Induced ferrite formation above the Ae 3 during plate rolling simulation of a X70 steel
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.343
Induced ferrite formation above the Ae3 during plate rolling simulation of a X70 steel Samuel F. Rodrigues1*, Thiago B. Carneiro1, Clodualdo Aranas Jr.2, Eden S. Silva1, Fulvio Siciliano3, Gedeon S. Reis1 and John J. Jonas 4 1 Department of Materials Engineering, Federal Institute of Education, science and Technology of Maranhao, Sao Luis 65075-441, Brazil.
2
Department of Mechanical Engineering, University of New Brunswick, Fredericton, E3B 5A3, Canada.
3
Dynamic Systems Inc. 323 NY 355, Poestenkill, New York 12140, United States of America.
4
Materials Engineering, McGill University, Montreal, QC H3A 0C5, Canada.
ABSTRACT
Partial amount of austenite can be dynamically transformed into ferrite above the Ae3 temperature when it is being deformed. This happens by a displacive mechanism. On removal of the load, it retransforms back into the stable austenite by diffusional processes. Plate rolling simulation under continuous cooling conditions was carried out on a high Nb X70 steel. Pass strains of 0.2 together with interpass times of 10, 20 and 30 s were employed. The initial and final temperatures for the finishing simulation were 920 and 830 °C, respectively. The mean flow stresses (MFS`s) behaviour indicates that dynamic transformation (DT) and recrystallization (DRX) were taking place during straining. It is shown that ferrite is formed during the roughing passes and increases its volume fraction throughout the finishing rolling steps. The ferrite formation is favoured by strain accumulation, shorter time between passes and also when the temperature reaches the Ae3 line. The results obtained here can be used to design improved models for transformation on accelerated cooling. *Correspondence: [email protected]
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INTRODUCTION Dynamic transformation (DT) has received considerable attention by industry and scientists around the world since the last decade [1,2]. The results obtained so far have shown a great potential to produce steel with ultra-fine ferrite (UFF) [3-5]. Actually, the phenomenon of DT started to be investigated in the 1980’s by Yada and coworkers [6,7]. Real-time evidence by using in-situ X-ray diffraction for the occurrence of DT above the Ae3 was provided later by the same authors [8,9]. Basabe et al. investigated the effects of strain, strain rate and temperature on DT in 2010 [10]. In their research, torsion experiments were performed on two different steels, a 0.036% Nb microalloyed steel and a plan C steel. They observed that the reverse transformation (ferrite transforming back into austenite by diffusional mechanism) was retarded in the Nb-steel during intervals between passes and holding after strain. However, this did not happen for the plain C steel. They point
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