• Bainite

It's not pearlite or martensite. A blog written by Mathew Peet.

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.

2 Responses

1. This is a nice graph and very important for all the metallurgists who wants to model a coupled heat transfer and phase transformation phenomenon. I had a lot of trouble first when I tried to model the phase transformation in a rod being cooled inside and outside “water boxes”, something that we have in Wire Rod Mills (WRM). We also had the same problem while modelling the cooling of rolls in Hot Strip Mills (HSM). The problem arises because the heat-transfer coefficient is different at different zones shown in this plot. If you look at our paper “Mathematical Modelling of Roll Cooling and Roll Surface Stress” in ISIJ International, Vol. 45 (2005), No. 11, pp. 1641–1650, you will get an idea about what I am trying to tell. In HSM or WRM we have a situation when the steel is quenched and periodically experiences all the stages of quenching shown in this plot.

2. This is not the most elaborate experiment, but it is a start. We took two pieces of an old 3mm dia thermocouple from our oven and welded them together. We then heated the welded area to 50millivolts which corresponds to 2250F. (We also checked the mv at 212F and 1330F and it was very close to expected values.) We stopped heating and quenched the heated area of the thermocouple in a pan of water. The voltage dropped to ambient faster than the display on the monitor could keep up, definitely less than a second. We are planning another test on May 8th when we our better method of recording data arrives. We will also try with on a 1.5mm thick thermocouple instead of 3mm dia. I dont think our material is thick enough to have enough core heat to allow a vapor barrier to form. I will let you know what happens next.