TRANSFORMATION HARDENING OF MEDIUM-CARBON STEEL WITH A FIBER LASER: THE INFLUENCE OF LASER POWER AND LASER POWER DENSITY
AbstractThis paper investigates the effects of laser power density of a fiber laser on surface transformation hardening of two types of medium-carbon steels. An out-of-focus laser beam produced by a fiber laser system is used to produce an irradiated track on the surface of the samples. The tests use two types of medium-carbon steels with different initial microstructures, including X15 containing ferrite and pearlite and AC16 composed of tempered martensite. The tests on X15 show that for each laser power there is an optimum power density that produces the maximum hardness. With increased laser power, the optimal power density for both surface hardness and hardened depth is lowered. For AC16 tests, the maximum hardness value is not found to be dependent on laser power density. Alloying elements may increase the hardened depth. Slight surface melting may facilitate the hardening process and increase the surface hardness. The hardened depth is generally increased with higher laser power and/or laser power density. Compared with other types of lasers, fiber laser is a competitive tool in hardening of medium-carbon steels.