The operating temperature is below 370℃, medium carbon steel after tempering is generally selected; More than 370℃, choose heat resistant steel; Below 480℃, low chromium molybdenum alloy pearlite heat resistant steel; Below 540℃, choose low alloy perlite heat resistant steel; Below 570℃, the use of high chromium martensitic heat resistant steel, but the linear expansion coefficient of this steel is small, when the cold preload can not be too large, in order to prevent the working temperature, the fastener overload and yield.