US20090183802A1 - Forging steel, and forged products obtainable therefrom - Google Patents

Forging steel, and forged products obtainable therefrom Download PDF

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US20090183802A1
US20090183802A1 US12/345,100 US34510008A US2009183802A1 US 20090183802 A1 US20090183802 A1 US 20090183802A1 US 34510008 A US34510008 A US 34510008A US 2009183802 A1 US2009183802 A1 US 2009183802A1
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dissolved
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steel
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ppb
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Tetsushi Deura
Motohiro Nagao
Takashi Abiko
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Kobe Steel Ltd
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Kobe Steel Ltd
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Assigned to KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL, LTD.) reassignment KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL, LTD.) ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ABIKO, TAKASHI, DEURA, TETSUSHI, NAGAO, MOTOHIRO
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
    • B21K1/00—Making machine elements
    • B21K1/06—Making machine elements axles or shafts
    • B21K1/08—Making machine elements axles or shafts crankshafts
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/072—Treatment with gases
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten

Definitions

  • This invention relates to forging steel and forged products obtainable from the use of the above forging steel. While the forged products manufactured from the forging steel of the present invention are being utilized usefully and widely in such industrial fields as machinery, ships and vessels, electrical equipment, etc., explanation hereunder is going to be made centering on an application to the crankshaft used for a power transmission member in a marine driving source as an example of typical application.
  • the large-size crankshaft used as a power transmission member in a marine driving source requires superior fatigue characteristics that rarely cause fatigue breakdown even under a very severe use environment.
  • the Non-patent Document 1 describes that improvement in fatigue characteristics was tried by free command of processing technology.
  • the Non-patent Document 1 indicates that the RR (Roedere Ruget) method was adopted to achieve a remarkable betterment in fatigue strength as compared to the case of a crankshaft manufactured by the flat die forging method and also that cold roll processing was applied for improvement of fatigue strength.
  • the Non-patent Document 2 examines possibility of improving fatigue characteristics of the low-alloy steel used for the marine crankshaft. To be more precise, the Non-patent Document 2 indicates that (1) the inclusion in the steel is apt to become a starting point of fatigue breakdown and such inclination is likely to become more apparent as steel develops to have higher strength; (2) the larger the size of the inclusion is, the lower the fatigue strength is likely to be; and (3) any steel material containing elongated inclusion has a tendency of easily showing anisotropy in fatigue strength. The Document concludes that for the betterment of fatigue characteristics of the forging material, it is effective to make the inclusion globular in shape and smaller in size.
  • Non-patent Documents do not go as far as to disclose concrete means about how to realize globalizing the shape of the inclusion and making it smaller. It is neither made clear in what range the inclusion should be controlled kind-wise and size-wise. Therefore, further studies seem to be required to realize morphology control of the inclusion useful for enhancement of fatigue characteristics.
  • Patent Document 3 and the Patent Document 4 show that by super-refining the oxide type inclusions, it is possible to increase plane fatigue strength and tooth-bend fatigue strength in relation to gear material.
  • these documents suggest that MgO and MgO.Al 2 O 3 , which are less cohesive and coalesced, should be created as the oxide type inclusions. It is also made clear that replacing a part of sulfide MnS with (Mn.Mg)S can help suppress elongational tendency of the inclusions and reduce anisotropy in mechanical strength.
  • the Patent Document 5 discloses that as sulfide, MnS, CaS, MgS, (Ca, Mn)S, and (Ca, Mg, Mn)S were made to be present for the purpose of producing machine structural steel with superior machinability.
  • the Patent Document 5 clarifies specifically that if the morphology of sulfide can be controlled by having REM, Ca and Mg contained, it becomes possible to suppress anisotropy of mechanical property and also to enhance the machinability to a level higher than that of a S-contained free cutting steel.
  • the Patent Document 6 may be marked as one that is targeted at forged products used for the above power transmission member, etc., in the marine driving source.
