JP6953918B2 - Metal powder, sintered body, and method for manufacturing sintered body - Google Patents

Description

The present invention relates to a metal powder, a sintered body, and a method for producing a sintered body, and more particularly, a metal powder that can be used as a raw material for powder metallurgy, and can be produced by sintering such a metal powder. It relates to a sintered body and a method for producing such a sintered body.

A metal powder material made of stainless steel or the like is molded into a predetermined shape by injection molding, press molding, or the like, and then the molded body is sintered to obtain a sintered body. The metal molding member is formed by a powder metallurgy process. The method of manufacturing is known. At this time, the obtained metal molding member may be required to have high hardness and corrosion resistance.

When high hardness and high corrosion resistance are required for stainless steel, martensitic stainless steels such as SUS440C and SUS420J2 have been generally used. Of these, SUS440C has a very high hardness, but does not have sufficient corrosion resistance due to the small amount of solid solution Cr in the matrix phase. On the other hand, SUS420J2 has a relatively small amount of carbon, so that sufficient hardness cannot be obtained.

Therefore, as a martensitic steel having both high hardness and high corrosion resistance, a steel having a component composition as shown in Patent Document 1 filed by the applicant has been newly developed. The martensite steel of Patent Document 1 has 0.15% ≤ C <0.70%, 0.05% ≤ Si ≤ 1.00%, 0.05% ≤ Mn ≤ 1.00%, P ≤ 0.10. %, S ≤ 0.10%, 0.001% ≤ Cu ≤ 0.50%, 0.05% ≤ Ni ≤ 0.50%, 11.0% ≤ Cr ≤ 18.0%, 0.05% ≤ Mo ≤ 2.0%, 0.01% ≤ W ≤ 0.50%, 0.01% ≤ V ≤ 0.50%, 0.05% ≤ N ≤ 0.40%, O ≤ 0.02%, It contains Al ≤ 0.080% and 0.0005% ≤ B ≤ 0.0050%, and the balance is substantially composed of Fe and unavoidable impurities, 0.4% <C + N <0.7%, and C. It has a component composition of / N ≧ 0.75.

Japanese Unexamined Patent Publication No. 2007-277369

If martensite steel, which has both high strength and high corrosion resistance as disclosed in Patent Document 1, is used as a material for forming a metal powder, it can be obtained as a sintered body having high strength and high corrosion resistance through a powder metallurgy process. , There is a possibility that a metal molding member can be obtained. However, the martensitic steel disclosed in Patent Document 1 is assumed to be a steel material constituting a mold used for injection molding of plastics, and is formed into a predetermined shape by melting and casting, and then appropriately heat-treated to obtain gold. It is used as a mold.

Even if alloy materials having the same composition are used, the physical phenomena that occur in the structure of the alloy material differ between the melting / casting process and the sintering process in powder metallurgy, and as a result, the resulting metal member In, the microstructure and physical properties of the structure may differ. Therefore, even if the composition of the martensite steel of Patent Document 1 formed by melting and casting is applied to the metal powder as a raw material for powder metallurgy as it is, the physical properties such as hardness, corrosion resistance, and mechanical strength are obtained through the powder metallurgy process. It is not always possible to obtain a sintered body having excellent characteristics.

An object to be solved by the present invention is to provide a metal powder which can be suitably used as a raw material for powder metallurgy and can give a sintered body having excellent hardness, corrosion resistance and mechanical strength. Another object of the present invention is to provide such a sintered body and a method for producing the same.

In order to solve the above problems, the metal powder according to the present invention contains C and contains 0.05% ≤ Si ≤ 1.00% and 0.05% ≤ Mn ≤ 1.00% in mass%. , P ≤ 0.10%, S ≤ 0.10%, 0.001% ≤ Cu ≤ 0.50%, 0.05% ≤ Ni ≤ 0.50%, 11.0% ≤ Cr ≤ 18.0% , 0.05% ≤ Mo ≤ 2.0%, 0.01% ≤ V ≤ 0.50%, N ≤ 0.40%, 0.02% <O ≤ 0.60%, Al ≤ 0.080% , 0.0005% ≤ B ≤ 0.0050%, the balance consisting of Fe and unavoidable impurities.

Here, it is preferable that the content of C is mass% and C ≦ 1.00%.

Further, the content of N is preferably 0.005% ≦ N ≦ 0.40% in terms of mass%.

The total content of C and N is preferably 0.4% <C + N <0.7% in mass%.

The ratio of the contents of C and N is preferably C / N ≧ 0.75.

The metal powder may further contain at least one selected from 0.001% ≤ Co ≤ 0.50% and 0.01% ≤ W ≤ 0.50% in mass%.

Further, the metal powder is 0.001% ≤ Se ≤ 0.3%, 0.001% ≤ Te ≤ 0.3%, 0.0002% ≤ Ca ≤ 0.10%, 0.001 in mass%. It is preferable to contain at least one selected from% ≤ Pb ≤ 0.20%.

The metal powder further contains 0.001% ≤ Nb ≤ 0.30%, 0.001% ≤ Ta ≤ 0.30%, Ti ≤ 0.20%, 0.001% ≤ Zr ≤ 0 in mass%. It is preferable to contain at least one selected from .30%.

