HIGH-TEMPERATURE DEFORMATION BEHAVIOR OF HIGH-NB MICROALLOYED STEEL DURING PLATE ROLLING SIMULATION
Samuel Filgueiras Rodrigues, Fulvio Siciliano, Clodualdo Aranas Júnior, Eden Santos Silva, Gedeon Silva Reis, John Joseph Jonas
When austenite is deformed above the Ae3 temperature, partial amount of it transforms dynamically into ferrite by a displacive mechanism. After unloading, it retransforms back into the stable austenite by a diffusional process. This phenomenon influences the rolling load, which either decreases under isothermal rolling condition or does not progressively increase with decreasing temperature during cooling. In this work, plate rolling simulations employing isothermal and continuous cooling conditions were carried out on a 0.09 wt.% Nb X-70 steel. Pass strains in the range of 0.2-04, interpass times between 10- 30 s and strain rate of 1s-1 were employed. The results showed that the critical strains for the initiation of dynamic transformation fell around 0.06 while the critical strain for dynamic recrystallization was 0.12. Under cooling conditions, the ferrite formation is favored as the temperature approaches the Ae3 line. Such ferrite forms when the driving force for dynamic transformation is higher than the total free energy barrier. Increasing the holding time after rolling increases the amount of austenite available for microstructure control on subsequent stages. The dynamic transformation (DT) mechanism can be used to design improved rolling schedules.
1 Grewal R, Aranas C, Chadha K, Shahriari D, Jahazi M, Jonas JJ. Formation of Widmastatten ferrite at very high temperatures in the austenite phase field. Acta Materialia. 2016;109:23-31.
2 Aranas C, Jung IH, Yue S, Rodrigues SF, Jonas JJ. A metastable phase diagram for the dynamic transformation of austenite at temperatures above the Ae3. International Journal of Materials Research. 2016;107:881-886.
3 Yada H, Matsumura Y, Senuma T. Proceedings of the International Conference on Martensitic Transformations. Sendai, Japan: Japan Institute of Metals; 1986. p. 515.
4 Yada H, Matsumura Y, Senuma T. A new thermomechanical heat treatment for grain refining in low carbon steels. In: Proceedings of the 1st International Conference on Physical Metallurgy of Thermomechanical Processing of Steels and Other Metals (THERMEC’88); 1988; Keidanren Kaikan, Tokyo, Japan. Tokyo: ISIJ; 1988. p. 200.
5 Yada H, Li CM, Yamagata H. Dynamic γ - α transformation during hot deformation in Iron-Nickel-Carbon alloys. ISIJ International. 2000;40:200-206.
6 Chen Y, Chen Q. Dilatometric investigation on isothermal transformation after hot deformation. Journal of Iron and Steel Research International. 2003;10:46-48.
7 Liu Z, Li D, Lu S, Qiao G. Thermal stability of high temperature deformation induced ferrite in a low carbon steel. ISIJ International. 2007;47:289-293.
8 Sun X, Luo H, Dong H, Liu Q, Weng Y. Microstructural evolution and kinetics for post-dynamic transformation in a plain low carbon steel. ISIJ International. 2008;48:994-1000.
9 Basabe VV, Jonas JJ. The ferrite transformation in hot deformed 0.036% Nb austenite at temperature above the Ae3. ISIJ International. 2010;50:1185-1192.
10 Ghosh C, Basabe VV, Jonas JJ, Kim Y, Jung I, Yue S. The dynamic transformation of deformed austenite at temperatures above the Ae3 . Acta Materialia. 2013;61:2348-2362.
11 Aranas C, Jonas JJ. Effect of Mn and Si on dynamic transformation of austenite above the Ae3 temperature. Acta Materialia. 2015;82:1-10.
12 Aranas C, Nguyen-Minh T, Grewal R, Jonas JJ. Flow softening-based formation of Widmanstatten ferrite in a 0.06%C steel deformed above the Ae3 . ISIJ International. 2015;55:300-307.
13 Rodrigues SF, Aranas C, Sun B, Siciliano F, Yue S, Jonas JJ. Effect of grain size and residual strain on the dynamic transformation of austenite under plate rolling conditions. Steel Research International. 2018;89:1-7.
14 Rodrigues SF, Aranas C, Wang T, Jonas JJ. Dynamic transformation of an X70 steel under plate rolling conditions. ISIJ International. 2017;57:162-169.
15 Bale CW, Belisle E, Chartrand P, Decterov SA, Eriksson G, Hack K, Jung IH, Kang YY, Melancon J, Pelton AD, et al. FactSage thermomechanical software and database-recent developments. Calphad. 2009; 33: 295–311.
16 Ghosh C, Aranas C, Jonas JJ. Dynamic transformation of deformed austenite at temperatures above the Ae3 . Progress in Materials Science. 2016;82:151-233.