HT80母材の応力緩和特性

Abstract

In order to make clear the effect of stress relief heat treatment on the reduction of residual stress in base metal, high temperature tensile test, creep test and tensile relaxation test, both anisothermal and isothermal, were carried out using two kinds of HT80 steels. Relaxation property was discussed on the basis of creep phenomena and a method of forecasting stress drop during S.R. treatment was studied. The findings are summarized as follows:1. In the anisothermal stress relaxation test, stress drop during heating was larger than that predicted from high temperature tensile properties. This fact points to the occurrence of creep strain during heating. this creep strain became larger with increasing initial stress and with temperature rise.2. In the isothermal stress relaxation test, stress drop occurred mainly in the initial 1 hour from beginning. The isothermal stress relaxation curve could be calculated from creep test data on the application of strain hardening concept.3. A higher heating rate during anisothermal stress relaxation test led to an increase in residual stress immediatelly after heating, but this effect became almost negligible as holding continued more than 1 hour and then the stress decreased to a certain value regardless of heating rate.