Experimental Determination of Elastic Modulus during Martensitic Transformation of Low Transformation Temperature Steel

摘要

When steel undergoes a transition from the austenite to the ferrite phase, the molar volume increases with decrease in temperature. The technology that utilizes this characteristic of steel, i.e. increase in molar volume, is suggested in the research field of welding. For instance, low-transformation temperature (LTT) steel is considered to minimize residual stress and deformation after welding. The martensitic phase expansion at low-transformation temperature reduces residual stress.1"3' The reduction in residual stress subsequently affects the fatigue properties of steel. To verify the effect of martensitic transformation on residual stress, extensive quantitative research has been conducted using the finite element method.M) However, because it is difficult to measure elastic parameters during the cooling process, including the period of martensitic transformation, many studies employ different elastic parameter models in their calculations. Some methods such as ultrasonic5~8) and electromagnetic acoustic resonance9' have been used for measuring the elastic parameters of metals and ceramics during the thermal cycle. However, most studies have focused on the elastic behaviour primarily during the heating process,5'9' while few have considered the transformation behaviour during cooling.6'