Sintered 17-4ph steel part and method for forming

Abstract

A method of sintering a 17-4PH alloy powder and a sintered 17-4PH sintered part are disclosed. The part is formed by selective laser sintering a 17-4PH alloy powder and binder mixture to form a green part that is sintered to form a part having a substantially pure martensitic structure. The metal powder includes boron. The sintered part may be further processed by shot peening to improve crack resistance.

1 . A sintered part, comprising:
 15.5-17.5% Cr;   3.5-4.5% Ni;   3.5-4.5% Cu;   0.15-0.45% Cb+Ta;   0.1-0.3% B;   0-0.5% Mn;   0-0.04 P;   0.07% max C; and   balance Fe.   
     
     
         2 . The sintered part of  claim 8 , wherein the B is about 0.1%. 
     
     
         3 . The sintered steel part of  claim 9 , wherein the steel part has a substantially pure martensitic structure. 
     
     
         4 . The sintered steel part of  claim 9 , wherein the steel part has a density of greater than 7.5 g/cm 3 . 
     
     
         5 . A sintered part formed by a method comprising the steps of:
 mixing binder powder and metal powder to form a powder mixture;   selective laser sintering the powder mixture to form a green part comprising a binder constituent;   heating the green part to remove the binder constituent and form a brown part;   cooling the brown part to ambient temperature; and   sintering the brown part to form a sintered metal part;   wherein the metal powder comprises 17-4PH alloy powder.   
     
     
         6 . The method of  claim 12  wherein the metal powder comprises between about 0.1% and about 0.3% boron. 
     
     
         7 . The method of  claim 13 , wherein the metal powder comprises about 0.1% boron. 
     
     
         8 . The method of  claim 13 , wherein the sintered part has a density of greater than 7.5 g/cm 3 . 
     
     
         9 . The method of  claim 15 , wherein the sintered part has a substantially pure martensitic structure. 
     
     
         10 . The method of  claim 12 , wherein the powder mixture comprises about 1.0% binder powder. 
     
     
         11 . The method of  claim 12 , wherein powder mixture comprises about 1.0% binder powder. 
     
     
         12 . The method of  claim 12 , wherein metal powder has a composition comprising:
 15.5-17.5% Cr;   3.5-4.5% Ni;   3.5-4.5% Cu;   0.15-0.45% Cb+Ta;   0-0.5% Mn;   0-0.04 P;   0.07% max C; and   balance Fe.   
     
     
         13 . The method of  claim 12 , wherein the selective laser sintering is performed by a laser having a power in the range of about 10 W to about 35 W. 
     
     
         14 . The method of  claim 19  further including 0.1-0.3 wt % boron. 
     
     
         15 . The method of  claim 19  wherein the step of sintering the brown part to form a sintered metal part produces a sintered steel part having a substantially martensitic structure. 
     
     
         16 . The method of  claim 19  further including a step of providing metal power comprising 17-4PH metal powder having a sized in the range of 1-55 microns prior to the mixing step. 
     
     
         17 . The method of  claim 12  wherein the step of mixing includes mixing powder having a size in the range of 22-55 microns. 
     
     
         18 . The method of  claim 12  wherein the step of mixing binder poweder with meal powder includes coating a first 17-4PH powder with binder and mixing the coated powder with uncoated 17-4PH powder. 
     
     
         19 . The method of  claim 12  wherein the step of laser sintering the powder mixture further includes:
 i. spreading a first layer of powder mixture to a thickness of about 0.001 to about 0.020 inches; 
 ii. laser sintering the powder mixture to a temperature just below the melting point of the binder powder, causing localized melting of the binder powder to bind the powder mixture; 
 iii. applying a second layer of powder mixture over the first layer; 
 iv. laser sintering the second layer of powder mixture to a temperature just below the melting point of the binder powder, causing localized melting of the binder powder to bind the powder mixture; and 
 v. repeating steps (c) and (d) until the green part is formed. 
 
     
     
         20 . The method of  claim 12  wherein the step of sintering the brown part is performed in a furnace under a vacuum of 300 torr at about 1350° C., followed by cooling to about 750° C. at a rate of about 10-20° C. per minute, then back-filling the furnace with argon while cooling to room temperature at a rate of about 10-20° C. to produce a sintered 17-4PH steel part having a martensitic structure. 
     
     
         21 . The sintered steel part of  claim 8  wherein the part further includes an outer surface having a residual compressive stress from shot peening.