US20020094297A1 - Method for the preparation of a sintered body of high-hardness high-chromium cast iron - Google Patents
Method for the preparation of a sintered body of high-hardness high-chromium cast iron Download PDFInfo
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- US20020094297A1 US20020094297A1 US09/735,518 US73551800A US2002094297A1 US 20020094297 A1 US20020094297 A1 US 20020094297A1 US 73551800 A US73551800 A US 73551800A US 2002094297 A1 US2002094297 A1 US 2002094297A1
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- 238000000034 method Methods 0.000 title claims abstract description 40
- 239000011651 chromium Substances 0.000 title claims abstract description 38
- 229910052804 chromium Inorganic materials 0.000 title claims abstract description 36
- 229910001018 Cast iron Inorganic materials 0.000 title claims abstract description 27
- 238000002360 preparation method Methods 0.000 title claims abstract description 11
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 22
- 239000000956 alloy Substances 0.000 claims abstract description 22
- 238000005245 sintering Methods 0.000 claims abstract description 21
- 238000010791 quenching Methods 0.000 claims abstract description 16
- 230000000171 quenching effect Effects 0.000 claims abstract description 16
- 239000000155 melt Substances 0.000 claims abstract description 15
- 238000007711 solidification Methods 0.000 claims abstract description 13
- 230000008023 solidification Effects 0.000 claims abstract description 13
- 239000007921 spray Substances 0.000 claims abstract description 8
- 230000006835 compression Effects 0.000 claims abstract description 7
- 238000007906 compression Methods 0.000 claims abstract description 7
- 238000000889 atomisation Methods 0.000 claims abstract description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 25
- 239000002245 particle Substances 0.000 claims description 21
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 15
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 12
- 229910052799 carbon Inorganic materials 0.000 claims description 12
- 229910052742 iron Inorganic materials 0.000 claims description 12
- 229910002058 ternary alloy Inorganic materials 0.000 claims description 10
- 238000001816 cooling Methods 0.000 claims description 9
- 229910001339 C alloy Inorganic materials 0.000 claims description 2
- 229910000599 Cr alloy Inorganic materials 0.000 claims description 2
- 239000000203 mixture Substances 0.000 abstract description 14
- 239000000843 powder Substances 0.000 abstract description 11
- 238000005299 abrasion Methods 0.000 abstract description 8
- 238000005260 corrosion Methods 0.000 abstract description 6
- 230000007797 corrosion Effects 0.000 abstract description 6
- 239000000126 substance Substances 0.000 abstract description 4
- 238000005266 casting Methods 0.000 description 8
- 239000013078 crystal Substances 0.000 description 6
- 230000005496 eutectics Effects 0.000 description 5
- 235000000396 iron Nutrition 0.000 description 5
- 239000011159 matrix material Substances 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 3
- 238000000227 grinding Methods 0.000 description 3
- 238000012423 maintenance Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 150000001247 metal acetylides Chemical class 0.000 description 3
- 238000010298 pulverizing process Methods 0.000 description 3
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000010419 fine particle Substances 0.000 description 2
- 238000000465 moulding Methods 0.000 description 2
- 239000004576 sand Substances 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000005507 spraying Methods 0.000 description 2
- 238000009825 accumulation Methods 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 239000012159 carrier gas Substances 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 238000000748 compression moulding Methods 0.000 description 1
- 238000007596 consolidation process Methods 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000010310 metallurgical process Methods 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
Images
Classifications
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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
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
- B22F3/105—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C37/00—Cast-iron alloys
- C22C37/06—Cast-iron alloys containing chromium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/02—Making ferrous alloys by powder metallurgy
- C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
- C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
- C22C33/0285—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5% with Cr, Co, or Ni having a minimum content higher than 5%
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/08—Making cast-iron alloys
-
- 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
- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
- B22F2998/10—Processes characterised by the sequence of their steps
-
- 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
- B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
Definitions
- the present invention relates to an efficient method for the preparation of a sintered body of a high-chromium cast iron having an outstandingly high hardness, abrasion resistance, heat resistance and corrosion resistance as compared with bodies of the same high-chrome cast iron prepared by a conventional casting method so as to be useful as a part of crushers, grinding machines and the like as well as in thermal electric power plants, iron- and steel-making plants, cement-making plants and many other industrial facilities.
