Correlation among Solidification Process, Microstructure, Microsegregation and Solidification Cracking Susceptibility in Stainless Steel Weld Metals(Materials, Metallurgy & Weldability)

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This study was undertaken on about 60 Fe-Cr-Ni ternary stainless steels to obtain a better understanding of the effect of primary and eutectic delta(δ)-ferrite on cracking resistance with the object of developing a highly crack-resistant alloy by defining a correlation between solidification process and cracking susceptibility. According to the microstructural observation of weld metals quenched rapidly from high temperatures during TIG welding and normal weld metals cooled continuously to room temperature after welding, solidification processes and related microstructures of stainless steel weld metals were classified into five different types and correspondingly eight characteristic modes, respectively. It was noted that a small content of residual δ-ferrite at room temperature resulted from primary ferrite in cell axes (Mode VF (vermicular ferrite) and Mode LF (lacy ferrite)) for lower Cr and Ni equivalents, while it came from eutectic ferrite at solidification grain and cellular dendritic boundaries (Mode IF (intercellular eutectic ferrite)) for higher Cr and Ni equivalents. Solidification crack susceptibility was assessed by the BTR (solidification brittleness temperature range) in the Trans-Varestraint test and LT (total crack length) in TIG and resistance spot welds. It was found that there was a close relationship between solidification cracking susceptibility and solidification process: Type A (austenitic single-phase solidification)-Mode FA (fully austenitic structure) steels were the most susceptible to cracking and Type FE (primary ferrite and eutectic ferrite-austenite solidification)-Mode VF (vermicular ferrite) or Mode LF (lacy ferrite) weld metals were the most resistant. It was therefore confirmed that an austenitic stainless steel containing only 2% residual δ-ferrite exhibited an excellent resistance to cracking due to Type FE solidification process. Moreover, it was revealed that some Type AE (primary austenite and eutectic austenite ferrite solidification)-Mode IF materials were resistant and the reason was attributed to the beneficial effects of eutectic ferrite on the decrease in microsegregation of P and the resistance to cracking propagation.
大阪大学の論文

Correlation among Solidification Process, Microstructure, Microsegregation and Solidification Cracking Susceptibility in Stainless Steel Weld Metals(Materials, Metallurgy & Weldability)

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