Abstract
A mechanical and microstructural evaluation of a weld mock-up was carried out for the same Cr–Mo–V rotor steel used in Part 1 of this study. The weldment was a submerged arc weld processed by a commercial fabricator; the welding parameters and heat treatments were not made available. One of the objectives of this study was to determine whether stresses associated with welding a large rotor section played a significant role in the development of reheat cracking. It was found that a butter weld layer was deposited before the multipass full thickness weld. This procedure led to significant grain refinement at the heat affected zone of the base metal, yielding excellent impact properties relative to the rotor base material. This welding technique and the selection of filler metal of lower strength than the rotor material apparently contributed to the elimination of reheat cracking. The Charpy impact energies of the full thickness and butter welds were much greater than those of the rotor steel; however, temper embrittlement resulted when full thickness weld specimens were subjected to thermal aging at 538°C or step cooled from 593°C. A second objective was the evaluation of the joint strength and its microstructure stability after high temperature exposure. It was determined that improvement in the impact properties of the weldment was obtained at the expense of poor room temperature tensile strengths and inferior stress rupture properties. However, it was determined that the weld metal used had not been intended for service at the high temperature end of a high pressure rotor.
MST/1235
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