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The effects of temperature, composition, and weld-process variations on the fracture toughness behavior for Types 308 and 16-8-2 stainless steel (SS) welds were examined using the multiple-specimen J-resistance-curve procedure. Fracture characteristics were found to be dependent on temperature and weld process, but not on filler material. Gas-tungstenarc (GTA) welds exhibited the highest fracture toughness, a shielded-metal-arc (SMA) weld exhibited an intermediate toughness, and submerged-arc (SA) welds yielded the lowest toughness. Minimum expected fracture properties were defined from lower bound fracture toughness and tearing modulus values generated here and in previous studies.
Fractographic examination revealed that microvoid coalescence was the operative fracture mechanism for all welds. Second-phase particles of manganese silicide were found to be detrimental to ductile fracture behavior because they separated from the matrix during the initial stages of plastic straining. In SA welds, the high density of inclusions resulting from silicon pickup from the flux promoted premature dimple rupture. The weld produced by the SMA process contained substantially less manganese silicide, while GTA welds contained no silicide inclusions. Delta ferrite particles, present in all welds, were substantially more resistant to local failure than the silicide phase. In welds containing little or no manganese silicide, delta ferrite particles initiated microvoid coalescence, but only after extensive plastic straining.
fracture of materials, fracture toughness, J, -integral, elevated temperature tests, fractography, stainless steel welds, fracture mechanics
Fellow engineer, Westinghouse Hanford Co., Richland, WA