- high-chromium cast irons are generally excellent in abrasion resistance and heat resistance by virtue of the high content of a carbide phase of high hardness and also has high corrosion resistance not only at room temperature but also at high temperatures because a large amount of chromium forms a solid solution in the matrix phase of iron.
- These excellent properties of a high-chromium cast iron, in combination with the relatively low material cost, are fully utilized as a material of high-performance parts such as protective tubes, coal crushers, nozzles, impellers and the like in the industries of thermal electric power generation, cement manufacturing and others.
- a possible and effective way therefor is to have a content of carbon equal to or higher than the eutectic line in the iron/chromium/carbon ternary alloy system so as to increase precipitation of the high-hardness carbide phase of the composition of the M 7 C 3 type.
- a body of such a hypereutectic composition of the alloy usually exhibits remarkable anisotropy due to inhomogeneous crystallization of coarse carbide crystals along the direction of the heat flow or, namely, the direction of solidification unavoidably decreasing the mechanical properties including embrittlement. This is the reason for the fact that high-chromium cast irons of a hypereutectic composition have rarely come under practical applications heretofore.
- the present invention accordingly has an object, under the above described circumstances in the prior art, to provide a novel and efficient method for the preparation of a high-hardness body of a high-chromium cast iron having outstandingly excellent abrasion resistance, heat resistance and corrosion resistance in combination and suitable as a material of parts in plants and machines which can be dispensed with the maintenance services or of which the intervals of the maintenance services can be substantially extended.
- the present invention provides a method for the preparation of a high-hardness sintered body of a high-chromium cast iron which comprises the steps of:
- the quenching solidification of the alloy melt in step (a) is conducted by the method of centrifugal spray atomization.
- Photos A and B of FIG. 1 are each a microscopic photograph showing the metallographic structure of the sintered bodies of high-chromium cast irons of hypoeutectic and hypereutectic compositions, respectively, prepared in Example.
- Photos C and D of FIG. 1 are each a microscopic photograph showing the metallographic structure of the metal mold-cast bodies of the same hypoeutectic and hypereutectic compositions as in Photos A and B, respectively, prepared in Comparative Example.
- FIG. 2 is a bar chart showing the Rockwell hardness of the shaped bodies at room temperature, in which the columns A, B, C and D correspond to Photos A, B, C and D, respectively, of FIG. 1.
- the method of the present invention comprises two essential steps (a) and (b), each of which is very unique as compared with the conventional powder metallurgical process including the steps of casting of an alloy melt into a mold to give an ingot, pulverization of the alloy ingot into fine particles, shaping the alloy particles by compression molding into a powder compact and sintering of the powder compact in a sintering furnace.
- step (a) of the inventive method is for the preparation of alloy particles from a melt of a high-chromium cast iron of the specified composition, in which the alloy melt is subjected to quenching solidification or, preferably, by the method of centrifugal spray atomization directly into alloy particles at a cooling rate higher by at least 10 5 times or sometimes by 10 7 times than the cooling rate in the conventional casting method.
- the alloy particles prepared as above are then subjected to a discharge plasma sintering treatment under compression in the atmospheric air into a sintered body.
- the above described inventive method is applicable not only to a hypoeutectic iron/chromium/carbon ternary alloy, of which the content of carbon is lower than the eutectic line, as a matter of course but also to a hypereutectic iron/chromium/carbon ternary alloy, of which the content of carbon is higher than the eutectic line.
- the metallographic texture of the thus obtained sintered body is much finer and much more uniform beyond comparable than that of the same cast iron body prepared by the casting method.
