Akiyoshi Fuji

Study on a stainless steel overlay welding process for superior resistance to disbonding - Characteristics of disbonding and carbide precipitation of stainless overlay weld.

The first layer overlay weld metal with austenitic/martensitic duplex microstructure provides the overlay welds with better resistance to the hydrogen-induced disbonding than that with the conventional austenitic microstructure containing several percents ferrite as previously reported.The resistance to the hydrogen-induced disbonding occurring at the bond of the stainless steel overlay weld is affected by the carbide precipitated at the bond region.Based on this consideration, the properties of the disbonding surface and the carbide precipitation of the disbonding resistant overlay weld were studied and compared with those of the conventional overlay weld.The main results obtained in this study are as follows:(1) The disbonding mainly occurred at the bond in the disbonding resistant overlay weld, while it occurred at coarse grain boundaries in the first layer weld metal adjacent to the bond in the conventional overlay weld.(2) Fine M23C6 carbides precipitated in the first layer weld metal adjacent to the bond in the disbonding resistant overlay weld.(3) Large M23C6 carbides precipitated at the coarse grain boundary in the conventional overlay weld.(4) The amount of precipitated carbide of the disbonding resistant overlay weld was almost equal to that of the conventional overlay weld.

Study on a stainless steel overlay welding process for superior resistance to disbonding. Report 4 Tensile strength of bond of stainless steel overlay weld after absorption of hydrogen.

The first layer overlay weld metal with austenitic/martensitic duplex microstructure provides the overlay welds with better resistance to the hydrogen-induced disbonding than that with the conventional austenitic microstructure containing several percents ferrite as previously reported.In this report, the notch tensile strength of the bond of the overlay weld the first layer of which is composed of duplex microstructure (the disbonding resistant overlay weld) after absorption of hydrogen was studied and compared to that of the conventional overlay weld.The main results obtained in this study are as follows:(1) The notch tensile strength of the bond of the improved overlay weld was higher than that of the conventional overlay weld.(2) The notch tensile strength of the bond of the conventional overlay weld decreased as decreasing crosshead speed.(3) The notch tensile strength of the bond of both overlay welds decreased as increasing of PWHT temperature and holding time.(4) The notch tensile strength of the coarse grain boundary of the conventional overlay weld after PWHT at 973K for 7.2 × 104 S was lower than that of the bond.It was concluded that the coarse grain in the first layer weld metal adjacent to the bond strongly affected the resistance to hydrogen-induced disbonding of the stainless steel overlay weld.