The effect of plastic pre-strain on low-temperature surface carburization of AISI 304 austenitic stainless steel

In this paper, the influence of plastic pre-strain on low-temperature surface carburization of AISI 304 austenitic stainless steel was investigated. The materials were strained to different degrees of engineering strain including 5%, 10%, 15%, 20% and 25%. Low-temperature surface carburization of the pre-strained specimens was performed at 470 °C for 30 h. In order to elucidate the effect of plastic pre-strain on low-temperature surface carburization, optical microscopy (OM), X-ray diffractometer (XRD), scanning electron probe micro-analyzer (EPMA), microhardness tester and residual stress analyzer were used. Meanwhile, dislocation density and the martensite volume fraction of the pre-strained specimens were quantitatively measured by means of XRD analysis. Based on the experimental results, the role of dislocations and martensite on carbon diffusion and related phase transformation during low-temperature surface carburization was discussed. The results show that the thicknesses of the carburized layers are independent of the pre-strain degree. Dislocations and strain-induced martensite almost have no effect on the growth of the carburized layers at the given carburizing temperature. Increasing dislocation density does not promote the development of carbides formation, while strain-induced martensite does. Due to the supersaturated carbon atoms introduced into the materials during carburization, strain-induced martensite transforms into austenite. As a result of carburization, an outstanding strengthening layer of the material develops, and plastic pre-strain has no effect on strengthening of carburization.