Modelling of austenite decomposition transformation of heat affected zone in API-X65 and X70 pipeline steels

Document Type : Research Paper

Author

• Gholamreza Khalaj

Islamic Azad University, Saveh Branch

Abstract

In this study, the simulation of the heat affected zone of welding was carried out based on the practical conditions of four-wire submerged arc welding in two X65 and X70 microalloy steel. Initially, thermal cycles of the heat affected zone were analyzed. By applying heating and cooling thermal cycles to peak temperatures of 950, 1150 and 1350 °C, in a dilatometric device, transformation behavior and microscopic structure were studied. With increasing peak temperature in transformation, despite the constant cooling rate (23 ° C / s) in the range of 800 to 500 ° C, the start and end temperatures of transformation are delayed and shear structures replace polygonal structures. The reasons are the coarsening of austenite grains, the dissolution of niobium carbide precipitates and the solute-drag effect of solved niobium in austenite.The size of the shear packs and the size of the austenite grains are also noticeably larger. By analyzing the dilatometry results, continuous cooling diagram and the kinetics of decomposition of austenite were investigated. Austenite decomposition modeling was performed using the JMAK classic equation. It was found that the parameter n has a small dependence on temperature; while the parameter k is strongly dependent to temperature, phase fraction transformed and austenite grain size. The results of modeling of phase transformations using the JMAK equation were in good agreement with the dilatometric results.

Keywords

• microalloyed steel
• heat affected zone
• Austenite
• dilatometry

20.1001.1.22285946.1397.9.33.11.5

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References

References: 1- T. Gladman, The Physical Metallurgy of Microalloyed Steels, The Institute of Materials, London, 2002.
2- B. Verlinden, J. Driver, I. Samajdar, R. D. Doherty, Thermo-Mechanical Processing of Metallic Materials, Elsevier, UK, 2007.
3- Y. Weng, Dong H., Gan Y. (editors), Advanced Steels The Recent Scenario in Steel Science and Technology, Springer-Verlag, Berlinm, 2011.
4- W. Sha, Steels: From Materials Science to Structural Engineering, Springer-Verlag, London, 2013.
5- K.E. Eaterling, Introduction to the Physical Metallurgy of Welding, Butterworth-Heinemann Ltd, Oxford, 1992.
6- K. Poorhaydari, B. M. Patchett, and D. G. Ivey, "Estimation of Cooling Rate in the Welding of Plates with Intermediate Thickness", Welding Journal, vol. 84, pp. 149S-155S, 2005.
7- D.P. Dunne, "Review: Interaction of precipitation with recrystallisation and phase transformation in low alloy steels", Materials Science and Technology, vol. 26, pp. 410-420, 2010.
8- P.R. Rios, "Relationship between non-isothermal transformation curves and isothermal and non-isothermal kinetics",
X و 70 X 136 مدلسازی دگرگونی تجزیه آستنیت در منطقهی متاثر از حرارت جوش دو فولاد خط لوله 65
Acta Materialia, vol. 53, pp. 4893-4901, 2005.
9- L.M. Fu, H.R. Wang, W. Wang, A.D. Shan, "Austenite grain growth prediction coupling with drag and pinning effects in low carbon Nb microalloyed steels", Materials Science and Technology, vol. 27, pp. 996-1001, 2011.
10- M. Shome, D.S. Sarma, O.P. Gupta, O.N. Mohanty, "Precipitate dissolution and grain growth in the heat affected zone of HSLA-100 steel", ISIJ International, vol. 43, pp. 1431-1437, 2003.
11- Sanjeev Kumar, S.K. Nath, Vinod Kumar, "Continuous cooling transformation behavior in the weld coarse grained heat affected zone and mechanical properties of Nb-microalloyed and HY85 steels", Materials & Design, vol. 90, pp. 177-184, 2016.
12- Yu Gu, Peng Tian, Xu Wang, Xiu-lin Han, Bo Liao, Fu-ren Xiao, "Non-isothermal prior austenite grain growth of a high-Nb X100 pipeline steel during a simulated welding heat cycle process", Materials & Design, vol. 89, pp. 589-596, 2016.
13- V.V. Natarajan, S. Liu, V.S.A. Challa, R.D.K. Misra, D.M. Sidorenko, M.D. Mulholland, M. Manohar, J.E. Hartmann, "Processing-structure-mechanical property relationship in Ti-Nb microalloyed steel: Continuous cooling versus interrupted cooling", Materials Science and Engineering: A, vol. 671, pp. 254-263, 2016.
14- F.L.G. Oliveira, M.S. Andrade, A.B. Cota, "Kinetics of austenite formation during continuous heating in a low carbon steel", Materials Characterization, vol. 58, pp. 256-261, 2007.
15- K. Banerjee, M. Militzer, M. Perez, X. Wang, "Nonisothermal austenite grain growth kinetics in a microalloyed x80 linepipe steel", Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, vol. 41, pp. 3161-3172, 2010.
16- M. Maalekian, R. Radis, M. Militzer, A. Moreau, W.J. Poole, "In situ measurement and modelling of austenite grain growth in a Ti/Nb microalloyed steel", Acta Materialia, vol. 60, pp.1015–1026, 2012.
17- T. Garcin, M. Militzer, W. J. Poole, L. Collins, "Microstructure model for the heat-affected zone of X80 linepipe steel", Materials Science and Technology, vol. 32, pp. 708-721, 2016.
18- J. Moon, S. Kim, H. Jeong, J. Lee, C. Lee, "Influence of Nb addition on the particle coarsening and microstructure evolution in a Ti-containing steel weld HAZ", Materials Science and Engineering A,vol. 454-455 , pp. 648-653, 2007.
19- Y.Q. Zhang, H.Q. Zhang, J.F. Li, W.M. LIU, "Effect of Heat Input on Microstructure and Toughness of Coarse Grain Heat Affected Zone in Nb Microalloyed HSLA Steels", Journal of Iron and Steel Research International, vol. 16 (5) , pp. 73-80, 2009.
20- G. Khalaj, H. Yoozbashizadeh, A. Khodabandeh, M. Tamizifar, "Austenite grain growth modelling in weld heat affected zone of Nb/Ti microalloyed linepipe steel", Materials Science and Technology (United Kingdom), vol. 30, pp. 424- 433, 2014.
21- Q. Sha, Z. Sun, "Grain growth behavior of coarse-grained austenite in a Nb-V-Ti microalloyed steel", Materials Science and Engineering A, vol. 523, pp. 77-84, 2009.