JP2001294971A - Method for producing stainless steel sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder metallurgy method for producing a stainless steel sintered body by which a product excellent in corrosion resistance and mechanical properties and also capble to form a complicated shape can easily be obtained. SOLUTION: In a process in which a composition obtained by adding a binder to metal powder containing, by weight, 16 to 20% Cr and 1.0 to 1.5% C, and the balance substantially Fe is subjected to injection molding, and the obtained molded body is subjected to debinder treatment and is sintered, the molded body is sintered at a temperature in which the molded body starts to be shrinked in a gaseous mixture atmosphere of hydrogen and carbon monoxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a stainless steel sintered body having excellent corrosion resistance and having mechanical properties comparable to those of SUS440C as an ingot.

[0002]

2. Description of the Related Art SUS440 specified by JIS
In order to manufacture a C product, a cutting method of machining a molten material and a precision casting method are generally known. However, when manufacturing a product having a complicated shape, a plate obtained by processing a cast product is used in the cutting method. Since it is cut out from a lump or lump and machined to a predetermined shape, the processing cost is increased and the yield is poor.

Further, the precision casting method has a problem that the dimensional accuracy of a sharp portion cannot be obtained and casting defects such as large and small pores generated during casting remain inside. Therefore, in order to compensate for such a disadvantage, SUS 440C
Attempts have been made to produce a stainless steel powder having an alloy composition corresponding to the above by powder metallurgy. However, the amount of carbon contained in the raw material powder varies depending on the production lot of the powder used, and it has been difficult to stably satisfy the amount of carbon specified in JIS standards. Furthermore, the powder contains unavoidable oxygen and reacts with the carbon contained in the powder,
There was a problem that the carbon amount specified in the standard could not be satisfied.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and the present invention has been made to improve the sintering quality of smelted materials by devising the atmosphere and conditions during sintering using powder metallurgy.
Corrosion resistance and mechanical properties equivalent to US 440C,
It is another object of the present invention to provide a method for manufacturing a stainless steel sintered body that can easily obtain a product having a complicated shape.

[0005]

The method for producing a stainless steel sintered body according to the present invention comprises the steps of:
A step of injection molding a composition obtained by adding a binder to a metal powder containing 0 to 1.5% by weight and the balance substantially consisting of Fe, and subjecting the obtained molded body to a binder removal treatment and sintering Wherein the compact is sintered in a mixed gas atmosphere of hydrogen and carbon monoxide at a temperature at which the compact starts shrinking. Further, as the processing conditions in the mixed gas atmosphere of hydrogen and carbon monoxide, the carbon monoxide content is 5% to 20%, and the processing time is 5 minutes to 60 minutes. Further, an atomized powder is used as the metal powder.

In the present invention, the starting metal powder may be an alloy powder adjusted and blended in advance to a desired composition, or a mixed powder obtained by adjusting and blending a powder having a different composition to a target composition. Good. For example, a method of adding C powder to Fe-Cr alloy powder can also be adopted.

[0007] When the Cr content in the metal powder is 16 to 20
The reason why the content is limited to wt% is that when the Cr content in the metal powder is less than 16 wt%, the corrosion resistance and strength of the obtained sintered body are inferior, and when the Cr content exceeds 20 wt%, the raw material becomes expensive. That's why.

[0008] Similarly, the C content is 1.0 to 1.5% by weight.
(Preferably 1.1 to 1.3% by weight)
If the C content in the metal powder is less than 1.0% by weight, the required hardness cannot be obtained even if heat treatment is performed after sintering, resulting in insufficient mechanical strength. If the content exceeds 5% by weight, the corrosion resistance and toughness of the sintered body are adversely affected.

[0009] Further, the metal powder to be used, 0.05 ~
Oxygen in the raw material powder reacts with C in the raw material powder at the time of sintering in the subsequent step, and
Since the gas is generated and released (decarburized), the C
The amount decreases. Therefore, the amount of carbon in the sintered body after sintering is in a range substantially equivalent to SUS440C.
It is added in excess to 95 to 1.2% by weight.

Next, the compact is sintered at a shrinkage start temperature with a mixed gas of hydrogen and carbon monoxide for the following reasons. In other words, this treatment is performed to compensate for the carbon reduced by decarburization, but when performed at the shrinkage start temperature, if sintering with hydrogen and a mixed gas before the start of shrinkage, many cracks are generated in the sintered body That's why. This is because in the stage before the binder is removed and sintering starts, the strength of the molded body is reduced, and cracks occur due to expansion due to carburization. Further, even if the shrinkage is started and the treatment is performed with a mixed gas of hydrogen and carbon monoxide at the stage where sintering has progressed, carburization is not performed to the inside of the molded body, resulting in an uneven structure.

