Method of forging a nickel base superalloy

Abstract

A method of forging a nickel base superalloy comprising providing a nickel base superalloy preform ( 40 ) with a first predetermined shape, the nickel base superalloy preform having been produced by powder metallurgy. The nickel base superalloy preform ( 40 ) is forged to produce a nickel base superalloy forged component ( 50 ) with a second predetermined shape. The first predetermined shape and the second predetermined shape are arranged such that the effective strain at the end of the forging is less than 1. The nickel base superalloy forged component ( 50 ) is given a supersolvus heat treatment to produce a large grain size in the nickel base superalloy forged component ( 50 ).

1 . A method of forging a nickel base superalloy comprising the steps of:
 (a) providing a nickel base superalloy preform with a first predetermined shape, the nickel base superalloy preform having been produced by powder metallurgy,   (b) forging the nickel base superalloy preform to produce a nickel base superalloy forged component with a second predetermined shape, wherein the first predetermined shape and the second predetermined shape are arranged such that the effective strain at the end of forging is less than 1,   (c) supersolvus heat treating at least a region of the nickel base superalloy forged component to produce a large grain size in the at least a region of the nickel base superalloy forged component, wherein the large grain size in the nickel base superalloy is 80 to 140 micrometers.   
     
     
         2 . A method as claimed in  claim 1  wherein in step (b) the effective strain at the end of the forging is less than or equal to 0.75. 
     
     
         3 . A method as claimed in  claim 1  wherein in step (b) the effective strain at the end of the forging is less than or equal to 0.5. 
     
     
         4 . A method as claimed in  claim 1  wherein step (a) comprises providing a stepped cylindrical preform, the cylindrical preform having a first substantially cylindrical portion and a second substantially annular portion arranged coaxially around the first portion, the first cylindrical portion having a first thickness, the second annular portion having a second thickness and the second thickness is less than the first thickness and step (b) comprises forging the stepped cylindrical preform to a substantially disc shaped forged component and after step (c) the second portion having coarser grains than the first portion. 
     
     
         5 . A method as claimed in  claim 4  wherein step (a) comprises providing a substantially cylindrical preform, the cylindrical preform having a third substantially annular portion arranged coaxially around the second annular portion, the third annular portion having a third thickness and the third thickness is less than the second thickness and after step (c) the third portion having coarser grains than the second portion. 
     
     
         6 . A method as claimed in  claim 5  wherein in the first cylindrical portion the effective strain is about 0.9, in the second annular portion the effective strain is about 0.75 and in the third annular portion the effective strain is about 0.5. 
     
     
         7 . A method as claimed in  claim 4  wherein step (c) comprises a subsolvus heat treatment in a first region of the forged component and a supersolvus heat treatment in a second region of the forged component. 
     
     
         8 . A method as claimed in  claim 7  wherein the first region comprises the first portion and the second region comprises the second portion. 
     
     
         9 . A method as claimed in  claim 5  wherein step (c) comprises a supersolvus heat treatment in a first region of the forged component and a supersolvus heat treatment in a second region of the forged component. 
     
     
         10 . A method as claimed in  claim 9  wherein the first region comprises the first portion and the second region comprises the second portion and the third portion. 
     
     
         11 . A method as claimed in  claim 1  wherein step (c) comprises supersolvus heat treating all of the nickel base superalloy forged component to produce a large grain size in all of the nickel base superalloy forged component. 
     
     
         12 . A method as claimed in  claim 1  wherein the forged component comprises a forged component for a turbine disc or a compressor disc. 
     
     
         13 . A method as claims in  claim 1  wherein the nickel base superalloy consists of 18.5 wt % cobalt, 15 wt % chromium, 5 wt % molybdenum, 2 wt % tantalum, 3.6 wt % titanium, 3 wt % aluminium, 0.5 wt % hafnium, 0.015 wt % boron, 0.06 wt % zirconium, 0.027 wt % carbon and the balance nickel plus incidental impurities. 
     
     
         14 . A method as claimed in  claim 1  wherein step (b) comprises forging at a temperature in the range of 1050° C. to 1150° C. and at a strain rate in the range of 0.001 to 0.1 per second. 
     
     
         15 . A method as claimed in  claim 1  wherein step (c) comprises supersovlus heat treating at 20° C. to 50° C. above the gamma prime solvus temperature for up to 4 hours. 
     
     
         16 . A method as claimed in  claim 1  wherein step (c) comprises supersolvus heat treating at a temperature of 1110° C. to 1150° C. for up to 4 hours. 
     
     
         17 . A method of forging a nickel base superalloy comprising the steps of:
 (a) providing a nickel base superalloy preform with a first predetermined shape, the nickel base superalloy preform having been produced by powder metallurgy.   (b) forging the nickel base superalloy preform to produce a nickel base superalloy forged component with a second predetermined shape, wherein the first predetermined shape and the second predetermined shape are arranged such that the effective strain at the end of forging is less than 1,   (c) supersolvus heat treating at least a region of the nickel base superalloy forged component to produce a large grain size in the at least a region of the nickel base superalloy forged component.   
     
     
         18 . A nickel base superalloy forged component with a large grain size in at least a region, wherein the large grain size is 80 to 140 micrometers.