Acta Metallurgica Sinica (English Letters) ›› 2020, Vol. 33 ›› Issue (11): 1556-1570.DOI: 10.1007/s40195-020-01125-w

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Microstructure and Mechanical Properties of Low-Carbon Q235 Steel Welded Using Friction Stir Welding

Hongduo Wang1,3, Kuaishe Wang1,2(), Wen Wang1,2(), Yongxin Lu3, Pai Peng1,2, Peng Han1,2, Ke Qiao1,2, Zhihao Liu1,2, Lei Wang3   

  1. 1School of Metallurgical Engineering, Xi’an University of Architecture and Technology, Xi’an, 710055, China
    2National and Local Joint Engineering Research Center for Functional Materials Processing, Xi’an, 710055, China
    3School of Materials Science and Engineering, Xi’an Shiyou University, Xi’an, 710065, China
  • Received:2020-04-19 Revised:2020-06-14 Accepted:2020-06-18 Online:2020-11-10 Published:2020-11-17
  • Contact: Kuaishe Wang,Wen Wang

Abstract:

This study focuses on the microstructure and mechanical properties of the joints of Q235 mild steel, which was formed by the friction stir welding (FSW). The results indicated that, after the FSW, the heat-affected zone (HAZ) of the retreating side (HAZRS) and the HAZ of the advancing side (HAZAS) recovered under the influence of the heating cycle. The transformation of the phases in the thermo-mechanically affected zone (TMAZ) of the retreating side (TMAZRS), the stir zone (SZ) and the TMAZ of the advancing side (TMAZAS) generated the pearlite and acicular ferrite. The continuous dynamic recrystallization occurred in all the three zones, whereas the grains were refined. The SZ mainly consisted of D1, D2 and F shear textures, while the TMAZAS was made up of only the F shear texture. The fine-grained structure, pearlite and the acicular ferrite improved the hardness and tensile strength of the joint. Its ultimate tensile strength was 479 MPa, which was 1.3% higher than that of the base metal. However, the uniform elongation was 16%, which showed a decrease of 33%. The fracture was a ductile fracture with the appearance of dimples. Besides, the joints of the FSW showed an excellent bending performance.

Key words: Low-carbon steel, Friction stir welding, Recrystallization, Phase transformation, Mechanical properties