Creep Rupture Strength for Weld Joint of 23Cr-45Ni-7W Alloy

The creep rupture strength and the degradation mechanism of 23Cr-43Ni-7W alloy weld joints were investigated by creep rupture tests and microstructure observation of the ruptured specimens. The creep rupture tests were conducted at 973, 1023, and 1073 K at stresses from 80 to 180 MPa. The creep strength of the weld joints was higher than that of the base metal. The ruptured area of every specimen was over 10 mm away from the bond line. The microcracks increased gradually up to 10 mm from the bond line, above which they increased suddenly. In the grains, traces of M23C6 were observed near the bond line, and the sizes of the M23C6 deposits increased further away from the bond line. But the size of the Laves phase was constant in every observed area. On the grain boundary, the grain boundary shielding ratio by precipitates was constant until 10 mm from the bond line, above which it decreased. These observations show that the creep strength near the bond line is higher than that of the base metal because of both precipitation strengthening in the grain and grain boundary.