Fatigue Behaviors of Resistance Spot Welds for 980 MPa Grade TRIP Steel

Abstract

The fatigue life of the resistance spot weld of 980 MPa grade transformation induced plasticity (TRIP) steel was investigated and failure modes and fracture surfaces according to the fatigue load were analyzed. The fatigue life according to the nugget size was observed by using two electrodes with face diameters of 8 mm and 10 mm. When an electrode face diameter with 10 mm was used, the nugget size was large, and the fatigue life was further increased. After the fatigue test, three types of failure modes were observed, namely pull-out, plug, and heat affected zone (HAZ) failure, depending on the fatigue load. The fracture surfaces in each failure mode were analyzed. In all failure modes, a crack was initiated in the HAZ region, which is the interface between the two materials in all failure modes. In the case of pull-out failure, the crack propagates as if it surrounds the nugget at the outer edge of the nugget. In the case of HAZ failure, the crack propagates in the thickness direction of the material and outward in the nugget shell. Plug failure occurs with pull-out failure and HAZ failure mixed. The propagation patterns of cracks were different for each failure mode. The reason why the failure mode and the fracture surface are different according to the fatigue load is that the propagation speed of the fatigue crack is fast when the fatigue load is relatively large and is slow when the fatigue load is low.

A shrinkage-based criterion for evaluating resistance spot weldability of alloyed steels

“…1 from Refs. ( 19 , 27–31 , 47–55 ) and 4 , from Refs. ( 19 , 27–31 , 47–59 ) respectively, together with the corresponding fracture mode of RSW nugget in TS test.…”

“…( 19 , 27–31 , 47–55 ) and 4 , from Refs. ( 19 , 27–31 , 47–59 ) respectively, together with the corresponding fracture mode of RSW nugget in TS test. Alloy content is the sum of weight percentages of all the elements included in these equations except for C.…”

“…In addition, it was found that the paint baking after RSW can significantly improve the CT strength in the dissimilar MMS/dual phase (DP) steel weldment ( 24 ), hinting that the low-temperature tempering of martensite may indeed improve weldability. Nevertheless, the PF could be achieved during the RSW of TRIP steel ( 27 ), DP steel ( 28 ), and martensitic steel ( 29 , 30 ) without tempering or baking, i.e. the tempering of martensite in nugget is not necessarily required for improving weldability.…”

Study on microstructures and fatigue behavior of dissimilar Al/steel resistance spot welded joint

“…Therefore, the study on fatigue performance of spot welded joints is a major issue that must be solved in the durability design of the whole body structure. The traditional automobile body plate is usually made of low carbon steel, high alloy steel, and high strength steel; the research on the spot welded joint performance mainly focuses on the joints with various steel plates as the base metal for a long time 16–20. In the published literature, the analysis about fatigue behavior on dissimilar material Al/steel spot welded joint was rare.…”

“…carbon steel, high alloy steel, and high strength steel; the research on the spot welded joint performance mainly focuses on the joints with various steel plates as the base metal for a long time. [16][17][18][19][20] In the published literature, the analysis about fatigue behavior on dissimilar material Al/steel spot welded joint was rare. Ibrahim et al 21 investigated the fatigue behavior of A6061 aluminum alloy/304 stainless steel joint fabricated by resistance spot welding with Al-Mg interlayer.…”