The sintered body according to the present invention has 0.15% ≤ C <0.70%, 0.05% ≤ Si ≤ 1.00%, 0.05% ≤ Mn ≤ 1.00%, P in mass%. ≤0.10%, S≤0.10%, 0.001%≤Cu≤0.50%, 0.05%≤Ni≤0.50%, 11.0%≤Cr≤18.0%, 0 0.05% ≤ Mo ≤ 2.0%, 0.01% ≤ V ≤ 0.50%, 0.05% ≤ N ≤ 0.40%, 0.02% <O ≤ 0.60%, Al ≤ 0 .080%, 0.0005% ≤ B ≤ 0.0050%, the balance is made of martensite steel consisting of Fe and unavoidable impurities, 0.4% <C + N <0.7%, and C / N ≧ 0.75.

The sintered body may further contain at least one selected from 0.001% ≦ Co ≦ 0.50% and 0.01% ≦ W ≦ 0.50% in mass%.

Further, the sintered body was obtained in terms of mass% of 0.001% ≤ Se ≤ 0.3%, 0.001% ≤ Te ≤ 0.3%, 0.0002% ≤ Ca ≤ 0.10%, 0. It is preferable to contain at least one selected from 001% ≤ Pb ≤ 0.20%.

Further, the sintered body is 0.001% ≦ Nb ≦ 0.30%, 0.001% ≦ Ta ≦ 0.30%, Ti ≦ 0.20%, 0.001% ≦ Zr ≦ in mass%. It is preferable to contain at least one selected from 0.30%.

The method for producing a sintered body according to the present invention is to produce the sintered body according to the above invention by molding and sintering the metal powder according to the above invention.

Here, it is preferable to perform sintering in an atmosphere containing nitrogen.

Since the metal powder according to the above invention has a predetermined component composition, it can be sintered to give a sintered body having excellent hardness, corrosion resistance, and mechanical strength. In particular, by containing O exceeding 0.02% by mass together with Si, the structure of the sintered body is miniaturized by exhibiting a pinning effect at the grain boundaries as _{SiO 2 at the time of sintering.} As a result, the mechanical strength of the sintered body is increased, and the toughness and fatigue strength are improved.

By having a predetermined component composition, the sintered body according to the above invention becomes a metal molding member having excellent hardness, corrosion resistance, and mechanical strength. In particular, by containing O exceeding 0.02% by mass together with Si, the structure of the sintered body is refined by the pinning effect of _{SiO 2 generated at the time of sintering.} As a result, the mechanical strength of the sintered body is increased, and the sintered body has high toughness and fatigue strength.

In the method for producing a sintered body according to the above invention, a sintered body having excellent mechanical strength as well as hardness and corrosion resistance is obtained by molding and sintering using a metal powder containing a predetermined amount of O as a raw material. Can be manufactured. It is also possible to adjust each characteristic by controlling the content of C and N in the sintered body according to the conditions at the time of molding and sintering.

Hereinafter, the metal powder, the sintered body, and the method for producing the sintered body according to the embodiment of the present invention will be described in detail.

[Sintered body]
First, the sintered body according to the embodiment of the present invention will be described. The sintered body according to the present embodiment is formed by molding a metal powder material into a desired member shape and sintering the material.

The sintered body according to this embodiment is made of martensitic steel. That is, it is made of sintered stainless steel powder and has a martensite structure. The sintered body according to the present embodiment contains the following elements, and the balance is composed of Fe and unavoidable impurities. The types of additive elements, component ratios, reasons for limitation, etc. are as follows. The unit of the component ratio is mass%.

(1) 0.15% ≤ C <0.70%.
C is an element necessary for ensuring strength and wear resistance, and is an element that forms carbide by combining with carbide-forming elements such as Cr, Mo, W, V, and Nb. Further, C is dissolved in a matrix when it is heated during the production of a metal powder, the production of a sintered body, the quenching of a sintered body, or the like, and the matrix is organized into martensite to form a hardness. It is an element that secures. The amount of C is preferably 0.15% or more in order to obtain the effects of improving the strength and wear resistance and ensuring the hardness.
On the other hand, when the amount of C becomes excessive, C combines with a carbide-forming element to form a carbide, and the amount of solid solution of Cr, Mo, etc. in the matrix decreases. A decrease in the amount of solid solution of Cr, Mo, etc. in the matrix causes a decrease in corrosion resistance. Therefore, the amount of C is preferably less than 0.70%.

(2) 0.05% ≤ Si ≤ 1.00%.
Si is added primarily for antacid or nitrogen addition. In addition, it combines with O to form SiO ₂ , which contributes to the miniaturization of the crystal structure due to the pinning effect at the grain boundaries when the metal powder material is sintered. In order to obtain these effects, the amount of Si is preferably 0.05% or more.
On the other hand, when the amount of Si becomes excessive, the toughness is lowered. Therefore, the amount of Si is preferably 1.00% or less.

