STRATEGIES TO REPLACE LEAD IN FREE-CUTTING STEELS

Quantitative investigations on the micromechanisms of tool wear have confirmed that dissolution of the tool into the workpiece by a diffusion mechanism is the dominant mode of tool crater wear during the machining of commercial grade AISI 12L14 and AIS1 1215 steels with cemented carbide tools at moderately high cutting speeds (140-200 m/min). At higher cutting speeds, the tribology of seizure operates at tool-chip interface that determines the tool life. Neither lead nor sulfide inclusions are found to be effective in suppressing tool dissolution wear. Deformable anorthitic oxide inclusions engineered into the workpiece as well as coating the tool with hafnium nitride, a compound with very low equilibrium solubility in the workpiece at the typical tool-chip interface temperature are demonstrated to be two effective methods for suppressing tool dissolution crater wear. Thus inclusion engineering of the workpiece and coating of the tool are viable options to replace lead in free cutting steels designed for machining at high cutting speeds with carbide tools.