J. Mater. Sci. Technol. ›› 2018, Vol. 34 ›› Issue (4): 720-731.DOI: 10.1016/j.jmst.2017.06.015

• Orginal Article • Previous Articles     Next Articles

Transition and fracture shift behavior in LCF test of dissimilar welded joint at elevated temperature

Xiongfei Wanga, Chendong Shaoa, Xia Liub, Fenggui Lua*()   

  1. aShanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University,Shanghai 200240, China
    bShanghai Turbine Plant of Shanghai Electric Power Generation Equipment Co. Ltd., Shanghai 200240, China
  • Received:2017-01-03 Revised:2017-04-25 Accepted:2017-06-08 Online:2018-04-20 Published:2018-05-04
  • Contact: Lu Fenggui

Abstract:

This work focused on the low-cycle fatigue (LCF) behavior of modified 9Cr/CrMoV dissimilar welded joint at elevated temperature. Narrow gap submerged arc welding (NG-SAW) process via multi-pass and multi-layer techniques was employed to fabricate the welded joint. LCF tests at different strain amplitude range from 0.22% to 0.75% were performed at strain ratio R = -1. The two-slope behavior based on fracture location shift was presented both on the cyclic stress-strain (CSS) curve and Manson-Coffin (M-C) curve, which could be applied to predict the fatigue life more precisely especially at relatively low strain amplitude. The results indicated that the joint failed in CrMoV-base metal (BM) at relatively low strain amplitude below 0.4% while failure shifted to CrMoV-over tempered zone (OTZ) at higher strain amplitude above 0.4%. Fatigue failure occurred in CrMoV-BM at low strain amplitude could be attributed to temperature softening effect in CrMoV-BM combined with cyclic strengthening in CrMoV-OTZ. While CrMoV-OTZ with a comparable number of grain boundaries and much lower hardness than that of CrMoV-BM was deemed to be the weakest zone across the welded joint at higher strain amplitude. EBSD investigations also revealed that CrMoV-BM experienced more fatigue damage at relatively low strain amplitude, while CrMoV-OTZ accumulated more plastic strain at higher strain amplitude.

Key words: Low-cycle fatigue, 9Cr/CrMoV dissimilar welded joint, Elevated temperature, Fracture transition, EBSD analysis