The microstructure and mechanical properties of direct-quenched and tempered AISI 4140 steel

Direct quenching process (DQ) is an appropriate method in heat treatment of steel products. The advantages of DQ process are increasing of production rate, decreasing of energy consumption and avoiding of environments contamination. In this study hot-rolled AISI 4140 steel billets with different diameters (from 70 to 115 mm) length of 20 m were quenched directly in a water tank. The quenched samples were then tempered in a temperature range of (620 -660) C for 2 hours. The mechanical properties of heat treated samples included tensile strength, yield strength, elongation, impact toughness were identified. The samples were also analyzed from microstructural view point and the hardenability of this steel under various conditions was determined. These results were compared with samples conventionally heat treated samples which showed that the direct quenching and tempering process (DQ-T) increases the tensile strength and hardenability of this steel. DQ process is affected by various parameters such as steel temperature before quenching, temperature of water, quenching time, billet size.