Abstract
Laser hardening process in various plain carbon steels containing 0.1-0.84%C has been analyzes based on hardness distributions, change in micro-structure observed and thermal conduction theory. Results obtained are summerized as follows:1) In laser hardening with cooling rates faster than the critical values of Ar transition, the hardness depends only on the maximum temperature attained during heating, not on heating and cooling rates and holding time above the transformation temperature.2) Hardening occurs at heating temperatures above 750°C, independently of carbon content and carbide distribution of material. For hypo-eutectoid carbon steel having a ferrite and pearlite structure, two-step change in hardness has been observed whereas eutectoid steels having spherodized carbide gives onestep curve.3) Carbon steel containing pearlite structure gives a narrower transient hardness region between maximum hardness layer at the surface and the mother matrix than that for steel having spherodized carbide.4) The heating temperature θn corresponding to the maximum hardness in ferrite-pearlite steel decreases with increasing carbon content, approaching progressively about 880°C for eutectoid steel. θn in spherodized steel is higher than θn/ in eutectoid pearlite steel.5) In laser hardening carbon steel with carhon content less than 0.84%, the effect of retained austenite on the hardness has been found to be negligible.
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