Effects of atmosphere on flank wear of high-speed steel tools used to turn medium-carbon steel in built-upedge conditions

Abstract

The effect of atmosphere on the flank wear of high-speed steel tools under conditions of built-up-edge formation has been studied in a series of turning tests. Four sintered high-speed steels and a wrought M2 were used to turn an En 8D steel bar with a water-based coolant applied alone, with nitrogen and with oxygen blown into the flank crevice while maintaining the flow of water-based coolant on the rake face, and without coolant in air. Tool wear was observed metallographically, and a subsidiary study made of the stability of built-up edges. In dry conditions high adhesion between the built-up edge and the flank produced a cracked and torn wear surface, but a stationary layer also formed which protected the flank from sliding wear. With coolant alone, lesser adhesion resulted in a smooth wear surface but the stationary layer was not formed; overall there was more wear than in dry conditions. The addition of nitrogen to the flank region in wet-cutting tests resulted in a torn wear surface, demonstrating the importance of flank atmosphere. When oxygen was blown into the flank in wet conditions, wear was greatly reduced, demonstrating that oxygen was more effective than water vapour in lubricating the flank by forming a surface film. The results are compared with earlier studies.