Effect of low-temperature surface carburization on stress corrosion cracking of AISI 304 austenitic stainless steel

The effect of low-temperature surface carburization on the stress corrosion cracking (SCC) behavior of AISI 304 austenitic stainless steel in boiling magnesium chloride (MgCl2) solution at 155 ± 1 °C was investigated. The SCC tests were carried out for untreated and carburized AISI 304 with varying four-point bend loading. In order to elucidate the influence of low-temperature surface carburization on SCC resistance, optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometry (XRD) and residual stress analyzer were used. The results show that the tensile stress on the surface of untreated four-point bend loaded AISI 304 and the occurrence of pits during SCC tests had bad influence on the SCC resistance. The surface of carburized four-point bend loaded AISI 304 was in a state of compressive stress over the whole loading range due to the presence of carburization-induced huge compressive residual stress. The chloride-induced SCC resistance of AISI 304 can be obviously improved by low-temperature surface carburization due the carburization-induced compressive residual stress and the improved pitting corrosion resistance. The carburization-induced compressive residual stress was the dominant reason for the improvement of SCC resistance. No relaxation happened in carburization-induced compressive residual stress and the phase of the expanded austenite was stable during SCC tests.