Ranges of application of free-cutting steels and recommended tool materials

Abstract

Four low carbonfree-cutting steels (0·11% carbon resulphurised, 0·11% carbon leaded–resulphurised, 0·08% carbon resulphurised, and 0·15% carbon leaded) were turned, dry, with a series of six types of cutting tool in which rake angle, tool material, and coating were varied (5° rake, high speed steel, TiN coated and uncoated; 15° rake, high speed steel, TiN coated and uncoated; 5° rake, cemented carbide, TiN coated and uncoated) in order to determine the optimum tool–workpiece combination for three cutting speed ranges: a low speed range in which the built-up edge (BUE) was forming or about to form; a speed range covering the BUE regime; and a higher speed range in which the BUE became a built-up layer (BUL). Tool–workpiece interaction was assessed by measurement of cutting forces, chip form, surface finish, tool temperature, and wear. It is suggested by the results that the best combination in the low speed range is that of leaded–resulphurised steel and uncoated high speed steel. In the BUE range, the combination of leaded steels and uncoated tools should be avoided; at higher speeds, coated tools are preferred, with non-resulphurised leaded steel giving the lowest tool temperatures and highest cutting speeds before ultimate failure. These recommendations should be treated with caution and used only as guidelines.

MST/867