  • This Patent Document 6 prescribes contained amount for each of S, Ca, Mg, Al, and O, and indicates that fatigue characteristic can be improved if the contained amounts of Ca and Mg are so arranged as to satisfy the formula (1).
  • further studies seem to be needed on the basis of more concrete knowledge on the morphology of inclusions existing in large-size steel ingots.
  • Non-patent Document 1 “Progress and Improvement of Crankshaft,” Journal of the Marine Engineering Society of Japan, October 1973, Vol. 8, No. 10, pp. 54-59
  • Patent Document 1 Japanese Examined Patent Application Publication No. 58-35255 (JP-B-58-35255)
  • Patent Document 2 Japanese Examined Patent Application Publication No. 57-59295 (JP-B-57-59295)
  • Patent Document 3 Japanese Unexamined Patent Application Publication No. 07-188853 (JP-A-07-188853)
  • Patent Document 4 Japanese Unexamined Patent Application Publication No. 07-238342 (JP-A-07-238342)
  • Patent Document 5 Japanese Unexamined Patent Application Publication No. 2000-87179 (JP-A-2000-87179)
  • Patent Document 6 Japanese Unexamined Patent Application Publication No. 2004-225128 (JP-A-2004-225128)
  • This invention has been made in view of the forgoing circumstances and has the object of providing forging steel with refined inclusions so as to make available forged products (including parts) having excellent fatigue characteristics and also providing forged products (including parts) (crankshafts in particular) that is obtainable from the use of the above-mentioned forging steel and can exhibit excellent fatigue characteristics.
  • the forging steel according to a primary aspect of the present invention is to comply with the following conditions concerning contained amounts.
  • dissolved Ca and dissolved Mg should satisfy any one of the following (I) to (IV).
  • ppb and ppm denote respectively “ppb by mass” and “ppm by mass.”
  • the forging steel of the aspect of the present invention may as well contain other elements shown below and on the conditions shown together.
  • the forging steel of the aspect of the present invention may contain inclusions in it, the largest one of which is less than 100 ⁇ m in equivalent of diameter of a circle to which the inclusion is assumed to be approximated.
  • the aspect of the present invention includes the forged product (a crankshaft in particular) manufactured from the forging steel of the present invention.
  • the aspect of the present invention is configured as described above, and by adjusting the amount of the dissolved Ca and the dissolved Mg in the steel, it has become possible to control the morphology of the inclusions formed and thereby to provide forging steel with refined inclusions.
  • the forged products available from the use of such forging steel can be expected to show excellent fatigue characteristics and prove particularly useful for large-size forged products such as crankshafts for ships and vessels.
  • FIG. 1 is a graph showing the range of amount of Total Ca and the range of amount of Total Mg prescribed in the present invention.
  • FIG. 2 is a graph showing the correlation between the diameter of an assumed circle equivalent area-wise to the largest inclusion existing in the steel.
  • the inventors of the present invention have been making studies from various angles, while setting our final target at enhancement of fatigue characteristics of the forged products which are subject to use under severe environment.
  • large-size steel ingots for example, of a size more than 20 tons
  • the present invention firstly sets forth that the amounts of the dissolved Ca and the dissolved Mg in the steel should be limited within any one of the above ranges (I) to (IV). More explanation follows on each range.
  • low-melting oxides (Ca, Al, Mg)O ⁇ this expression means oxides comprising all the elements in the parenthesis; this applies to other cases hereinafter ⁇ are created. As these oxides are easily deformable during forging, it is possible to refine the size of inclusions contained in the forged products.
  • low-melting (Ca, Mg, Mn)S this means sulfides comprising all the elements in the parenthesis; this applies to other cases hereinafter ⁇ or (Ca, Mg)S are created (when the contained amounts of dissolved Ca and dissolved Mg are relatively abounding, the sulfide tends to become (Ca, Mg)S).
  • the sulfides (Ca, Mg)S which get more easily refined and dispersed as compared to MnS, are able to work effectively to make the inclusions contained in the forging products refined in size.
