Improvements in Machinability, Microhardness, and Impact Toughness of AISI O1 and AISI D2 Alloy Steels by Controlling the Grain Size During Heat Treatment

This research aims to study the effects of grain size of heat-treated alloy steels, AISI D2 and AISI O1, on their machinability, impact toughness, and hardness.The hardening temperatures for AISI D2 steel ranged from 950 to 1070 °C, with increments of 40 °C.Meanwhile, the hardening temperatures for AISI O1 steel ranged from 780 to 870 °C, with increments of 30 °C.For AISI D2 and O1 specimens, the tempering temperatures were set at 550 °C and 250 °C, respectively.The impact toughness, average surface roughness (Ra) after turning process, and hardness test were conducted.The main findings are; very smooth surface roughness, for AISI O1 specimens, Ra = 0.115 μm, at a grain size of 46 μm, depth of cut of 0.15 mm, cutting speed of 120 m/min, and feeding of 0.05 mm/rev.For AISI D2, the Ra value is 0.134 μm, at grain size =14.6 μm, depth of cut of 0.2 mm, feed rate 0.05 mm/rev, and cutting speed of 120 m/min for AISI O1 steel, moreover, a pronounced enhancement in hardness and impact energy for both alloy steels were achieved.