US3887402A - Method for producing high density steel powders - Google Patents

Method for producing high density steel powders Download PDF

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US3887402A
US3887402A US428013A US42801373A US3887402A US 3887402 A US3887402 A US 3887402A US 428013 A US428013 A US 428013A US 42801373 A US42801373 A US 42801373A US 3887402 A US3887402 A US 3887402A
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Yoshikazu Kondo
Mitsuo Ohhori
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/02—Making metallic powder or suspensions thereof using physical processes
    • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
    • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
    • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/14—Treatment of metallic powder
    • B22F1/142—Thermal or thermo-mechanical treatment

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  • ABSTRACT [30] ⁇ Foreign Application Priority Data Dec. 25 l972 Japan 47- 129379 A Process for Producing high density Steel Powders for Powder metallurgy is disclosed, wherein the molten 52 1 g 143 12 75 5 75 5 stream of low carbon steel or low carbon alloy steel is 75/2 1 atomized by high pressure water jet or inert gas jet to 51 tm. m B22f 9/00 be Powders, and after drying, the Powders are heated [58] Field of Search rs/.5 c, 211, 213. .5 BA; in Such inert gas as nitrogen or argon, whereby the 43 12 duction, decarburization and softening of the powders are simultaneously carried out. [56] References Cited llJNITED STATES PATENTS 14 Claims, 4 Drawing Figures 13,732,092 Ifill973 Wieland, llr. et al. 75/.5 BA
  • the present invention relates to a method for producing steel powders. comprising that the molten stream of low carbon steel or low carbon alloy steel is atomized by high pressure water jet or inert gas jet (hereinafter called water atomization or gas atomization) to be powders, and after drying, said powders are heated in such inert gas as nitrogen or argon, whereby the reduction, decarburization and softening of said powders are simultaneously carried out.
  • water atomization or gas atomization high pressure water jet or inert gas jet
  • the low carbon steel powders obtained by water atomization of molten steel, are heated in reducing gas, such as hydrogen gas or dissociated ammonia gas in order to soften and reduce the oxide formed on the surface of the powder due to the reaction with water at the time of atomization.
  • reducing gas such as hydrogen gas or dissociated ammonia gas
  • reduction and softening may be achieved.
  • the decarburization reaction of the carbon, contained in the steel powder can be simultaneously carried out by the moisture, which is generated by the reaction of hydrogen gas and oxides.
  • the obtained powder it is the present condition that there is earnestly asked for the powder, having a higher density.
  • the method of the present invention is to solve the 5 defects of or to improve the above mentioned conventional method as well as to obtain the steel powder, having such a high density as equivalent to or to exceed that of the conventional method.
  • the inventive method is not such an ordinary method that the reduction of the oxide film, on the surface of steel powder due to the water atomization, as well as decarburization and softening are carried out by heating in a reducing atmosphere of hydrogen or mainly hydrogen, but the reduction as well as decarburization and softening are performed by a heat treatment in such inert gas as nitrogen or argon.
  • the quantity of oxgen is kept small in the low carbon steel powder, subjected to water atomization, and the quantities of oxygen and carbon, contained in the powder, are given with the relation, obtained by the above-mentioned test results, whereby there has been developed a method for producing steel powders, having small quantities of oxygen and carbon and such a high density that at the time of compaction forming, the green density of the compact is equivalent to or higher than that of the conventional method, so that it is suitable for powder metallurgy, such as sintering or powder forging.
  • the inventive method is characterized in that low carbon steel, having 0.02 to 0.38 percent, preferably 0.02 to 0.26 percent of carbon, or low carbon alloy steel, having alloying elements, such as Cu, Ni, Mo, Co, Cr, Mn, V, W etc.
  • K 0.375 to 0.75 shows the quantity of oxygen (7: by weight), decreased in the reaction in case of reduction by heating in inert gas
  • C% shows the necessary quantity of carbon (70 by weight) to be consumed in the reaction in case of reduction by heating in inert gas), being treated in heat at 600 to 1,250C in inert nitrogen gas or inert argon gas, whereby the powder can be reduced so as to make the oxygen content below 0.20 percent, preferably below 0.15 percent in the powder, and decarburized so as to make the carbon content below 0.02 percent, preferably below 0.01 percent, and simultaneously softened.
  • the oxygen content of the powder after water at omization or gas atomization should be made as small as possible between 0.20 and 0.50 percent, preferably between 0.20 and 0.35 percent, and kept constant.
