US3615880A - Ferrous metal die casting process and products - Google Patents

Ferrous metal die casting process and products Download PDF

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US3615880A
US3615880A US718640A US3615880DA US3615880A US 3615880 A US3615880 A US 3615880A US 718640 A US718640 A US 718640A US 3615880D A US3615880D A US 3615880DA US 3615880 A US3615880 A US 3615880A
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iron
cast
casting
metal
die
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Ronald L Barto
Dallas T Hurd
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General Electric Co
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General Electric Co
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure

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  • This invention relates to processes for casting and heattreating graphitic ferrous metals, and to the products of such processes. More particularly, it relates to processes for producing precision parts or articles of commerce of ferrous metals by pressure injection die casting in relatively permanent molds, followed by certain heat treatments.
  • an object of the present invention to provide a practical and economical process for repetitive pressure injection die casting of ferrous metals coupled with short heat treatments to produce castings with closely controlled dimensions, surface conditions, and metallurgical structures. Furthermore, an objective of the invention is to produce improved ferrous metal castings having greater strength, ductility, fine-grained structure for a substantial depth from the surface of the casting, and other properties generally superior to those obtainable from previously known casting methods, including an unusual ability to be beneficially altered or transformed in structure and properties by short and more economical post-casting thermal treatment.
  • the present invention in one of its embodiments provides a method for pressure injection die casting of articles of ferrous metals containing at least 50 percent of iron and more carbon than the maximum amount that is soluble in the matrix phase, followed by short heat treatments. (Percentages herein are by weight except where indicated otherwise.)
  • the casting is done in dies which are made of or have inserts or liners of certain refractory metals which have high heat transfer characteristics, adequate mechanical properties and high melting points.
  • the refractory metals are efficiently thermally coupled to a heat sink, such as the casting machine itself together with the surrounding atmosphere or a cooling system, to permit rapid extraction of heat from the castings.
  • the refractory metal should have a thermal diffusivity of at least about l ft.”/hr., a heat ditTusivity of at least about 40 B.t.u./ft. F.
  • the dies should be maintained at an elevated temperature such as about 500 F. or higher, depending on the particular ferrous alloy being cast, but below the freezing point of the ferrous metal being cast, while casting the metal, so as to essentially prevent surface irregularities and structural nonuniformities and discontinuities in the castings which would be caused by premature freezing of the liquid metal as it is being moved into the die.
  • Thermal diffusivity and heat diffusivity are useful measurements of the rate at which heat will be extracted from a casting by a mold material.
  • Thermal diffusivity is defined as K/pC,, where K is thermal conductivity in units of B.t.u./ft. F. hr., p is density in units of lb./ft. and C, is heat capacity in units of B.t.u./lb. F.
  • Thermal diffusivity is a measure of how fast heat can be transferred through a mold.
  • Heat diffusivity is defined as the square root of the product KpC and is a measure of the heat absorbing ability of a mold material.
  • B.t.u. means British Thermal Units
  • lb. means pounds avoirdupois
  • ft. means feet
  • hr. means hour
  • temperature is measured in degrees Fahrenheit.
  • the several specific embodiments of the invention include processes for producing articles of several types of alloys of iron and carbon, and also include the products of such processes.
  • the alloys of articles produced according to the invention include gray iron encased in white iron which is converted to malleable iron on heat treatment, white which is converted to malleable iron on heat treatment, and nodular iron which is sometimes known as ductile iron and having the free carbon in the form of regular spheroidized nodules of graphite.
  • Heat treatments of the invention alter the metallurgical structure in a way that can be seen by microscopy, improve at least certain mechanical properties, and have the effects of precipitating carbon from solution essentially all in the form of dispersed nodules in less than about 4 hours.
  • the effects include specifically: for malleable iron, malleablizing the as-cast white iron and preferably producing a matrix grain size smaller than the irregular spheroids or particles of graphite in the structure; and for nodular iron, the development of spheroidal nodules and increasing the amount of graphite in the nodules.
  • nodules includes both the irregular but rather compact spheroidal and nonflakey graphite typical of malleable iron. and also the regular spheroidal graphite particles typical of ductile iron; synonyms for ductile iron are nodular iron and spheroidal iron.
  • the heat treatments of the invention can be performed in the conventional temperature ranges for corresponding sand-cast alloys, or at lower temperatures.
