Novel Cost-Efficient Method of Producing Ausferritic Steels Displaying Excellent Combination of Mechanical Properties

Abstract:

Round bars Ø 53 mm were hot-rolled from a 1.4 tonne ingot forged to 165 × 165 mm. The composition of the steel was 0.45 wt. % C and 3.33 wt. % Si plus alloying elements for hardenability. Microstructure after air cooling from 1010 °C on the cooling bed was predominantly ausferritic. Tensile testing of as-rolled bars resulted in yield strength 846 ± 22 MPa, ultimate tensile strength 1169 ± 99 MPa and A₅-elongation of 1.7 ± 0.8 % (without prior necking). When as-rolled steel was baked in air at T = {M_{s initial} -30 K} for six hours, the yield stress raised to 1121 ± 4 MPa, the ultimate tensile stress raised to 1447 ± 5 MPa and the elongation raised to 22.6 ± 1.6 % (with necking > 18 %). For as-rolled bars during continuous cooling, the exposure time within the temperature range 460 – 320 °C was estimated to be about 10 minutes. The microstructure of as-rolled “semi-finished” bars is stable at room temperature. The first baking was done six months after hot-rolling. Optical and scanning electron microscopy showed that remaining areas of austenite, not transformed during continuous cooling but stable at room temperature, transforms to ausferrite when properly baked.

• Periodical: Defect and Diffusion Forum (Volume 405)
• Pages: 11-18
• DOI: https://doi.org/10.4028/www.scientific.net/DDF.405.11
• Online since: November 2020
• Authors: Per Rubin*, Richard Larker, Erik Navara, Marta Lena Antti
• Keywords: Ausferrite, Ausferritic Steel, Baked, Continuously Cooled, High Silicon, Medium Carbon

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