Process Adjustments to Improve Fracture Behaviour in Resistance Spot Welds of EHSS and UHSS
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In recent years new types of sheet steels, combining higher strength with better ductility have been developed. Some of these steels have shown limited weldability compared to mild steels. The hardness of the welds for these steels stretches from 380 HV for DP 600 to approximately 500 HV for TRIP (Transformation Induced Plasticity) and boron steels. Static peel tests of eight types of steels resulted in plug failures for the DP 600 steels, but some interfacial failures for higher strength steels. Generally, welds with a hardness exceeding 400–450 HV caused unstable fractures. To modify the hardness of the weld an in-process tempering of weld martensite was performed on a TRIP steel. Guidance to a proper tempering pulse was obtained through simulation of phase transformation and cooling of the weld. Welding experiments showed that the weld hardness could be reduced to approximately 350 HV, i.e. below the limit where interfacial failures start to occur.
IIW-Thesaurus keywordsResistance welding Spot welding In Process Tempering, Welded joints Spot welds Hardness High strength steels Tensile tests Peel tests Martensite Tempering Heat treatment Simulating Fractures Failure Experiment design Practical investigations blReferences
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- 1.Cretteur, L., Koruk, A.I.: Doc. III-1218-02 Improvement of weldability of TRIP Steels by use of in-situ pre- and post-heat treatment. 55th Annual Assembly of the International Institute of Welding (IIW) 2002.Google Scholar
- 2.Peterson, W.: Dilution of weld metal to eliminate interfacial fractures of spot welds in high and ultra high strength steels. Inland Steel Flat Products Company, Research and Development Department.Google Scholar
- 3.Chuku, W.L., Gould, J.E.: Development of appropriate resistance spot welding practice for transformation-hardened steels. Welding Journal Research Supplement, January 2002.Google Scholar
- 4.Eliasson, M.: Improvement of mechanical properties of laser-welded Trip 700, Volvo Materials Technology, ER-503968.Google Scholar