A newly developed freezing-cycle simulator which permits in situ melting, freezing and tensile testing was used to investigate the high temperature ductility and strength of various materials, including ferritic low alloy steels, austenitic stainless steels and Ni base superalloys. Based on the results, the correlation between those high temperature properties and the severity of weld high temperature cracking was described.
It was demonstrated that embrittlement of simulated weld occurred in the melting temperature region as well as in the austenite temperature region, and that both cases of embrittlement might be related qualitatively to the severity of high temperature cracking in welding.
An embrittlement parameter, ΔT=NST-NDT, where NST and NDT are the nil strength and nil ductility temperatures, respectively, was introduced for the melting temperature region embrittlement. Good correlation was found between ΔT and solidification cracking susceptibility of weld metals.
It was also demonstrated that the austenite region embrittlement was associated with the melting of grain boundaries, and that it was promoted by the elements which produce a wide γ+L region in the constitutional phase diagram.