Effect of Double Pulse Resistance Spot Welding Process on 15B22 Hot Stamped Boron Steel

Abstract

Double pulse resistance spot welding process by applying a second step welding current is a new pathway to alter the mechanical properties for advanced high strength steels. Herein, the resistance spot welding (RSW) of hot stamped boron steel 15B22 by one-step and two-step welding with different welding currents is investigated. The results of the tensile–shear test, size of the weld nugget, hardness distribution, microstructure, and failure mode of different welding parameters are analyzed. The weldment of the two-step RSW with a higher heat input exhibits a lower tensile–shear load and lower fracture energy when the size of the weld nugget is large. The microstructural study reveals the appearance of a partially melted zone and sub-critical heat affected zone in the weldment where the fracture readily occurred. Thus, the two-step RSW process weakens the strength of the sample, which is attributed to the partial softening in the weldment due to the higher heat input.

Double Pulse Resistance Spot Welding of Dual Phase Steel: Parametric Study on Microstructure, Failure Mode and Low Dynamic Tensile Shear Properties

“…This indicates that a certain amount of heat is retained in the weldment at the end of cooling, which supplements the total heat input. Aghajani et al [21] and Lee et al [33] reported similar observations that the FZ size increases using double pulse RSW.…”

“…It can be observed that welds (i.e., SPW, sample 1, sample 2, sample 3, sample 4, sample 5, sample 6, sample 9 and sample 13) failed in the IF mode, while other welds failed in the PF/PIF/PTPP modes. Lee et al [ 33 ] also reported that double-pulse RSW results in higher heat input, which in turn affects the weld size, microstructure of the HAZ and failure mode. Increasing heat input during the second pulse intensifies the martensite tempering both in the FZ and the HAZ.…”

“…However, more softening is observed in the SCHAZ compared to other regions of the weld, which in turn improve the toughness of weldment. It is well known that softening reduces the strength of the SCHAZ and results in strain localization, and hence encouraged the PF mode [ 6 , 33 ]. Moreover, Figure 14 also indicates that the conventional weld size criterion based on D = 5√t is not sufficient to produce the PF mode.…”

“…Moreover, Figure 14 also indicates that the conventional weld size criterion based on D = 5√t is not sufficient to produce the PF mode. Heat input is the dominant factor that causes the failure mode to change from IF to PF during in situ PWHT [ 33 ]. Spot welds that experienced lower heat input failed in the IF mode with low peak load and failure energy compared to welds experiencing higher heat input and failure in PF/PIF/PTPP mode.…”

An Exploratory Study on Resistance Spot Welding of Titanium Alloy Ti-6Al-4V

“…To define the best quality of Ti-6Al-4V weld nugget strength, it is important to investigate the weld nugget’s physical and mechanical properties. The RSW parameters such as the welding current, time, and force are proved to be the most significant affected parameters to develop the weld nugget properties [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Similar materials with different thicknesses were previously studied [ 23 , 24 ].…”