Determination of continuous constitutive relationship of weld zone of high-strength steel rectangular welded tube
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ORIGINAL PAPER
Determination of continuous constitutive relationship of weld zone of high‑strength steel rectangular welded tube Hai‑long Liu1,2 · Yu‑li Liu1,2 · Zhong Yang2 · Kun Wang2 · Meng‑meng Liu1,2 Received: 22 November 2019 / Revised: 15 March 2020 / Accepted: 17 March 2020 © China Iron and Steel Research Institute Group 2020
Abstract For QSTE700 high-strength steel rectangular welded tube, the mechanical properties of the weld zone vary with the distance from the centerline of the weld. Therefore, the accurate description of constitutive relationship of the weld zone is of great significance for the study of formability of QSTE700 rectangular welded tube. Firstly, the mechanical properties of parent and mixed specimens containing weld zone and parent zone were obtained by uniaxial tensile test. And based on the microhardness test, the width and the microhardness distribution of the weld zone were determined. Secondly, by subdividing the weld zone into several small areas, and combining with the rule of mixtures and nanoindentation test, the continuous functional relationships of strength coefficient K, hardening coeffecient n and elastic modulus E were obtained, and then, the continuous constitutive relationship of QSTE700 rectangular welded tube was established. Finally, the validity and reliability of the continuous constitutive relationship of welded tube were verified by nanoindentation test and rotary draw bending of rectangular welded tube. Besides, it was found that the finite element model of rotary draw bending of QSTE700 rectangular welded tube established by using the continuous constitutive relationship can well simulate the cross section deformation and wall thickness variation. Keywords QSTE700 high-strength steel rectangular welded tube · Continuous constitutive relationship · Nanoindentation test · Rotary draw bending process · Cross section deformation · Wall thickness variation
1 Introduction With the demand of environmental energy conservation and protection, thin walled welded tubes have been widely used in automotive industry because of its low manufacturing cost and high strength [1, 2]. QSTE700 high-strength steel rectangular welded bent tube plays a great important role in reducing the weight and enhancing the safety of automotive body structures. However, in the welding process of tubes, different peak temperatures and cooling rates inevitably lead to inhomogeneous tissue region near the weld line [3], and actually the hardness varies continuously from * Yu‑li Liu [email protected] 1
Research and Development Institute of Northwestern Polytechnical University in Shenzhen, Shenzhen 518057, Guangdong, China
State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, Shaanxi, China
2
the weld centerline to the parent [4, 5], so that mechanical properties such as elastic modulus and plastic parameters also vary continuously from the weld centerline to the parent [6]. Therefore, it is nec
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