Effect of tempering on laser remelted AISI H13 tool steel

The effect of tempering temperature on surface hardened AISI H13 tool steel by laser remelting process using an Yb-fiber laser has been investigated. Single remelting tracks were produced in argon environment at different laser power and scan speed in the range of 400-600 W and 200-1600 mm/min respectively, maintaining the laser spot diameter fixed at 3 mm. Their effects on geometrical aspects, microstructure and microhardness were analyzed considering the thermal history of molten pool recorded using an IR pyrometer. Microstructure was found to be associated with cooling rate and melt pool lifetime, estimated from the temperature signal. Thereafter, remelted surface with 30% overlapping tracks was generated and subjected to 1 h tempering cycle at different temperatures in 500-900 degrees C range followed by hardness and wear tests. Hardness was retained fully up to 500 degrees C and significant softening occurred at 600 degrees C and 700 degrees C. At 800 degrees C and higher temperatures, effects of laser remelting were impaired completely, but substrate got hardened through martensite formation in a conventional manner. Wear resistance followed the trend of hardness. Changes in microstructure and formation of various phases were found to be the reasons behind the modifications in hardness.