Analysis of Gas Nitriding Characteristics under Different Cold Hardening and Nitriding Pressure Conditions for Low-Carbon Low-Alloy Steel

摘要

A new approach to quick preparation of a nitrided case for low-carbon low-alloy steels was proposed. It is based on cold hardening and pressurized gas nitriding. The microstructure, surface hardness, thickness, and corrosion resistance of the nitrided layer on low-carbon low-alloy steel (20CrMnTi) were investigated after the nitriding at 510°C for 5 h under different cold rolling reduction (0-60% CR) and nitriding pressure (1-5 atm). The results show that this technique can significantly improve the nitriding steel efficiency with the nitrided layer mainly composed of Fe_(2-3)N and Fe_4N nitrides. At constant nitriding pressure, the nitrided layer hardness first increases and then decreases with the amount of cold hardening. At the constant hardening, the nitrided layer hardness and corrosion resistance increase with the nitriding pressure. For the sample nitrided at 510°C for 5 h under 30% CR and a pressure of 5 atm, the nitrided layer exhibits optimal properties: hardness of 825 HV and thickness of 310 μm.