximately 30 for the ferritic structure) - elongation greater than 1~/o (like the ferritic tube);
- breaking strength 70 to 110 daN/mm2 (ferritic tube 45 daN/mm2 approximately).
Figure 7 shows a bainitic micrographic structure.
In this structure~ the black areas which can be seen in the upper and lower left-hand corners are parts of ~5 graphite nodules. ~he elongated forms resembling ferns are ferrite areas. It can be seen that they cover the maaor part of the surface of the micrograph. 'rhe largest white areas correspond to residual austenite. It will be seen that they cover only a small portion of the sur~ace of the micrograph. It is the whole of this structure, recogni~able solely ~ith an enlargement of 1000 and not with an enlargement of 100, which is termed "bainitic"~
By T,Jay of comparison, according to the miGrograph of figure 8, with an enlargement of 100, when attacked with NI'rA~ this is a ferrito-perlitic spheroidal graphite cast-iron, contt~;ning 40% ferrite t~nd 50% perlite, ~ ~I''v. ~ Y o ~ k, "~ 3~G3 the rem~;n~er being spheroidal graphite~ The round black æeas æe graphite nodules. The nodules are surrounded by white areas consituting the ferrite. ~he rer~i~;ng grey areas are perlite. This is the structure of a centrifugally cast tube of conventional type.
_. .... . -~'~,Jj~ 3 As regards the mechanical characteristics of the tube according to the invention, the following table gives numerical examples of dimensions, weights, guaranteed working pressure and ovalisation for tubes intended to be buried at a depth of ~ metres and for large diameter pipes, i.e. greater than 700 mm nominal diameter. The ~alues relatlng to the bainitic tube of the invention are compared with those of the prior art relating to a ferritic tube and a lightened ferritic tube. In thi~
table, the coefficient K, defined by the international standard ISO 2531, characterises the thicX~ess of the tube according to the formula: e = K (0.5 + 0.001 D.N~) in which:
e = thickness of the tube wall in mm DN = nom~nal diameter.
- ~arge ~iameter Tubes -Depth of covering provided = 4 metres Nominal Prior firt ferritic and Prior art lightened Invention Diameter perlitic tube ferritic tube Bainitic Tube (K - 9) (with coating) ~ lightened~ coated wall mean Working Ovali- wall mean Ovali- wall mean '.lorking Ovali-thick- weight pressure sation thick- weight PS sation thick- weight pressure satio~
ness kg/m Ps under ness kg/m bars under ness kg/m Ps unàer mm own mm bars own uarsweight weight ~ei~ht (%~ (%) ~c ~
800 11.5211 28.50.09 8 147.8 23 0.22 5.9 109.3 29 0.56 11000 13.2303 28 0.13 9.7 223.1 23.2 0028 6.8 156.~ 28.7 Q.74 ;~
1200 15.0412 27.5 11.3 311~3 23 7.9 218.2 28.5 0.90 `~
1400 16.8536 2703 13.0 417.2 2302 9.0 189.6 28~5 1.05 1600 ~8~5677 26.9 14.5 531 23 10.0 367.2 28.4 l.21 1800 20.~833 26.5 -3 16.2 666.6 23 0.5111.1 458 28.3 1~36 2000 22.11006 26.30.34 17.8 813 23 ~.5612.3 ~3-3 28 1~47 i~ general, centrifugal inner coating of cement mortar and outer coating of black varnish~
~'~JJ~
The above table shows that the saving o~ unit weight which the invention makes it possible to obtain is much gretater the greater the diameter of the tube.
By way of comparison and to the advantage of the tube having a bainitic structure of the invention, the mechanical characteristics obtained are as follows:
- elastic limit 55 to 75 daN/mm~ (instead of appr~ximately 30 for the ferritic structure) - elongation greater than 1~/o (like the ferritic tube);
- breaking strength 70 to 110 daN/mm2 (ferritic tube 45 daN/mm2 approximately).
