Dynamic Transformation during the Torsion Simulation of Strip Rolling

Abstract:

Seven-pass strip rolling simulations were carried out on a 0.06%C and a 0.09%C-0.036%Nb steel. The rolling loads (mean flow stresses or MFS’s) did not increase as the temperature decreased during the simulation. This is ascribed to the occurrence of dynamic transformation. The simulation results are compared to the high temperature flow curves determined on eight plain C and Nb-modified steels in both compression and torsion and at a series of temperatures and strain rates. When the associated MFS’s are plotted against inverse absolute temperature in the form of Boratto diagrams, the stress drop temperatures, normally defined as the upper critical temperature applicable to rolling, A_r3*, are shown to be about 40 degrees above the paraequilibrium and about 20-30 degrees above the orthoequilibrium A_e3’s. These drops are ascribed to the dynamic transformation of austenite to ferrite, a softer phase. The characteristics of the ferrite produced dynamically are described and the transformation is shown to be displacive in nature, leading to the appearance of fine Widmanstätten plates. These plates coalesce into polygonal grains on further deformation and on holding.

• Periodical: Materials Science Forum (Volumes 783-786)
• Pages: 39-44
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.783-786.39
• Online since: May 2014
• Authors: John J. Jonas*, Clodualdo Aranas Jr., Vladimir V. Basabe, Chiradeep Ghosh
• Keywords: A_e3, A_r3, Austenite, Dynamic Transformation, Hot Rolling, Mean Flow Stress, Torsion Testing, Widmanstätten Ferrite

References

[1] Samuel F H, Yue S, Jonas J J and Zbinden B A. Modeling of Flow Stress and Rolling Load of a Hot Strip Mill by Torsion Testing. ISIJ Int., 29 (1989) 878-886.

DOI: 10.2355/isijinternational.29.878

[2] Karjalainen L P, Maccagno T M and Jonas J J.: Softening and Flow Stress Behavior of Nb Microalloyed Steels during Hot Rolling Simulation. ISIJ Int., 35 (1995) 1523-1531.

DOI: 10.2355/isijinternational.35.1523

[3] John J. Jonas, Vladimir V. Basabe, Chiradeep Ghosh and Clodualdo Aranas Jr: Dynamic Transformation During the Simulation of Strip Rolling: Proceedings of the 5th Baosteel Biennial Academic Conference, Shanghai, China, June 2013, C1-C6.

DOI: 10.4028/www.scientific.net/msf.783-786.39

[4] John J Jonas, Chiradeep Ghosh and Vladimir V Basabe: Dynamic Transformation during Simulated Hot Rolling: Proceedings, 7th International Conference on Physical and Numerical Simulation of Materials Processing, Oulu, Finland, Materials Science Forum, 762 (2013).

DOI: 10.4028/www.scientific.net/msf.762.1

[5] Chiradeep Ghosh, Vladimir V Basabe, John J Jonas, Stephen Yue and Xiang Y. Xiong: Dynamic Transformation of a Deformed High Carbon Steel at Temperatures above the Ae3: ISIJ Int., 53 (2013) 900-908.

DOI: 10.2355/isijinternational.53.900

[6] Vladimir V Basabe, John J Jonas and Chiradeep Ghosh: Formation of Widmanstätten Ferrite in a 0. 036% Nb Low Carbon Steel at Temperatures Above the Ae3: Steel Research Int., DOI: 10. 1002/srin. 201200226.

DOI: 10.1002/srin.201200226

[7] Vladimir V Basabe, John J Jonas and Chiradeep Ghosh: Formation of Strain-induced Ferrite in Low Carbon Steels at Temperatures above the Ae3: ISIJ Int., in press.

DOI: 10.2355/isijinternational.53.2233

[8] John J Jonas, Chiradeep Ghosh, Xavier Quelennec and Vladimir V Basabe: The Critical Strain for Dynamic Transformation in Hot Deformed Austenite: ISIJ Int., 53 (2013) 145-151.

DOI: 10.2355/isijinternational.53.145

[9] Chiradeep Ghosh, Vladimir V. Basabe, John J Jonas: Determination of the Critical Strains for the Initiation of Dynamic Transformation and Dynamic Recrystallization in Four Steels of Increasing Carbon Contents: Steel Research International, 84 (2013).

DOI: 10.1002/srin.201200188

[10] Chiradeep Ghosh: The Dynamic Transformation of Deformed Austenite at Temperatures above the Ae3; Ph.D. thesis, McGill University, (2013).

[11] John J Jonas, Chiradeep Ghosh and Vladimir Basabe: Effect of Dynamic Transformation on the Mean Flow Stress: Steel Research International, 84 (2013) 253-258.

DOI: 10.1002/srin.201200166

[12] Chiradeep Ghosh, Vladimir V Basabe, John J Jonas, Young-Min Kim, In-Ho Jung and Stephen Yue: The Dynamic Transformation of Deformed Austenite at Temperatures above the Ae3: Acta Mater., 61 (2013) 2348-2362.

DOI: 10.1016/j.actamat.2013.01.006

[13] D.N. Hanlon, J. Sietsma and S. van der Zwaag: The Effect of Plastic Deformation of Austenite on the Kinetics of Subsequent Ferrite Formation: ISIJ Int., 41 (2001) 1028-1036.

DOI: 10.2355/isijinternational.41.1028

[14] Chiradeep Ghosh, Vladimir V Basabe and John J. Jonas: Thermodynamics of Dynamic Transformation of Hot Deformed Austenite in Four Steels on Increasing Carbon Contents: submitted to Mater. Sci. &Engin. A.

DOI: 10.1016/j.msea.2013.10.077

[15] John J. Jonas and Chiradeep Ghosh: Role of Mechanical Activation in the Dynamic Transformation of Austenite: Acta Mater, 61 (2013) 6125-6131.

DOI: 10.1016/j.actamat.2013.06.054