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Microstructure and properties of inter-critically reheated coarse grained heat-affected zones in X70 steels with different Ti/N ratios

Conference Paper


Abstract


  • This work investigates the effect of different levels of Ti, N and Ti/N ratios on microstructure and properties in the inter-critically reheated coarse grained heat affected zone (IC-CGHAZ) of double submerged arc welds (DSAW) in API 5L grade X70 pipe. Gleeble simulation was employed to reproduce the IC-CGHAZ of the real DSAW welds. Hardness and Charpy V-notch (CVN) tests were performed on the simulated samples. The microstructure of the simulated IC-CGHAZ was characterised by optical microscopy and scanning electron microscopy. LePera colour etching technique was employed to identify and quantify the martensitic-austenitic (M-A) constituent. Results show that the simulated IC-CGHAZ exhibited extremely low toughness, but in the studied range of the Ti and N, there was no correlation with Ti/N ratio. The beneficial effect of near-stoichiometric Ti/N ratio observed in CGHAZ did not translate to IC-CGHAZ. This was due to the negative effect of the blocky M-A constituent formed on prior austenite grain boundaries overriding the slight improvement arising from austenite grain size control.

UOW Authors


  •   Zhu, Zhixiong (external author)
  •   Kuzmikova, Lenka (external author)
  •   Li, Hui Jun.
  •   Barbaro, Frank (external author)
  •   Fletcher, Leigh L. (external author)
  •   Zheng, Lei (external author)
  •   Bai, Mingzhuo (external author)

Publication Date


  • 2015

Citation


  • Zhu, Z., Kuzmikova, L., Li, H., Barbaro, F., Fletcher, L., Zheng, L. & Bai, M. (2015). Microstructure and properties of inter-critically reheated coarse grained heat-affected zones in X70 steels with different Ti/N ratios. 9th Pipeline Technology Conference 2014 (pp. 1-13).

Start Page


  • 1

End Page


  • 13

Abstract


  • This work investigates the effect of different levels of Ti, N and Ti/N ratios on microstructure and properties in the inter-critically reheated coarse grained heat affected zone (IC-CGHAZ) of double submerged arc welds (DSAW) in API 5L grade X70 pipe. Gleeble simulation was employed to reproduce the IC-CGHAZ of the real DSAW welds. Hardness and Charpy V-notch (CVN) tests were performed on the simulated samples. The microstructure of the simulated IC-CGHAZ was characterised by optical microscopy and scanning electron microscopy. LePera colour etching technique was employed to identify and quantify the martensitic-austenitic (M-A) constituent. Results show that the simulated IC-CGHAZ exhibited extremely low toughness, but in the studied range of the Ti and N, there was no correlation with Ti/N ratio. The beneficial effect of near-stoichiometric Ti/N ratio observed in CGHAZ did not translate to IC-CGHAZ. This was due to the negative effect of the blocky M-A constituent formed on prior austenite grain boundaries overriding the slight improvement arising from austenite grain size control.

UOW Authors


  •   Zhu, Zhixiong (external author)
  •   Kuzmikova, Lenka (external author)
  •   Li, Hui Jun.
  •   Barbaro, Frank (external author)
  •   Fletcher, Leigh L. (external author)
  •   Zheng, Lei (external author)
  •   Bai, Mingzhuo (external author)

Publication Date


  • 2015

Citation


  • Zhu, Z., Kuzmikova, L., Li, H., Barbaro, F., Fletcher, L., Zheng, L. & Bai, M. (2015). Microstructure and properties of inter-critically reheated coarse grained heat-affected zones in X70 steels with different Ti/N ratios. 9th Pipeline Technology Conference 2014 (pp. 1-13).

Start Page


  • 1

End Page


  • 13