Corrosion Fatigue Life Predictive Model of 304 Stainless Steel from Tungsten Inert Gas Welding Process

Abstract

The austenitic stainless steel has been known for a good corrosion resistance and mechanical properties. For this reason, they are usually used in several fields such as welding process, food production, and medical equipment. In welding industry of stainless steel, problem of residual stresses occurring in the welded products is major concern, especially in distortion problem of a single-pass weld using tungsten inert gas (TIG) process. This thesis aims to study and analyze the corrosion fatigue under considering residual stresses occurring in the welded products of AISI 304 austenitic stainless steel from the TIG welding process. Moreover, relationship between the residual stresses and the corrosion fatigue was investigated. Experiment and simulation models were performed. Design of experiment (DOE) and research methodology were as follows; 1) In the TIG welding process of AISI 304 austenitic stainless steel, specimens of a single-pass butt weld joint with 150 mm of length are used, 2) To measure the residual stress occurring welded products, X-ray Diffraction (XRD) with measuring 6 points on the welded products is used, 3) Vickers Hardness number (HV) testing is performed to indicate surface hardness of welded products, 4) the corrosion fatigue test with axial stress constant fatigue load is used under 3.5% of NaCl condition at room temperature. FEA models were created using ANSYS software as 3D problems, using Birth & Death technique combined with the Goldak's double ellipsoid heat source. The hardness results showed that highest values were in the HAZ and then the values continuously decreased when the measured points shift out further. The average of HV numbers from the center of the weldment, were 168, 190, 190, 178, 179 and 182 respectively. The residual stress distribution result obtained from FEA model was compared with those obtained from the XRD measurement. It can be seen that, the distance between 0 to 40 mm, the transverse and longitudinal residual stresses results obtained from the XRD were greater than those of FEA model’ s. The magnitude of transverse residual stresses model FEA were -1 8 .0 5 MPa, 2 7 .3 5 MPa, -1 8 .9 7 MPa, - 15.23 MPa, -18.65 MPa, -25.27 MPa and longitudinal residual stress are -123.2 MPa., 186.9 MPa, -299.6 MPa, -204 MPa, -180.1MPa, and -1 5 7 .2 MPa, respectively. At the distance between 0.25 mm to 0.75 mm (HAZ), the residual stresses results were tensile. It was also found that, at the distance from 20 mm to 40 mm, both stresses results tend to be convergent to zero. In FEA models, the corrosion fatigue life presented the maximum value at 10.577×106 cycle occurring on the weld toe of the weldment, while the experiment result presented the corrosion fatigue life at 12×106 cycles. The percentage error of between the FEA model and the actual experiment was about 13.45%.