Influence of Weld Imperfections on the Fatigue Behaviour of Resistance Spot Welded Advanced High Strength Steels

2014 ◽  
Vol 891-892 ◽  
pp. 1445-1450 ◽  
Author(s):  
Michael Rethmeier
Keyword(s):  
Fatigue Life ◽  
High Strength Steels ◽  
High Strength ◽  
Fatigue Behaviour ◽  
Whole Body ◽  
Surface Cracks ◽  
Significant Drop ◽  
Resistance Spot ◽  
Advanced High Strength Steels ◽  
Body In White

The use of advanced high strength steels (AHSS) in the automotive body-in-white is increasing. Those steels are predominantly joined by resistance spot welding. For the performance of the whole body-in-white, the fatigue behaviour is of high interest, especially as during production, weld imperfections such as cracks and manufacturing-related gaps cannot be avoided. In this study the TRIP steel HCT690 was used as it is a typical advanced high strength steel in automotive production. The investigation into the influence of cracks was split depending on the crack location in the weld area. Surface cracks in the electrode indentation area as well as in the heat affected zone were produced during welding and analyzed. The results showed that surface cracks independent of their position have no effect on the fatigue life. The produced internal imperfections have shown only a marginal impact on the fatigue life. It was ascertained that gaps of 3 mm lead to a significant drop in fatigue life compared to gap free shear tension samples under a load ratio R of 0.1. This fact was attributed to decreased stiffness, higher transverse vibration and higher rotation between the sheets. Furthermore, FE-simulations have shown an increase in local stresses in gapped samples.

Relationship between Microstructure and Mechanical Properties in Q&P-Steels

2016 ◽  
Vol 879 ◽  
pp. 1933-1938 ◽  
Author(s):  
Richard G. Thiessen ◽  
Georg Paul ◽  
Roland Sebald
Keyword(s):  
Mechanical Properties ◽  
Dual Phase Steel ◽  
High Strength Steels ◽  
High Strength ◽  
The Body ◽  
Advanced High Strength Steels ◽  
Passenger Safety ◽  
Back Scattering ◽  
Body In White ◽  
Expected Increase

Third-Generation advanced high strength steels are being developed with the goal of reducing the body-in-white weight while simultaneously increasing passenger safety. This requires not only the expected increase in strength and elongation, but also improved local formability. Optimizing elongation and formability were often contradictory goals in dual-phase steel developments. Recent results have shown that so-called "quench and partitioning" (Q&P) concepts can satisfy both requirements [1]. Many Q&P-concepts have been studied at thyssenkrupp Steel Europe. Thorough investigation of the microstructure has revealed relationships between features such as the amount, morphology and chemical stability of the retained austenite and the obtained mechanical properties. An evaluation of the lattice strain by means of electron-back-scattering-diffraction has also yielded a correlation to the obtained formability. The aim of this work is to present the interconnection between these microstructural features and propose hypotheses for the explanation of how these features influence the macroscopically observed properties.

scholarly journals Liquid Metal Embrittlement of Galvanized TRIP Steels in Resistance Spot Welding

Metals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 787 ◽  
Author(s):  
Wook-Sang Jeon ◽  
Ashutosh Sharma ◽  
Jae Pil Jung
Keyword(s):  
Liquid Metal ◽  
Resistance Spot Welding ◽  
Spot Welding ◽  
High Strength Steels ◽  
High Strength ◽  
Liquid Metal Embrittlement ◽  
Surface Cracks ◽  
Resistance Spot ◽  
Research Activities ◽  
Microscopic Features

Liquid metal embrittlement (LME) in Zn-coated steels is a serious issue in automotive design. The risk of rising LME surface cracks in resistance spot welding (RSW) of Zn-coated high strength steels has triggered significant research activities across the globe. This paper presents a state-of-the-art review of the various phenomena and issues related to LME during RSW. Various aspects of LME surface cracks have been described in this review, focusing on the macro- and microscopic features of LME, spot weld cracks, the sensitivity of the LME cracks towards surface locations, welding conditions, and susceptibility to high strength and galvanized steels. We also focus on the effects of various processing factors, such as temperature, stress, microstructure, and the nature of the galvanized layer, related to studies with actual spot welds LME cracks. Finally, we summarize the possible mechanisms of embrittlement and the remedies for minimizing LME cracks, with suitable guidelines to suppress surface cracks during RSW.

Resistance spot welding and weldbonding of advanced high strength steels

2010 ◽  
Vol 41 (11) ◽  
pp. 931-939 ◽  
Author(s):  
G. Weber ◽  
H. Thommes ◽  
H. Gaul ◽  
O. Hahn ◽  
M. Rethmeier
Keyword(s):  
Resistance Spot Welding ◽  
Spot Welding ◽  
High Strength Steels ◽  
High Strength ◽  
Resistance Spot ◽  
Advanced High Strength Steels
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