Method of manufacturing a weld-free apparatus for connection of dissimilar metals using functionally graded compositionally control powder metallurgy and hot isostatic processing methods

Abstract

A method of manufacturing a weld-free apparatus for use in the connection of dissimilar metals includes the steps of providing a mold designed to replicate a reverse of the apparatus, introducing a low alloy, ferritic steel composition atomized powder into a first portion of the mold, introducing a series of atomized powders incrementally into a second portion of the mold to form a transition region between the ferritic steel composition and an austenitic stainless steel composition, and introducing an austenitic stainless steel composition atomized powder into a third portion of the mold. The method further includes the step of consolidating and melting the atomized powders in a high temperature, high pressure inert gas atmosphere to form the apparatus.

We claim: 
     
         1 . A method of providing a weld-free apparatus for use in the connection of dissimilar metals, comprising the steps of:
 (a) providing a mold designed to replicate a reverse of the apparatus;   (b) providing a first metal powder and introducing the first metal powder into a first portion of the mold;   (c) providing a second metal powder and introducing the second metal powder into a second portion of the mold;   (d) providing a third metal powder and introducing the third metal powder into a third portion of the mold, wherein the second metal powder forms a transition between the first metal powder and the third metal powder;   (e) pulling a vacuum on the mold and sealing the mold to maintain the vacuum;   (f) placing the mold into a hot isostatic pressing (HIP) furnace to consolidate and melt the first, second, and third powders; and   (g) cooling the mold to room temperature and removing the apparatus from the mold.   
     
     
         2 . The method according to  claim 1 , wherein the first metal powder is a low alloy ferritic steel composition atomized powder. 
     
     
         3 . The method according to  claim 1 , wherein the third powder is an austenitic stainless steel composition atomized powder. 
     
     
         4 . The method according to  claim 1 , wherein the mold is maintained in the HIP furnace at a high temperature and high pressure within an inert gas atmosphere. 
     
     
         5 . The method according to  claim 1 , further including the step of heat treating the apparatus. 
     
     
         6 . The method according to  claim 1 , further including the step of pickling, boring, and grinding to remove the mold from the apparatus. 
     
     
         7 . The method according to  claim 1 , further including the step of machining the apparatus to final dimensions. 
     
     
         8 . A method of providing a weld-free apparatus for use in the connection of dissimilar metals, comprising the steps of:
 (a) providing a mold designed to replicate a reverse of the apparatus;   (b) introducing a low alloy, ferritic steel composition atomized powder into a first portion of the mold;   (c) introducing a series of atomized powders incrementally into a second portion of the mold to form a transition region between the ferritic steel composition and an austenitic stainless steel composition;   (d) introducing an austenitic stainless steel composition atomized powder into a third portion of the mold; and   (e) consolidating and melting the atomized powders in a high temperature, high pressure inert gas atmosphere to form the apparatus.   
     
     
         9 . The method according to  claim 8 , wherein the series of atomized powders that form the transition region start with a lower alloy steel powder and increases in each series to a higher alloy steel powder. 
     
     
         10 . The method according to  claim 8 , wherein the transition region comprises a series of four atomized powders, wherein the first atomized powder is a 5 Cr steel powder, the second atomized powder is an 8 Cr steel powder, the third atomized powder is an 11 Cr steel powder, and the fourth atomized powder is a 15 Cr steel atomized powder. 
     
     
         11 . The method according to  claim 10 , wherein the ferritic steel composition atomized powder is a 2¼ Cr steel powder and the austenitic stainless steel composition atomized powder is an 18 Cr steel powder. 
     
     
         12 . The method according to  claim 8 , wherein the transition region comprises a series of three atomized powders, wherein the first atomized powder is a 12 Cr steel powder, the second atomized powder is a 14 Cr steel powder, and the third atomized powder is an 16 Cr steel powder. 
     
     
         13 . The method according to  claim 12 , wherein the ferritic steel composition atomized powder is a 9 Cr steel powder and the austenitic stainless steel composition atomized powder is an 18 Cr steel powder. 
     
     
         14 . The method according to  claim 8 , wherein the first and third portions of the mold comprise about three-fourths of the mold and the second portion of the mold comprises about one-fourth of the mold. 
     
     
         15 . The method according to  claim 8 , further including the step of heat treating the apparatus to normalize and temper low alloy sections of the apparatus. 
     
     
         16 . The method according to  claim 8 , further including the step of removing the mold from the apparatus. 
     
     
         17 . The method according to  claim 8 , further including the step of machining the apparatus to final dimensions.