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Effect of austenitization at 920 °C on the mechanical properties and microstructure of microalloyed steel

In this paper the effect of heat treatment on mechanical properties and microstructure for microalloyed high-strength low-alloy (HSLA) steel is investigated. Austenitization of the steel samples was performed at 920 °C for 15 minutes. After austenitization the quenching procedure was carried out in both, hot water (at 70 °C) and lead bath at 400 °C, following by cooling on air. Tensile strength, hardness and Charpy impact energy are tested. Microstructural analysis was carried out using optical and scanning electron microscopy (SEM). Values of tensile strength were in the range from 1160 to 1824 MPa, while values of hardness were in the range from 205 to 282 HV5. The microstructure of base material consisted of acicular ferrite and degenerated pearlite. The quenching in water from 920 oC produced a coarse microstructure with platelets of ferrite and lath primary martensite. The cooling in lead bath from 920 °C to 400 °C produced microstructure consisted from ferrite and bainite. Fractography analysis by SEM method showed that cleavage fracture occurred.

microalloyed steel, heat treatment, mechanical properties, microstructure

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