Microstructure and Mechanical Properties of Electric arc welded Low-alloy Steel at Varied Welding Heat Input

In fusion welding technique, heat input has a significant effect on the microstructure and mechanical properties of the welded joint. In this study, effects of varied welding heats on the microstructure and mechanical properties of low-alloy steel were investigated using electric arc welding technique. Optical emission spectrometry (AR 4 30 metal analyzer) was used to determine the chemical composition of the as-received low alloy steel sample. Based on ASTM A778/778M, five butt-joint samples were produced at different voltages, and constant speed and current. A portion of the welded sample was prepared by conventional metallographic grinding and polishing techniques for metallurgical examination using Philips SEM (XL30 TMP). The remaining portions were machined to standard tensile and hardness and impact specimens, using lathe machine. The tensile and hardness specimens were prepared in accordance with ASTM E 8-04 standard and the impact specimen based on ASTM A370 standard. The test specimens were subjected to mechanical testing using INSTRON tensile testing machine, digital Rockwell hardness scale B (HRB) and Charpy impact tester respectively. Results obtained revealed microstructures with varied volume fraction of ferrite, interspersing the austenite matrix. Pearlite and martensite phases were also sparsely dispersed within the austenite matrix. In addition, microstructures of the weldments were characteristically inhomogeneous, and at high heat inputs, increased presence of precipitates were seen within the microstructures. Maximum tensile properties (UTS, 498MPa, YS, 329 MPa) were obtained at heat input of 17.43 J/mm and least tensile properties (UTS, 469MPa, YS, 312 MPa) were obtained at 857.14 J/mm; maximum hardness property (484HRB) and least hardness property (394HRB) were obtained at 171.43 J/mm and 857.14 J/mm respectively; maximum impact energy (112.02 J) and least impact energy (88.79 J) were obtained at 514.29 J/mm and 857.14 J/mm respectively.