  • the oxides available change from high-melting MgO to low-melting (Ca, Al, Mg)O
  • Sulfides also change from high-melting MgS to low-melting (Ca, Mg)S.
  • the above (Ca, Al, Mg)O which are easily deformable during forging, and (Ca, Mg)S which get more easily refined and dispersed as compared to MgS, are able to work effectively to make the inclusions contained in the forging products refined in size.
  • MgS and MgO owing to their high-melting property, are difficult to be deformed in the course of forging but are likely to remain as coarse and large inclusions in the forged product.
  • the amount of dissolved Mg is below 0.04 ppm and the amount of dissolved Ca is below 2 ppb, this will lead to an undesired result of creating the coarse and large oxide Al 2 O 3 and the coarse and large sulfide MnS.
  • the contained amounts of the above dissolved Ca and dissolved Mg in the steel were measured by SIMS (Secondary Ion Mass Spectrometer) as shown in the embodiment described afterward.
  • Total Ca 0.0030% or less (0% not included)
  • the present invention lays it down that the Total Ca amount be suppressed at 0.0030% or less.
  • it should be 0.0020% or less, and more preferably, it should be 0.0015% or less.
  • Total Mg 0.0015% or less (0% not included)
  • the present invention lays it down that the Total Mg amount be suppressed at 0.0015% or less.
  • it should be 0.0010% or less, and more preferably, it should be 0.0008% or less.
  • FIG. 1 is a graph showing the ranges of the above Total Ca amount and Total Mg amount prescribed in the present invention, organized by using the data of the embodiment described later.
  • the amount of S contained in the steel should be held at 0.008% or less, preferably at 0.005% or less, more preferably at 0.003% or less, and still more preferably at 0.001% or less.
  • the present invention is characterized in that adjustment is applied to the above components with a view to refining the inclusions in the steel.
  • a crankshaft for example, or any other forged end product will acquire the strength and toughness as required and further the enhanced fatigue strength targeted in the present invention, it is recommended for the steel material to satisfy the composition shown below.
  • C is the element to contribute to improvement of strength, and to secure enough strength it should be contained at 0.2% or more, preferably at 0.25% or more, or more preferably at 0.3% or more. However, if the amount of C is excessive, it will tend to deteriorate toughness, so that C should be held at 0.6% or less, preferably at 0.55% or less, or more preferably at 0.5% or less.
  • Si also functions as a strength enhancing and deoxidation element, and to have both effect fully exerted, Si should be contained at 0.05% or more, preferably at 0.1% or more, or more preferably at 0.15% or more. However, if the amount of Si is excessive, inverted V segregation will tend to become intensive. It is necessary, therefore, that Si should be held at 0.5% or less, preferably at 0.45% or less, or more preferably at 0.4% or less.
  • Mn is another element enhancing strength besides boosting hardenability, and to secure enough strength and hardenability it should be contained at 0.2% or more, preferably at 0.5% or more, or more preferably at 0.8% or more. However, if the amount of Mn is excessive, inverted V segregation tends to become fostered. It is necessary, therefore, that Mn should be held at 1.5% or less, or preferably at 1.2% or less.
  • Ni is useful as an element for enhancing toughness, and it should be contained at 0.1% or more, and preferably at 0.2% or more. However, since excessive amount of Ni obliges increase in cost, Ni should be held at 3.5% or less, or preferably at 3.0% or less.
  • Cr is an element useful for increasing toughness as well as enhancing hardenability, and these functions are effectively exhibited when Cr is contained at 0.9% or more, preferably at 1.1% or more, or more preferably at 1.3% or more. However, if the amount of Cr is excessive, it will tend to foster inverted V segregation to become intensive making it difficult to obtain clean steel ingots, so that Si should be held at 4% or less, or preferably at 2% or less.