The reason why the content of carbon monoxide is limited to 5% to 20% in this treatment is that if it is less than 5%, the concentration is insufficient to make up for the decarbonized and reduced carbon.
This is because no further effect can be seen at a concentration exceeding 0%.

The reason why the processing time is set to 5 to 20 minutes is as follows.
If the time is less than 5 minutes, the time is insufficient to compensate for the decarbonized carbon, and if the time exceeds 20 minutes, no further effect is obtained.

On the other hand, various metal powders as a starting material preferably have an average particle size of 45 μm or less in the case of injection molding, and known polyethylene, polypropylene, wax and the like can be used as a binder.
The amount of the binder relative to the compounding raw material powder is preferably in the range of 25 to 60% by volume in the composition after compounding.

Further, as a method for removing the binder from the obtained molded body after injection-molding the composition comprising the raw material powder and the binder, a known method such as heat degreasing, solvent degreasing or the like can be used.

Although the injection molding powder metallurgy method has been described above, a conventional press sintering method can also be used to manufacture the powder metallurgy using a known method.

[0016]

EXAMPLES Example 1 As a raw material powder, a water atomized alloy powder of Fe-17.0% by weight and Cr-1.1% by weight C having an average particle diameter of 9 μm was used, and a wax-based binder was added to 40% by volume. The mixture was kneaded at 150 ° C. and granulated into pellets. This pellet was injected at an injection pressure of 800 kg / c using an injection molding machine.
Injection molding was performed in a mold under the conditions of m2. The obtained molded body (a rectangular parallelepiped having a width of 10 mm, a length of 50 mm, and a thickness of 5 mm) is reduced to 30
The mixture was heated to 0 ° C. and held for 60 minutes to remove the wax binder. Thereafter, the molded body subjected to the binder removal treatment is heated to 1000 ° C. in a vacuum, and subjected to a treatment in hydrogen containing 10% of carbon monoxide for 20 minutes at 1000 ° C. at which the molded body starts shrinking. 12
After holding at 50 ° C. for 5 hours, cooling was performed. The sintering density, hardness, corrosion resistance, and residual carbon content of the processed product thus obtained were examined. At that time, the sintered density was measured with a hydrometer, and the hardness was 150 kg with a Rockwell hardness meter.
(HRC). The corrosion resistance was evaluated as 3
The sample was immersed in a 50% aqueous solution of NaCl at 50 ° C. for 24 hours, and the occurrence of rust was visually observed and evaluated.

Example 2 As a raw material powder, a water atomized alloy powder of Fe-18.0% by weight and Cr-1.2% by weight C having an average particle size of 9 μm was used, and a wax-based binder was used at 40% by volume. After kneading at 150 ° C., the mixture was granulated into pellets. This pellet was injected at an injection pressure of 800 kg / c using an injection molding machine.
Injection molding was performed in a mold under the conditions of m2. The obtained molded body (a rectangular parallelepiped having a width of 10 mm, a length of 50 mm, and a thickness of 5 mm) is reduced to 30
The mixture was heated to 0 ° C. and held for 60 minutes to remove the wax binder. Thereafter, the molded body subjected to the binder removal treatment is heated in hydrogen to 1000 ° C., and is subjected to a treatment in hydrogen containing 10% of carbon monoxide at 1000 ° C. for 30 minutes at 1000 ° C., at which the molded body begins to shrink, and subsequently in hydrogen 12
After holding at 50 ° C. for 5 hours, cooling was performed. The treated product thus obtained was evaluated in the same manner as in Example 1.

Example 3 As a raw material powder, Fe-18. A water atomized alloy powder of O weight% and Cr-1.2 weight% C was used, a wax-based binder was added thereto to a volume of 40% by volume, kneaded at 150 ° C., and granulated into pellets. This pellet was injected at an injection pressure of 800 kg / c using an injection molding machine.
Injection molding was performed in a mold under the conditions of m2. The obtained molded body (a rectangular parallelepiped having a width of 10 mm, a length of 50 mm, and a thickness of 5 mm) is reduced to 30
The mixture was heated to 0 ° C. and held for 60 minutes to remove the wax binder. Thereafter, the molded body subjected to the binder removal treatment is heated in hydrogen to 1000 ° C., and subjected to a treatment in hydrogen containing 20% of carbon monoxide at 1000 ° C. for 10 minutes at 1000 ° C., at which the molded body begins to shrink. 12
After holding at 50 ° C. for 5 hours, cooling was performed. The heat-treated product thus obtained was evaluated in the same manner as in Example 1.