  • malleable iron with a gray iron core is produced with a heat treatment about in the range of l,500 to 1,900 F. for 10 minutes to 2 hours, malleable iron in the same ranges but also up to 4 hours, and ductile iron about in the range of 1,500 to 2,000 F. for 10 minutes to 2 hours.
  • FIG. I is a schematic drawing of the central operating parts of a cold chamber pressure injection die casting machine, illustrating part of the method of the invention. In particular, it shows molten ferrous metal being poured into the chamber from which it is forced into the die for casting.
  • the inner parts of the die are formed of massive refractory metal inserts.
  • FIG. 2 shows the same apparatus after the molten metal has been forced into the die and as it is solidifying.
  • FIG. 3 once again shows the same apparatus, but in this case after the die has opened to permit removal of the casting and its feeding system or sprue.
  • FIG. 3a shows the die block with a different embodiment of the invention, that is, a relatively thin layer of refractory metal lining the die in place of the massive inserts of refractory metal of FIGS. 1 through 3.
  • FIG. 4 is the iron-rich end of the iron carbon phase diagram, locating specific compositions described herein.
  • FIGS. 5 through 8 are sets of photomicrographs showing the effects on metallurgical microstructure of the processes of the invention, in several cases as compared with prior art processes including sand casting and large ingot casting.
  • the microstructure for a particular pressure injection die cast ferrous metal alloy is shown as cast over the letter a and, where available, the corresponding microstructure produced by sand casting and equivalent in composition is shown over the letter b.
  • Each of the photomicrographs is originally at a stated magnification before about one-third reduction for reproduction in the printed United States Patent. Therefore, the actual magnification of the figures as shown in the printed United States Patent will be about 67 percent of the stated magnification.
  • FIGS. 5a and 5b respectively show die cast and sand cast gray iron having a carbon equivalent of about 4.3 percent at a magnification of 200X.
  • FIG. 60 at 500x shows die cast white cast iron with a carbon equivalent of about 3.0 percent. Sand cast white cast iron would look about the same but with somewhat larger grain and particle sizes.
  • FIGS. 7a and 7b at 200x respectively show malleable iron produced by annealing die cast white cast iron of the type shown in FIG. 6a and comparable sand cast white iron.
  • the malleable iron produced from die cast white iron was produced by heat treating or annealing 2 hours at l,650 F., a
  • the die cast matrix grains are substantially smaller than the graphite nodules, which is not the usual malleable iron structure.
  • FIGS. 8a, 8b, and 8c at lOOX show unetched microstructures of nodular or ductile iron containing 3.6% percent carbon, 2.12% silicon, and trace amounts of other elements and impurities which have been inoculated while molten and just before casting with magnesium in amount of about 0.12 percent, added to the melt as ferrosilicon containing 5 percent magnesium.
  • FIG. 8a shows the metal as die cast in accordance with the invention, but before heat treatment. Although small graphite particles are present in a white iron matrix, the typical ductile iron structure has not been fully developed.
  • FIG. 8b shows the same metal as sand cast with a typical ductile structure.
  • FIG. 8c is the microstructure of the die cast ductile iron after a heat treatment of l,700 F. for 30 minutes to develop the ductile iron structure.
  • Table I compares the thermal difiusivity and heat diffusivity of tungsten and molybdenum with a typical tool steel used for dies, AISI-SAE H-l I die steel, which has a composition of about 5.00% chromium, l.50% molybdenum, vanadium, 0.35% carbon, balance iron.
  • the thermal diffusivity and heat diffusivity parameters were defined above in the Summary section.
  • the melting point of the refractory metal alloy itself should be above about 3,000 F.
  • certain composite materials could be satisfactory having small amounts of lower melting materials dispersed through the refractory metal, such as copper-infiltrated tungsten, or composites of refractory metal particles or other shapes, such as wires, rods or plates, bonded together by minor amounts of lower melting metals, so long as there is not even incipient melting of separate minor phases at so low a temperature as to make the alloy or composite material unsuitable for reasons such as weakness.
  • thin coatings of lubricants, die washes, or other materials that do not interfere with characteristics of the invention can be used on the dies.
  • the thermal diffusivity and heat difi'usivity depend on thermal conductivity, density and heat capacity and determine the rate at which castings can be produced in die inserts or composite cavities made in accordance with the present invention and the type of efi'ective solidification and cooling given to the castings.
  • the refractory metal die liners of the invention be repairable by building up material thickness by means such as welding or plasma spraying, or repairable by brazing, sintering, drilling and inserting plugs shrink fitted into holes, and otherwise.
