University of Groningen
Resistance spot welding of advanced high strength steels
Chabok, Ali
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Publication date:
2019
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Citation for published version (APA):
Chabok, A. (2019). Resistance spot welding of advanced high strength steels: Mechanical properties and
failure mechanisms. University of Groningen.
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The research presented in this thesis was performed in the Advanced Production Engineering (APE) group of Engineering and Technology institute Groningen (ENTEG) and Materials Science Group of Zernike Institute for Advanced Materials at the University of Groningen, The Netherlands.
This research was carried out under Project Number T22.7.13508 in the framework of the Partnership Program of the Materials innovation institute M2i (www.m2i.nl) and the Technology Foundation TTW (www.stw.nl), which is part of the Netherlands Organization for Scientific Research (www.nwo.nl).
Front cover: Cross section of a double pulse resistance spot weld of DP1000 steel. Stitched [001] inverse pole figure, optical micrograph and kernel average misorientation maps.
Back cover: Notched micro-cantilever bending used to measure the fracture toughness at micro-scale.
ISBN: 978-94-034-1451-5 (Printed version) ISBN: 978-94-034-1450-8 (Electronic version) Print: Zalsman Groningen B.V.
Resistance Spot Welding of
Advanced High Strength Steels
Mechanical Properties and Failure Mechanisms
PhD thesis
to obtain the degree of PhD at the
University of Groningen
on the authority of the
Rector Magnificus Prof. E. Sterken
and in accordance with
the decision by the College of Deans
This thesis will be defended in public on
Monday 18 March 2019 at 11.00 hours
by
Ali Chabok
born on 10 September 1984
in Shabestar, Iran
Supervisors
Prof. Y.T. Pei
Prof. J.Th.M. de Hosson
Assessment Committee
Prof. I.M. Richardson
Prof. L.A.I. Kestens
Prof. P.R. Onck
Dedicated to my parents, my wife
and
to my all mentors
Contents
Chapter 1 Introduction ... 1
1.1 Resistance spot welding ... 1
1.2 Advanced high strength steels ... 3
1. 2.1 DP steels ... 5
1.3 Problem definition ... 7
1.4 Outline of the thesis ... 8
Reference ... 9
Chapter 2 Resistance spot welding of AHSS - a literature review
... 11
2.1 Resistance spot weld attributes ... 12
2. 2 Mechanical testing of resistance spot welds ... 15
2.3 Stress distribution and damage mechanism during mechanical testing ... 19
2.4 Microstructural evolution and hardness distribution in FZ ... 26
2.5 HAZ softening ... 30
2.6 Segregation ... 33
2.7 Weld fracture toughness ... 35
2.8 Failure mode prediction ... 36
2.9 Conclusion ... 38
Reference ... 39
Chapter 3 Weld scheme effect - microstructure and mechanical performance ... 43
3.1 Introduction ... 44
3. 2 Experimental ... 45
3. 3 Results and discussion ... 46
3.3.1 Mechanical properties ... 47
3.3.2 Microstructure of the sub-critical heat affected zone ... 48
3.3.3 Crystallographic features of martensite ... 51
3.4 Conclusion ... 59
Reference ... 60
4.1 Introduction ... 64
4. 2 Experimental ... 64
4. 3 Results and discussion ... 65
4.3.1 Residual stress ... 67
4.3.2 Weld cross section and hardness distribution ... 74
4.3.3 Crystallographic features of martensite ... 76
4.4 Conclusion ... 81
Reference ... 82
Chapter 5 Micro-mechanical characterization ... 83
5.1 Introduction ... 84
5. 2 Experimental ... 85
5. 3 Results and discussion ... 86
5.3.1 Microstructure ... 86
5.3.2 Mechanical properties ... 87
5.3.3 Fracture toughness ... 89
5.4 Conclusion ... 98
Reference ... 98
Chapter 6 Effect of chemical composition ... 101
6.1 Introduction ... 102
6. 2 Experimental ... 103
6. 3 Results and discussion ... 104
6.3.1 Microstructural evolution ... 104
6.3.2 Mechanical properties ... 110
6.4 Conclusion ... 117
Reference ... 118
Chapter 7 3rd generation AHSS resistance spot weld ... 119
7.1 Introduction ... 120
7. 2 Experimental ... 121
7. 3 Results and discussion ... 122
7.3.2 Effect of PB ... 125
7.3.3 Effect of weld scheme ... 126
7.3.3 Micromechanical properties ... 131 7.4 Conclusions ... 144 Reference ... 144 Summary ... 147 Samenvatting ... 151 Publications ... 155 Acknowledgment ... 157