- the chemical composition of the melt of the high-chromium cast iron used in the inventive method is limited such that the contents of chromium and carbon are in the ranges from 11 to 30 mass % and from 2.2 to 5.0 mass %, respectively, the balance being substantially iron with small amounts of unavoidable impurity elements.
- the melt of the high-chromium cast iron is subjected in step (a) to a quenching solidification treatment at a cooling rate of at least 10 4 ° C./second or, desirably, at least 10 5 ° C./second.
- the cooling rate of the melt in the quenching solidification can be readily estimated according to a known procedure by utilizing the established relationship between the cooling rate and the metallographic structure of the solidified alloy.
- This quenching solidification treatment of the melt is conducted preferably by the centrifugal spray atomization method, in which the melt is ejected at a quenching disk rotating at a high velocity to be atomized by the centrifugal force into fine droplets, which are quenched by blowing of an inert gas to be solidified to give fine particles.
- the so-called quenching roller method using a single quenching roller or twin quenching rollers is applicable to step (a) though less preferable than the centrifugal spray atomization method because the quenching roller method produces thin ribbons of the solidified alloy which are more bulky than powders and need an additional step of pulverization or grinding with an unavoidable risk of contamination from the pulverization or grinding machine.
- the other advantages of the centrifugal spray atomizing method over other powder-making methods include: (1) the high cooling rate of the melt; (2) unnecessity of any carrier gas for spraying to ensure little gaseous occlusion in the particles; (3) little formation of oxidized surface film on the particles; (4) good sphericity of the particle configuration with little adhesion of satellite particles; and (5) independent controllability of the spraying conditions and quenching conditions to facilitate running of the process with stability.
- the quench-solidified particles of the high-chromium cast iron are then subjected to sintering by the so-called discharge plasma sintering method or pulse-current sintering method at a temperature in the range from 1000 to 1200° C. under compression with a molding pressure of 10 to 50 MPa with application of a pulsewise direct-current power.
- the sintering treatment can be completed within a very short time of a few minutes.
- plasma discharge is first generated between particles so as to activate the particle surfaces by the accumulation of the impact energy thereby in the form of heat or strain so as to expose clean surfaces by removing the gases and contaminants adsorbed on the particle surfaces and destroying the oxidized surface film having a thickness of several nanometers order. Thereafter, Joule's heat is generated at the contacting points between particles by passing an electric current through the powder under compression so that the particles are bonded together to effect sintering giving a sintered body.
- This discharge plasma sintering treatment can be conducted in the atmospheric air. This process is effective for the consolidation of the particles in the non-equilibrium conditions.
- the sintered body of the high-chromium cast iron obtained in the above described manner is characterized by the very fine and uniform metallographic texture, which is absolutely free from anisotropy in contrast to the shaped body prepared by casting of a melt more or less having anisotropy of the texture.
- the sintered body of the high-chromium cast iron prepared by the inventive method has a Rockwell hardness greatly exceeding that of the bodies prepared by casting along with excellent abrasion resistance as a conesquence of strengthening by the fine texture.
- the element of chromium forms a solid solution in the iron matrix and plays a very important role to increase the corrosion resistance of the iron matrix and to form a primary crystals of carbide (Fe,Cr) 7 C 3 .
- the content of chromium in the ternary alloy is limited to the range of from 11 to 30 mass % because, when too small, the above mentioned advantageous effects cannot be fully exhibited while, when too large, a decrease is resulted in the hardness of the alloy.
- carbon is an indispensable element to form the phase of carbides with chromium and the content of carbon in the alloy is limited to the range of from 2.2 to 5.0 mass % because, when too small, the amount of the carbides formed therefrom is naturally so small that a decrease is caused in the hardness and abrasion resistance of the sintered body while, when too large, the amount of the carbides formed from carbon is so large that the sintered body suffers a decrease in the toughness.
- Quench-solidified powders were prepared by the centrifugal spray atomizing method from a melt of a hypoeutectic high-chromium cast iron of the chemical composition of Fe-25.3Cr-2.60C and a melt of a hypereutectic high-chromium cast iron of the chemical composition of Fe-24.4Cr-4.74C.
