Method for enhancing strength and hardness of powder metallurgy stainless steel

Abstract

A method for enhancing strength and hardness of powder metallurgy stainless steels comprises steps of fabricating a stainless steel powder into a green compact; placing the green compact in a reducing environment and maintaining the green compact at a sintering temperature to form a sintered body; and placing the sintered body in a carbon-bearing atmosphere and maintaining the sintered body at a carburizing temperature below 600° C. to implant carbon atoms into the sintered body and form carburized regions in the sintered body. Thereby, the strength and hardness of powder metallurgy stainless steels can be improved. As the carburizing temperature is lower than 600° C., chromium would not react with carbon. Therefore, the strength and hardness of powder metallurgy stainless steels can be enhanced and the superior corrosion resistance is still preserved.

1 . A method for enhancing strength and hardness of powder metallurgy stainless steels, comprising steps of:
 fabricating a stainless steel powder into a green compact;   placing the green compact in a reducing environment and maintaining the green compact at a sintering temperature to form a sintered body; and   placing the sintered body in a carbon-bearing atmosphere and maintaining the sintered body at a carburizing temperature below 600° C. to implant carbon atoms into the sintered body and form carburized regions in the sintered body.   
     
     
         2 . The method for enhancing strength and hardness of powder metallurgy stainless steels according to  claim 1 , wherein the reducing environment is vacuum or hydrogen-bearing atmosphere. 
     
     
         3 . The method for enhancing strength and hardness of powder metallurgy stainless steels according to  claim 1 , wherein the sintering temperature ranges from 1,050 to 1,400° C. 
     
     
         4 . The method for enhancing strength and hardness of powder metallurgy stainless steels according to  claim 1 , wherein the carburizing temperature ranges from 400 to 580° C. 
     
     
         5 . The method for enhancing strength and hardness of powder metallurgy stainless steels according to  claim 1 , wherein the sintered body has a relative density of greater than 30%. 
     
     
         6 . The method for enhancing strength and hardness of powder metallurgy stainless steels according to  claim 1 , wherein the green compact is fabricated with an Metal Injection Molding method. 
     
     
         7 . The method for enhancing strength and hardness of powder metallurgy stainless steel according to  claim 1 , wherein the green compact is fabricated with a powder-compaction method. 
     
     
         8 . The method for enhancing strength and hardness of powder metallurgy stainless steels according to  claim 1 , wherein the carbon-bearing atmosphere is an atmosphere containing carbon monoxide, methane, or propane. 
     
     
         9 . The method for enhancing strength and hardness of powder metallurgy stainless steels according to  claim 1 , wherein the stainless steel powder is an iron-based material containing less than 2.0 wt % carbon, less than 1.0 wt % silicon, less than 2.0 wt % manganese, 12.0-19.0 wt % chromium, less than 15.0 wt % nickel, less than 6.0 wt % molybdenum, and less than 6.0 wt % copper.