  • Mo is an element to effectively act on betterment of all of hardenability, strength, and toughness, and for the effective exhibition of these functions, Mo should be contained in the steel at 0.1% or more, preferably at 0.20% or more, or more preferably at 0.25% or more. However, since Mo has a low equilibrium distribution coefficient leading to easy occurrence of micro segregation (normal segregation), the amount of Mo in the steel should be held at 0.7% or less, preferably 0.6% or less, or more preferably 0.5% or less.
  • Al amount (hereafter, Al amount means “total Al amount”) should be set at 0.005% or more, or preferably at 0.010% or more.
  • Al has the tendency of fixing N in the form of AlN, etc., thus disturbing such functions as reinforcing the steel with composition of N, V, or other added elements.
  • the Al amount should be limited to 0.1% or less, or preferably to 0.08% or less.
  • O oxygen
  • SiO 2 , Al 2 O 3 , MgO, and CaO oxides as SiO 2 , Al 2 O 3 , MgO, and CaO, which then turn out to be inclusions. Therefore, the amount of O (total O amount) is desirable to be kept as low as possible and should be held at 0.0025% or less, or preferably at 0.0015% or less.
  • the composition used in the forging steel of the present invention is as explained above, and the remaining portion not shown above is composed of iron and inevitable impurities.
  • the latter may include P, N, etc., for example.
  • P is desired to be 0.03% or less, or preferably 0.02% or less.
  • N should be 0.01%, or preferably 0.008% or less.
  • V, Nb, Ta, and Hf have a good effect on precipitation strengthening and structural refinement and are useful for supporting the tendency toward intensified high-strength steel.
  • the steel In order to have these elements to effectively show their functionalities, one or more elements selected out of the group consisting of V, Nb, Ta, and Hf, it is desirable for the steel to contain a total of 0.005% or more, and preferably 0.01%. However, if the contained amount is excessive, the above effects will become saturated ending up economically wasted. Therefore, the total of contained amount should be held at 0.2% or less, and preferably at 0.15% or less
  • Ti is an element inevitably included in the impurities or otherwise contained purposely in expectation for the effect of improvement on resistance to hydrogen induced cracking.
  • Ti-related inclusions take the form of refined inclusions such as TiN, TiC, and Ti 4 C 2 S 2 , which, dispersed in the steel, occludes and captures excess hydrogen in the steel, achieving substantial effect in improving resistance to hydrogen cracking of the steel.
  • the amount of Ti to be contained in the steel should be 0.0002% or more, preferably 0.0004% or more, and still more preferably 0.0006% or more.
  • the amount of Ti included over 0.05% is likely to cause formation of coarse and large nitrides in the steel leading to decrease in fatigue strength. Therefore, the amount of Ti in the steel should be held at 0.05% or less, preferably at 0.03% or less, and more preferably 0.01% or less.
  • Cu may be either included in the steel as inevitable impurities or purposely added as a toughness enhancing element (when Cu is contained as a toughness enhancing element, the amount of Cu should be set at 0.05% or more, preferably 0.1% or more). However, if the contained amount of Cu becomes over 1.0%, this will probably necessitate increase in cost and might cause hot tearing. Therefore, the amount of Cu should be set at 1.0% or less, and preferably at 0.5% less.
  • the following method is recommendable as one suitable.
  • the present invention does not go as far as to specify the manufacturing method of forging steel and is not limited to the process described afterward.
  • the contained amount of S can be adjusted by controlling the composition of the top slag at the time of secondary refining. More precisely, the ratio of the CaO concentration in the top slag against the SiO 2 concentration (CaO/SiO 2 ; this may be expressed as C/S herein) should be set preferably at as high as 3.0 or over, thereby making it possible for the contained amount of S in the steel to be reduced. As a supplementary means, if the ratio of the Ca concentration against the Al 2 O 3 concentration (CaO/Al 2 O 3 ) is set as well high, it becomes possible to reduce the contained amount of S in the steel.
  • the MgO concentration in the top slag be set at 5% or over and the CaO concentration be set at 30% or over.
