Study On Resistance Spot Welding Technology And The Properties And Microstructure Of Q235B Steel Sheet Joints

Resistance spot welding is one of the most important resistance welding technologies, which has advantages of high production rate, being convenient for mechanization and automation etc. So this technology was applied in the practical production and scores of research on its theory has been carried out by the investigators. Although, the study on spot welding of identical material under different welding standards has been merely reported yet. In this thesis, three varieties of welding standards were chosen to apply on type Q235B steel sheet in the spot welding process. Otherwise, the effect of welding current on the properties and microstructure of welded joint was investigated, with the purpose of providing experimental basis that used for selecting proper welding parameter and standards in practical production.In the thesis, resistance spot welding technology was applied under different welding standards to conduct a test on type Q235B steel sheet respectively. After that, a tensile experiment was carried out in all the welded joints and fracture of typical welded joint was observed. And then, partial welded joints were chosen to test their weld nugget sizes on the base of tensile experiment, proceeding with synthetical analysis to acquire optimal welding parameter. Make a study of the influence of welding standard on the weld nugget morphology and microhardness. ANSYS method was adopted to analyse the resistance spot welding process of preloading contact of type Q235B steel sheet.The results show that : Both tensile strength and microhardness of welded joints begin to increased and then decrease with the increasing of welding current, Weld nugget diameter and indentation depth increase with increasing of welding current, coarse grain was obtained under strong welding current;Quality joints break at HAZ evenly, the fracture surface under hard welding standards is apt to assume brittle fractrue and tough break under soft welding standards;It's can get satisfactory properties of welded joints under all the different welding standards; The phenomenon of easily abrasion on the surface of tip end in spot welding experiment is contributed to stress concentration on this area, It is also found when the contact area between two workpieces is greater than the area between electrode and workpiece, the contact pressure is more well-distributed,the peak value of contact pressure between two workpicecs is closer contact with the contact area centre.