(3) 0.05% ≤ Mn ≤ 1.00%.
Mn is added as a hardenability improving element to improve the hardenability when quenching the sintered body. It also has the effect of fixing the S contained inevitably and preventing a decrease in toughness. In order to obtain such an effect, the amount of Mn is preferably 0.05% or more.
On the other hand, since Mn tends to form an oxide, if the amount of Mn becomes excessive, the O concentration in the metal powder or the sintered body tends to increase more than necessary. Therefore, the amount of Mn is preferably 1.00% or less.

(4) P ≦ 0.10%.
(5) S ≦ 0.10%.
P and S are inevitably contained in the steel. P causes segregation to grain boundaries, and S forms sulfide, which causes a decrease in toughness. Therefore, when P and S are unavoidably contained, the amount of P is preferably 0.10% or less. The amount of S is preferably 0.10% or less.

(6) 0.001% ≤ Cu ≤ 0.50%.
Cu is an element that improves corrosion resistance. In order to obtain the effect of improving corrosion resistance, the amount of Cu is preferably 0.001% or more.
On the other hand, when the amount of Cu becomes excessive, the amount of retained austenite increases, causing aging of the dimensions. Therefore, the amount of Cu is preferably 0.50% or less.

(7) 0.05% ≤ Ni ≤ 0.50%.
Ni contributes to increasing the nitrogen content in the sintered body and in the metal powder as a raw material. In order to obtain such an effect, the amount of Ni is preferably 0.05% or more.
On the other hand, when the amount of Ni becomes excessive, the amount of retained austenite increases, causing aging of the dimensions. Therefore, the amount of Ni is preferably 0.50% or less.

(8) 11.0% ≤ Cr ≤ 18.0%.
Cr contributes to increasing the nitrogen content in the sintered body and in the metal powder as a raw material. In order to obtain such an effect, the amount of Cr is preferably 11.0% or more.
On the other hand, when the amount of Cr becomes excessive, the amount of retained austenite increases and the hardness decreases even if the subzero treatment is performed. Therefore, the amount of Cr is preferably 18.0% or less.

(9) 0.05% ≤ Mo ≤ 2.0%.
Mo is an element that improves corrosion resistance. In order to obtain such an effect, the amount of Mo is preferably 0.05% or more.
On the other hand, when the amount of Mo is excessive, coarse carbonitride is formed, which causes a decrease in mirror quality. Therefore, the amount of Mo is preferably 2.0% or less.

(10) 0.01% ≤ V ≤ 0.50%.
V contributes to increasing the nitrogen content in the sintered body and in the metal powder as a raw material. In order to obtain such an effect, the amount of V is preferably 0.01% or more.
On the other hand, when the amount of V is excessive, coarse carbonitride is formed, which causes a decrease in mirror quality. Therefore, the amount of V is preferably 0.50% or less.

(11) 0.05% ≤ N ≤ 0.40%.
N is an invasive element that forms an invasive solid solution and contributes to an increase in the hardness of the martensite structure. Further, when N is dissolved in the matrix, the corrosion resistance is improved. In order to obtain such an effect, the amount of N in the sintered body is preferably 0.05% or more.
On the other hand, when the amount of N is excessive, carbonitride is excessively generated, so that the toughness of the sintered body is lowered. Therefore, the amount of N is preferably 0.40% or less.

(12) 0.02% <O ≦ 0.60%.
When the metal powder raw material is sintered to form a sintered body, if O is contained in the metal powder raw material, it is combined with Si to form _{SiO 2.} SiO ₂ exerts a pinning effect at the crystal grain boundaries at the time of sintering, and has an effect of suppressing coarsening of crystal grains. The finer grain size improves the mechanical strength of the sintered body. In particular, the toughness and fatigue strength of the sintered body are improved. The improvement of these characteristics is reflected as the improvement of the bending force of the sintered body. From the viewpoint of sufficiently obtaining such an effect, the amount of O in the sintered body is preferably more than 0.02%.
On the other hand, if the amount of O is too large, the sinterability of the metal powder deteriorates and the porosity in the sintered body increases. Then, it becomes difficult to obtain a high-density sintered body. Therefore, the amount of O in the sintered body is preferably 0.60% or less. It is more preferably 0.50% or less, more preferably 0.24% or less.

(13) Al ≦ 0.080%.
Al is an element added as an antacid. However, when the amount of Al becomes excessive, coarse nitrides are formed and the mirror surface property is deteriorated. Therefore, when Al is added, the amount of Al is preferably 0.080% or less.

(14) 0.0005% ≤ B ≤ 0.0050%.
B is an element that strengthens grain boundaries and reduces cracking during heat treatment such as quenching and subzero treatment. In order to obtain such an effect, the amount of B is preferably 0.0005% or more.
On the other hand, when the amount of B becomes excessive, a nitride is formed and the corrosion resistance is lowered. Therefore, the amount of B is preferably 0.0050% or less.