- the cooling rate in the quenching solidification was estimated to be in the range from 10 5 to 10 4 ° C./second.
- each of the powders was subjected to a discharge plasma sintering treatment in a graphite mold for 3 minutes under a molding pressure of 32 MPa with application of an on-off pulsed electric voltage of 33 milliseconds pulse width.
- the sintering temperature was 1140° C. for the powder of the hypoeutectic composition and 1100° C. for the powder of the hypereutectic composition.
- the time taken for arriving at the sintering temperature was about 300 seconds.
- Photos A and B of FIG. 1 are each a microscopic photograph showing the metallographic structure of the thus obtained sintered bodies of the hypoeutectic alloy and hypereutectic alloy, respectively. As is understood from these photographs, each of these sintered bodies has a uniform texture with extremely fine dispersion of the iron matrix phase and the carbide phase.
- FIG. 2 is a bar chart showing the Rockwell hardness HRC of these sintered bodies, of which the columns A and B are for the sintered bodies having the hypoeutectic and hypereutectic compositions of which the Rockwell hardness was 63 HRC and 68 HRC, respectively.
- Metal mold-cast bodies were prepared by casting of the melts of the same hypoeutectic and hypereutectic high-chromium cast irons used in the above described Example.
- the solidification rate of the melt could be estimated to be larger than in a sand mold leading to an improvement of the mechanical properties of the cast body.
- Photos C and D of FIG. 1 are each a microscopic photograph showing the metallographic structure of the thus obtained cast bodies of the hypoeutectic alloy and hypereutectic alloy, respectively.
- Photo C indicates primary crystallization of coarse dendritic austenite crystals, i.e. ⁇ -phase, with intervention of coarse eutectic crystals of the ⁇ -phase and carbide in the interstices.
- Photo D indicates that the cast body of the hypereutectic alloy consists of coarse primary crystals of the carbide and eutectic crystals of the ⁇ -phase and carbide.
- the texture has developed in the direction of solidification or, namely, in the direction of the heat flow.
- columns C and D show the Rockwell hardness of 50 HRC and 57 HRC of the hypoeutectic and hypereutectic cast bodies, respectively. It is evident that the sintered bodies of the high-chromium cast iron prepared according to the inventive method are very superior in the mechanical properties as compared with the cast bodies of the same alloy composition.
Abstract
Disclosed is a method for the preparation of a sintered body of a high-chromium cast iron of a specified chemical composition having greatly improved mechanical, abrasion-resistant and corrosion-resistant properties as compared with conventional cast bodies of the same cast iron. The inventive method comprises the steps of preparing a powder of the cast iron alloy by quenching solidification of a melt, e.g., by centrifugal spray atomization, and sintering the powder under compression by the discharge plasma sintering method.
Description
- The present invention relates to an efficient method for the preparation of a sintered body of a high-chromium cast iron having an outstandingly high hardness, abrasion resistance, heat resistance and corrosion resistance as compared with bodies of the same high-chrome cast iron prepared by a conventional casting method so as to be useful as a part of crushers, grinding machines and the like as well as in thermal electric power plants, iron- and steel-making plants, cement-making plants and many other industrial facilities.
- As is well known, high-chromium cast irons are generally excellent in abrasion resistance and heat resistance by virtue of the high content of a carbide phase of high hardness and also has high corrosion resistance not only at room temperature but also at high temperatures because a large amount of chromium forms a solid solution in the matrix phase of iron. These excellent properties of a high-chromium cast iron, in combination with the relatively low material cost, are fully utilized as a material of high-performance parts such as protective tubes, coal crushers, nozzles, impellers and the like in the industries of thermal electric power generation, cement manufacturing and others.
- To be in compliance with the requirements in these industries in recent years for improving the productivity and economic merit more and more by accomplishing extension of the intervals or dispensability of the maintenance services of the plants, parts of the machines and plants made from a high-chromium cast iron by the conventional procedure are not quite satisfactory in respect of their abrasion resistance, heat resistance, corrosion resistance and other properties so that it is eagerly desired to develop a method for satisfying the requirements.
