How does the strength of steel vary with increasing temperature?
Plain carbon manganese steels behave similarly when heated, in that the yield strength decreases approximately linearly with increasing temperature at the rate of around 0.1% of room temperature strength per 1°C increase in temperature. This means that most steels have about 50% of their room temperature strength at 500°C. Above this temperature, the rate of softening increases more rapidly. Addition of alloying elements such as molybdenum and chromium slow down the rate of softening and allow the steel to be used at higher temperatures. However, other factors are important at higher temperatures. These include creep where the material will fail over a time period at a stress level much lower than the strength of the steel. Further, oxidation of the surface accelerates rapidly. For these reasons, plain carbon steels are not generally suitable for applications above 400°C.