Figure 7 shows a bainitic micrographic structure.
In this structure~ the black areas which can be seen in the upper and lower left-hand corners are parts of ~5 graphite nodules. ~he elongated forms resembling ferns are ferrite areas. It can be seen that they cover the maaor part of the surface of the micrograph. 'rhe largest white areas correspond to residual austenite. It will be seen that they cover only a small portion of the sur~ace of the micrograph. It is the whole of this structure, recogni~able solely ~ith an enlargement of 1000 and not with an enlargement of 100, which is termed "bainitic"~
By T,Jay of comparison, according to the miGrograph of figure 8, with an enlargement of 100, when attacked with NI'rA~ this is a ferrito-perlitic spheroidal graphite cast-iron, contt~;ning 40% ferrite t~nd 50% perlite, ~ ~I''v. ~ Y o ~ k, "~ 3~G3 the rem~;n~er being spheroidal graphite~ The round black æeas æe graphite nodules. The nodules are surrounded by white areas consituting the ferrite. ~he rer~i~;ng grey areas are perlite. This is the structure of a centrifugally cast tube of conventional type.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Centrifugally cast tube of spheroidal graphite cast-iron, characterised in that the cast-iron has the following composition by weight:
- carbon : 2.5 - 4.0%
- silicon : 2 - 4.0%
- manganese: 0.1 - 0.6%
- nickel: 0 - 3.5%
- copper: 0 - 11%
- magnesium: 0 - 0.5%
- sulphur: 0.01% maximum - phosphorus: 0.06% maximum - the remainder being iron, this cast iron having a bainitic structure.
- carbon : 2.5 - 4.0%
- silicon : 2 - 4.0%
- manganese: 0.1 - 0.6%
- nickel: 0 - 3.5%
- copper: 0 - 11%
- magnesium: 0 - 0.5%
- sulphur: 0.01% maximum - phosphorus: 0.06% maximum - the remainder being iron, this cast iron having a bainitic structure.
2. Tube according to claim 1, characterised in that the cast-iron has the following composition:
- carbon: 3.6%
- silicon: 2.4%
- manganese: 0.5%
- nickel: 0.2%
- copper: 0.5%
- magnesium: 0.03%
- sulphur: ?0.01%
- phosphorus: ? 0.06%, the remainder being iron.
- carbon: 3.6%
- silicon: 2.4%
- manganese: 0.5%
- nickel: 0.2%
- copper: 0.5%
- magnesium: 0.03%
- sulphur: ?0.01%
- phosphorus: ? 0.06%, the remainder being iron.
3. Tube according to one of claims 1 and 2, characterized in that it corresponds to the following table:
4. Method for the manufacture of a centrifugally cast tube of spheroidal graphite cast-iron, the cast-iron having a bainitic structure and a composition by weight of carbon: 2.5-4.0%, silicon: 2-4.0%, manganese: 0.1-0.6%, nickel: 0-3.5%, copper: 0-11%, magnesium: 0-0.5%, sulphur:
0.01% maximum, and phosphorus: 0.06% maximum, the remainder being iron, characterized in that one starts with a spher-oidal graphite cast-iron having the composition mentioned, this cast-iron is poured into a centrifugal chill-mould pro-vided with a refractory coating and cooled externally by water, the centrifugally cast tube is left to cool in the chill-mould to a temperature of the order of 800-1000°C in order to acquire an austenitic structure, then, still in the chill-mould, it is cooled vigorously and uniformly over its entire length by spraying water or a mixture of air and water onto its inner wall, to a temperature of approximately 250-400°C, in order to give it an austenitic or bainitic struc-ture, then the tube is removed from its chill-mould and placed inside a furnace kept at a temperature of between 250 and 450°C in order to create or maintain a bainitic structure and the tube is removed from the furnace in order to allow it to cool in the air.
