Ferrous articles sintered using a fluidized bed

Abstract

A process for preparing a sintered article of a compacted iron-based metallurgical powder. The green compact is sintered at a closely held predetermined temperature in order to achieve desired density and dimensional stability.

We claim:  
     
         1 . A process for preparing a sintered article comprising the steps of: 
 selecting an iron-based P/M powder;    pressing the P/M powder to produce a green compact; and    sintering the green compact at a predetermined temperature of 1120-1250° C. for up to 20 minutes, where the predetermined temperature is maintained ±1° C. for at least 5 minutes.    
     
     
         2 . A process for preparing a sintered article comprising the steps of: 
 selecting an iron-based P/M powder;    pressing the P/M powder to produce a green compact; and    sintering the green compact at a predetermined temperature of 1120-1250° C. for up to 20 minutes, in a fluidized bed, where the predetermined temperature is maintained ±1° C. for at least 5 minutes.    
     
     
         3 . The process according to  claim 1  or  2 , wherein the predetermined temperature is 1155°-1165° C.  
     
     
         4 . The process according to  claim 1  or  2 , wherein the sintering atmosphere consists of a mixture of nitrogen and hydrogen  
     
     
         5 . The process according to  claim 1  or  2 , wherein the sintering atmosphere consists of a mixture of nitrogen with from 5 to 25% hydrogen.  
     
     
         6 . The process according to  claim 1  or  2 , further comprising initially heating the green compact to vaporize lubricant prior to maintaining the predetermined temperature.  
     
     
         7 . The process according to  claim 1  or  2 , further comprising rapidly cooling the sintered article.  
     
     
         8 . The process according to  claim 1  or  2 , wherein said P/M powder comprises a ferrous powder.  
     
     
         9 . The process according to  claim 1  or  2 , wherein said P/M powder comprises an iron-graphite composite powder.  
     
     
         10 . The process according to  claim 1  or  2 , wherein said P/M powder comprises an iron-carbon-silicon alloy.