| Due to its few of nickel element content, TTS443 ferritic stainless steel has low price, good mechanical properties and corrosion resistance. It is widely used in transportation, elevator decoration, kitchen utensils, holding tanks and so on. However, the stainless steel welding heat-affected zone TTS443 ferrite grain growth leading to a sharp decline in the performance of welded joints, to a certain extent, limits the promotion TT443 steel. In the actual production process, especially on important parts of the car, mostly manufactured by resistance spot welding sheet completed. Therefore, the research on the resistance spot welding process of ferritic stainless steel sheet structure for TTS443 is important to promote the use of steel.In this work, microstructural characteristics and properties of the TTS443 FSS resistance spot welding are investigated, temperature field of spot welding joints can be obtained by finite element simulation method, then combined with the equilibrium phase diagram of the joint microstructure characteristics、grain growth and precipitates are studied, On this basis, the effects of heat input on weld nugget size、microstructure and mechanical properties of resistance spot welded joints were analyzed to provide a theoretical basis for its practical application.TTS443 ferritic stainless spot-welding process finite element model is established by using ABAQUS finite element software, TTS443 ferritic stainless steel resistance spot welding model can achieve thermal- electricity-three direct coupling calculation which to give an electric field, temperature field analysis results of RSW. Through comparing simulation results and the actual weld nugget specimen shape and size, rationality of resistance spot welding model and accuracy of resistance spot welding simulation results can be proved.The model couples between the displacement, temperature, and electrical potential fields makes it necessary to obtain solutions for all three fields simultaneously; It can achieve the strong interactions during the spot welding process involving the thermal, electrical and mechanical phenomena. The model takes into the temperature-dependent material properties and the thermal-electricity-mechanical field interactions account.Based on the accuracy of numerical results, the current density and variation of temperature distribution in the joint spot welding process was revealed, the nugget formation process discussed. Combined with experimental results, the microstructure of resistance spot welding joints, grain growth behavior、the effect of precipitates(Ti N) on the grain growth mechanism were analyzed.Four welded joints in different welding power: 3.2k VA, 4.8k VA, 6.4k VA 8.0k VA were prepared by resistance spot welding process. Calculated nugget diameter under different heat input conditions were 1.68 mm, 2.74 mm, 3.44 mm, 3.93mm; According to the welding heat cycle curve and grain growth formula,the grain size of weld heat-affected zone in the different heat input were calculated: 50.13μm, 56.15μm, 64.75μm, 72.27μm.Mechanical test results show that hardness of weld nugget、HAZ in the resistance spot welding joint increases with increasing welding heat input. weld nugget size effected by welding heat input plays an important role in the mechanical properties of steel TTS443 resistance spot welding joints, The specific performance was reflected in the peak load, fracture energy and fracture mode. With increasing heat input welding, spot welding joints peak load and fracture absorbed energy were increased, failure mode of welded joints transformed from the interfacial failure to the pullout failure. In the conditions of welding heat input 6.4k VA, tensile properties of spot welding joints is good, fatigue strength of spot welding joints is 46.1MPa. |
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