Steels continued tempering temperature

The Leeds Northrup Co. has developed a two-couple continuous curve recorder for automatically heating furnaces to definite temperatures. As applied in carburizing and tempering of steel one thermocouple is placed in the furnace chamber and the other in contact with the steel piece. The controller automatically maintains the furnace for instance at 1,000°C. until the steel has reached 900°C. and then it drops the furnace to 900 C. Such an arrangement for control can be applied to a great many processes. 

For hardening and subsequent tempering operations, the heat treatment contractor should be guided by the recommendations of the steel maker given in the data sheets for the material concerned. These heat treatment recommendations are derived from the chemical composition of the steel used. Material-specific, continuous and isothermal Time-Temperature-Transformation (TTT) diagrams, as shown in Figure 4.80, describe the transformation behaviour of the steel s microstructure [3]. 

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