Machinability of High Mn Steel Using Tool Life Criteria

High Mn steel alloys have shown to provide both high strength and ductility. However, current literature offers limited guidance on the machinability of these steel alloys. Therefore, this work provides turning recommendations for high Mn steel that is based on tool life data. Several indexable carbide inserts with various rake angles were used to machine cast billets of high Mn steel. Turning characteristics from various feed rates, cutting speeds, and depths of cut were analyzed. Through a design of experiments, it was determined that the feed rate was the most significant factor affecting tool life and that a tool with a negative rake angle had a longer tool life than one with a positive rake angle. The effect of coolant on tool life was seen to be dependent on the tool material. Optimal cutting conditions, which provided a long tool life while maintaining a decent material removal rate, were found for a cutting speed of 150 ft/min, a feed rate of 0.008 in/rev, and a depth of cut of 0.080 inches. In addition, microhardness analysis was used to determine the thickness of the work-hardened layer on machined surfaces. Microhardness was seen to increase between 0.028 and 0.040 inches from the machined surfaces for each cutting condition, explaining the difficulty experienced in machining high Mn steel alloys. The availability of these recommendations for machining high Mn steel encourages the application of this material in a more efficient and productive manner