A creep technique for monitoring MnS precipitation in Si steels

Abstract

A newly developed creep method is described for investigating the kinetics of manganese sulfide precipitation in two Si steels at hot working temperatures. The method was also applied to a Ti steel, in which the precipitation kinetics were previously determined using a stress relaxation technique. Prior to loading, the specimens are solution-treated for half an hour and then immediately cooled to the test temperature. A constant stress is applied to the sample by means of a computerized MTS machine, and the strain is recorded continuously during testing. The resulting creep rate is sensitive to the occurrence of precipitation; thus, the slope of the true strain-log (time) curve decreases immediately after the initiation and increases on the completion of precipitation. The precipitation-time-temperature (PTT) diagrams determined in this way on the three tested steels are of classical C shape. Because higher dislocation densities and internal stress levels are maintained, the present technique is more effective for monitoring the precipitation events occurring in both austenitic and ferritic phases than the previously developed stress relaxation method.