Evaluation of Fire Resistance for a Recycled 0.15 mass% Carbon Steel
2021
A recycled steel with 0.2 % offset stress higher than 295 MPa was verified as a candidate for fire-resistant use, based on an academic standard in Japan. The chemical compositions were 0.15 mass% carbon-0.02 mass% silicon-0.5% mass% manganese and unavoidable alloy elements. The amount of elements inevitably contained in recycling was kept within the regulation, and then the dispersion of tensile properties among hot coils was controlled to be sufficiently small. The recycled steel satisfied the requirements by the academic standard in terms of tensile properties at elevated temperatures. No significant evolution was observed in the ferrite-based microstructure within the temperature and time range tested. The plastic deformation is apparently a strain-controlled one up to 400°C and a strain rate-controlled one at 600°C and 700°C. At 500°C, it is in the middle of the two. In the adopted test method, a constant strain rate was realized over the entire strain range except for the beginning stage of deformation. A peak strain rate occurs at about 0.2 % strain, which brings about the uncertainty in determination of 0.2 % offset stress at elevated temperatures. However, the constant strain rate requirement is satisfied in the determination of 1 % offset stress that the academic standard specifies.
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