Quenching (update)

Quenching heat transfer
Schematic showing stages of Quenching

Heat transfer during quenching into liquid is complicated when the quench medium forms a gas when heated to high temperatures.

The quenching process is usually split into 3 -5 stages.

Stage 1. Vapour blanket.

Depends upon surface roughness, quenchant temperature, quenchant type, oxidation. Heat transfer by radiation through vapour layer into quenchant.

Stage 1b. Partial film boiling.

Stage 2. Nucleate boiling.

Conduction and Convection.

Stage 3. Convection.

Dominated by heat transfer in the quenchant by convection which can be natural, forced with turbulence or forced with lamellar flow.

Hala Salman-Hasan has been investigating heat transfer problems, a series of experiments have been made for quenching using an experimental rig we built at Cambridge. Here we can see a video of a 2 mm probe made from steel which has a thermocouple embedded. Data logging is from a computer with data logger. I think data logging at these speeds could also be achieved using an Oscilloscope, that would probably need an electrical engineer, and more importantly a trigger to start logging at the correct time.

Quenching into water

Typical Quenching Curve
Quenching curve for water at 42 Celcius, Heat Transfer as a function of temperature.