  • Such articles are characterized by smooth surfaces, an unusual degree of fineness of grain structure, and superior physical properties such as tensile and rupture strength, ductility, and, at least in some cases, corrosion resistance.
  • a primary advantage of such cast articles is their increased susceptibility to various heat treatments which are more economical than those of the prior art and which retain and improve characteristics of the castings.
  • the entire mass of molten metal is injected into the heated die in a very short time, which can be less than about I second depending on the size of the mold. With most graphitic ferrous metal alloys being cast, solidification can be essentially completed in processes of the invention within less than about 2 seconds if the maximum section thickness of the casting is less than about one-half inch.
  • the present invention provides for the casting of metals of low heat conductivity in dies which have high heat conductivity. Therefore, beyond a certain point, the rate of heat transfer from casting to the mold during freezing will be determined primarily by the rate of transfer of heat energy from the interior of the casting through the frozen metal to the mold wall surface rather than the temperature differential at the interface between the mold and the casting. Also, relatively uniform, low temperature through the cross section of the molten metal leads to greater nucleation and finer as-cast grain size.
  • the versatility of the present invention is further demonstrated by the realization that the ability to keep parts of the mold at quite high temperatures permits controlled uniform freezing of complex casting configurations to eliminate thermal stresses in the solidified metal which might otherwise be caused by nonuniform or zonal freezing and cooling.
  • heating or cooling methods can be applied in different sections of the mold to control different rates of heat removal from different parts of the castings, as desired.
  • the mold surfaces are kept at elevated temperatures, such as above about 500 F., or sometimes preferably in the range of about 700l,000 F., depending on the particular metal being cast, still maintaining a high degree of heat flow from the casting to and through the mold.
  • elevated temperatures such as above about 500 F., or sometimes preferably in the range of about 700l,000 F., depending on the particular metal being cast, still maintaining a high degree of heat flow from the casting to and through the mold.
  • FIGS. 1 through 3 illustrate the'process of the invention.
  • a conventional die casting machine well known in the art, preferably of the coldchamber type, is illustrated at l by a box in dashed lines.
  • a cold-chamber die casting machine can be distinguished from a hot-chamber machine in accordance with the following description.
  • the molten metal 5 is transferred manually as by pouring from ladle 2 through metal supply opening 15, or automatically, to a shot-sleeve 3.
  • Plunger 4 is designed to push the molten metal 5 from shotsleeve 3 through gate 16 into die cavity chamber 6 when plunger 4 is moved by an external power source as indicated at 7, such as a hydraulic cylinder.
  • a hot-chamber machine which could be used with the present invention, provides for automatic pumping of the molten metal from beneath the surface of a holding tank of the metal, not shown in these drawings.
  • the pressure source or pump in a hotchamber machine is normally immersed in the molten metal and operates at the temperature of the molten metal. It will be understood by those skilled in the art that a hot-chamber machine could be made to operate in the pressure die casting of ferrous metals if the metal pump was properly designed of suitable materials.
  • the die backup blocks comprise a movable half 8 and a fixed half 9.
  • Massive inserts of refractory metals are illustrated at 10 and 11 and are fixed in each of the halves 8 and 9.
  • Suitable means are provided for moving the movable half of the die 8 with its refractory metal insert 10 away from the fixed half 9 and its insert 11, such as by means of toggle linkages l2 and I3.
  • Suitable die casting machines known in the art provide substantial restraint between die backup block halves 8 and 9, and the dies are restrained in relation to the energy source 7 for plunger 4, so that the dies will not be forced open by the very large pressures generated in the liquid metal casting by plunger 4!.
  • injection pressures preferably in the order of about [,000 to 10,000 pounds per square inch are generally used, although substantially lower or higher pressures may be used within the scope of the invention.
  • FIG. 2 illustrates the die casting machine of FIG. I in which plunger 4 has forced liquid metal 5 into the casting cavity 6.
  • the liquid metal 5 is preferably caused to move into the cavity 6 very rapidly, depending on size such as in considerably less than I second, and would normally freeze substantially completely within less than I or 2 seconds after it fills the mold.
  • the plunger 4 seals off the metal supply opening 15 as plunger 4 advances past opening 15, so that molten metal 5 is forced into die cavity 6.
  • the refractory metal inserts are maintained at temperatures high enough to prevent premature freezing of the cast metal to avoid casting surface defects and faithfully reproduce the die cavity surfaces, generally above about 500 F., the actual temperature depending on the metal being cast.