  • the oxygen content of the steel powder, subjected to water atomization under the ordinary conditions is about 0.8 to 3 percent. But the oxygen content can be kept in the steel powder within the limits of 0.20 to 0.50 percent, and further, within the narrow limits of 0.20 to 0.35 percent, by the increase of the flow of jet water at the time of water atomization, by making the water tank air-tight for atomization and by introducing nitrogen and argon so that the water atomization may be carried out in an inert atmosphere.
  • the upper limit of the oxygen content of the powder is determined to be 0.5 percent after atomization.
  • the lower limit may be still lowered according to the conditions of production, while in case of the present method of water atomization, it is fairly difficult to make the oxygen content below 0.20 percent after atomization, so that the lower limit is determined to be 0.20%. Of course, the oxygen content become 0.20 percent gives good results.
  • FIG. 1 shows an optical microstructure of etched low cross section of carbon steel powder, in which the oxygen content is 0.295% and the carbon content is 0.103 percent after water atomization and which is treated by a reduction annealing at 900C for 1 hour in nitrogen gas according to the method, shown in Example 1 of the present invention. It proves that the powders have a high density without almost any pore.
  • FIG. 2 shows the cross section of powders, unetched of which the oxygen content after atomizing is 1.63 percent, subjected to a reduction annealing in a hydrogen at 900C for one hour. It proves the existence of porous powders with pores, made in the traces of oxygen, which is reduced and dispersed.
  • the thus-obtained atomized steel powder contains only a small amount of oxygen, but it is necessary to make the oxygen content still smaller than 0.20 per cent, preferably smaller than 0.15 percent in order to give the suitable properties for powder metallurgy.
  • carbon content in the atomized powder In order to reduce the oxygen content enough to the objective value below the above mentioned value by the heat treatment in inert gas, and to keep the carbon content in the powder to lower level below 0.02 percent after heat treatment, carbon content in the atomized powder must keep within the ranges of 0.02 to 0.38 percent, preferably 0.02 to 0.26 percent and the quantities of carbon and oxygen in the atomized powder must meet the relation, shown by the before mentioned equation 1 In the equation (1 0% shows the necessary quantity of carbon by weight) to be consumed in a reducing reaction.
  • the quantity of carbon, contained in the powder after atomization, is A% and the carbon content is B% after this powder is treated in heat in inert gas, it can be expressed by C% (A B) 0% shows the quantity of oxygen by weight), reduced in a reducing reaction by the heat treatment.
  • the oxygen content of the powder is D% after atomization, and the oxygen content is E% after this powder is treated in heat in inert gas, it can be expressed by 0% (D E) K is a constant and takes a value between 0.375 and 0.750, and it changes within the above-mentioned limits according to the temperature of heating in inert gas and the flow rate of inert gas.
  • the carbon content of the powder can be sufficiently lowered after the heat treatment, but the oxygen content cannot be decreased to the objective value, so that the object of the present invention cannot be achieved.
  • the upper and lower limits of the quantity of carbon, contained in the powder after atomization are determined corresponding to the upper and lower limits of the oxygen content of the powder.
  • the value of K is within the extent of 0.40 to 0.63, but the value of K changes according to the temperature of heating and the flow rate of inert gas.
  • FIG. 4 shows the relation between the carbon content of the powder after atomization (before the heat treatment) and the carbon content 7: after the heat treatment, in the test examples.
  • various kinds of powders, having 0.27 to 0.3l percent of oxygen contained after atomization are treated in heat at 900C for 1 hour in the atmosphere of nitrogen gas, whereby the quantity of oxygen to be contained in the powder is made below 0.15 percent after the heat treatment.
  • the quantity of carbon to be contained in the powder after atomization may be about 0.13 percent or below in order that the carbon content is made below 0.02 percent after the heat treatment, and further, that the carbon content becomes below 0.005 percent after the heat treatment if the quantity of carbon to be contained in the powder after atomization is made 0.06 to 0.08 percent.
  • the reaction of reduction in inert gas according to the present invention is the reaction between the oxide, formed on the surface of the powder mainly by atomization, and the carbon, contained in the powder particles in a few amount. It seems that the carbon, contained as a solid solution or a carbide compound in the steel powder after atomization, is rapidly diffused to the surface of the powder and reacts on the oxygen, contained in the oxide layer to be a gas mixture of carbon monoxide and carbon dioxide, so that the reducing reaction can proceed. And this reaction proceeds quickly.