In the sintered body according to the present invention, in addition to the additive elements being in the above-mentioned range, the C amount and the N amount have the following relationship.
(A) 0.4% <C + N <0.7%.
(B) C / N ≧ 0.75.
As described above, N is an element that improves both corrosion resistance and hardness. However, N alone cannot obtain sufficient hardness. On the other hand, when N is further added to the steel containing C, the solid solution limit of C at the temperature at which it is heated by quenching or the like becomes large, and high hardness is obtained after martensitic transformation. In order to obtain such an effect, the amount of C + N is preferably larger than 0.4%.
On the other hand, when the amount of C + N becomes excessive, coarse carbonitride is formed and the mirror surface property is deteriorated. Therefore, the amount of C + N is preferably less than 0.7%.
Further, if C is relatively small with respect to N, hardness cannot be secured after martensitic transformation. Therefore, the C / N is preferably 0.75 or more.

The sintered body according to the present embodiment contains the above-mentioned predetermined amounts of C, Si, Mn, P, S, Cu, Ni, Cr, Mo, V, N, O, Al and B, and the balance is Fe. Consists of unavoidable impurities. As described above, the contents of P and S are preferably suppressed to 0.10% or less, respectively, but the metal powder is mixed with an organic material such as a binder and molded to form a sintered body. Is not excluded when P and S derived from an organic material are contained in the sintered body as unavoidable impurities in excess of the above range.

The sintered body according to the present embodiment may contain at least one of the following first additive elements in addition to the various essential elements described above.
(15) 0.01% ≤ W ≤ 0.50%.
(16) 0.001% ≤ Co ≤ 0.50%.
W is an element that improves hardenability. In order to obtain such an effect, the amount of W is preferably 0.01% or more.
On the other hand, when the amount of W becomes excessive, coarse carbonitride is formed, which causes a decrease in mirror quality. Therefore, the amount of W is preferably 0.50% or less.
Like W, Co can be added to improve hardenability. In order to obtain such an effect, the amount of Co is preferably 0.001% or more.
On the other hand, even if Co is added excessively, the effect is saturated and there is no actual benefit. Therefore, the amount of Co is preferably 0.50% or less.

The sintered body according to the present embodiment may further contain at least one of the following second additive elements in addition to or instead of the first additive element described above.
(17) 0.001% ≤ Se ≤ 0.3%.
(18) 0.001% ≤ Te ≤ 0.3%.
(19) 0.0002% ≤ Ca ≤ 0.10%.
(20) 0.001% ≤ Pb ≤ 0.20%.
Se, Te, Ca, Pb and Bi can all be added to improve machinability. In order to obtain such an effect, the amount of each element added is preferably at least the above-mentioned lower limit value.
On the other hand, excessive addition of these elements causes a decrease in toughness. Therefore, the amount of each element added is preferably not more than the above-mentioned upper limit value.

The sintered body according to the present embodiment further contains at least one of the following third additive elements in addition to or in place of the first additive element and / or the second additive element described above. You can stay.
(21) 0.001% ≤ Nb ≤ 0.30%.
(22) 0.001% ≤ Ta ≤ 0.30%.
(23) Ti ≤ 0.20%.
(24) 0.001% ≤ Zr ≤ 0.30%.
Ti, Nb, Ta and Zr all combine with C and N to form a carbonitride, which is effective in suppressing the coarsening of crystal grains. In order to obtain such an effect, the amount of these elements added is preferably at least the above-mentioned lower limit.
On the other hand, excessive addition of these elements deteriorates machinability. Therefore, the amount of these elements added is preferably not more than the above-mentioned upper limit value.

The sintered body according to the present embodiment contains N in addition to C as an intrusive element, and the amount of C + N and the C / N ratio are adjusted to predetermined values. Therefore, when heating is performed by quenching or the like. The solid solution limit of C at the temperature of is increased (that is, the austenite region is widened). Therefore, high hardness can be obtained after martensitic transformation. Further, in addition to adding various elements for improving corrosion resistance, if an appropriate amount of N is dissolved in the matrix, the corrosion resistance is further improved. Further, by adding B to the steel, the grain boundaries are strengthened, and cracks during heat treatment such as quenching and subzero treatment can be reduced.

Since the sintered body according to the present embodiment contains O exceeding 0.02%, the crystal grains are refined by the pinning effect of _{SiO 2, and the sintered body has high mechanical strength.} .. The degree of fineness of the crystal grains can be evaluated by, for example, the crystal grain size number defined in JIS G0551, and the crystal grain size number is preferably 4.0 or more, more preferably 5.0 or more. Further, the bending force of the sintered body is preferably 3000 MPa or more.

On the other hand, since the O content is suppressed to 0.60% or less, a high-density sintered body can be obtained. The density of the sintered body is preferably 92% or more in relative density. The relative density is more preferably 94% or more, more preferably 96% or more.

The specific type of metal molding member composed of the sintered body according to the present embodiment is not particularly limited. From the viewpoint of utilizing the characteristics of powder metallurgy, which makes it easy to form into complicated shapes, and the physical characteristics such as hardness, corrosion resistance, and mechanical strength of the sintered body, it is preferable to construct sliding parts such as bearings. It can be given as an example.

[Metal powder]
Next, the metal powder according to the embodiment of the present invention will be described. The metal powder according to the present embodiment can be used as a raw material for powder metallurgy, and by forming it into a desired shape and sintering it, hardness, corrosion resistance, and mechanical like the sintered body according to the above embodiment. It is possible to give a sintered body having excellent strength.

The metal powder according to this embodiment contains the following elements, and the balance consists of Fe and unavoidable impurities.