  • the concentrations of MgO and CaO in the top slag are excessively high, slag may become solidified making it difficult to proceed with the refinery work itself. Therefore, it is suggested that the MgO concentration in the top slag should be maintained at 25% or below and the CaO concentration in the top slag should be maintained at 65% or below.
  • the concentration of the dissolved Al in the molten steel at the time of refinery is maintained within the range of 50-900 ppm. If the concentration of the dissolved Al in the molten steel is less than 50 ppm, the amount of dissolved oxygen increases and the number of oxides crystallized into the solidified steel also increases with the unfavorable result that the cleanliness of the steel changes for the worse. On the other hand, if the dissolved Al concentration goes up higher than 900 ppm, it leads to an unfavorable result that the concentration of dissolved oxygen decreases and the amounts of the dissolved Ca and Mg in the steel become excessive.
  • the amounts of dissolved Ca and the dissolved Mg in the steel can be maintained within the prescribed ranges.
  • the present invention is effective to conduct the first course of heating and composition adjustment to the molten steel tapped out of a converter or electrical furnace, apply degassing treatment to the molten steel after the above first course of heating and composition adjustment, and again conduct second course of heating and composition adjustment to the molten steel after degassing treatment; that is to say, it is effective to carry out the operation of a series of refining processes including [heating and composition adjustment—degassing treatment—heating and composition adjustment].
  • the above first course of heating and composition adjustment is a treatment to control the composition of the molten steel within the prescribed range
  • the degassing treatment is a treatment to remove hydrogen and other gas content from the inside of the molten steel. Therefore, both the treatments need to intensify the stirring power density, while avoiding entrapment of the top slag floating on the surface of the molten steel as much as possible.
  • the second course of heating and composition adjustment is mainly assigned the function to promote the flotation of the top slag particles entrapped into the molten steel during the above degassing treatment process and to do fine adjustment of composition and temperature.
  • stirring be carried on with a low stirring power density so that entrapment of any new top slag may not occur.
  • stirring at 50-200 W/ton is recommendable.
  • the flow rate of blowing gas should be adjusted so that the stirring power density may be controlled preferably at 50 W/ton or over; more preferably at 60 W/ton or over and 200 W/ton or below; still more preferably at 180 W/ton or below.
  • the flow rate of blowing gas should be adjusted so that the stirring power density may be controlled at 140 W/ton or below, or preferably at 120 W/ton or below (0 W/ton not included).
  • the flow rate of blowing gas should be adjusted so that the stirring power density may be controlled at 25 W/ton or below, or preferably at 20 W/ton or below, and at 2.0 W/ton or over.
  • the molten steel is first tapped out of the converter or electrical furnace into the ladle and is brought to the secondary refining, where the molten steel goes through the first course of heating and composition adjustment (hereafter, this process may be called as “LF-I”).
  • LF-I first course of heating and composition adjustment
  • the molten steel is stirred by Ar gas blowing with a gas blowing means.
  • the kinds and amounts of flux should be determined so that the composition of the top slag after finishing the vacuum degassing treatment (in other words, at the time the second course of heating and composition adjustment has started) may satisfy the following three conditions at the same time.
  • the heating temperature and the feed amount of the auxiliary material should be controlled or adjusted accordingly.
  • VD vacuum degassing treatment
  • the gas above the molten steel in the ladle is exhausted through an exhaust pipe to the extent that the ambient pressure “P” inside the ladle comes close to a vacuum state of about 0.5 Torr.
  • stirring is applied to the molten steel by blowing Ar gas by a gas blowing means. In the above manner, the treatment of removing hydrogen is carried out from the molten steel for which adjustment of composition is almost completed.
  • the flow rate Q g of bottom blowing gas is controlled so as to maintain the stirring power density ⁇ within the range of 50-200 W/ton, it becomes possible to effectively conduct dehydrogenation while holding entrapment of top slag to a minimum.