  • the reducing reaction in nitrogen gas for low carbon steel powders having 0.075 percent of carbon and 0.30 percent of oxygen contained, proceeds to the almost finished condition by soaking at 900C for l0 min, and the quantity of carbon contained in the powder after reduction becomes 0.001 percent and the oxygen content becomes 0.15 percent. It is known that the reduction proceeds in a remarkably short time as compared with the time, necessary for the softening of the powder and the velocity is enough for the performance in the industry. Further, the comparison concerning the decarburization rate is shown in Example 4. The carbon content is decreased to the objective value far more quickly than that of heating in gas, of which the main ingredient is hydrogen. The powder, having the carbon content decreased sufficiently, can be surely obtained in a short time.
  • the reduction and decarburization of the powder can be carried out in such a short time as similar to or less than that of the case of hydrogen being used.
  • the heating in inert gas is carried out within the limits of 600 to l,250C.
  • the effect of the heating in inert gas is that the property to be welded by heating at a high temperature is weak as compared with the case of heating in hydrogen gas or in a reducing gas, having hydrogen gas mainly contained, as explained hereinafter in the paragraph of the effect of the present invention.
  • the heating at a high temperature can be more easily performed. Then the reduction rate and the softening rate can be increased.
  • the upper limit of heating is made 1,250C, because it is favourable for the reducing reaction to raise the heating temperature when such ele ments as Cr or Mn, difficult to be reduced, are contained.
  • the lower limit is made 600C in consideration of the above-mentioned.
  • the heating time is the time, during which the reduction and softening proceed. It is about 10 min. or more, but it is not particularly limited.
  • the object can be fully achieved by the flow of i0 l/h or less per 1 kg of the powder to be treated. Even in case a horizontal type of continuous furnace, it is not necessary to flow an excess of gas in order to prevent explosion as necessitated in the case of hydrogen gas or dissociated ammonia gas. Thus, the quantity of gas to be used can be drastically decreased.
  • the quantity of oxygen to be contained in the low carbon steel powder after atomization can be controlled to a. low value and an almost constant value by keeping the conditions of atmization constant.
  • the quantity of carbon, contained in the powder can be controlled within the narrow limits by controlling the carbon, contained in molten steel, so that the inventive method can be easily performed.
  • Such aluminium oxide, magnesium oxide, calcium oxide or silica as difficult to be reduced, has the tendency to be mixed from the refractory materials of a furnace or others when the raw material is molten. Therefore, it goes without saying that it must be kept as little as possible.
  • the oxygen content is expressed in this specification as a percentage by weight of oxygen decreased in the powder by reduction with hydrogen gas in case of heating at l,050C for 60 min. in hydrogen gas, namely hydrogen loss.
  • atomized steel powders or atomized alloy steel powders having 0.20 to 0.50 percent, preferably 0.20 to 0.35 percent of oxygen, less than 0.38 percent, preferably less than 0.26 percent of carbon and besides the carbon content, showing a value smaller than the quantity of carbon, necessary for reduction, as shown by the equation (1), are added and mixed with carbon or graphite particles in the quantity of carbon, insufficient to meet the above-mentioned equation (1). And then, by heating at 600 to 1,250C in inert gas, the oxygen, contained in the powder is reduced to less than 0.2 percent, preferably less than 0.15 percent and the carbon is decarburized to less than 0.02 percent, preferably less than 0.01 percent. The softening may be simultaneously carried out.
  • the carbon powders are sometimes mixed not uniformly.
  • the reaction velocity for reduction with carbon powders is lower than that of the case of carbon, contained in the steel powders and there may be sometimes produced an unevenness in reduction due to the ununiformity of mixing. Attention must be paid, accordingly, to mix sufficiently small carbon powders fully.
  • atomized steel powders or atomized alloy steel powders are made to contain 0.20 to 0.50 percent, preferably 0.20 to 0.35 percent of oxygen and also the maximum 0.6 percent of carbon in excess of the quantity of carbon (C%), necessary to reduction as shown in the equation l
  • the reduction and softening of powders are carried out by heating these powders in inert gas, whereby the carbon steel powders, having a sufficiently small quantity of oxygen and the carbon content of the maximum 0.6 percent, can be easily manufactured.