- When improvement of the abrasion resistance is desired of a body made from a high-chromium cast iron, for example, a possible and effective way therefor is to have a content of carbon equal to or higher than the eutectic line in the iron/chromium/carbon ternary alloy system so as to increase precipitation of the high-hardness carbide phase of the composition of the M7C3 type. A body of such a hypereutectic composition of the alloy, however, usually exhibits remarkable anisotropy due to inhomogeneous crystallization of coarse carbide crystals along the direction of the heat flow or, namely, the direction of solidification unavoidably decreasing the mechanical properties including embrittlement. This is the reason for the fact that high-chromium cast irons of a hypereutectic composition have rarely come under practical applications heretofore.
- The present invention accordingly has an object, under the above described circumstances in the prior art, to provide a novel and efficient method for the preparation of a high-hardness body of a high-chromium cast iron having outstandingly excellent abrasion resistance, heat resistance and corrosion resistance in combination and suitable as a material of parts in plants and machines which can be dispensed with the maintenance services or of which the intervals of the maintenance services can be substantially extended.
- Thus, the present invention provides a method for the preparation of a high-hardness sintered body of a high-chromium cast iron which comprises the steps of:
- (a) subjecting a melt of a ternary alloy of iron, chromium and carbon containing from 11 to 30 mass % of chromium and from 2.2 to 5.0 mass % of carbon, the balance substantially being iron, to a quenching solidification treatment at a cooling rate not lower than 104° C./second to give particles of the ternary alloy; and
- (b) subjecting the particles of the ternary alloy to a sintering treatment by the method of electric discharge plasma sintering under compression in the atmospheric air.
- In particular, it is preferable that the quenching solidification of the alloy melt in step (a) is conducted by the method of centrifugal spray atomization.
- Photos A and B of FIG. 1 are each a microscopic photograph showing the metallographic structure of the sintered bodies of high-chromium cast irons of hypoeutectic and hypereutectic compositions, respectively, prepared in Example. Photos C and D of FIG. 1 are each a microscopic photograph showing the metallographic structure of the metal mold-cast bodies of the same hypoeutectic and hypereutectic compositions as in Photos A and B, respectively, prepared in Comparative Example.
- FIG. 2 is a bar chart showing the Rockwell hardness of the shaped bodies at room temperature, in which the columns A, B, C and D correspond to Photos A, B, C and D, respectively, of FIG. 1.
- As is described above, the method of the present invention comprises two essential steps (a) and (b), each of which is very unique as compared with the conventional powder metallurgical process including the steps of casting of an alloy melt into a mold to give an ingot, pulverization of the alloy ingot into fine particles, shaping the alloy particles by compression molding into a powder compact and sintering of the powder compact in a sintering furnace.
- Namely, step (a) of the inventive method is for the preparation of alloy particles from a melt of a high-chromium cast iron of the specified composition, in which the alloy melt is subjected to quenching solidification or, preferably, by the method of centrifugal spray atomization directly into alloy particles at a cooling rate higher by at least 105 times or sometimes by 107 times than the cooling rate in the conventional casting method. The alloy particles prepared as above are then subjected to a discharge plasma sintering treatment under compression in the atmospheric air into a sintered body.
- The above described inventive method is applicable not only to a hypoeutectic iron/chromium/carbon ternary alloy, of which the content of carbon is lower than the eutectic line, as a matter of course but also to a hypereutectic iron/chromium/carbon ternary alloy, of which the content of carbon is higher than the eutectic line. The metallographic texture of the thus obtained sintered body is much finer and much more uniform beyond comparable than that of the same cast iron body prepared by the casting method.
- The chemical composition of the melt of the high-chromium cast iron used in the inventive method is limited such that the contents of chromium and carbon are in the ranges from 11 to 30 mass % and from 2.2 to 5.0 mass %, respectively, the balance being substantially iron with small amounts of unavoidable impurity elements.
