Effect of carburization on residual stress field of 20CrMnTi specimen and its numerical simulation

In this work, specimens with dimensions of Ø 25 mm × 100 mm were made of low-carbon low-alloy 20CrMnTi steel and were quenched in oil or carburized (to get a carburized layer for about 1.2 mm) and then quenched. The residual stress fields in the surface region were determined by using an X-ray stress analyzer for both specimens. The results show that, on the (non-carburized) quenched specimen, the residual stress is tensile at the surface and is compressive in the center; while, on the carburized specimen, it is compressive in the surface zone with a maximum value at the position about 0.7 mm beneath the surface. A model for FEM calculation, in which the austenite-martensite transformation is taken into account, was established for calculation of the transient and residual stress fields of both specimens during quenching. In order to get needed parameters of materials at different positions of the carburized layer, dilatometric tests were carried out by using small simulative specimens carburized “thoroughly” in different atmospheres with given carbon potentials. The calculated residual stress distributions fit well to the measured ones in both specimens, which indicates that the proposed simulation model is effective for calculation of transient and residual stress field of steel specimens, occurring martensite transformation during quenching.