  • the quantity of carbon to be added as an alloying element is within the extent to be ordinarily used for powder metallurgy.
  • the upper limit of the quantity of carbon after the reduction treatment is 0.6 percent.
  • the breaking operation may be a light worlt. Because of a weal: property to be welded by heating, it is possible to treat in heat at a higher temperature than that of the case of having hydrogen gas as the main ingredient. Even in case there is contained such metal ox ides of Cr and Mn as difficult to be reduced, it is possible to treat at a higher temperature to increase the reductibility. And also, it is favourably possible to heat at a higher temperature in order to accelerate the reac tions of reduction, decarburization and softening.
  • the inert gas does not take part in the reducing reaction and is not consumed at all at the time of heating. Therefore, the quantity of inert gas to be used may be remarkably smaller than that of the reduction with a reducing gas, having hydrogen as the main ingredient. in case of a horizontal continuous furnace being used, a large amount of excessive gas must be used in order to prevent explosion when the gas contains hydrogen chiefly. But according to the present invention there is not such necessity and the quantity of gas to be used can be considerably decreased.
  • the reducing reaction proceeds quickly, and also, the decarburization of carbon, contained in the powder, can be surely carried out more quickly as compared with the case of gas, having hydrogen as the main ingredient.
  • the powder, obtained according to the present invention has few pores and a high density.
  • the density of a compact shows such high value at the time of compaction forming as equivalent to or higher than that of the powder, obtained by the conventional method as shown in the examples.
  • the compact has a good edge stayability, namely a high Ratra value and is excellent for powder metallurgy.
  • the inventive method has a great effect in that the reducing power is greater than that of the reaction with hydrogen gas, because of a reducing reaction with carbon, contained a little in the powder particle.
  • the method has also predominance in this point.
  • FIG. 1 shows a photograph (x250) of optical microstructure of the cross sention of the powder, obtained in Example I.
  • the crystal structure was developed by etching with 5% of alcohol nitrate.
  • FIG. 2 is an optical microphotograph (x250) of the cross section of the comparative powder, without etching.
  • FIG. 3 shows some test results concerning the relation between the quantity of oxygen in the powder, reduced by heating in inert gas, and the necessary quantity of carbon, contained in the powder to be consumed in reduction.
  • FIG. t shows some test results concerning the relation between the quantity of carbon, contained in the powder after atomization and the quantity of carbon
  • EXAMPLE 1 With use of an electric furnace, low carbon steel scraps were melted. The quantity of carbon was so controlled as to be 0.10 percent.
  • the molten steel was continuously discharged down from a tandish, having a hole of 12 mm d), by gravity into an atomizing tank, in which water was filled in the lower part. From a waterjet nozzle, installed below the tandish, water was impinged to the molten steel stream under the pressure of 65 kg/cm at the flow of 950 l/min. The molten steel was pulverized to be powders.
  • the atomizing tank is closely sealed.
  • the air in the tank was replaced by nitrogen gas before water atomization.
  • the atmosphere of nitrogen gas was maintained during the atomization.
  • the quantity of oxygen, contained in the powder after atomization, was controlled to be 0.30 percent.
  • the chemical composition of the atomized low carbon steel powder was carbon 0.103%, silicon 0.01%, monganese 0.09%, phosphorus 0.015%, sulphur 1,1013%, oxygen 0.295% and nitrogen 0.001%. After coarse particles were removed, the size distribution was as follows:
  • the powder particles looked to be slightly welded each other after heating, but were fragile and easily restored to the original size by a light smashing.
  • the powder After heating, the powder contained 0.002 percent of carbon, 0.036 percent of oxygen and 0.001 percent of nitrogen.
  • the apparent density was 3.10g/CC and the flow rate, 134.9sec/50g.
  • the handness of the powder was 87 of micro-Vickers.
  • the oxygen content and the carbon content were sufficiently small without any increase of nitrogen. The hardness was sufficiently decreased and the powder was softened.
  • the optical microstructure of the powder after treatment in heat teaches that the density is high without any pore and the recrystallization proceeds fully due to the heating as shown in FIG. 1.
  • the green density of the compact was a high density of 7.08g/cc.
  • the edge stayability (Ratra value) showed a sufficient value of 0.46 percent.
  • the powder obtained by the inventive method, had the sufficiently small contents of oxygen and carbon, and the green density of the compact was so high that the powder was possessed of the characteristics and the high density, excellent for powder metallurgy.