- The melt of the high-chromium cast iron is subjected in step (a) to a quenching solidification treatment at a cooling rate of at least 104° C./second or, desirably, at least 105° C./second. The cooling rate of the melt in the quenching solidification can be readily estimated according to a known procedure by utilizing the established relationship between the cooling rate and the metallographic structure of the solidified alloy. This quenching solidification treatment of the melt is conducted preferably by the centrifugal spray atomization method, in which the melt is ejected at a quenching disk rotating at a high velocity to be atomized by the centrifugal force into fine droplets, which are quenched by blowing of an inert gas to be solidified to give fine particles.
- Alternatively, the so-called quenching roller method using a single quenching roller or twin quenching rollers is applicable to step (a) though less preferable than the centrifugal spray atomization method because the quenching roller method produces thin ribbons of the solidified alloy which are more bulky than powders and need an additional step of pulverization or grinding with an unavoidable risk of contamination from the pulverization or grinding machine.
- The other advantages of the centrifugal spray atomizing method over other powder-making methods include: (1) the high cooling rate of the melt; (2) unnecessity of any carrier gas for spraying to ensure little gaseous occlusion in the particles; (3) little formation of oxidized surface film on the particles; (4) good sphericity of the particle configuration with little adhesion of satellite particles; and (5) independent controllability of the spraying conditions and quenching conditions to facilitate running of the process with stability.
- The quench-solidified particles of the high-chromium cast iron are then subjected to sintering by the so-called discharge plasma sintering method or pulse-current sintering method at a temperature in the range from 1000 to 1200° C. under compression with a molding pressure of 10 to 50 MPa with application of a pulsewise direct-current power. When undertaken under adequate conditions, the sintering treatment can be completed within a very short time of a few minutes. In the process of discharge plasma sintering, as is usually accepted, plasma discharge is first generated between particles so as to activate the particle surfaces by the accumulation of the impact energy thereby in the form of heat or strain so as to expose clean surfaces by removing the gases and contaminants adsorbed on the particle surfaces and destroying the oxidized surface film having a thickness of several nanometers order. Thereafter, Joule's heat is generated at the contacting points between particles by passing an electric current through the powder under compression so that the particles are bonded together to effect sintering giving a sintered body. This discharge plasma sintering treatment can be conducted in the atmospheric air. This process is effective for the consolidation of the particles in the non-equilibrium conditions.
- The sintered body of the high-chromium cast iron obtained in the above described manner is characterized by the very fine and uniform metallographic texture, which is absolutely free from anisotropy in contrast to the shaped body prepared by casting of a melt more or less having anisotropy of the texture.
- Accordingly, the sintered body of the high-chromium cast iron prepared by the inventive method has a Rockwell hardness greatly exceeding that of the bodies prepared by casting along with excellent abrasion resistance as a conesquence of strengthening by the fine texture.
- In the sintered body of the high-chromium cast iron prepared by the inventive method, the element of chromium forms a solid solution in the iron matrix and plays a very important role to increase the corrosion resistance of the iron matrix and to form a primary crystals of carbide (Fe,Cr)7C3. The content of chromium in the ternary alloy, however, is limited to the range of from 11 to 30 mass % because, when too small, the above mentioned advantageous effects cannot be fully exhibited while, when too large, a decrease is resulted in the hardness of the alloy.
- On the other hand, carbon is an indispensable element to form the phase of carbides with chromium and the content of carbon in the alloy is limited to the range of from 2.2 to 5.0 mass % because, when too small, the amount of the carbides formed therefrom is naturally so small that a decrease is caused in the hardness and abrasion resistance of the sintered body while, when too large, the amount of the carbides formed from carbon is so large that the sintered body suffers a decrease in the toughness.
- In the following, the method of the present invention is described in more detail by way of an Example and a Comparative Example, which, however, never limit the scope of the invention in any way.
