Effect of plasma nitriding on pistol slides

This study investigates the effects of traditional quenching and plasma (ion) nitriding on the microstructure and mechanical properties of cold-drawn low-alloy AISI 4140 steel, which is widely utilised in the light weapons and defence industries. AISI 4140 alloy is widely used in pistol slides in the small arms industry. The quenching method enhances the strength of pistol slides, which endure high loads during firing. However, the distortions and restrictions encountered during this process affect the strength of the slides. In this study, cold-drawn AISI 4140 material was subjected to plasma nitriding, a thermochemical process increasingly used in the defense industry, and various properties were compared with the traditional quenching process. The structural and mechanical properties of the alloy were analyzed in the raw material (cold-drawn, untreated), quenched-tempering (QT) and quenched-tempering-plasma nitriding (QT + plasma nitrided) conditions, focusing especially on fatigue performance. The results revealed that the raw material consists of deformation-induced grain-oriented ferrite and pearlite phases. The QT process transformed the microstructure predominantly into bainite and martensite. QT + plasma nitrided resulted in chemical modifications at the surface, forming a white layer containing iron nitrides and a diffusion layer containing alloy nitrides. The effective hardening depth due to nitrogen diffusion was measured as 0.25–0.30 mm. The QT + plasma-nitrided specimen showed the highest hardness, tensile strength, impact toughness, and better fatigue performance. In particular, fatigue cracks initiated from the surface in the raw material and QT specimens. In contrast, fisheye cracks between the diffusion layer and the core in the QT + plasma-nitrided specimens indicated an improved fatigue-resistance mechanism. These findings highlight the advantages of plasma nitriding as an advanced surface-hardening technique for improving the dimensional stability and performance of critical components, especially in the small-arms industry.