Microstructural and Mechanical Properties of One-Step Quenched and Partitioned 65Mn Steel
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RESEARCH ARTICLE-MECHANICAL ENGINEERING
Microstructural and Mechanical Properties of One-Step Quenched and Partitioned 65Mn Steel Muhammad Arslan Hafeez1 Received: 22 August 2020 / Accepted: 23 October 2020 © King Fahd University of Petroleum & Minerals 2020
Abstract The novel quenching and partitioning processes concerned with the stabilization of carbon enriched austenite and provision of higher strength with higher toughness. The microstructural and mechanical properties of one-step quenched and partitioned 65Mn steel were investigated under various partitioning times, ranging from 30 to 600 s. The optical microscopy revealed that microstructure transformed from ferrite and pearlite to supersaturated lath martensite and retained austenite phases after one-step quenching and 30 s of partitioning. The unstable epsilon carbides were nucleated with the increase in partitioning time to 60 s and 180 s, whereas a further increase in partitioning time to 300 s transformed these unstable epsilon carbides into a stable cementite phase. Prolonged partitioning for 600 s produced carbon depleted martensite phase and nucleated ferrite phase. A maximum improvement of 88% in hardness and tensile strength and maximum reduction of 64% in elongation and 44% in impact toughness were achieved after 30 s of partitioning, compared to the as-received steel sample. On the other hand, partitioning for 600 s offered almost identical mechanical properties to the as-received steel. Partitioning for 180 s offered an optimum combination of mechanical properties of one-step quenched and partitioned 65Mn steel. Keywords One-step quenching and partitioning · 65Mn steel · Carbon enriched austenite · Carbon depleted martensite · Mechanical properties
1 Introduction The applications of advanced high strength (AHS) steels are increasing progressively in automotive and other applications because of their excellent amalgamation of properties. These properties include high strength, high ductility, reduced weight, excellent crash resistance, great energy absorption capacity, fatigue resistance, formability, weldability, efficient fuel consumption, reduced CO2 emission, better environmental impact, and low costs [1–4]. Due to excellent amalgamation of properties, AHS steels are used in chassis, body-in-white (BIW) components, such as A-pillars, B-pillars, front cross member, side sills, roof railing, longitudinal beams, bumper reinforcements, door, hoods, and trunks in the automotive industry [5, 6]. A variety of AHS steels have been developed in the last decade and are classified into three
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Muhammad Arslan Hafeez [email protected] School of Civil and Environmental Engineering, National University of Sciences and Technology, Islamabad 44000, Pakistan
generations based on their mechanical properties [7, 8]. Firstgeneration AHS steels, having ferrite-based microstructure, 500–1600 MPa tensile strength, and 5–30% elongation [9], include transformation induced plasticity (TRIP) steels, complex-phase steels, martensitic (MART) steels,
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