Application Specific Microstructure Development in Microalloyed Bainitic Hot Strip

Abstract:

During the hot rolling of bainitic steels, time and temperature must be controlled within narrow limits to avoid undesirable ferritic or martensitic phase fractions. In order to design a reliable process window for the production of bainitic steels, the effects of the different process parameters on the phase transformation and the final properties of a microalloyed and a non-microalloyed steel were investigated. Thermomechanical tests with the possibility of producing secondary samples were conducted to analyze the influence on the mechanical properties strength and toughness. Transmission electron microscopy (TEM) and electron probe micro analysis (EPMA) were used to investigate the origin of the differing properties. In particular, it has been found that thermomechanical rolling of the microalloyed steel leads to an improvement in strength. This is partly due to the transformation kinetics and partly to strain-induced precipitations. Further, the hardening behavior is affected by the secondary phase within the bainitic matrix configured through the cooling strategy. Coarse Martensite/Austenite (MA) structures reduce toughness, whereas finely dispersed MA islands increase the hardening potential. Furthermore, the results from the material experiments were used to develop a rate model in combination with a nucleation model to predict the kinetics of the phase transformation and the shape of the bainitic microstructure.

• Periodical: Materials Science Forum (Volume 949)
• Pages: 76-84
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.949.76
• Online since: March 2019
• Authors: Max Menzel, Anastasia Höhne, Gerhard Gevelmann, Andreas Tomitz, Ulrich Prahl, Wolfgang Bleck*
• Keywords: Bainite, Hot Rolling, Modelling, Nucleation Model, Rate Model

References

[1] V. C. Igwemezie, P. C. Agu, Development of Bainitic Steels for Engineering Applications, Int. J. Eng. Res. Tech. 2 (2014) 2698-2711.

[2] H. K. D. H. Bhadeshia, The bainite transformation: unresolved issues, Mat. Sci. Eng. A (1999) 58-66.

[3] R. F. Hehemann, The bainite reaction, Am. Soc. Met. (1970) 397-432.

[4] A. Matsuzaki, H. K. D. H. Bhadeshia, Effect of austenite grain size and bainite morphology on overall kinetics of bainite transformation in steels, Mat. Sci. Tech. 5 (2013) 518-522.

DOI: 10.1179/026708399101506210

[5] P. Shipway, H. K. D. H. Bhadeshia, Mechanical stabilisation of bainite, Mat. Sci. Tech. 11 (1995) 1116-1128.

[6] S. J. Lee, J. S. Park, Y. K. Lee, Effect of austenite grain size on the transformation kinetics of upper and lower bainite in a low-alloy steel, Scr. Mat. 1 (2008) 87-90.

DOI: 10.1016/j.scriptamat.2008.02.036

[7] C. Y. Huang, J. R. Yang, S. C. Wang, Effect of Compressive Deformation on the Transformation Behavior of an Ultra-Low-Carbon Bainitic Steel, Mat. Trans. 8 (1993) 658-668.

DOI: 10.2320/matertrans1989.34.658

[8] F. G. Caballero, C. Capdevila, J. Chao, J. Cornide, C. Garcia-Mateo, H. Roelofs, S. Hasler, G. Mastrogiacomo, The microstructure of continuously cooled tough bainitic steel. International Conference Super-High Strength Steels. Milano (2010).

DOI: 10.1179/1743284710y.0000000047

[9] J. B. Leblond, J. Devaux, A new kinetic model for anisothermal metallurgical transformations in steels including effect of austenite tgrain size, Acta metall. mater. 1 (1984) 137-146.

DOI: 10.1016/0001-6160(84)90211-6

[10] M. Azuma, M. Fujita, M. Takahashi, T. Senuma, D. Quidort, T. Lung, Modelling Upper and Lower Bainite Transformation in Steels, ISIJ International. 2 (2005) 221-228.

DOI: 10.2355/isijinternational.45.221

[11] D. Hömberg, A numerical simulataion of the jominy end-quench test, Acta Mat. 11 (1996) 4375-4385.

DOI: 10.1016/1359-6454(96)00084-5

[12] P. Suwanpinij, N. Togobytska, U. Prahl, W. Weiss, D. Hömberg, W. Bleck, Numerical Cooling Strategy Design for Hot Rolled Dual Phase Steel, Ste. Res. Int. 11 (2010) 1001-1009.

DOI: 10.1002/srin.201000091

[13] P. Suwanpinij, X. Li, U. Prahl, W. Bleck, Modeling Bainite Transformation and Retained Austenite in Hot Rolled TRIP Steel by Instantaneous Carbon Enrichment, steel research int. 12 (2017) 1700122.

DOI: 10.1002/srin.201700122

[14] M. Takahashi, H. K. D. H. Bhadeshia, A Model for the Microstructure of Some Advanced Bainitic Steels, Mat. Trans. 8 (1991) 689-696.

DOI: 10.2320/matertrans1989.32.689

[15] M. Menzel, Anwendungsspezifische Gefügeentwicklung in mikrolegiertem bainitischem Warmband. RWTH Aachen. Aachen (not published yet).

[16] R. Barbosa, F. Boratto, S. Yue, J. J. Jonas, The influence of chemical composition on the recrystallisation behaviour of microalloyed steels, International symposium on processing, microstructure and properties of HSLA steel (1988) 51-61.

[17] M. P. Phaniraj, Y.-M. Shin, W.-S. Jung, M.-H. Kim, I.-S. Choi, Understanding dual precipitation strengthening in ultra-high strength low carbon steel containing nano-sized copper precipitates and carbides, Nano convergence. 1 (2017) 16.

DOI: 10.1186/s40580-017-0110-5

[18] Z. Wang, X. Mao, Z. Yang, X. Sun, Q. Yong, Z. Li, Y. Weng, Strain-induced precipitation in a Ti micro-alloyed HSLA steel, Materials Science and Engineering: A (2011) 459-467.

DOI: 10.1016/j.msea.2011.09.062

[19] H. K. D. H. Bhadeshia, Atomic Mechanism of the Bainite Transformation, HTM. 6 (2017) 340-345.

[20] H. F. Lan, L. X. Du, X. H. Liu, Microstructure and Mechanical Properties of a Low Carbon Bainitic Steel, steel research int. 4 (2013) 352-361.

DOI: 10.1002/srin.201200186

[21] S. Chatterjee, H.-S. Wang, J. R. Yang, H. K. D. H. Bhadeshia, Mechanical stabilisation of austenite, Mat. Sci. Tech. 6 (2013) 641-644.