  • temperatures can be attained by the use of electric heaters 19 in the die block itself, by preheating the die blocks internally or externally with torches or otherwise before commencing casting operations, or by heat from the metal being cast.
  • 4 kilowatts of electric heat input was more than sufficient to raise the dies to and maintain them at about 700 F. operating temperature.
  • the casting operations themselves tend to keep the dies at quite high elevated temperatures, and supplementary heat input may or may not be necessary, depending on the temperature of the metal, the time of the casting cycle, the heat absorbing ability of the die casting machine and its environment, and other factors.
  • FIG. 3 illustrates the same die casting machine after the casting has solidified.
  • Toggles l2 and 13 have opened to pullthe movable die half 8 with its refractory metal insert 10 away from fixed die half 9 with its refractory metal insert 11.
  • Simple means such as knock-out pins known in the art are normally provided to remove casting 17 with its solidified biscuit 18 from the fixed half 9 of the die backup block once the movable half 8 has moved out of the way.
  • the biscuit l8 and gate 16 can be cut off at section X-X.
  • Plunger 4 has retracted beyond the metal inlet 15 to allow metal to be poured in for the next casting.
  • the dies then can be closed again as illustrated in FIG. 1 to prepare for the next casting cycle.
  • FIG. 3a illustrates another embodiment of a die made for use with the invention having a relatively thin layer of refractory metal liner 10a in the die instead of the more massive inserts l and 11 ofFlGS. l, 2 and 3.
  • the efficient thermal coupling of the refractory metal insert or liner to the heat sink can be accomplished by carefully matching and fitting the insert or liner into the backup blocks.
  • the heat sink which can be the die backup blocks 8 and 9 or cooling water, or other means.
  • Thin liners could be physically bonded to the backup blocks as by brazing with a material that is a good heat conductor.
  • refractory metal inserts as massive as those illustrated at 10 and 11 be used.
  • the necessary minimum thickness of the refractory metal layer will depend on the backup material, as well as the nature of the ferrous alloy to be cast. With a backup material that has high heat conductivity, thinner refractory metal layers can be used, depending also on the respective thermal expansion characteristics of the backup and liner materials. Also, composite dies made of several layers of different materials are conceivable, so long as the material facing the molten metal is a refractory metal of the invention and is thick enough to control the heat transfer characteristics of the mold and withstand the rigors of repetitive casting.
  • massive inserts of at least 15-inch minimum thickness of refractory metals are used in steel molds.
  • thinner inserts which might be made by plasma spraying or otherwise bonding suitable refractory metals as cladding on other materials such as copper alloys or die steels could have a refractory metal thickness as little as about 0.06 inch or less.
  • a suitable refractory metal is unalloyed molybdenum produced by conventional commercial powder metallurgical techniques.
  • unalloyed tungsten also preferably produced by powder metallurgical techniques, or produced by are melting or electron beam melting, also may be desirable.
  • alloys such as, for example, molybdenum strengthened by the addition of small amounts of precipitate-phase forming elements such as titanium, zirconium, and hafnium, together with carbon, nitrogen, boron or other elements, or tungsten strengthened by the addition of rhenium or other soluble alloying additions, are use in] as molds and mold lining materials.
  • molybdenum and tungsten metals wrought tungsten, wrought molybdenum, and alloys or composites that have suitable thermal characteristics can be used, including tungsten containing a dispersed phase of about 2 percent thon'a, tungsten or molybdenum powders liquid-phase sintered with nickel, iron or other metals, and, in some applications, copperor silver-infiltrated porous pressed and sintered tungsten.
  • the refractory metal part of the die is thick enough, it can be used without die steel or other backup material.
  • the working portions or highly stressed portions of castings should be thin enough to have uniform structures and grain sizes characteristic of the invention throughout their cross sections.
  • the cross sections in these portions should not be so thick that the preferred structure does not extend substantially through it.
  • Other portions of the same casting can be made thicker and have a cored structure with more conventional structure and grain sizes at the center, such as useful die cast objects of malleable iron having centers or cores of gray iron.
  • the mold or die considered as a structural entity, must have certain minimum properties of strength, thermal absorptivity and conductivity, and melting point.
  • the yield strength of the die material should be such at every point within the structure so as to resist the stresses at that point as determined by injection pres sure, cavity geometry, and distance of that point from the mold-casting interface.
