1998 Volume 16 Issue 4 Pages 512-521
Precipitation behaviors in W alloyed 9Cr weld metal during PWHT (Post Weld Heat Treatment) and creep rupture test have been studied by analyzing extracted residues from the weld metals after PWHT and creep rupture test. The results of analysis were compared with the prediction by THERMO-CALC.
M23C6 and MX type carbo-nitrides were predicted to precipitate at PWHT temperatures in equilibrium states by THERMO-CALC. In addition to M23C6 and MX type carbo-nitrides, Laves phase was predicted to precipitate at creep rupture test temperatures in equilibrium states by THERMO-CALC. X-ray diffraction analysis showed that M23C6 and MX type carbo-nitrides precipitates in the weld metal during PWHT in accordance with the results from THERMO-CALC. Less than 100 hours in creep rupture test at 873 K, M23C6 and MX type carbo-nitrides were detected in weld metals by X-Ray diffraction analysis. Laves phase precipitates more than 100-1000 hours during creep rupture test at 873 K. Presence of Laves phase in the weld metal after creep rupture test at 873 K/1126.7 hours was revealed by X-ray diffraction analysis. Content of W in extracted residues from weld metals after creep rupture test at 873 K increased substantially with time more than 100-1000 hours. This increase in W content in extracted residue is probably due to the precipitation of Laves phase. Contents of W and Mo in extracted residues from weld metals after creep rupture test at 873 K reach constant values at roughly more than 10000 hours, and these values are in good agreement with those predicted by THERMO-CALC. Time dependence of W content in extracted residue from weld metals of creep rupture test at 873K and 923K are in good agreement with the calculated results based on Jhonson-Mehel-Avrami type equation.