  • the temperature of the bottom blowing gas before blowing T 0 (temperature of Ar gas before blowing) is to be ordinary temperature (298K), and the temperature of the bottom blowing gas after blowing T g (temperature of Ar gas after blowing) is to be equal to the temperature of the molten steel T L .
  • T 0 Temperature before blowing of bottom blowing gas (ordinary temperature of 298K)
  • this second course may hereafter be called as “LF-II”) to the molten steel after VD, it becomes possible to manufacture super clean steel.
  • the molten steel after completion of the vacuum degassing treatment, just as is in the ladle, is transported to the secondary refining equipment and is made to go through the second course of heating and composition adjustment.
  • the flow of Ar gas Q g should be controlled so that the stirring power density ⁇ calculated according to the above formula (1) may be kept within the range of 25 W/ton or below to 2.0 W/ton or over.
  • LF-II starts with the top slag having the following composition.
  • composition of the molten steel is surely prevented from reoxidation by the oxides in the top slag.
  • the refinery process is enough if it includes the processes of [heating and composition adjustment ⁇ degassing treatment ⁇ heating and composition adjustment], and it is not limited to anteroposterior processes.
  • the processes of [degassing treatment ⁇ heating and composition adjustment] or [degassing treatment ⁇ heating] may be added by one cycle on the same conditions as above or on any other conditions than the above, or otherwise, either or both of these two sets of processes to be repeated plural times may be added; or further otherwise, after the above processes of [heating and composition adjustment ⁇ degassing treatment ⁇ heating and composition adjustment], it is all right if only the process of [degassing] may be repeated again on the same conditions as above or on any other conditions than the above.
  • the present invention includes the forged products obtainable from the use of the above forging steel, but there is no particular limitation on the manufacturing method for the forged products.
  • manufacturing can be conducted if it covers such processes as heating of the above forging steel to forging in material stage, in-process inspection followed by heating and forging into product shape, heated homogenization treatment followed by quench hardening and normalizing, and finishing by machining.
  • crankshafts solid type crankshaft and assembly type crankshaft. Because of the excellent fatigue strength, other high-strength products than crankshafts can also be listed, such as intermediate shafts and transmission shafts for marine ships and vessels, throws of assembly type crankshafts, parts for general machinery, pressure vessels, hollow forgings, and so forth.
  • the solid type crankshaft is preferable, because the portion of the steel where cleanliness is higher can be arranged to occupy the surface layer of the shaft thereby enabling the shaft to obtain excellent strength and fatigue characteristics.
  • the manufacturing method of the solid type crankshaft in such a case is not particularly specified, but recommendable is to manufacture the crankshaft according to the R.R. and T.R.
  • forging processing is performed so that the axis center of the ingot may become concentric with the shaft center of the crankshaft, and further, forging processing is made in such a state that the portion of the ingot where deterioration in characteristics is likely to occur due to center segregation may compose the entire shaft center of the crankshaft, in a unified manner).
  • crank arm and crankpins are forged in one block and formed into the shape of crankshaft by gas-cutting and machining.
  • molten steel processing was carried out.
  • the first course of heating and composition adjustment (LF-I) was conducted to the molten steel tapped out of the converter or electric furnace; the degassing treatment (VD) was applied to the molten steel after completion of the first heating and composition adjustment; and the second heating and composition adjustment (LF-II) was carried out to the molten steel after completion of the degassing treatment.
  • slag formation agents as CaO, Al 2 O 3 , and MgO were added to the surface of the molten steel for formation of top slag including CaO and MgO in the amounts shown in Table 1.
  • Al was added to deoxidize the molten steel, and also dehydronegation was conducted by vacuum treatment with lid degassing equipment. While processing of the molten steel, sampling of the molten steel was made properly to measure the concentration of the dissolved Al. In order to maintain the concentration of the dissolved Al within a preferred range, Al was additionally supplied according to need. The concentrations of the dissolved Al in the molten steel are shown in Table 1.
