Effects of quenchants on microstructures and mechanical properties of steel grade AISI 5160

บทคัดย่อ

This research aims to study the effects of the quenchants in hardening process on microstructures and mechanical properties of alloy steel grade AISI 5160. The heat treatments include hardening at 900 (Q1), 870 (Q2), 840 (Q3), 810 (Q4) and 780°C (Q5), respectively, followed by quenching into water, oil and brine solution. Microstructures were measured by optical microscopy and scanning electron microscopy and energy dispersive X-ray spectroscopy. For each condition, hardness and tensile testing were measured. It was found that the microstructure in the as-sheet condition consisted of ferrite and pearlite. The observed microstructures after quenching process were martensite with a small amount of retained austainite. The hardening at 810°C for 30 min (Q4) showed carbide distribution in martensite matrix. The coarse ferrite grains were occurred after hardening at 780°C for 30 min (Q5). The hardness of as-sheet condition was 40 HRC. Highest hardness was obtained after hardening follow by water quenching. The ultimate tensile strength in as-sheet condition was about 510 MPa. As hardening at all conditions, the maximum ultimate tensile strength was after hardening at 810°C for 30 min (Q4). Heat treatment conditions increased the hardness and ultimate tensile strength compared with the as-sheet condition while %elongation gradually decreased. For heat treatment conditions, however, water quenching is more suitable.