In present-day automobiles, new high-strength steel grades are being extensively utilized, which have different alloy concentration, microstructure and properties, and results in different spot welding behavior. In the present work, the effect of weld current was studied on four widely used automotive grades, such as IF 270, TRIP 690, DP 780 and TRIP 980, in a laboratory welding machine. The welding current was varied between 5 and 15 kA. Weld quality was assessed based on tensile shear, mode of failure, weld nugget diameter, metallographic observations and hardness tests. Experimental results showed that weld strength increased with an increase in base metal tensile strength but with a drop at the point of expulsion. Variation in hardness along the cross section was found to be higher in high-strength steels. The initial microstructure and phase transformation during cooling affected the final properties. Critical currents for peak strength, expulsion, sticking and failure mode transition were determined for each grade for industrial applications. This study helped in determining the criterion-based optimized welding parameters for specific applications of these automotive-grade steels.

在当今的汽车中，新的高强度钢种正在被广泛使用，它们具有不同的合金浓度，微观组织和性能，并导致不同的点焊行为。在当前的工作中，在实验室焊接机中研究了四种电流广泛使用的汽车级焊接电流的影响，例如IF 270，TRIP 690，DP 780和TRIP 980。焊接电流在5至15 kA之间变化。焊缝质量基于拉伸剪切，破坏模式，焊核直径，金相观察和硬度测试进行评估。实验结果表明，焊接强度随母材抗拉强度的增加而增加，而在驱出点则有所下降。发现在高强度钢中沿横截面的硬度变化较高。冷却过程中的初始微观结构和相变影响了最终性能。确定了用于工业应用的每个等级的峰值强度，排出，粘着和破坏模式转变的临界电流。这项研究有助于确定针对这些汽车级钢的特定应用的基于准则的优化焊接参数。