Measuring of Residual Stress in TIG Welding of the 304 Stainless Steel by Ultrasonic Method

In this research, the effect of different welding parameters on residual stress and microstructure of the weld region, as well as the comparison of two methods of measuring residual stress using critical fracture longitudinal wave method and preformation method have been investigated. For this purpose, the taguchi DOE methodology is used as a statistical method to optimize four parameters of pulse current, base current, and pulse on time% and pulse frequency to minimize longitudinal residual stresses in austenite 304 AISI stainless steel. After welding, stress measurements were performed using two methods critical fracture longitudinal and perforation, and hardness, tensile and OM tests were performed on the specimens. The tests results show that at all levels of the pulse parameters arranged with the standard L9 Taguchi array, the incident heat input is irrefutable and the effect of this parameter is move then 50%. The optimum conditions obtained while the highest frequency level should be considered. The general trend is achieved from the residual stress measurement charts is consistent with the logic of stress distribution in both methods. Sample number 1 with stress equivalent to 232 MPa and sample number 9 with stress of MPa 126 in ultrasonic method with frequency 4 MHz have the highest and lowest stress among different samples, respectively. The size of the coaxial grains weld was directly related to the incoming heat, so that the least amount of coaxial grains in the welding center was related to specimens NO. 3 and 9 with grain size of 8 µm and 9 µm, which in these samples had the lowest amount of welding heat is measured. The samples 1 and 4 with HV 128 and HV 144 hardness and MPa 633 and MPa 639 have the least hardness and tensile strength and the highest strength and hardness of sampled 3 and 9 with 166 and 161 hardness and tensile strength MPa 703 and MPa 695.