DefinePK

Abstract

The objective of this study is to investigate the effects of welding parameters in the welding process on the mechanical properties and micro structure to compare the design of experiment (DOE) for the high-frequency resistance welding process (HFRW) of ASTM SA-192high-carbon steel. The different butt weld T joints of finned-tubes were prepared by varying the welding parameters, including current (A), voltage (kV) and frequency (rpm) which were also related to the heat input and mechanical properties. DOE analysis of the welding parameters was performed at 9A, 13kV, 250 rpm and heat input of 474 J/mm. The results showed that the ultimate tensile strength was 749 MPa which meets the standard requirements of the Association of Finned Tube Manufacturers and is at a good level in the production viewpoint. However, the examination of the micro-and macrostructure of the weld line using an inverted microscope showed some melting on the specimens and it was found that some specimens had high weld width and weld depth. In addition, the tensile strength was also higher. However, too high tensile strength was changed the material structure, the cause of HAZ. Through the validation of the welding process which was compared to the fatigue strength, the following results were indicated: (1) the ultimate tensile strength at the highest tensile stress was not the ultimate fatigue strength and the heat input affected the weld width and weld depth of the weld line. (2) In the welding process, the weld width and weld depth must be also considered since they can affect the specimen failure during the experiment. Therefore, extreme care must be taken when using a high-frequency resistance welding process.