<![CDATA[AISI 4140 steel is a low alloy steel which is also categorized as chromium-molybdenum steel, and it is widely used to make automotive components. Based on carbon composition, AISI 4140 steel is included in the medium carbon steel with 0.4 wt.% carbon. Therefore, the mechanical properties of AISI 4140 steel can be improved by heat treatment. The AISI 4140 specimens undergoes several stages of heat treatment, austenitized at 850°C for 30 minutes, then quenched in oil. After that each specimens is tempered at two temperatures of 400°C and 500°C with holding time of 15 and 30 minutes. The heat treatment process results in increased strength and hardness but lower in ductility than that of the as-received specimen. The optimum result is obtained at tempering temperature of 500°C with holding time of 15 minutes, which shows a significant increase in tensile strength without sacrificing ductility. Finally, the microstructure of the as-received AISI 4140 steel plate shows the presence of α-ferrite and pearlite phases, while the heat-treated specimens may form martensite or tempered martensite and retained austenite.]]>
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