ON HOW TO AVOID STRAIN-AGE CRACKING IN SUPERALLOYS GH302 AND K9

The possibility of applying pre-weld or post-weld heat treatment to the welding and surfacing of superalloys GH302 and K9 to avoid strain-age cracking was studied. The tests were conducted on a "circular patch" specimen for welding and on an as-cast turbine blade specimen for surfacing.The C-curve which characterizes the susceptibility of GH302 to strain-age cracking and the suitable temperature and the heating speed for K9 alloy in post-weld heat treatment were obtained.The nose of C-curve of GH302 located at 45 rain.on the time scale indicates that the alloy is insusceptible to strain-age cracking.The suitable heating speed for K9 alloy,on the other hand,shows strong susceptibility to strain-age cracking.The strain-age cracking of both alloys can be reduced by pre-weld overage treatment.For K9 alloy,1080℃ overage heat treatment before welding is essential,but for GH302,only stress relieving heat treatment at 1050℃ after welding is necessary and no pre-weld heat treatment is needed.