  • the thermal absorptivity, which is the heat diffusivity, of the mold structure is such that the heat of fusion together with any usual degree of superheat can be removed from the critical section of the casting with sufficient rapidity to achieve the desired fine-grained cast structure.
  • the thermal conductivity of the mold structure be sufficient so that such heat of fusion, superheat, and any portion of residual heat transferred to the mold following solidification but prior to ejection of the casting, be transferred efficiently by the refractory metal mold liner or insert to the heat sink, such as into cooling water, conducted to the body of the casting machine, or radiated to the atmosphere, or otherwise disposed of, with sufficient rapidity so that the average temperature of the mold surface preferably remains essentially constant with time during extended sequences of repetitive casting, or at least does not reach deleteriously high levels.
  • the average operating temperature is determined from the maximum and minimum temperatures occurring during cyclical operation. Further, it is highly desirable that the mold surface have a melting point substantially higher than that of the metal being cast.
  • the properties of the mold must be such that it not only has a high degree of permanence for extended casting operations, but
  • the minimum properties which a mold must have to meet the above requirements will depend on several parameters including: the size and shape of the casting, the precasting mold temperature, the temperature at which the liquid metal is injected into the mold, the pressure of injection, the heat capacity, density, and thermal conductivity of the particular metal or alloy being cast, and other factors. It also will be apparent that different combinations of refractory metal mold surface and substrate can be devised to meet such requirements, depending on all the above parameters as well as the particular mold material, backup material, heat-sink mechanism, and other parameters.
  • the invention is applicable to the production of a broad variety of articles of commerce cast from ferrous metals containing at least 50 percent iron.
  • the invention can be used to produce such products as: automotive components such as rocker arms, steering knuckles, bearings, and fittings; appliance parts such as linkages, gears, valves, and pulleys; architectural fittings; miscellaneous hardware; and many other types of products.
  • FIG. 4 is the iron-rich end of the iron-carbon phase diagram showing the phases present at metastable equilibrium at the indicated temperatures with the indicated percentages of carbon in a binary iron-carbon alloy.
  • the metastable nature of the equilibrium stems from the fact that Fe C, called iron carbide or cementite, is thermodynamically unstable at elevated temperatures with respect to decomposition to free carbon and iron-carbon solid solution.
  • other alloying elements such as chromium, nickel, phosphorus, and silicon
  • pure iron containing no carbon is seen to melt at about 2,800 F.
  • the minimum melting point for the eutectic composition occurs with 4.3 percent carbon at 2,066 F.
  • commercial gray cast irons can be found to melt at lower temperatures.
  • Ferrite (a-iron) and B-iron have body-centeredcubic (BCC) crystalline structures, while austenite (y-iron) has a face-centered-cubic (FCC) structure.
  • Austenite, ferrite and S-iron are solutions of carbon in iron. Austenite normally is not stable at temperatures below about 1,333" F., but its stability at lower temperatures may be enhanced by certain alloying additions, such as nickel, for example.
  • Iron-carbon alloys containing more than about 1.7 percent carbon or the equivalent thereof, the maximum amount of carbon that is soluble in austenite, are known as cast or graphitic irons, and are characterized by the presence of free carbon or graphite as a dispersed phase after heat treatments of the iron.
  • the matrix phase may retain more or less carbon in solution depending on the nature and duration of the heat treatment.
  • Iron-carbon alloys are quite sensitive to heat treatments which cause variations in their structure and can harden or soften the metal in various ways.
  • the cast irons often contain silicon and other alloying elements.
  • the carbon equivalent of a cast iron is detennined by adding to the actual percentage carbon content one-third of the silicon percentage and making other adjustments known in the art for other elements present such as phosphorus.
  • the solidified product normally is gray cast iron, which is a matrix of ferrite with dispersed platelets of graphite. If any pearlite is present, suitable heat treatment can convert it to ferrite and graphite.
  • the casting can be annealed to remove casting stresses at lower temperatures, leaving the gray iron matrix in a pearlitic condition.
  • Carbon equivalents over 4.3 percent are generally undesirable since coarse graphite flakes, known as kish, form in the melt and can deleteriously affect the castings.
  • Graphite flakes in cast iron can be considered mechanically as almost a notch or void, so the size, shape and distribution of graphite in cast irons is most important.
  • the fine grain size and small graphite particles in products of the invention are very desirable.
  • malleable iron or ductile iron can be used.
