Comparative Experimental Study of Cutting Forces and Surface Roughness in Tangential Turning of 42CrMo4 Low-Alloy Steel and X5CrNi18-10 Austenitic Stainless Steel from a Sustainability Perspective

This study investigates the performance of tangential turning in machining two industrially relevant materials, 42CrMo4 low-alloy steel and X5CrNi18-10 austenitic stainless steel. A full factorial experimental design was employed to evaluate the effects of cutting speed, feed, and depth of cut on cutting force components, areal surface roughness parameters, and derived performance indicators. Regression models were developed to describe the relationships between process parameters and machining responses, resulting high coefficients of determination (0.935–0.996 for force components and 0.869–0.961 for surface parameters). Response surface analysis revealed that feed and depth of cut dominate cutting force behavior, while feed and cutting speed primarily influence surface roughness. Material-dependent differences were clearly observed. 42CrMo4 exhibited 10–30% higher cutting forces and higher roughness values, while X5CrNi18-10 showed lower forces but more variable surface characteristics due to strain hardening effects. Pareto front analysis demonstrated that 42CrMo4 enables simultaneous improvement of productivity and surface quality, whereas X5CrNi18-10 shows weaker coupling between these objectives. A composite sustainability index was introduced to integrate mechanical load, productivity, efficiency, and surface integrity. The results indicate that optimal conditions for 42CrMo4 reduce the sustainability index by up to 65%, while X5CrNi18-10 exhibits 20–40% higher index values under comparable conditions. The study highlights the importance of material-dependent analysis and multi-objective optimization for sustainable machining of advanced materials.