On Industrial Gas Nitriding of 42CrMo Steels for Tie Bars of Two Platen Injection Molding Machines

An industrial nitriding unit was performed on 42CrMo steel parts as the tie bars of two platen injection molding machines. The surface topography, microstructure, residual stress, and phase identification of the nitriding steel samples were studied. At the same time, the mechanical tensile and impact properties, microhardness, fatigue life, and wear and corrosion resistance of the nitriding steel samples and components were investigated in detail. The surface of the nitriding steel was composed of a white layer with thickness of 8-10 μm and a diffusion layer with thickness of 500 μm. The white layer was composed of ε-Fe₃N and γ′-Fe₄N phases. Compressive residual stress was present in the nitriding layer and gradually decreased with the depth of the nitriding layer. Compared to the original steel, the tensile and impact properties of the nitriding steel samples were slightly reduced, but the hardness, wear resistance, and corrosion resistance of the nitriding steel were significantly improved. In preliminary study, the fatigue life of the nitriding steel counterparts or tie bars for injection molding machines was enhanced significantly.