Abstract
Effects of free-cutting additives, heat-treated structures, and cold working on the machinability of low chromium case-hardening steels based on the chip-breaking characteristics have been investigated.
The order of free-cutting additives in decreasing contribution to a favourable broken chip were Bi>Pb>S>Se and Te at the same amount of addition in weight per cent. The effects of P and N on the contribution to a broken chip were comparatively small.
The machinability of case-hardening steels based on the chip-breaking characteristics was the best for spheroidized structure and decreased in the order of annealed structure to normalized structure. Cold working was detrimental to the machinability of spheroidized structure in terms of the chip-breaking characteristics.
The effects of heat-treated structures and cold working on the machinability based on the chip-breaking characteristics is mainly explained by the ratio of the chip thickness to the diameter of a helical chip, i. e., a high ratio provides a favourable broken chip.
