Study On The Geometric Structure And Mechanical Performance Of Resistance Spot Welding Cold-rolled 301L Joints

The traditional theory of spot welding technology are based on the research results of steady-state alloy, which believes the spot welding specimen's carrying capacity is low and fracture absorbed energy is small when its fracture mode is interfacial fracture. Traditional theory proposes to use pull-out fracture mode which it thinks has better performance. The diameter of JIS Z 3140 recommended is d=5(?) which can make sure nugget achieve pull-out fracture. But to high-strength 301L cold-rolled sheet, specimens with the diameter of JIS Z 3140 recommended can't achieve pull-out fracture, and the strength of pull-out fracture does not higher than the strength of interfacial fracture.In this thesis, the research objects are the main bearing spot-welded joints of the railway stainless steel car body. Resistance spot welded tensile shear specimens with three nugget diameters 5(?),6(?),7(?) were prepared with low and high strength cold-rolled 301L plates. The static overload and fatigue examinations of the spot welds were conducted to investigate the effects of nugget diameters on their mechanical properties and failure mode.The results showed that, to 301L cold rolled plate, static tensile shear strength increased with nugget diameter and the weld defects had little effect to the value of static strength. All spot welded high strength plates were completely interfacial failure, and their static ultimate loads increased linearly with the nugget diameters. Only part of spot welded low strength plates with nugget size 7(?) came out pull-out failure, the ultimate loads were lower than that of those fractured by interfacial failure. Anti-fatigue properties of four combination samples increased with nugget diameter and this effect in thick plate spot welding was more obvious. The spot welding samples which nugget diameter of 6(?) had better performance of technology and machinery. Doing system of static shear and fatigue tests with these samples to research deformation behavior and fatigue limit of different combinations of plate and reliability of spot welded joint. The research data and results can provide the basis reference for the design and manufacture of stainless steel car.