improving the weldability of hp heat-resistant steel modified by niobium after long-term service at high temperature

In this study, the effect of solution annealing on the microstructure and weldability of aged hp heat-resistant steel was investigated. the microstructure of the alloy was investigated using an optical and scanning electron microscope. to evaluate the weldability and susceptibility to hot cracking, the longitudinal varestraint test was used. it was found that the long-term service in high temperatures caused many metallurgical changes such as the formation of cr23c6 chromium carbide and the transformation of nbc niobium carbide into g phase with ni16nb6si7 composition. studies have shown that solution annealing for 2 hours at 1200 degrees celsius has caused the dissolution of precipitates and the microstructure to return to conditions before aging. the results of the varestraint test showed that aging has caused a sensible increase in susceptibility to hot cracking and a decrease in weldability. it was found that solution annealing improved the weldability and reduced susceptibility to hot cracking of this alloy. after solution annealing, no sensitivity to hot cracking was observed in augmented strain below 2%.