Metallurgical aspects in welding Cr–Mo–V turbine rotor steels Part 1 Evaluation of base material and heat affected zone

Abstract

A metallurgical evaluation of the weldability of a high pressure/intermediate pressure turbine rotor has been undertaken to determine whether AS1M A470 (class 8) rotors can be weld repaired. The work was carried out using a retired rotor that had been in service for over 20 years. The rotor base material was found to have experienced embrittlement during service. It was determined that no heat treatment was necessary before welding, as long as a post-weld heat treatment at 677°C was performed. The coarse grained bainitic structure and embrittled condition of the rotor material were metallurgical factors for possible reheat cracking of the heat affected zone (HAZ) in this type of rotor. However, the grain refinement experienced by the HAZ and the coarsening of carbides in the coarse grain HAZ improved the toughness greatly and eliminated or reduced the susceptibility of reheat cracking. The weldment produced shows good room temperature mechanical properties; however, the stress rupture properties of the HAZ could not be evaluated owing to the premature failure of the weld metal.

MST/822