Role of Dilatometer in Designing New Bainitic Steels

Abstract:

Dilatometric measurements were used to design the processing parameters of two types of bainitic steels. The first type is a hypoeutectoid ultra fine bainite steel, for which the dilatometer was used to locate the temperature at which cementite is completely dissolved during intercritical annealing (TC). The intercritical annealing temperatures are then selected will above TC. To obtain the martensite start temperatures (MS), the steel is quenched to the room temperature (RT) from these selected temperatures and then the bainite transformation temperatures were selected to be well above MS. The dilatometer was then used to monitor the bainite transformation kinetics from which the required time frames for cessation of the bainitic reactions were estimated. In the second type, bimodal bainite had been produced in thermo-mechanically processed TRIP-steel. A deformation dilatometer is used to perform three deformation-steps before slow cooling to form approx. 30% polygonal ferrite. The material was then rapidly cooled to the first bainite formation temperature. During this step, the dilatometer was used to monitor the bainite reaction from which the required time for 50% decomposition of austenite is estimated. The martensite start of the undecomposed austenite was located by quenching to RT. The second bainite transformation step was then performed well above the new MSII to form a second generation of finer bainite.

• Periodical: Advanced Materials Research (Volumes 89-91)
• Pages: 35-40
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.89-91.35
• Online since: January 2010
• Authors: Mohamed Soliman, Mehdi Asadi, Heinz Palkowski
• Keywords: Bainite Transformation, Dilatometry, Intercritical Annealing, Process Design, Retained Austenite

References

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DOI: 10.1520/a1033-10r15

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[6] H.K.D.H. Bhadeshia: Bainite in Steel (IOM commercial Ltd, London, 2nd Edition, 2001). Fig. 11 Dilatation versus temperature curve obtained during continues cooling together with the obtained microstructure. Fig. 12 Dilatation versus time observed during single (solid) and two-step (dashed) bainite transformation. Fig. 13 Dilatation versus temperature obtained during two-step bainite transformation 0.

DOI: 10.3390/met7090330

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35250 270 290 310 330 350 370 390 410 430 450 Temperature (°C) ΔL/L0 (%) MSII Formation of second bainite generation Formation of first bainite generation 0.

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35 0 120 240 360 480 600 Time (s) ΔL/L0 (%) -58 -57. 95 -57. 9 -57. 85 -57. 8 0 200 400 600 800 Temperature (°C) Relative length change (%) 1Ks -1 Ferrite Martensite Bainite.