0.01% maximum, and phosphorus: 0.06% maximum, the remainder being iron, characterized in that one starts with a spher-oidal graphite cast-iron having the composition mentioned, this cast-iron is poured into a centrifugal chill-mould pro-vided with a refractory coating and cooled externally by water, the centrifugally cast tube is left to cool in the chill-mould to a temperature of the order of 800-1000°C in order to acquire an austenitic structure, then, still in the chill-mould, it is cooled vigorously and uniformly over its entire length by spraying water or a mixture of air and water onto its inner wall, to a temperature of approximately 250-400°C, in order to give it an austenitic or bainitic struc-ture, then the tube is removed from its chill-mould and placed inside a furnace kept at a temperature of between 250 and 450°C in order to create or maintain a bainitic structure and the tube is removed from the furnace in order to allow it to cool in the air.
5. Method according to claim 4, characterised in that an aqueous mixture of silica and bentonite is used as the refractory coating for the centrifugal chill-mould.
6. Method according to one of claims 4 and 5, characterised in that during the first stage of cooling to a temperature of approximately 800 to 1000°C and during the stage of vigorous cooling by spraying water onto the inner wall of the tube from 800-1000°C to 250-400°C, the tube is set in rotation by means of the centrifugal chill-mould.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8203827 | 1982-03-01 | ||
| FR8203827A FR2508984B1 (en) | 1981-07-06 | 1982-03-08 | LEVER CONTROL DEVICE, PRESSURE ACCUMULATION VALVE OPERATING APPARATUS AND HYDRAULIC CONTROL CIRCUIT |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1201366A true CA1201366A (en) | 1986-03-04 |
Family
ID=9271726
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000422457A Expired CA1201366A (en) | 1982-03-01 | 1983-02-25 | Centrifugally cast tube of spheroidal graphite cast- iron and its method of manufacture |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1201366A (en) |
-
1983
- 1983-02-25 CA CA000422457A patent/CA1201366A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4448610A (en) | Centrifugally cast tube of spheroidal graphite cast-iron and its method of manufacture | |
| CN111187979B (en) | Graphite-containing bainite semi-steel section steel finish rolling working roll | |
| CN1106981A (en) | Wear-resistant and seizure-resistant hot-rolled rolls | |
| WO2011015005A1 (en) | Method for casting planet carrier made of ductile cast-iron | |
| JP2013144313A (en) | Method for producing austempered spheroidal graphite cast iron article | |
| JPH09296215A (en) | Method for manufacturing spheroidal graphite cast iron member | |
| CN112458356A (en) | Phi 14mm wire rod for 1860MPa bridge cable galvanized steel wire and preparation method | |
| CN110964973B (en) | A kind of high manganese CADI and its heat treatment method | |
| CN116638060B (en) | Production method of centrifugal spheroidal graphite cast iron pipe | |
| CN110052589B (en) | Isostatic pressing heat preservation furnace and method for horizontal continuous casting of nodular cast iron section | |
| US4810311A (en) | Process for manufacturing a high strength rail | |
| US3998664A (en) | Cast iron | |
| US4619713A (en) | Method of producing nodular graphite cast iron | |
| JPH0259202B2 (en) | ||
| CN112893779B (en) | Sand-free molding method for roller | |
| JPS6347773B2 (en) | ||
| JPS61199035A (en) | Manufacture of composite roll having tough neck part | |
| KR100398384B1 (en) | A method of manufacturing wire fod for presiressed concrete wire having superior strength and toughness | |
| JPH0512411B2 (en) | ||
| CN111560559A (en) | Shock absorber blank based on austempered ductile iron and production process thereof | |
| KR100398387B1 (en) | A method of manufacturing high strength wire rods having superior fatigue life for engine valve-spring | |
| US1846684A (en) | Heat treatment of rails | |
| CN121344304A (en) | A method for preparing high-strength, large-section ductile iron base components | |
| SU1671711A1 (en) | Method of normalizing iron castings | |
| Fitzgerald | Vacuum Heat Treating Premium H-13 Die Casting Dies |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |