Plastic Strain in Circular Stainless Steel Plate Subjected to Spot Heating

Abstract

The distributions of residual strain produced by spot heating are studied on an austenitic stainless steel plate. The relations between dimensions of plastic region and heat input are clarified experimentally to obtain the fundamental properties of welding deformation.
Various diameters of concentric circles are previously marked on the surface of specimens for measuring the strain (Fig.2). The specimens are spot heated at their center with different heat inputs by means of a TIG arc welding set. The thermal cycle of each specimen is observed at several locations, and then the specimen is cut into concentric rings to release the residual stresses. In this procedure the changes in diameter of marked circles due to heating and cutting are measured and the components of residual strain on the concentric circles in the plates are calculated.
The results obtained are as follows: The thermal cycle at any point of the plate can be presumed using the equation of heat conduction for instantaneous line heat source (Figs. 4, 5 and 6). The components of the total, elastic and plastic strains in circumferential and radial directions can be calculated from the changes in diameter of the concentric circle (Figs. 8 and 9). A plastic region is produced around the heated point and it causes residual tensile stresses, which are roughly equal to the proof stress of the material. The plastic region is extended in radius with an increase of heat input (Fig. 12). The observed maximum temperature at the boundary of plastic region is about 20 to 30°C, which is lower than the expected value. The measured results of residual stresses well agree with those derived in accordance with the inherent stress theory from the plastic strain distributions (Fig.10).