Improving the weldability of HP heat-resistant steel modified byniobium after long-term service at high temperature

In this study, the effect of solution annealing on the microstructure and weldabilityof aged HP heat-resistant steel was investigated. The microstructure of the alloy wasinvestigated using an optical and scanning electron microscope. To evaluate the weldabilityand susceptibility to hot cracking, the longitudinal varestraint test was used. It was found thatthe long-term service in high temperatures caused many metallurgical changes such as theformation of Cr۲۳C۶ chromium carbide and the transformation of NbC niobium carbide intoG phase with Ni۱۶Nb۶Si۷ composition. Studies have shown that solution annealing for ۲ hoursat ۱۲۰۰ degrees Celsius has caused the dissolution of precipitates and the microstructure toreturn to conditions before aging. The results of the varestraint test showed that aging hascaused a sensible increase in susceptibility to hot cracking and a decrease in weldability. It wasfound that solution annealing improved the weldability and reduced susceptibility to hotcracking of this alloy. After solution annealing, no sensitivity to hot cracking was observed inaugmented strain below ۲%.

Keywords:

HP steel , weldability , hot cracking , varestraint test , solution annealing , microstructure