Resistance Spot Welding Process And The Microstructures And Properties Of SUS301L Stainless Steel Joints

In modern society, with the rapid development of economics and culture, the processof urbanization is accelerating and the population density of the city is also increasing,which makes the public traffic fail to meet people’s daily needs. The railway train possessthe advantage of high speed and security performance, rarely late，as well as largeaccommodation of tourists, which can alleviate traffic pressure effectively.As the main material of railway trains, the SUS301L stainless steel has manysuperiorities，such as good anti-corrosive property, long service life， beautifulappearance, high strength, excellent resistance to wear, low costs and good weldability.Moreover, resistance spot welding is the main connecting method of the stainless steelcarriage body, which is easy to operate and can gain a high production.Based on the reasons above, this paper used the SUS301L stainless steel to carry outa series resistance spot welding experiments. The spot welding process parameter and themicrostructure and mechanical properties of the welded joint was investigated via thetests of metallographic structure, microhardness and the tensile test. The conclusions areas follows:（1）With the appropriate welding process parameters,the welded joint of SUS301Lstainless steel had smooth appearance without obvious deformation， homogeneousindentation and no damage surface.(2) The welded joint of SUS301L consisted nugget zone and heat affected zone(HAZ).The HAZ was made up of coarse equiaxed austenite grain which was not melted.The microstructure of nugget zone was epitaxial solidification, and generated lots ofcolumnar crystal, growing towards the direction of the weld center. The columnar crystalis perpendicular to the fusion line， and it stops growing in the middle of two plates dueto mutual resist eventually. (3)The microhardness curve of SUS301L welded joint was in the shape of ‘W’.Compared to the base metal, the microhardness of the HAZ and the weld joint was muchlower.(4) There were mainly two types of fracture mechanisms of SUS301L welded joint:interfacial fracture and button fracture.(5)The nugget diameter and the maximum tensile shear of joint showed increasingtendency as the welding current increased；the electrode force hindered the nuggetexpansion. The bigger electrode force, the smaller nugget diameter; with the increase ofthe welding time, the nugget diameter and the joint’s maximum tensile shear increased；comprehensive comparison, when welding current is6.0kA, welding time is14cyc, electrode force is4200N, diameter of nugget reached5.23mm, the nuggetpeeling occurs shear, tensile shear stress reached12.8kN, the quality of joint is good.