Evaluation of Impact Tensile Strength of Welded Joints Made of Different Steel Sheets for Automobiles

This paper is concerned with the impact tensile strength of laser welded butt joints made by combining different steel sheets. Three classes of steel sheets for automobiles, mild steel (HR 270), high tensile strength steels (HR 590 and HR 780), were used in this study. Two kinds of CO2 laser welded butt joints specimens made of their different steel sheets, abbreviated as HR 270 & HR 590 joint and HR 270 & HR 780 joint, were investigated in static and impact tests, together with the three kinds of laser welded joints made of the same steel sheets, that is, HR 270 & HR 270, HR 590 & HR 590 and HR 780 & HR 780 joint. The measurement of the impact tensile strength was performed by the apparatus of split Hopkinson tension bar. The static tensile strength of HR 270 & HR 590 joint and HR 270 & HR 780 joint were similar to that of HR 270 & HR 270 joint, but their impact tensile strengths significantly incresed in comparison with the static ones due to the effect of strain rate, especially in part of HR 270 base metal.