Nanoindentation and microstructure analysis of resistance spot welded dual phase steel

A nanoindentation hardness study has been conducted on the tempered region and the base metal in a dual phase steel subjected to rapid thermal cycles of resistance spot welding. Nanohardness results revealed “softening” at nano-scale for tempered martensite when compared to martensite in the base metal. At the tempered region, the ferritic matrix presented a slight reduction in hardness while the tempered martensite seemed to have a major contribution to the measured softening at micro-scale.