Method for manufacturing sintered and carburized porous stainless steel parts

a technology of stainless steel and carburizing technology, which is applied in the direction of solid-state diffusion coating, coating, transportation and packaging, etc., can solve the problems of limiting applications, unsuitable for powder metallurgy sintered body hardening, and high cost of chromium coating, so as to increase the strength and hardness of porous powder metallurgy stainless steel, the effect of superior corrosion resistan

Inactive Publication Date: 2018-03-08
TAIWAN POWDER TECH CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention aims to increase the strength and hardness of porous sintered stainless steels without compromising their superior corrosion resistance. The invention achieves this by producing a carburized layer at a temperature below 600° C. without forming carbides and without carrying out any activation or cleaning process using halogenated materials in advance. This prevents chromium in the stainless steel from reacting with carbon to form chromium carbide. Overall, the invention achieves increased strength and hardness of porous powder metallurgy stainless steels while still maintaining their superior corrosion resistance.

Problems solved by technology

Both types of these sintered stainless steels, particularly those with an austenitic structure like 316L, are usually soft, which limits the applications.
However, the abovementioned hardening method is unsuitable for a powder metallurgy sintered body because of its complicated shapes.
However, the chromium coating is expensive and good adhesion to the substrate is difficult to achieve.
Shot-peening can only increase the hardness at the outer surface and by a limited extent.
For parts with complicated shapes, some regions are difficult to be shot-peened.
Therefore, shot-peening is not an effective hardening method either for powder metallurgy parts.
When powder metallurgy parts are porous, it becomes even more difficult to use the abovementioned processes to strengthen or harden the sintered body.
In summary, there is few cost-effective method available to improve the strength and hardness of sintered porous stainless steel materials.

Method used

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  • Method for manufacturing sintered and carburized porous stainless steel parts
  • Method for manufacturing sintered and carburized porous stainless steel parts

Examples

Experimental program
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Effect test

embodiment i

[0025]This embodiment adopts a stainless steel powder of Composition 2 and a mean particle size of 39.7 μm, and uses a powder-compaction process to fabricate the stainless steel powder into a green compact. The green compact is debinded and then sintered in a vacuum furnace at a sintering temperature of 1,250° C. for 2 hours to form a sintered body 10a. After being cooled, the sintered body 10a is taken out from the vacuum furnace and placed in a carburizing furnace for carburization at a temperature of 500° C. for 24 hours. The sintered body 10a has a relative density of 86% and has a microstructure shown in FIG. 1. As can be observed in FIG. 1, the sintered and carburized body 10a has a carburized region 11a (the white region). The sintered body 10a has a macroscopic (apparent) hardness of HRB75, a surface microhardness of HV820 and a core microhardness of HV220. The sintered body 10a has a tensile strength of 520 MPa and an elongation of 20%. The sintered body 10a has qualified c...

embodiment ii

[0026]This embodiment adopts a stainless steel powder of Composition 3 and a mean particle size of 40.2 μm, and uses a powder-compaction process to fabricate the stainless steel powder into a green compact. The green compact is debinded and then sintered in a vacuum furnace at a sintering temperature of 1,250° C. for 2 hours to form a sintered body 10b. After being cooled, the sintered body 10b is taken out from the vacuum furnace and placed in a carburizing furnace for carburization at a temperature of 500° C. for 24 hours. Thus, the sintered body 10b has a relative density of 86% and has a microstructure shown in FIG. 2. It can be observed in FIG. 2 that the sintered and carburized body 10b has a carburized region 11b (the white region). The sintered body 10b has a macroscopic (bulk) hardness of HRB74, a surface microhardness of HV811 and a core microhardness of HV245. The sintered body 10b has a tensile strength of 519 MPa and an elongation of 16%. The sintered body 10b has quali...

embodiment iii

[0027]This embodiment adopts a stainless steel powder of Composition 1 and a mean particle size of 12.1 μm. The stainless steel powder is processed with the MIM process to form a green compact. The green compact is debinded and then sintered in an atmosphere furnace under cracked ammonia at a sintering temperature of 1,200° C. for 1 hour to form a sintered body. After being cooled, the sintered body is taken out from the furnace and placed in a low pressure carburizing (vacuum carburizing) furnace for carburization at a temperature of 480° C. for 12 hours using a mixture of acetylene, ethylene, and hydrogen at a pressure of 10 mbar. The sintered body has a relative density of 76% and has a carburized region. The sintered body has a surface microhardness of HV801, a core microhardness of HV242, and a high macroscopic hardness of HRB95, which is attributed to the use of cracked ammonia atmosphere.

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Abstract

This invention presents a method for manufacturing sintered and carburized porous stainless steel parts, comprising steps of: sintering stainless steel powders to obtain a porous sintered stainless steel, wherein the porous sintered stainless steel comprises a three dimensional network skeleton structure with a large number of interconnected pore channels; and carburizing the porous sintered stainless steel by a non-halogenated carbon-bearing gas, wherein the porous sintered stainless steel being maintained at a carburizing temperature below 600° C. such that carbon atoms can be implanted into the porous sintered stainless steel and converts a surface portion of the skeleton structure, that is in contact with the carbon-bearing gas in the interconnected pore channels, into a carburized layer. A carburized layer is formed and spread over a skeleton structure of the sintered porous body. Thereby, the strength, surface hardness, and core hardness of the sintered body are significantly increased.

Description

[0001]This application is a continuation-in-part, and claims priority, of from U.S. patent application Ser. No. 14 / 669,740 filed on Mar. 26, 2015, entitled “SINTERED AND CARBURIZED POROUS STAINLESS STEEL PART AND METHOD THEREOF”, which is a continuation-in-part, and claims priority, of from U.S. patent application Ser. No. 13 / 074,652 filed on Mar. 29, 2011, entitled “METHOD FOR ENHANCING STRENGTH AND HARDNESS OF POWDER METALLURGY STAINLESS STEEL”.FIELD OF THE INVENTION[0002]The present invention relates to a method for manufacturing stainless steel parts, particularly to a method for manufacturing sintered and carburized porous stainless steel parts.BACKGROUND OF THE INVENTION[0003]Powder metallurgy has been extensively used to fabricate various metallic products. A various techniques had been disclosed, such as U.S. Pat. No. 6,669,898, U.S. Pat. No. 5,985,208, U.S. Pat. No. 7,211,125, U.S. Pat. No. 4,708,741, U.S. Pat. No. 7,311,875, U.S. Pat. No. 5,460,641, and U.S. Pat. No. 5,856...

Claims

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Application Information

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IPC IPC(8): B22F3/24C23C8/22B22F3/22B22F3/11C22C38/44C22C38/20C22C38/02C22C38/04B22F1/05
CPCB22F3/11B22F2301/35C22C38/20C22C38/02B22F3/225B22F2003/241C22C38/44B22F3/24C23C8/22C22C38/04B22F3/1146C23C8/02C22C1/08C22C33/0285C22C38/42B22F2201/30B22F2998/10B22F1/05B22F3/101B22F2201/013B22F2201/20B22F3/1021
InventorHWANG, KUEN-SHYANGCHENG, LI-HUILU, YUNG-CHUNG
OwnerTAIWAN POWDER TECH CO LTD