Solidification microstructure of laser welded stainless steels

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Abstract
The solidification microstructures of pulsed Nd:YAG laser or CW CO2 laser welds were studied in commercial SUS 310S and 304 (corresponding to AISI Types 310S and 304) austenitic stainless steels and in other several austenitic and duplex stainless steels. In the pulsed laser welding of Type 310S, neither grain growth nor recrystallization grain-refining was observed in the heat-affected zones (HAZ), and planar and cellular growth occurred epitaxially in weld metals from adjacent, incompletely-melted grains in the HAZ. According to the data relating a primary dendrite arm spacing to the cooling rate in Type 310S weld metals, the average local cooling rates within the single laser shot welds were extrapolated to be so rapid as to range from 5×104 to 5×106°C/s depending mainly on the pulse energy. In the case of Type 304, the pulsed laser weld metals were almost fully austenitic in contrast to GTA or CO2 laser weld metals containing about 5% residual delta(δ)-ferrite. It was significantly confirmed that almo...

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