(1) C: The content is not specified.
(2) 0.05% ≤ Si ≤ 1.00%.
(3) 0.05% ≤ Mn ≤ 1.00%.
(4) P ≦ 0.10%.
(5) S ≦ 0.10%.
(6) 0.001% ≤ Cu ≤ 0.50%.
(7) 0.05% ≤ Ni ≤ 0.50%.
(8) 11.0% ≤ Cr ≤ 18.0%.
(9) 0.05% ≤ Mo ≤ 2.0%.
(10) 0.01% ≤ V ≤ 0.50%.
(11) N ≦ 0.40%.
(12) 0.02% <O ≦ 0.60%.
(13) Al ≦ 0.080%.
(14) 0.0005% ≤ B ≤ 0.0050%.

In the above, except for (1) C and (11) N, the range of the content of each essential element is the same as the range mentioned for the sintered body above, and is the same as described for the sintered body. For some reason, it is limited to those ranges. Each of the essential elements other than C and N does not substantially change when the metal powder is formed into a molded product through molding and sintering, and is contained in the metal powder in the above-mentioned predetermined range. As a result, each effect can be exhibited in the sintered body. Regarding C and N, in addition to the content in the metal powder, the content in the sintered body can be controlled by the conditions at the time of molding and sintering of the metal powder.

Regarding (1) C, the amount of C in the sintered body is increased by adding an organic substance, graphite, or the like as a binder or the like when molding the metal powder. On the other hand, the amount of C in the sintered body is reduced by degreasing the molded body before sintering to remove the organic component derived from the binder or the like. Alternatively, the molded metal powder may be sintered in a vacuum to remove C derived from the metal powder and / or derived from an additive such as an organic substance in the form of CO bonded to O in the metal powder. The amount of C in the sintered body is reduced.

As described above, the amount of C can be widely controlled depending on the conditions at the time of molding and sintering of the metal powder, and therefore the content in the metal powder is not particularly specified. However, from the viewpoint of avoiding deterioration of corrosion resistance due to excessive C remaining in the sintered body, the amount of C in the metal powder is preferably 1.00% or less, more preferably less than 0.70%. ..
On the other hand, the lower limit of the amount of C in the metal powder is not particularly specified because C is inevitably contained in the sintered body due to mixing with a binder or the like. When an organic substance such as a binder is not used, the amount of C is preferably 0.15% or more.

(11) N is an element that has a high effect on improving the hardness and corrosion resistance of the sintered body by being contained in the sintered body as described above, but is sintered in an atmosphere containing nitrogen. It is not always necessary to be contained in the metal powder because it can be added in the sintering step by adopting a means such as. Therefore, the lower limit of the amount of N in the metal powder is not particularly specified. However, even if the conditions of the sintering step are such that it is difficult to introduce N into the sintered body, the N amount is 0.005% or more, and further, from the viewpoint of securing a predetermined N amount in the sintered body. Is preferably 0.05% or more.
On the other hand, from the viewpoint of avoiding excessive N remaining in the sintered body, the amount of N in the metal powder is preferably 0.40% or less.

Regarding (12) O, the content in the sintered body may change from the content of the metal powder depending on the conditions at the time of molding or sintering the metal powder. At the time of sintering, it combines with C derived from metal powder and additives such as organic substances to form CO, so it is removed from the sintered body by sintering in vacuum, and the amount of O in the sintered body. Decreases. Further, even when sintering is performed in a hydrogen atmosphere, the amount of O in the sintered body is reduced. On the contrary, when sintering is performed under conditions containing oxygen such as in the atmosphere, the amount of O in the sintered body increases.

As described above, the amount of O can change depending on the conditions at the time of sintering, but as described above, it is very important to contain more than a predetermined amount of O in the sintered body to secure the mechanical strength of the sintered body. Therefore, it is preferable that the amount of O in the metal powder is more than 0.02%.
On the other hand, from the viewpoint of ensuring the density of the sintered body, the amount of O in the metal powder is preferably 0.60% or less. It is more preferably 0.50% or less, more preferably 0.40% or less.

As described above, since the contents of C and N can vary depending on the conditions at the time of molding and sintering of the metal powder, the relationship between the contents of C and N in the metal powder according to the present embodiment. Is not particularly limited, but preferably has the following relationship.
(A) 0.4% <C + N <0.7%.
(B) C / N ≧ 0.75.
Since the metal powder has such a relationship, it is highly probable that the same relationship can be obtained in the sintered body obtained through sintering, and in the sintered body, those predetermined relationships are high. It is easy to achieve effects such as high hardness.

The metal powder according to the present embodiment may contain at least one of the following first additive elements in addition to the various essential elements described above.
(15) 0.01% ≤ W ≤ 0.50%.
(16) 0.001% ≤ Co ≤ 0.50%.

Further, the metal powder according to the present embodiment may further contain at least one of the following second additive elements in addition to or instead of the first additive element described above.
(17) 0.001% ≤ Se ≤ 0.3%.
(18) 0.001% ≤ Te ≤ 0.3%.
(19) 0.0002% ≤ Ca ≤ 0.10%.
(20) 0.001% ≤ Pb ≤ 0.20%.