  • the 20-ton steel ingot was treated by hot forging into the product in a shape of 250-450 mm diameter round bars
  • 50-ton steel ingot was treated by hot forging into the product in a shape of 350-700 mm diameter round bars
  • 100-ton steel ingot was treated by hot forging into the product in a shape of 600-1200 mm diameter round bars.
  • concentrations of CaO and MgO in the top slag were investigated by the ICP emission spectro chemical analysis. The results therefrom are as shown in Table 1.
  • the samples taken from the steel ingot are ground and loaded in the secondary ion mass spectrometer (“ims5f” registered trademark of AMETEK, Inc.).
  • ims5f registered trademark of AMETEK, Inc.
  • secondary ion image of Ca or Mg was observed within a region of 500 ⁇ 500 ( ⁇ m 2 ) to select therein three places where Ca or Mg is not thickened locally, and analysis was made in the direction of depth in those three places.
  • the first ion source in that case was O 2+ .
  • the concentration value at that time was deemed to be the concentration of the dissolved element.
  • the expression “Refined” in the columns of “Oxide Type” and “Sulfide Type” means that the diameter of an assumed circle equivalent area-wise to the largest inclusion is less than 100 ⁇ m.
  • the composition of inclusion indicated together in the table denotes the composition of the oxide, in case of oxide type inclusion, that covered more than 50% in number of pieces among all the oxide type inclusions having undergone the above analysis; in case of sulfide type inclusion, it denotes the composition of the sulfides that covered more than 50% in number of pieces among all the sulfide type inclusions having undergone the above analysis.
  • the expression “coarse and large” applies to the case in which one or more number of pieces of coarse and large inclusions were detected to have 100 ⁇ m or over in diameter of assumed circles equivalent area-wise to the inclusions; also, the compositions of the inclusion shown together indicate the compositions of the above coarse and large inclusions.
  • the expression “Inclusions in forged product,” covers oxides and sulfides when these exist individually, but it also includes the case where oxides and sulfides are in adjacent or composite state (for example, the case of composite inclusions such as an oxide taking the role of core while a sulfide surrounding the oxide core). It is to be understood that even in case of a composite inclusion, the sizes of the oxide and the sulfide in that composite inclusion are individually and separately determined and evaluated.
  • No. 18 is an example in which S-contained alloy, Mg-contained alloy, and Ca-contained alloy were added with stirring in refining being too strong. For this reason, amounts of all of S, Total Ca, Total Mg, and dissolved Ca exceeded the upper limits, failing to prevent oxides and sulfides from growing coarse and large beyond limit.
  • No. 21 involved addition of Ca-contained alloy, which made the amounts of Total Ca and dissolved Ca to increase beyond the upper limit, resulting in formation of coarse and large Ca-contained inclusion.
  • No. 22 was a case of Mg-contained alloy added with weak stirring at the stage of LF-II. Though the amount of dissolved Mg remained within the prescribed range, the amount of Total Mg went over the upper limit, failing to prevent growth of coarse and large Mg-contained inclusion.
  • No. 23 was a case of Ca-contained alloy added with weak stirring at the stage of LF-II. Though the amount of dissolved Mg remained within the prescribed range, the amount of Total Ca went over the upper limit, failing to prevent growth of coarse and large Ca-contained inclusion.
  • No. 25 was an example in which the stirring strength in the first half of VD was small and the stirring strength in the stage of LF-II was also weak. In this case, the amounts of dissolved Ca and dissolved Mg was not able to fill the prescribed lower limits, ending up generation of coarse and large Al 2 O 3 and MnS
  • No. 27 was a case in which the concentration of dissolved Al in the molten steel was below the recommended range and the amounts of dissolved Ca and Mg were short of the prescribed lower limits, ending up generation of coarse and large Al 2 O 3 and MnS.
  • the composition of the top slag is not in conformity with the range as recommended, and the amount of dissolved Ca is short of the prescribed lower limit. As a result, coarse and large Al 2 O 3 and MnS were generated.
