Influence of Cu, Al, and Si Contents on Thermophysical Properties in TWIP Steels and Their Comparison with Stainless and Carbon Steels

The thermophysical properties of four TWIP steels with varying Cu, Al, and Si contents were measured and compared with those of austenitic stainless steel and plain carbon steel over a temperature range of 25 to 1000 °C. The thermal expansion coefficient (β) of the TWIP steels was unaffected by alloying additions, averaging 22.87x10-6 °C-1, which is slightly higher than that of austenitic stainless steel (19.74x10-6 °C-1) and notably higher than that of plain carbon steel (12.61x10-6 °C-1). Density (ρ) decreased linearly with temperature across all compositions and was further reduced by higher Cu, Al, and Si contents due to the lower atomic mass of these elements compared with Fe, with Al showing the most pronounced effect in TWIP steels. Due to the high β of TWIP steel, the ρ reduction with increasing temperature was more pronounced in TWIP steel compared to that of conventional carbon steels and stainless steels. The specific heat capacity (Cp) of TWIP steels increased with temperature, showing a trend similar to that of austenitic stainless steel. Thermal diffusivity (α) and thermal conductivity (k) also increased with temperature but decreased with alloying additions, attributed to increased thermal resistivity by solute atoms. Among the alloying elements, Al had the strongest influence on reducing α and k, followed by Si, with Cu having minimal effect. Compared to other steels, TWIP steels exhibited significantly lower k and higher β, characteristics that may induce thermal stress and increase the risk of thermal cracking during rapid thermal processes such as welding, heat treatment, machining, casting, and hot forming.