S700 is a high-strength steel recently developed by Tata Steel. This paper describes the residual stress distributions in a multi-pass gas-metal-arc weld (GMAW), a single pass autogenous laser weld (ALW) and a multi-pass ultra-narrow gap laser weld (NGLW) in 13 mm thick high-strength (S700) steel plates, as measured by X-ray diffraction and the contour method. The relationships between microstructural variation and residual stress distributions were investigated. It was found that solid-sate phase transformations from austenite to ferrite, bainite and martensite changed both the magnitude and distribution of residual stresses in the three different welded specimens. The width of the regions sustaining tensile stress in each specimen decreased in the following order: GMAW > ALW > ultra-NGLW.
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