Further, the metal powder according to the present embodiment further contains at least one of the following third additive elements in addition to or in place of the first additive element and / or the second additive element described above. You can go out.
(21) 0.001% ≤ Nb ≤ 0.30%.
(22) 0.001% ≤ Ta ≤ 0.30%.
(23) Ti ≤ 0.20%.
(24) 0.001% ≤ Zr ≤ 0.30%.

The range of the contents of each of the first to third additive elements is the same as the range mentioned for the sintered body above, and is limited to those ranges for the same reason as described for the sintered body. NS. Each additive element does not substantially change when the metal powder is sintered, and when the additive element is contained in the metal powder in a content within the above-mentioned predetermined range, the respective effects are obtained in the sintered body. Can be demonstrated.

The crystal structure of the metal powder according to this embodiment is not particularly limited. Even when the metal powder has a structure other than martensite, it undergoes changes in the C and N contents during sintering, heating and subsequent cooling during sintering, and quenching treatment for the sintered body, and then martensite. It can be a sintered body having a structure. The particle size of the metal powder is not particularly specified, and may be appropriately set according to the details of the metal powder manufacturing process, sintering process, etc., but typically, the average particle size D50 is 1 to 1. A range of 20 μm can be exemplified.

The method for producing the metal powder according to the present embodiment is not particularly specified, but for example, the metal powder according to the present embodiment can be suitably produced by the atomizing method. In the atomizing method, a fluid is injected into the molten alloy, and the molten alloy is solidified in a finely divided state by collision with the fluid to produce an alloy powder.

As the atomizing method, a water atomizing method using water as a fluid to be injected into the molten alloy and a gas atomizing method using gas are known. The water atomization method has a higher pulverizing ability of the molten alloy than the gas atomization method, and can efficiently produce fine metal powder. On the other hand, in the water atomization method, the amount of O in the metal powder tends to increase due to oxidation due to contact with water. The metal powder according to the present embodiment contains a relatively large amount of O from the viewpoint of improving the mechanical strength of the sintered body, and is preferably produced by the water atomization method. However, among the metal powders according to the present embodiment, when producing a metal powder having a relatively small amount of O, such as approximately O ≦ 0.1%, it is preferable to adopt the gas atomizing method using an inert gas. ..

The metal powder obtained by the atomizing method or the like may be appropriately subjected to classification, heat treatment, mechanical treatment, chemical treatment, mixing and the like.

[Manufacturing method of sintered body]
Finally, a method for producing a sintered body according to an embodiment of the present invention will be described. In the production method according to the present embodiment, the sintered body according to the above embodiment is produced by powder metallurgy using the metal powder according to the above embodiment as a raw material, that is, by molding and sintering the metal powder according to the above embodiment. To manufacture.

In the production method according to the present embodiment, first, the metal powder is molded into a predetermined shape. The molding method is not particularly limited, and injection molding, press molding, extrusion molding and the like can be exemplified.

Here, it is preferable that the metal powder is prepared in a state suitable for each molding method prior to molding. For example, when injection molding is used, a compound is prepared by mixing additives such as a binder, wax, plasticizer, and graphite made of an organic material. Further, when press molding is used, it is advisable to carry out a granulation step of forming a granulation powder by binding a plurality of metal powders using a granulation agent or the like.

After molding the metal powder into a predetermined shape, it is advisable to carry out a degreasing step on the molded product, if necessary. The degreasing step is a step of reducing the organic content added to the metal powder as a binder, wax, or the like, and can be performed by decomposing the organic content by heating. Alternatively, it can be carried out by removing organic substances by contact with a solvent or a gas that decomposes a binder or wax. By going through the degreasing step, the amount of C in the sintered body obtained through sintering can be reduced.

Next, sintering (baking) is performed on the molded product that has been appropriately degreased. Sintering can be performed, for example, at a temperature of 1200 to 1350 ° C. Examples of the atmosphere at the time of sintering include atmosphere, vacuum, _{a reducing gas such as hydrogen (H 2} ), an inert gas such as argon, and an atmosphere containing nitrogen. Examples of the atmosphere containing nitrogen include a nitrogen gas (N ₂ ) atmosphere, a nitrogen-hydrogen mixed atmosphere (N ₂ + H ₂ ), and an ammonia decomposition gas atmosphere. At the time of sintering, if the heating temperature and the cooling conditions after sintering are properly selected, even if the metal powder as a raw material does not have a martensite structure, it undergoes martensitic transformation and is baked with a martensite structure. You can get a unity.

In the sintered body according to the above embodiment, as described above, the contents of C, N, and O have a great influence on the characteristics of the sintered body. The contents of C, N, and O largely depend on the conditions at the time of sintering such as the type of atmosphere, and the contents of these elements can be controlled by controlling the conditions at the time of sintering.

For example, it is preferable to perform sintering in an atmosphere containing nitrogen. Thereby, the N amount of the sintered body can be increased. When sintering is performed in a vacuum or in an inert gas, N escapes to the gas phase, and the amount of N in the sintered body tends to decrease as compared with the metal powder as a raw material. Therefore, in order not to reduce the amount of N in the sintered body and to increase it, it is preferable to perform sintering in an atmosphere containing nitrogen.