  • Malleable iron is produced by annealing white cast iron (a metastablestructure containing no free carbon) to cause the graphite to form as relatively compact nodules or irregular spheroids, similar in shape to popcorn balls, in contrast to the elongated flake graphite types in gray cast iron.
  • the white cast iron from which malleable iron is produced normally is a low carbon cast iron, such as containing 2.5 percent carbon and 1.5 percent silicon for a carbon equivalent of 3.0 percent; White iron can be produced with lower carbon contents in sand molds and with relatively high carbon contents in chill molds.
  • White iron is cast iron containing ferrite and cementite, generally with more or less pearlite, and no free graphite. lt is quite strong, hard and brittle. On proper annealing, the cementite decomposes to give graphite nodules in ferrite, or, if preferred, in a pearlitic matrix. This is malleable iron and is much more ductile and much softer than white iron, and tougher than gray iron.
  • Graphitizing agents such as silicon, nickel and copper encourage the formation of gray iron rather than white iron.
  • Duplex malleable/gray iron metal articles of the invention ascast have a white iron encasement or surface around a gray iron core. This white iron can be converted to a malleable iron by appropriate heat treatment, and graphitizing agents can be used to minimize thickness of the white iron case. Suitable heat treatments can convert the white iron at the surface to a malleable iron and leave the gray iron core in the desired metallurgical condition.
  • Ductile iron with regular spherical graphite particles can be produced by adding certain inoculants, such as magnesium, to molten graphitic iron compositions, just before pouring the castings. This type of structure can be further refined and developed by post-casting thermal treatments.
  • inoculants such as magnesium
  • Example I Duplex Malleable/Gray Cast iron A ferrous metal alloy of the composition: 3.5% carbon, 2.2% silicon, 0.7% manganese together with incidental amounts of other elements such as phosphorus, sulfur and others, balance iron, a member of the class of alloys known generally as gray cast iron and designated specifically as having a carbon equivalent of 4.23 percent, located as Ex. I on FIG. 4, was melted in an electric induction furnace. A suitable amount of this metal in the molten condition was ladled at a temperature of about 2,400 F.
  • the casting had substantially solidified, reproducing precisely the shape and closely duplicating the surface of the pressed and sintered molybdenum mold cavity, whereupon the adjoining halves of the mold cavity were opened by the mechanism of the casting machine and the solid metal part was ejected as illustrated by FIG. 3.
  • substantially solidified is meant that the casting was solidified sufiiciently to allow its removal from the mold. It is not known whether some molten metal might then still be present at the center of the casting.
  • the casting comprised an outer layer of white iron with an inner core of gray iron.
  • the unusual as-cast grain structure of the center of the solidified casting is illustrated in FIG. 5a. Heat treating at L650 F. for about 2 hours converted the working surfaces of the casting to malleable iron. Properties of this cast metal are documented in table II in comparison with properties for metal of the same composition cast in sand molds and given the same anneal.
  • ksi means thousands of pounds per square inch
  • R means hardness on the Rockwell 8" scale.
  • Rupture tests were made by three-point bending of bars 3X1 Axle inches with 2 inches between supports. All tests were made at room temperature of about 77 F.
  • Tensile tests were mostly performed on standard machined button head specimens with a gauge diameter of 0.250 inch and length of about 1.3 inches, using an elastic strain rate of 0.005 inchlinch/minute (in./in./min.) and a plastic strain rate of 0.05 in.lin./min.
  • the annealing treatment results in a maximum soft condition so as to allow equal comparison of properties without regard to strength improvements that may be obtained by other known heat treatments.
  • Example 2 Malleable Cast Iron A ferrous metal alloy of the composition: 2.5% carbon, l.5% silicon, 0.45% manganese, 0.6% molybdenum, together with incidental amounts of other elements such as phosphorus, sulfur and others, balance iron, to be cast as white iron, having a carbon equivalent of 3.0 percent, located as Ex. 2 on FIG. 4, and subsequently to be heat treated to form malleable cast iron, was melted in an electric induction furnace. A suitable amount of this metal in the molten condition was ladled at a temperature of about 2,450 F. into the injection chamber of a pressure injection die casting machine, whereupon it was cast in the same manner as example 1. The as-cast grain structure of the solidified white cast iron metal part is illustrated in FIG.
  • FIG. 7a Mechanical properties of the heat treated or annealed cast metal are documented in table II] in comparison with typical properties for metal otherwise the same but cast in sand molds and then malleablized or annealed for times in excess of at least 48 to 60 hours at a temperature in the range of l,600 to 1,700 F., as is customary in the art of making malleable iron.