  • the density of the compact, formed under the pressure of 5t/cm was 6.75 to 7.00g/cc.
  • EXAMPLE 2 With use of an electric furnace. low carbon steel scraps were melted. The carbon content of the molten steel was adjusted to 0.07 percent with the aim of 0.27 percent for the oxygen content after atomization. The molten steel was atomized with the flow of water of 1,050 liters min. in the atmosphere of nitrogen gas by the similar method to that of Example 1.
  • the chemical composition of the obtained powder was as follows:
  • This powder was sieved after drying. Those of mesh were taken away.
  • the size distribution was mesh 5.3 percent, 100 +325 mesh 71.6 percent, 325 mesh 23.1 percent.
  • the powder After treatment in heat, the powder contained 0.13 percent of oxygen, 0.002 percent of carbon and 0.001 percent of nitrogen.
  • the contents of oxygen and carbon can be made sufficiently small.
  • the flow of nitrogen gas was made to change to 10 liters, 25 liters or 50 liters per hour.
  • the carbon content was within the extent of 0.001 to 0.003 percent and the oxygen content, within the extent of 0.14 to 0.12 percent. The object could be fully achieved even if the flow of nitrogen gas was decreased.
  • the powder after treatment in heat was broken up extremely easily. According to the value of the chemical analysis carbon was 0.002%, oxygen, 0.053% and nitrogen 0.001%.
  • the apparent density of this powder was 3.39g/cc; the flow rate, 22.7 sec/50g; the green density of the compact, 6.61g/cc in case of compaction under the pressure of t/crn with zinc stearate being used for die lubrication; and the edge stayability (Ratra value), favourably 0.38 percent.
  • This powder was mixed with carbon powders and in addition of 1 percent of zinc stearate, was formed by compaction at 4.5t/cm to be a compact, having 58mm in diameter and about 40 mm in height.
  • the compact was sintered at 1,120C for 30 min. after dewaxing in dissociated ammonia gas.
  • This specimen was heated at 900C for 30 min. in nitrogen gas and then, forged under the pressure of about l4t/cm with use of a mechanical press.
  • This specimen was heated at 900C for 30 min. in nitrogen gas, and then, after oil quenching, tempered at 550C for 1 hour to make the Rockwell C hardness to be 30. It showed the tesile strength of 105.4 kg/mm the elongation of 14.8%, the reduction of 50.1% and the impact strength of 9.4 kg-mlcm
  • the powder forged articles, having excellent mechanical properties, were obtained
  • the quench hardenability was estimated on the basis of the quench hardenability testing method. JlS G0561.
  • the Rockwell C hardness was 46.5 at 1.5 mm distant from the quenched end, 44.5 at 5 mm, 39.5 at 10 mm, 31.5 at mm and 30.5 at 40 mm, and showed and excellent quench hardenability, exceeding the upper limit value, namely 46 at 1.5 mm distant from the quenched end, 42 at 5 mm, 31 at 11 mm, 26 at 20 mm and 23 at 40 mm, of the quenched Jominy band of chromiummolybdeum steel, SCM 21, the conventional structural steel, JlS G4105, which was the aim for this example.
  • EXAMPLE 4 The molten steel, having the quantities of copper, molybdeum, nickel and carbon adjusted to the prescribed quantity, was melted with use of an electric furnace. The powder was produced by water atomization in a similar method to that of Example 1.
  • the chemical analytical values of the obtained powder showed 0.123% of carbon, 0.06% of manganese, 2.65% of copper, 0.51% of molybdenum, 0.61% of nickel and the oxygen content was 0.321%. After +80 mesh was removed, the size distribution of the powder was as follows:
  • the chemical composition of this powder was 0.045% of carbon, 0.01% of silicon, 0.10% of manganese, 0.015% of phosphorus, 0.014% of sulphur, 0.001% of nitrogen and the oxygen content was 0.270%.
  • the carbon content was 0.008%, the oxygen content, 0.13% and nitrogen, 0.001% in the powder after the heat treatment.
  • the contents of carbon and oxygen were decreased to a low value.
  • alloy steel powders contain at least one alloying element of Cu. Ni, Mo, Co, Cr, Mn, W and V.
  • alloy steel powders contain at least one alloying element of Cu, Ni, Mo, Co, Cr, Mn, W and V.