- Quench-solidified powders were prepared by the centrifugal spray atomizing method from a melt of a hypoeutectic high-chromium cast iron of the chemical composition of Fe-25.3Cr-2.60C and a melt of a hypereutectic high-chromium cast iron of the chemical composition of Fe-24.4Cr-4.74C. The cooling rate in the quenching solidification was estimated to be in the range from 105 to 104° C./second.
- After particle size classification to collect the particles passing a mesh screen of 177 μm mesh opening, each of the powders was subjected to a discharge plasma sintering treatment in a graphite mold for 3 minutes under a molding pressure of 32 MPa with application of an on-off pulsed electric voltage of 33 milliseconds pulse width. The sintering temperature was 1140° C. for the powder of the hypoeutectic composition and 1100° C. for the powder of the hypereutectic composition. The time taken for arriving at the sintering temperature was about 300 seconds.
- Photos A and B of FIG. 1 are each a microscopic photograph showing the metallographic structure of the thus obtained sintered bodies of the hypoeutectic alloy and hypereutectic alloy, respectively. As is understood from these photographs, each of these sintered bodies has a uniform texture with extremely fine dispersion of the iron matrix phase and the carbide phase.
- FIG. 2 is a bar chart showing the Rockwell hardness HRC of these sintered bodies, of which the columns A and B are for the sintered bodies having the hypoeutectic and hypereutectic compositions of which the Rockwell hardness was 63 HRC and 68 HRC, respectively.
- Metal mold-cast bodies were prepared by casting of the melts of the same hypoeutectic and hypereutectic high-chromium cast irons used in the above described Example. As a consequence of the use of a metal mold instead of a sand mold conventionally employed in casting of cast irons, the solidification rate of the melt could be estimated to be larger than in a sand mold leading to an improvement of the mechanical properties of the cast body.
- Photos C and D of FIG. 1 are each a microscopic photograph showing the metallographic structure of the thus obtained cast bodies of the hypoeutectic alloy and hypereutectic alloy, respectively. In the cast body of the hypoeutectic alloy, Photo C indicates primary crystallization of coarse dendritic austenite crystals, i.e. γ-phase, with intervention of coarse eutectic crystals of the γ-phase and carbide in the interstices. Photo D indicates that the cast body of the hypereutectic alloy consists of coarse primary crystals of the carbide and eutectic crystals of the γ-phase and carbide. In each of these cast bodies, the texture has developed in the direction of solidification or, namely, in the direction of the heat flow.
- In FIG. 2, columns C and D show the Rockwell hardness of 50 HRC and 57 HRC of the hypoeutectic and hypereutectic cast bodies, respectively. It is evident that the sintered bodies of the high-chromium cast iron prepared according to the inventive method are very superior in the mechanical properties as compared with the cast bodies of the same alloy composition.
Claims (5)
1. A method for the preparation of a sintered body of a high-chromium cast iron which comprises the steps of:
(a) subjecting a melt of a ternary alloy of iron, chromium and carbon containing from 11 to 30 mass % of chromium and from 2.2 to 5.0 mass % of carbon, the balance substantially being iron, to a quenching solidification treatment at a cooling rate not lower than 104° C./second to give particles of the ternary alloy; and
(b) subjecting the particles of the ternary alloy to a sintering treatment under compression by the electric discharge plasma sintering method.
2. The method for the preparation of a sintered body of a high-chromium cast iron as claimed in claim 1 in which the quenching solidification of the alloy melt in step (a) is conducted by the centrifugal spray atomization method.
3. The method for the preparation of a sintered body of a high-chromium cast iron as claimed in claim 1 in which the pressure of compression in step (b) is in the range from 10 to 50 MPa.
4. The method for the preparation of a sintered body of a high-chromium cast iron as claimed in claim 1 in which the temperature of sintering in step (b) is in the range from 1000 to 1200° C.
5. The method for the preparation of a sintered body of a high-chromium cast iron as claimed in claim 1 in which the sintering treatment in step (b) is conducted in the atmospheric air.
