Mechanical properties of quenched and tempered steel welds

Welding is the most commonly used joining process in the industry. Generally, weld zone consists of three different regions such as base metal, heat-affected zone (HAZ) and weld metal (WM). Microstructure of HAZ and WM changes due to the heat effects after the welding process. These effects cause changes in mechanical properties such as Young modulus, tensile strength and hardness in weld zone. The aim of this paper is to identify the mechanical properties of weld zone by uni-axial tensile test, nanoindentation test and hardness test. For this aim, quenched and tempered steel plates were chosen as a test material having high strength. These plates were welded together by flux-cored arc welding method. To determine the effect of weld pass number on the mechanical properties, the weld was completed in single and multi-pass (MP) butt welds separately. For experiments, tensile test specimens were cut by plasma cutting method according to related standard on welded plates. These specimens were subjected to three different post weld heat treatments (PWHT) such as 200 degrees C, 300 degrees C and 400 degrees C to evaluate the hardness change in HAZ. The effect of weld-pass number and PWHT on mechanical properties such as Young modulus, tensile strength and hardness were obtained from WM and HAZ by uni-axial tensile test and nanoindentation test and compared to each other. The yield and ultimate tensile strength of weld zone of welded tensile test specimens (WTTS)-2 is lower than WTTS-1 due to MP welding process. Furthermore, the strain behaviour of weld zone is not affected by PWHT significantly.