Effect of heat input & shielding gas on microstructure of 2.25Cr-1MO steel in gmaw

Although there are various parameters which put effect on welding of steels but in Gas Metal Arc welding heat input and shielding gases are major concern. The soundness of welding is measured by its mechanical properties such as hardness, tensile strength and impact strength. But, there is big impact of microstructure on all mechanical properties. Present work is focus on effect of welding variables such as heat input and shielding gas on microstructure of 2.25 Cr-1Mo steel. A copper coated solid wire is used to weld V-groove but joint by varying current and voltage. The further variation in input are by taking two mixture of shielding gases, 90% Argon, 8% Carbon dioxide, 2% oxygen and 90% Argon 10% Carbon dioxide. Samples for microstructure testing were taken from four different welding joints, polished and examine under optical microscope (AXIO) at 100x. Results shows coarse bainitic structure formed at high heat input while presence of oxygen in shielding gas increase tendency of ferrite formation.