On the other hand, when the sintering is performed in a vacuum, the amount of C and the amount of O in the sintered body can be reduced by the generation and exhaust of CO by the reaction of C and O. O can be effectively reduced by sintering in a hydrogen atmosphere.

However, as described above, when sintering is performed in vacuum, it is difficult to maintain the amount of N in the sintered body. Therefore, sintering in an atmosphere containing nitrogen and sintering in vacuum may be performed in sequence. As a result, the maintenance of the N amount and the reduction of the C amount and the O amount can be achieved at the same time. The order of sintering in each atmosphere may be appropriately determined. For example, in the relatively low temperature period at the initial stage of sintering, sintering is performed in vacuum to reduce the amount of O, and then sintering. After the temperature of the body becomes sufficiently high, it is possible to switch to sintering in a nitrogen atmosphere and improve the density of the sintered body while increasing the amount of N.

The obtained sintered body can be further subjected to heat treatment or machining as appropriate. Examples of the heat treatment include quenching treatment, subzero treatment, tempering treatment, hot isotropic pressure pressurization (HIP) treatment, and the like. As the machining, cutting can be exemplified.

In the production method according to the present embodiment, the metal powder according to the above embodiment containing C and having N ≦ 0.40% and 0.02% <O ≦ 0.60% is used as a raw material. 15% ≤ C <0.70%, 0.05% ≤ N ≤ 0.40%, 0.02% <O ≤ 0.60%, 0.4% <C + N <0.7% and C / The sintered body according to the above embodiment having N> 0.75 is produced, but as described above, the content of C, N, and O in the sintered body is not limited to the component composition of the metal powder. It can vary depending on the conditions during molding and sintering of the metal powder. Therefore, it is also possible to produce the sintered body according to the above embodiment by using a metal powder having a content of at least one of C, N, and O different from the metal powder according to the above embodiment as a raw material.

Hereinafter, the present invention will be described in detail with reference to Examples.

<Preparation of sample>
(Making metal powder)
The metal powders for Samples 1 to 6 having the respective component compositions shown in Table 1 were produced by the atomizing method. At this time, the gas atomizing method was used for the sample 1, and the water atomizing method was used for the samples 2 to 6. Further, the average particle size D50 of each of the obtained metal powders was measured by a laser diffraction method.

(Preparation of sintered body)
A metal powder, a graphite powder, and an organic binder (a mixture of polypropylene, carnauba wax, and paraffin wax) were weighed and mixed, and kneaded with a kneader to prepare a compound. The amount of graphite powder added was adjusted so that the C content of the sintered body had a predetermined composition, and the proportion of the organic binder in the compound was 7.5% by mass.

Using the obtained compound, a rectangular parallelepiped molded product having a size of 5 mm × 7 mm × 50 mm was produced by an injection molding machine. Next, the obtained molded product was _{heated to 450 ° C. in a nitrogen (N 2} ) flow atmosphere and then held for 2 hours to perform degreasing treatment. The obtained degreased body was heated to 1000 ° C. in vacuum and then held for 2 hours. After that, the _{atmosphere was further switched to a nitrogen (N 2} ) atmosphere, the temperature was raised to 1250 ° C., and the temperature was maintained for 3 hours to prepare a sintered body.

The obtained sintered body was heated and held at 1050 ° C. for 30 minutes, and then quenched by gas cooling to perform quenching treatment. Subsequently, the mixture was kept at -196 ° C. for 1 hour and subjected to subzero treatment. Further, the sintered body subjected to the sub-zero treatment was held at 150 ° C. for 1 hour and tempered.

<Characteristic evaluation of sintered body>
The following characteristics were evaluated for the sintered body of each sample produced above.

(Relative density)
The relative density of each sintered body was measured by the Archimedes method by immersion in water.

(Crystal particle size)
The cross section of the sintered body was observed with a scanning electron microscope (SEM), and the crystal grain size number was determined according to JIS G0551.

(Hardness)
Each sintered body was subjected to a Rockwell hardness test in accordance with JIS Z2245, and the hardness was evaluated.

<Corrosion resistance>
Each sintered body was subjected to a salt spray test in accordance with JIS Z2371. After spraying with salt water for 96 hours, the surface of the sintered body was visually observed, and those in which no rust was observed were evaluated as having high corrosion resistance (A), and those in which rust was observed were evaluated as having low corrosion resistance. It was evaluated as (B).

<Anti-folding force>
The sintered body of Samples 1 to 3 was processed into a test piece having a size of 3 mm × 5 mm × 35 mm, and a folding test was performed. The test was carried out by a three-point bending test with a distance between fulcrums of 20 mm and a one-point load at the center, and the obtained breaking stress was recorded as a bending force.

<Test results>
Table 1 shows the component compositions of the metal powders of Samples 1 to 6 together with the average particle size. The balance consists of Fe and unavoidable impurities. Table 2 shows the composition and characteristic evaluation results of the sintered body produced from each metal powder. Regarding the component composition of the sintered body, only the values related to C, N, and O are shown. The other component elements have not changed from the content in the metal powder.

