Influence of six-step heat treatment on microstructures and mechanical properties of 5160 alloy steel

Abstract

AISI 5160 alloy steel grade with complete martensite structure to get the high-strength steel sheets quenched at 900 (Q1), 870 (Q2), 840 (Q3) and 810°C (Q4), respectively and temped at 780°C (Q5) and 680°C (Q6), respectively. The results show ferrite and pearlite microstructural appeared in as-sheet conditions. The strengthening rarely increased with increasing heat treatment steps, while the percentage elongation gradually decreased. The hardness change was secure with that of strengthening for the quenched martensite. In contrast, differences between the initial martensite hardness were no noticeable changes. The Q4 hardening involved the peak hardness and maximum ultimate tensile strength due to carbide distribution in the martensite matrix. The coarse ferrite grains have occurred after Q5 cause significantly reduced hardness and tensile strength. However, the percentage elongation increased with increasing quenching step to Q5 hardening. The excellent 5160 steel performed by Q6 hardening characteristic gained most hardness, ultimate tensile strength, and elongation approximately 60 HRC, 835 MPa, and 12.09%, respectively. Martensite structure transformed to among carbide distribution tempered martensite matrix.