  • Example 3 Ductile Cast Iron Copper-free pig iron having the following composition was used as a charge material: 4.4% carbon, 010% manganese, 0.029% phosphorous, 0.028% sulfur, and 0.73% silicon. In order to lower the carbon content, percent Armco iron was added to the charge. Another 1.4 percent silicon metal was added to increase the silicon content to the desired level.
  • Induction melting of a l00-pound charge was accomplished in a ZOO-pound capacity furnace. Temperature of the melt was maintained at 2800-2850" F. before inoculation. Carbon and silicon were quickly determined by the Leco and X-ray spectrographic methods respectively. Carbon was found to be 3.6 percent and silicon 2.1 percent.
  • the thickness of the die cast parts ranged from three-sixteenth of an inch to twenty-one thirty-seconds of an inch. Because of the chilling effect in die casting, the total thickness of the parts appeared, upon fracture, to be white, and the microstructure is shown in FIG. 8a. After annealing at 1700 F. for 30 minutes, the castings transformed to nodular iron, as illustrated in FIG. 8c. Mechanical testing of a 1 -inch gauge length sample at a strain rate of 0.02 in./in./min.
  • the sand-cast nodular iron had a Brinnell Hardness Number of about I85, indicating that the die cast nodular iron, even after the wk-hour anneal, is considerably harder and stronger than the sand-cast metal.
  • Example 4 Duplex Malleable/Gray Cast Iron Duplex malleable/gray cast iron was cast and then converted by heat treatment successfully as in example I, but in wrought molybdenum die inserts using a plunger speed of I30 ft./min. and a pressure of 3000 p.s.i.
  • Example 5 Malleable Cast Iron Malleable cast iron was produced successfully as in example 2, but in copper-infiltrated tungsten die inserts using a plunger speed of I30 ft./min. and a pressure of 9000 p.s.i. Examples 2 and 5 show that white cast iron can be produced by use of the invention with unusually high carbon equivalents. Broader ranges of composition can be used with the present invention generally, and particularly to produce malleable iron, than with methods of the prior art.
  • a process for repetitive pressure injection die casting and heat treating of articles of graphited iron compositions containing at least 50 percent by weight of iron and more than the maximum amount of carbon that is soluble in the composition comprising the sequential steps of;
  • said refractory metal being thick enough to enable control of the heat transfer characteristics of the mold and adequate to withstand the rigors of repetitive casting, and said process being operated with the surfaces of said dies at a sufficiently elevated average operating temperature above about 500 F. to substantially prevent surface irregularities in the cast articles due to premature freezing, but substantially below the freezing point of said ferrous metals,
  • said refractory metal is selected from the group consisting of tungsten and alloys containing at least 50 percent by weight of tungsten.
  • the metallurgical structure of said article is essentially that of fine-grained malleable iron having a core of fine-grained gray iron.
  • a process according to claim 5 in which said heat treating comprises heating said article at a temperature in the range of about l500 F. to about I900 F. for a time in the range of about 10 minutes to about 2 hours, to convert said white iron to malleable iron.
  • the metallurgical structure of said article is essentially that of malleable iron.
  • a process according to claim 7 in which said heat treating comprises heating said article at a temperature in the range of about l500 F. to about 1900 F. for a time in the range of about 10 minutes to about 4 hours, to convert said white iron to malleable iron.
  • a process according to claim 9 in which said heat treating comprises heating said article at a temperature in the range of about 1500" F. to about 2000 F. for a time in the range of about 10 minutes to about 2 hours to increae the amount of graphite precipitated in the form of spheroidal nodules.
  • a product of the process of claim 10. 16. A process of claim 1 in which the ferrous casting solidifies at a rapid enough rate to permit ejection of said casting from said die in a time of less than about 2 seconds for castings having a maximum thickness of no more than about one-half inch.

