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What is critical temperature in heat treatment? 

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Journal ArticleDOI
A M Gresnigt, C M Steenhuis 
58 Citations
It emphasizes heat-treating procedures, as heat treatment is critical to the performance of these steels.
For some materials, a critical temperature can be defined which represents an upper limit beyond which the heating is unstable whatever the convective heat transfers.
The heat loss was higher at -16 °C than at 0 °C and -9 °C (p ≤ .01), indicating that the lower critical temperature may have been between -9 °C and -16 °C.
This communication demonstrates that the critical factor is a temperature-dependent ΔCp° ( T ) (heat capacity change) of reaction that is positive at low temperature but switches to a negative value at a temperature well below the ambient range.
A conventional furnace heat treatment critically reduces hardness and fracture toughness after a certain temperature.
Results show that reaction temperature is a critical factor in this process.
These results support the concept that a critical temperature exists that limits exercise in the heat.
Short pre‐treatment at a high temperature (>42°C), immediately before a treatment at a lower temperature (<42°C) can enhance the heat toxicity of the lower temperatures.
This process can be considered as a high temperature heat treatment at intermediate pressures (<2 GPa).
We conclude that no single ‘critical temperature’ for thermal fracturing or heat treatment can be specified for any particular raw material, as has so often been attempted, because threshold temperatures exist in relationship to specimen sizes.

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