  • FIG. 2 is a graph in which the relation between the diameter of an assumed circle equivalent area-wise to the above largest inclusion existing in the steel as detected by EPMA and the endurance limit ratio is shown in an organized manner. It will be seen from this FIG. 2 that there is a good correlation between the endurance limit ratio and the diameter of an assumed circle equivalent to the above largest inclusion. When the diameter of an assumed circle equivalent to the above largest inclusion is less than 100 ⁇ m, it turns out that the steel can prove as excellent a fatigue characteristic as over 0.42 in endurance limit ratio.

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
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  • Heat Treatment Of Steel (AREA)
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EP2527476A1 (de) * 2011-05-27 2012-11-28 A. Finkl & Sons Co. Flexibles Lichtbogenofensystem mit minimalem Energieverbrauch sowie Verfahren zur Herstellung von Stahlprodukten
US20150144233A1 (en) * 2013-11-27 2015-05-28 Doosan Heavy Industries & Construction Co., Ltd. Hybrid mold steel and manufacturing method thereof
EP3040438A4 (de) * 2013-08-27 2017-05-17 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Hochfester stahl und mit diesem hochfester stahl hergestellte kurbelwelle
US10844466B2 (en) 2015-10-19 2020-11-24 Nippon Steel Corporation Hot forging steel and hot forged product
US11111568B2 (en) 2016-09-30 2021-09-07 Nippon Steel Corporation Steel for cold forging and manufacturing method thereof

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JP5783056B2 (ja) * 2012-01-18 2015-09-24 新日鐵住金株式会社 浸炭軸受鋼鋼材
JP5859384B2 (ja) 2012-06-06 2016-02-10 株式会社神戸製鋼所 大型高強度鍛鋼品
CN102808062B (zh) * 2012-07-19 2014-03-05 中国科学院金属研究所 一种通过钢水纯净化控制钢锭a偏析的方法
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JP2017128795A (ja) * 2016-01-18 2017-07-27 株式会社神戸製鋼所 鍛造用鋼及び大型鍛鋼品
CN105821304B (zh) * 2016-06-07 2018-07-03 马鞍山钢铁股份有限公司 一种含铌钛动车组车轴用钢及其热处理工艺
CN112501521A (zh) * 2020-11-30 2021-03-16 西安市康铖机械制造有限公司 一种超高强度航空结构钢的加工方法

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US20070051432A1 (en) * 2005-09-05 2007-03-08 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd) Steel wire rod having excellent drawability and fatigue properties, and manufacturing method of the same

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Publication number Priority date Publication date Assignee Title
EP2527476A1 (de) * 2011-05-27 2012-11-28 A. Finkl & Sons Co. Flexibles Lichtbogenofensystem mit minimalem Energieverbrauch sowie Verfahren zur Herstellung von Stahlprodukten
AU2012202044B2 (en) * 2011-05-27 2014-04-10 A. Finkl & Sons Co. Flexible minimum energy utilization electric arc furnace system and processes for making steel products
EP3040438A4 (de) * 2013-08-27 2017-05-17 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) Hochfester stahl und mit diesem hochfester stahl hergestellte kurbelwelle
US20150144233A1 (en) * 2013-11-27 2015-05-28 Doosan Heavy Industries & Construction Co., Ltd. Hybrid mold steel and manufacturing method thereof
US10844466B2 (en) 2015-10-19 2020-11-24 Nippon Steel Corporation Hot forging steel and hot forged product
US11111568B2 (en) 2016-09-30 2021-09-07 Nippon Steel Corporation Steel for cold forging and manufacturing method thereof

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CN101492789B (zh) 2011-02-02
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ES2376512T3 (es) 2012-03-14
ATE539175T1 (de) 2012-01-15
CN101492789A (zh) 2009-07-29
KR101082649B1 (ko) 2011-11-14
PL2110454T3 (pl) 2012-04-30
EP2110454B1 (de) 2011-12-28
JP2009173961A (ja) 2009-08-06

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