Microstructure and mechanical properties of low temperature carburizing layer on AISI 440C martensitic stainless steel

In this study, the microstructure and mechanical properties of AISI 440C martensitic stainless steel with low temperature carburizing (LTC) layers were investigated by microscopes, X-ray diffraction (XRD), Vickers indenter and pin-on-disc test device, etc. LTC treatment was conducted at 420 °C for 10-40 h on the quenched-tempered steel samples by pack method. Results indicated that the LTC layers formed on base metal exhibited compact and regular morphology, and carbon-expanded martensite (α′c), Fe3C and Cr23C6 compounds were examined in the LTC layers by XRD analysis. Besides, the layer hardness from 1430 to 1720 HV0.025 with processing time increased, which was approximately three times higher than that of the specimen without LTC treatment. However, as the processing time increased, the adhesion strength of LTC layers deteriorated and the indentation grade decreased from HF1 to HF3. In addition, the wear resistance was significantly improved after the LTC treatment, and the wear rate of the LTC layer decreased by 93.7% in comparison with the untreated condition.