As shown in Table 1, the metal powders of Samples 2 to 5 satisfy the component composition of the metal powder according to the embodiment of the present invention. Each of the sintered bodies produced from these metal powders also satisfies the component composition of the sintered body according to the embodiment of the present invention.

As a result, the sintered body of Samples 2 to 5 has a large grain size number of 5.5 or more in addition to a high hardness of 57 HRC or more and high corrosion resistance. The fact that the crystal grain size number is large, that is, the crystal structure is fine, suggests that the mechanical strength of the sintered body is high, and in fact, in Samples 2 and 3, A high bending force of 3000 MPa or more has been confirmed. Further, in each of the sintered bodies of Samples 2 to 5, the relative density of 97% or more is measured, and it is confirmed that a high-density sintered body is obtained. The reason why the fine crystal structure and the high sintering density are obtained as described above is that the content of O in the sintered body is in the range of 0.02% <O ≦ 0.60%. Is interpreted as. The same applies to the four samples in which Co: 0.20%, W: 0.10%, Pb: 0.005%, and Nb: 0.005% were added to the components of sample 2, respectively, in the same manner as in sample 2. Characteristics were observed.

On the other hand, in the metal powder of sample 1, the content of O is 0.02% or less. The content of O in the sintered body is also less than 0.02%. The crystal grain size number of the sintered body is as small as 3.1, and the bending force of less than 3000 MPa is obtained. Since the content of O in the metal powder is small, it is not possible to contain sufficient O in the sintered body, and as a result, the crystal grains become coarse and the mechanical strength of the sintered body is low. It can be interpreted that it has become.

On the other hand, in the metal powder of sample 6, the content of O exceeds 0.60%. In the case of a sintered body, the content of O is reduced and is within the range of 0.60% or less. However, the content of O in the sintered body is higher than that of the samples 1 to 5, and as a result, the relative density of the sintered body is lower than that of the samples 1 to 5.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

Claims (14)

Contains C and
By mass%
0.05% ≤ Si ≤ 1.00%,
0.05% ≤ Mn ≤ 1.00%,
P ≤ 0.10%,
S ≤ 0.10%,
0.001% ≤ Cu ≤ 0.50%,
0.05% ≤ Ni ≤ 0.50%,
11.0% ≤ Cr ≤ 18.0%,
0.05% ≤ Mo ≤ 2.0%,
0.01% ≤ V ≤ 0.50%,
N ≤ 0.40%,
0.02% <O ≤ 0.60%,
Al ≤ 0.080%,
A metal powder containing 0.0005% ≤ B ≤ 0.0050%, the balance of which is composed of Fe and unavoidable impurities. The content of C is mass%,
The metal powder according to claim 1, wherein C ≦ 1.00%. The content of N is mass%,
The metal powder according to claim 1 or 2, wherein 0.005% ≤ N ≤ 0.40%. The total content of C and N is mass%.
The metal powder according to any one of claims 1 to 3, wherein the metal powder is 0.4% <C + N <0.7%. The ratio of C and N contents is
The metal powder according to any one of claims 1 to 4, wherein C / N ≧ 0.75. In addition, in% by mass,
0.001% ≤ Co ≤ 0.50%,
0.01% ≤ W ≤ 0.50%
The metal powder according to any one of claims 1 to 5, wherein the metal powder contains at least one selected from the above. Furthermore, in% by mass, 0 . Metal powder according to any one of claims 1 6, characterized in that it contains 001% ≦ Pb ≦ 0.20%. Moreover, in mass%, the metal powder according to any one of claims 1 7, characterized in that it contains 0.001% ≦ Nb ≦ 0.30%. By mass%
0.15% ≤ C <0.70%,
0.05% ≤ Si ≤ 1.00%,
0.05% ≤ Mn ≤ 1.00%,
P ≤ 0.10%,
S ≤ 0.10%,
0.001% ≤ Cu ≤ 0.50%,
0.05% ≤ Ni ≤ 0.50%,
11.0% ≤ Cr ≤ 18.0%,
0.05% ≤ Mo ≤ 2.0%,
0.01% ≤ V ≤ 0.50%,
0.05% ≤ N ≤ 0.40%,
0.02% <O ≤ 0.60%,
Al ≤ 0.080%,
Made of martensitic steel containing 0.0005% ≤ B ≤ 0.0050% and the balance consisting of Fe and unavoidable impurities.
A sintered body characterized in that 0.4% <C + N <0.7% and C / N ≧ 0.75. In addition, in% by mass,
0.001% ≤ Co ≤ 0.50%,
0.01% ≤ W ≤ 0.50%
The sintered body according to claim 9, wherein the sintered body contains at least one selected from the above. Furthermore, in% by mass, 0 . Sintered body according to claim 9 or 10, characterized in that it contains 001% ≦ Pb ≦ 0.20%. Moreover, in mass%, the sintered body according to any one of claims 9 to 11, characterized in that it contains 0.001% ≦ Nb ≦ 0.30%. The baked product according to any one of claims 9 to 12 is produced by molding and sintering the metal powder according to any one of claims 1 to 8. How to make a body. The method for producing a sintered body according to claim 13, wherein sintering is performed in an atmosphere containing nitrogen.