Deep Cryogenic Treatment of AISI M2 Tool Steel and Optimisation of Its Wear Characteristics Using Taguchi's Approach

The present research paper focuses on optimisation of wear test parameters for different deep cryogenic treated AISI M2 tool steel material. Commercially available, AISI M2 tool steel material is machined as per ASTM G99-05 standards and was subjected to deep cryogenic treatment for the different holding time of 12, 24 and 36 h, followed by tempering for 2 h at $150{}^{\circ }\text{C}$. The specimens were tested for their wear resistance using a pin-on-disc wear testing setup adopting Taguchi's design of experiments approach. The control variables selected were deep cryogenic treatment holding time, the speed of the rotating disc and load applied to the specimen pin. The wear test was conducted as per trials generated by Taguchi's ${\text{L}}_{27}$ orthogonal array, and the results are analysed using signal-to-noise ratio and analysis of variance. The results show that the cryogenic holding time has majorly affected the wear resistance followed by the load on the pin and disc speed. It is also observed that 24 h holding time for deep cryogenic treatment yields better wear resistance compared to 12 and 36 h. Microstructure and X-ray diffraction analysis of the cryogenically treated specimens reveals the conversion of retained austenite into martensite and the formation of fine carbides in the martensite lattice after deep cryogenic treatment process which are responsible for the increase in wear resistance. Also, the worn surface analysis shows that the adhesion wear, oxidation wear and abrasion wear are the predominant wear mechanisms observed under different testing conditions.