Example 4 As a raw material powder, a water atomized alloy powder of Fe-20.0% by weight and Cr-1.4% by weight C having an average particle size of 9 μm was used, and a wax-based binder was used at 40% by volume. After kneading at 150 ° C., the mixture was granulated into pellets. This pellet was injected at an injection pressure of 800 kg / c using an injection molding machine.
Injection molding was performed in a mold under the conditions of m2. The obtained molded body (a rectangular parallelepiped having a width of 10 mm, a length of 50 mm, and a thickness of 5 mm) is reduced to 30
The mixture was heated to 0 ° C. and held for 60 minutes to remove the wax binder. Thereafter, the molded body subjected to the binder removal treatment is heated in hydrogen to 1000 ° C., and treated at 1000 ° C. for 50 minutes in hydrogen containing 15% of carbon monoxide, at which the molded body begins to shrink, and subsequently in hydrogen. 12
After holding at 50 ° C. for 5 hours, cooling was performed. The treated product thus obtained was evaluated in the same manner as in Example 1.

Comparative Example 1 The procedure of Example 1 was repeated except that a water atomized alloy powder of Fe-18.0% by weight and Cr-0.8% by weight C having an average particle diameter of 9 μm was used as a raw material powder. Processing was performed, and evaluation was performed in the same manner as in Example 1.

Comparative Example 2 The procedure of Example 1 was repeated except that a water atomized alloy powder of Fe-18.0% by weight and Cr-1.7% by weight C having an average particle size of 9 μm was used as a raw material powder. After the treatment, the corrosion resistance was evaluated in the same manner as in Example 1.

Comparative Example 3 The same procedure as in Example 1 except that the treatment of the mixed gas of carbon monoxide and hydrogen was performed from room temperature to a shrinkage starting temperature of 1000 ° C. at a rate of temperature increase of 4 ° C./min. And evaluated in the same manner as in Example 1.

Comparative Example 4 Same as Example 1 except that the mixed gas of carbon monoxide and hydrogen was treated from room temperature to a shrinkage starting temperature of 1000 ° C. at a heating rate of 0.4 ° C./min. The evaluation was performed in the same manner as in Example 1.

The results of Examples 1 to 4 and Comparative Examples 1 to 4 are summarized in Table 1. From the results in Table 1, all of Examples 1 to 4 of the present invention showed favorable values in all of the sintered density, hardness, corrosion resistance, and residual carbon amount. On the other hand, in Comparative Example 1, a sufficient hardness was not obtained because the C content was small. Comparative Example 2 is C
Due to the excessive content, the corrosion resistance was insufficient. In Comparative Example 3, the treatment temperature was inappropriate, and countless cracks occurred in the sintered body. Similarly, in Comparative Example 4, the treatment temperature was inappropriate, and countless cracks occurred in the sintered body.

[0025]

[Table 1]

[0026]

As described above, according to the present invention,
Since it is possible to perform sintering under appropriate atmosphere and conditions without generating cracks in the sintered body, SUS 440 of the ingot material can be used.
It has an excellent effect that a product having corrosion resistance and mechanical properties equivalent to C and having a complicated shape can be easily obtained.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akihito Otsuka 3860 Shimotsuruma, Yamato City, Kanagawa Prefecture Sumitomo Metal Mining Co., Ltd. Special alloy factory F-term (reference) 4K018 AA33 BA17 CA29 DA03 DA11 DA31 DA33

Claims (3)

[Claims] 1. Cr 16 to 20% by weight, C 1.0 to 1.
In a step of injection molding a composition containing 5% by weight and a binder added to a metal powder substantially consisting of Fe, the resulting molded body is subjected to a binder removal treatment and is sintered, and A method for producing a stainless steel sintered body, comprising sintering a green body in a mixed gas atmosphere of hydrogen and carbon monoxide at a temperature at which the green body starts shrinking. 2. The treatment in a mixed gas atmosphere of hydrogen and carbon monoxide, wherein the content of carbon monoxide is 5% to 20%.
%, And the treatment time is from 5 minutes to 60 minutes. 3. The method according to claim 1, wherein the metal powder is an atomized powder.