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US4121927A (en) * 1974-03-25 1978-10-24 Amsted Industries Incorporated Method of producing high carbon hard alloys
US4216011A (en) * 1979-04-23 1980-08-05 Hylsa, S.A. Method and apparatus for the secondary gaseous reduction of metal ores
US4385929A (en) * 1981-06-19 1983-05-31 Sumitomo Metal Industries Limited Method and apparatus for production of metal powder
US4448746A (en) * 1982-11-05 1984-05-15 Sumitomo Metal Industries, Ltd. Process for producing alloy steel powder
GB2198749A (en) * 1986-12-12 1988-06-22 Mannesmann Ag Method of manufacturing blocks or profiled sections by extrusion
US4954171A (en) * 1987-09-30 1990-09-04 Kawasaki Steel Corp. Composite alloy steel powder and sintered alloy steel
US5427600A (en) * 1992-11-30 1995-06-27 Sumitomo Electric Industries, Ltd. Low alloy sintered steel and method of preparing the same
WO1998003291A1 (en) * 1996-07-22 1998-01-29 Höganäs Ab Process for the preparation of an iron-based powder
US5846349A (en) * 1994-12-09 1998-12-08 Ford Global Technologies, Inc. Low alloy steel powder for plasma deposition having solid lubricant properties
US6342087B1 (en) * 1997-06-17 2002-01-29 Höganäs Ab Stainless steel powder
US6355087B1 (en) 1998-01-21 2002-03-12 Höganäs Ab Process of preparing an iron-based powder in a gas-tight furnace
US6749662B2 (en) 1999-01-29 2004-06-15 Olin Corporation Steel ballistic shot and production method
US20040211292A1 (en) * 1999-06-10 2004-10-28 Olin Corporation, A Company Of The State Of Illinois. Steel ballistic shot and production method
US20060099105A1 (en) * 2002-06-14 2006-05-11 Hoganas Ab Pre-alloyed iron based powder
US20110123383A1 (en) * 2006-08-28 2011-05-26 Panasonic Electric Works Co., Ltd. Metal powder for metal laser-sintering and metal laser-sintering process using the same
US20130180360A1 (en) * 2010-09-15 2013-07-18 Research Institute Of Industrial Science & Technology Method of Manufacturing Iron-Based Powder
CN105057655A (zh) * 2015-08-17 2015-11-18 湖南久泰冶金科技有限公司 一种金属粉末材料脱氧还原工艺

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JPS589807B2 (ja) * 1977-09-10 1983-02-23 川崎製鉄株式会社 シャフト炉による鋼粉の焼結還元方法
JPS55179937U (enrdf_load_stackoverflow) * 1979-06-13 1980-12-24
JPS60108541U (ja) * 1983-12-28 1985-07-23 日産ディーゼル工業株式会社 車両用シ−ト

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US3746584A (en) * 1970-02-18 1973-07-17 Nippon Kokan Kk Method for the continuous vacuum decarbonization of low carbon ferrochrome

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US3746584A (en) * 1970-02-18 1973-07-17 Nippon Kokan Kk Method for the continuous vacuum decarbonization of low carbon ferrochrome
US3732092A (en) * 1972-03-31 1973-05-08 Bethlehem Steel Corp Heat treatment of iron powder

Cited By (27)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4121927A (en) * 1974-03-25 1978-10-24 Amsted Industries Incorporated Method of producing high carbon hard alloys
US4216011A (en) * 1979-04-23 1980-08-05 Hylsa, S.A. Method and apparatus for the secondary gaseous reduction of metal ores
US4385929A (en) * 1981-06-19 1983-05-31 Sumitomo Metal Industries Limited Method and apparatus for production of metal powder
US4448746A (en) * 1982-11-05 1984-05-15 Sumitomo Metal Industries, Ltd. Process for producing alloy steel powder
GB2198749A (en) * 1986-12-12 1988-06-22 Mannesmann Ag Method of manufacturing blocks or profiled sections by extrusion
GB2198749B (en) * 1986-12-12 1990-07-25 Mannesmann Ag A method of manufacturing blocks or profiled sections
US4954171A (en) * 1987-09-30 1990-09-04 Kawasaki Steel Corp. Composite alloy steel powder and sintered alloy steel
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JPS5219823B2 (enrdf_load_stackoverflow) 1977-05-31
JPS4987561A (enrdf_load_stackoverflow) 1974-08-21
GB1435140A (en) 1976-05-12

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