4.7 Article

Mechanical properties and fracture behaviors in remote laser spot welding of quenching and partitioning 980 steel

Journal

OPTICS AND LASER TECHNOLOGY
Volume 140, Issue -, Pages -

Publisher

ELSEVIER SCI LTD
DOI: 10.1016/j.optlastec.2021.107053

Keywords

Quenching and partitioning steel; Remote laser spot welding; Mechanical properties; Fracture behavior; Orientation imaging microscopy

Funding

  1. Chinese Academy of Sciences [292017312D1100301]
  2. Shanghai Municipal Economic and Informatization Commission [GYQJ-2019-1-33]

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Quenching and partitioning (Q&P) steel is a critical material in the automotive industry due to its excellent mechanical properties and potential for weight reduction. However, poor weldability has been a bottleneck for its application. This study successfully welded Q&P steel using a newly-developed remote laser spot welding (R-LSW) process, revealing key stages and failure mechanisms during the welding process.
Quenching and partitioning (Q&P) steel is one of most critical third generation steels in the automotive industry, which provides excellent mechanical properties and have a huge potential to significantly reduce vehicle weight and improve fuel efficiency. One of the bottlenecks for their applications in the automotive industry is the poor weldability. In this paper, a newly-developed remote laser spot welding (R-LSW) process was used to weld Q&P steel with laser beam moving along a spiral path. The welds with full penetration were obtained with laser power ranged between 2400 W and 3600 W, the weld morphology and mechanical properties of the joints were consistent, except for a little drop in case of 3600 W with the crater size of 0.65 mm. Under the shear tensile force, all the welds failed in partial thickness-partial pullout (PT-PP) mode, which was attributed to the formation of a large weld diameter. The weld failure process can be divided into four stages: (I) crack initiation; (II) crack propagation along the thickness and circumference of the joint; (III) crack propagation along the circumference of the joint; and (IV) instantaneous fracture. Furthermore, it was found that the coarse grain heat affected zone (CG-HAZ) has a lowest fraction of high-angle grain boundaries (HAGBs), resulting in the crack propagated along the CG-HAZ during stage II. During crack propagation, the fracture took place as a ductile fracture, but the instantaneous fracture occurred in quasi-cleavage characteristic.

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