冷轧301LN等厚和不等厚板电阻点焊接头的疲劳强度

Fatigue Strength of Similar and Dissimilar Thickness Single-point Resistance Spot Welding Samples of 301LN Cold Rolled Stainless Steel

研究2种强度等级的301LN冷轧奥氏体不锈钢等厚、不等厚板电阻点焊接头的疲劳性能,分析焊接工艺对疲劳性能的影响。由于301LN冷轧板点焊接头的组织性能差异较大,熔核和热影响区的屈服强度远远低于冷轧母材,并且热影响区存在结构应力集中,在低疲劳载荷作用下,热影响区仍有塑性应变发生,并积累位错滑移带,导致产生低应力疲劳裂纹。减少焊接热量输入保持热影响区晶粒细小,能提高热影响区的屈服强度并减小滑移带尺寸,有助于提高点焊试样的抗疲劳性能。本文5种冷轧板双面单点电阻点焊试样90%置信度、50%和99.9%存活率的疲劳极限与静拉伸载荷之比都低于15%,其中1.5+1.5 mm等厚薄板点焊试样的抗疲劳性能最好。

Fatigue properties of similar and dissimilar thickness single-point resistance spot welding samples of 301LN austenite stainless steel cold rolled sheets of two different degrees of strength are studied, and the effects of the welding process on fatigue properties are investigated. Due to the large differences of microstructures of the spot welded joints, HAZ（heat affected zone） and base steel in the welded area, the yield strength of the nugget and HAZ is much lower than that of the base steel. Further more, with severe structural stress concentration in HAZ, there occur plastic strains in HAZ at low cyclic loads; plastic deformation and slipping bands are accumulated to develop fatigue cracks at low average stresses. Reducing the welding heat input to obtain small grains in HAZ can increase the yield strength and reduce the sizes of slipping bands, which is helpful to raise the fatigue limits of the resistance spot welding samples. The ratio between the fatigue limits at both 99.9% and 50% survival rates and the static tensile strength is less than 15% for all test samples. The 1.5＋ 1.5 mm thick welded sample demonstrates the best fatigue limit.