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Hydrogen embrittlement property of high strength steels has widely been evaluated for wire and bolt products. But there are not many evaluation methods of hydrogen embrittlement for steel sheets. In this work, a method for sheet products has been established. Using this method, effects of materials (tensile strength), applied stress and pre-strain on hydrogen embrittlement property can reasonably be evaluated for high strength steel sheets. Environmental embrittlement evaluation in cyclic corrosion test was also carried out for comparison with the results from the new method, which were in good agreement.

Experimental study on static strength of spot-welds for high-strength steel sheets is summarized, focusing on thicker and coated sheets. Tensile shear strength (TSS) increases with sheet strength and thickness. Cross tensile strength (CTS) also increases, but the variation with sheet strength is small. Welding with expulsion deteriorates CTS, especially for thicker or coated sheets with higher strength or carbon content. Blow-holes and shrinkage cavities are found frequently at thicker sheet welds, and their existence near nugget edge reduces CTS. Above-mentioned knowledge leads developments of galvannealed sheets with carbon content less than 0.1 % for tensile strength up to 980MPa.

Aluminum alloy sheets are used for automotive body-panels, but their small Young's modulus results in inferior shape-fixability than conventionally-applied steel sheets with similar strengths. Smaller radius of curvature, indicating better shape-fixability, is found at the center of a panel press-formed with higher blank holder force (BHF). Higher force can be applied for press-forming of alloy sheets with larger strain-hardening exponent (n value) induced by an increased addition of Mg. Recently-developed 5000 series alloy sheets containing 5.5 pct Mg and 0.3 pct Cu have an elongation over 33 pct at an ultimate tensile strength of 270 MPa and can be press-formed with better shape-fixability.