Priority Applications (1)
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EP20010204993 EP1215855A3 (en) | 2000-12-14 | 2001-12-18 | Method of network load management for voice over internet protocol |
Applications Claiming Priority (2)
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JP2000-143932 | 2000-05-16 | ||
JP2000143932A JP3694732B2 (en) | 2000-05-16 | 2000-05-16 | Manufacturing method of high hardness and high chromium cast iron powder alloy |
Publications (1)
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US20020094297A1 true US20020094297A1 (en) | 2002-07-18 |
Family
ID=18650676
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US09/735,518 Abandoned US20020094297A1 (en) | 2000-05-16 | 2000-12-14 | Method for the preparation of a sintered body of high-hardness high-chromium cast iron |
Country Status (4)
Country | Link |
---|---|
US (1) | US20020094297A1 (en) |
JP (1) | JP3694732B2 (en) |
KR (1) | KR100400989B1 (en) |
DE (1) | DE10064056B9 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN106029267A (en) * | 2014-01-27 | 2016-10-12 | 罗瓦尔玛股份公司 | Centrifugal atomization of iron-based alloys |
WO2020021122A1 (en) | 2018-07-27 | 2020-01-30 | Innomaq 21, S.L. | Method for the obtaining cost effective powder |
CN115029606A (en) * | 2022-06-14 | 2022-09-09 | 西安稀有金属材料研究院有限公司 | Powder metallurgy preparation method of double-enhanced-phase high-chromium cast iron wear-resistant composite material |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
BR112020011171A2 (en) * | 2017-12-04 | 2020-11-17 | Weir Minerals Australia Limited | corrosion resistant and white cast iron |
KR20190134043A (en) | 2018-05-24 | 2019-12-04 | 무진정밀(주) | High chromium cast iron with excellent abrasion resistance and corrosion resistance and parts containing the same used for wet type exhaust gas desulfurization equipment of thermoelectric power plant |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE3346089A1 (en) * | 1983-12-21 | 1985-07-18 | Dr. Weusthoff GmbH, 4000 Düsseldorf | METHOD FOR MANUFACTURING HIGH-STRENGTH, DUCTILE BODY FROM CARBON-BASED IRON-BASED ALLOYS |
SE9402672D0 (en) * | 1994-08-10 | 1994-08-10 | Hoeganaes Ab | Chromium containing materials having high tensile strength |
-
2000
- 2000-05-16 JP JP2000143932A patent/JP3694732B2/en not_active Expired - Lifetime
- 2000-12-14 US US09/735,518 patent/US20020094297A1/en not_active Abandoned
- 2000-12-21 DE DE10064056A patent/DE10064056B9/en not_active Expired - Fee Related
- 2000-12-30 KR KR10-2000-0087132A patent/KR100400989B1/en not_active IP Right Cessation
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN106029267A (en) * | 2014-01-27 | 2016-10-12 | 罗瓦尔玛股份公司 | Centrifugal atomization of iron-based alloys |
WO2020021122A1 (en) | 2018-07-27 | 2020-01-30 | Innomaq 21, S.L. | Method for the obtaining cost effective powder |
US11529683B2 (en) | 2018-07-27 | 2022-12-20 | Innomaq 21, S.L. | Method for the obtaining cost effective powder |
US11897035B2 (en) | 2018-07-27 | 2024-02-13 | Innomaq 21, S.L. | Method for the obtaining cost effective powder |
CN115029606A (en) * | 2022-06-14 | 2022-09-09 | 西安稀有金属材料研究院有限公司 | Powder metallurgy preparation method of double-enhanced-phase high-chromium cast iron wear-resistant composite material |
Also Published As
Publication number | Publication date |
---|---|
DE10064056B9 (en) | 2005-12-15 |
KR100400989B1 (en) | 2003-10-10 |
DE10064056A1 (en) | 2001-11-29 |
KR20010105145A (en) | 2001-11-28 |
JP2001329301A (en) | 2001-11-27 |
JP3694732B2 (en) | 2005-09-14 |
DE10064056B4 (en) | 2004-04-08 |
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