The inherent strain method is known to be very efficient in predicting the plate deformation by line heating. Traditionally, the inherent strain regions have been determined from the temperature distribution of welding. Though the phenomena of line heating are similar to those of welding, the results cannot reflect the effect of practical line-heating pattern. Furthermore, water-cooling in the actual heating process can change the phase of steel to martensite. In this study, in order to consider plastic strains occurring additionally under phase transformation, inherent strain regions were assumed to expand to Ac1 temperature zone. Also, when calculating inherent strain, material properties of steel in heating and cooling are applied differently considering phase transformation. In this process, a new method which can reflect volume expansion of martensite on thermal expansion is suggested. By the suggested method, the plate deformations by line heating were predicted. It is verified that the predicted results of the present method are in good agreement with those of experiments.
Plate deformation by line heating has been studied through two approaches which are FEM for thermal elasto-plastic analysis and inherent strain method. Among them, inherent strain method is widely used from the view point of efficiency and accuracy (Jang and Seo, 1997). But there are some limitations to this method with respect to appropriate assumption of inherent strain region, and calculate accurate strain by that region. Satoh (1976) presented the depth and the breath of inherent strain region which were obtained from welding experiments, and assumed that the region is elliptical. In line-heating, Jang and Seo (1997) suggested that inherent strain region can be substituted with mechanical melting point. They obtained inherent strain by adding residual plastic strains in heating and cooling for spot heat source.