Determination of quasi-static and residual stresses in the course of the thermoplastic hardening in a boundary layer of the material

Abstract

In order to induce residual compressive stresses in the boundary layer of a steel plate heated to temperature T0 = 600 °C, a method of jet water cooling with time-varying heat transfer coefficients is considered. By solving the corresponding heat conduction problem, it is shown that the maximum temperature difference between the surface and the center of a 2 mm thick plate is 105 °C. It is observed within 0.02 s since the start of cooling, the time of its complete cooling is equal to 0,32 s. Calculations of temperature stresses using the finite element method showed that temperature tensile stresses occur on the outer surface of the plate. They may reach 26 kg/mm2 which exceeds the yield strength of this material. As a result of plastic deformation, the thermal tensile stress relieving occurs in the course of cooling of the plate surface layer; when it is completely cooled, the residual compressive stresses 21.8kg/mm2. (on the surface of the plate) are induced in this layer (0,25 mm depth).