Effects of Heat Treatment on the Impact and Hardness Properties of Mild Steel [ASTM 36] Lap Welded Joint

Abstract

ASTM A36 is the most used type of mild steel especially in construction and manufacturing industry. Welding process is regularly employed to fix the crack that usually occurs in low carbon mild steel after a long time use especially in construction industry. In this study, the effects of heat treatment on the mechanical properties on mild steel [ASTM A36] lap welded joint were investigated. Seven pieces of 60 mm × 300 mm mild steel bar were used for this research. Five samples were heat treated in an electric muffle furnace and soaked at 6000 C for 65 minutes. Two samples were cooled in air and furnace while the remaining three were rapidly quenched in water, spent engine oil and diesel oil each. Hardness and Impact tests specimens were made from the control (as received) sample and the various heat-treated samples. The specimens were joined together using E6361 mild steel arch welding electrode, lap welding joints and Shielded Metal Arc Welding (SMAW). Hardness test and impact test are used to delineate the mechanical properties for heat treated welded specimens and control specimens. It was established from the research work that Brinel Hardness Number (BHN of ASTM A36 lap welded joint cooled/quenched in different media increased it significantly in the Heat affected Zone (HZ) in all the quenching media. There is also a substantial increase in both Impact Energy (IE) and Impact Strength (IS) of heat-treated ASTM A36 lap welded joint when cool/quenched in the air, furnace, water and spent engine oil.