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Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3810505A (en) * 1970-12-07 1974-05-14 R Cross Die casting method
US4013115A (en) * 1974-02-27 1977-03-22 G.K.N. Group Services Limited Method of die casting high melting point metal
US4178983A (en) * 1977-09-29 1979-12-18 Toshiba Kikai Kabushiki Kaisha Method for manufacturing stainless steel die cast products having low melting point
WO2002043903A1 (en) * 2000-11-30 2002-06-06 Copper Development Association Apparatus and method for die casting
US6454880B1 (en) 1999-09-29 2002-09-24 Herbert (Lonny) A. Rickman, Jr. Material for die casting tooling components, method for making same, and tooling components made from the material and process
US6662852B2 (en) * 1999-09-16 2003-12-16 Caterpillar Inc Mold assembly and method for pressure casting elevated melting temperature materials
US20040026059A1 (en) * 2002-02-25 2004-02-12 Helmut Schaefer Permanent casting die with ceramic lining
US20040238148A1 (en) * 2003-03-20 2004-12-02 Yazaki Corporation Apparatus for producing a composite material including ceramic hollow particles and aluminum or aluminum alloy and method for producing the composite material the same
US20060140245A1 (en) * 2003-01-29 2006-06-29 Wynn Andrew M Methods of making inductively heatble articles, induction furnaces and components and materials
US20070137827A1 (en) * 2005-12-19 2007-06-21 Howmet Corporation Die casting in investment mold
US20170087627A1 (en) * 2013-02-19 2017-03-30 United Technologies Corporation Die configuration for high temperature diecasting
EP2612930A3 (de) * 2012-01-03 2017-07-19 General Electric Company Verfahren zur Herstellung eines ADI-Artikels
US20200030914A1 (en) * 2018-07-25 2020-01-30 Kabushiki Kaisha Toshiba Welding method, method for manufacturing welded product, and welded product
CN115710611A (zh) * 2022-09-10 2023-02-24 宁波拓铁机械有限公司 一种大型注塑机用模板铸件的铸造方法
EP4166313A1 (de) * 2021-10-18 2023-04-19 IAG Industrie Automatisierungsgesellschaft mbH Presswerkzeug zum verpressen von compoundmischungen

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3810505A (en) * 1970-12-07 1974-05-14 R Cross Die casting method
US4013115A (en) * 1974-02-27 1977-03-22 G.K.N. Group Services Limited Method of die casting high melting point metal
US4178983A (en) * 1977-09-29 1979-12-18 Toshiba Kikai Kabushiki Kaisha Method for manufacturing stainless steel die cast products having low melting point
US6662852B2 (en) * 1999-09-16 2003-12-16 Caterpillar Inc Mold assembly and method for pressure casting elevated melting temperature materials
US6454880B1 (en) 1999-09-29 2002-09-24 Herbert (Lonny) A. Rickman, Jr. Material for die casting tooling components, method for making same, and tooling components made from the material and process
WO2002043903A1 (en) * 2000-11-30 2002-06-06 Copper Development Association Apparatus and method for die casting
US6786272B2 (en) * 2000-11-30 2004-09-07 Copper Development Association, Inc. Apparatus and method for die casting
US20040026059A1 (en) * 2002-02-25 2004-02-12 Helmut Schaefer Permanent casting die with ceramic lining
US20060140245A1 (en) * 2003-01-29 2006-06-29 Wynn Andrew M Methods of making inductively heatble articles, induction furnaces and components and materials
US20040238148A1 (en) * 2003-03-20 2004-12-02 Yazaki Corporation Apparatus for producing a composite material including ceramic hollow particles and aluminum or aluminum alloy and method for producing the composite material the same
US7011135B2 (en) * 2003-03-20 2006-03-14 Yazaki Corporation Apparatus for producing a composite material including ceramic hollow particles and aluminum or aluminum alloy and method for producing the composite material the same
US20070137827A1 (en) * 2005-12-19 2007-06-21 Howmet Corporation Die casting in investment mold
EP2612930A3 (de) * 2012-01-03 2017-07-19 General Electric Company Verfahren zur Herstellung eines ADI-Artikels
US20170087627A1 (en) * 2013-02-19 2017-03-30 United Technologies Corporation Die configuration for high temperature diecasting
US20200030914A1 (en) * 2018-07-25 2020-01-30 Kabushiki Kaisha Toshiba Welding method, method for manufacturing welded product, and welded product
EP4166313A1 (de) * 2021-10-18 2023-04-19 IAG Industrie Automatisierungsgesellschaft mbH Presswerkzeug zum verpressen von compoundmischungen
CN115710611A (zh) * 2022-09-10 2023-02-24 宁波拓铁机械有限公司 一种大型注塑机用模板铸件的铸造方法
CN115710611B (zh) * 2022-09-10 2024-05-03 宁波拓铁机械有限公司 一种大型注塑机用模板铸件的铸造方法

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