HEAT TREATMENT- AIR COOLING RATE
HEAT TREATMENT- AIR COOLING RATE
(OP)
I was hoping that someone could give me some info on how to work out the air cooling rate of a metal to room temperature.
If there is a rule of thumb instead of a particular equation then that would be fine also.
I am tempering tool steel from 500°C and the components are Ø600 x 8mm thick and I was trying to work out how long it would take to air cool to room temp.
Any help would be appreciated
If there is a rule of thumb instead of a particular equation then that would be fine also.
I am tempering tool steel from 500°C and the components are Ø600 x 8mm thick and I was trying to work out how long it would take to air cool to room temp.
Any help would be appreciated





RE: HEAT TREATMENT- AIR COOLING RATE
For an 8 mm wall thickness the part will cool very quickly- you can expect martensite or bainite to form unless you shield the parts from the ambient temperature . Refer to the TTT curves for that alloy. You can calculate the fourier number and /or the biot number and then estaimte the rate at which it will cool down, then refer to the TTT curve for that cool down rate.
By the same token , if you were processing a thick component ( say 35 mm thk) and wanted to form martensite ( as with P91) or bainite ( as with T23) then you want to ensure a fast cooldown , faster than 10 F/min. So make darn sure there is not shielding of the thermal radiaton from the part to ambient.
RE: HEAT TREATMENT- AIR COOLING RATE
RE: HEAT TREATMENT- AIR COOLING RATE
I have the TTT and CCT diagrams for the tool steel(D2)but I am struggling to determine the rate of cool down from that( I am not familiar with fourier and biot numbers and how they relate to the TTT CCT diagrams)
I basically want to determine how quickly I can put it back in the oven to do a second temper.
This part has already been hardened and quenched to produce martensite
RE: HEAT TREATMENT- AIR COOLING RATE
http://web.mit.edu/lienhard/www/ahtt.html
RE: HEAT TREATMENT- AIR COOLING RATE
That is, take one out of the furnace and check it's temperature every 10 minutes. That should give you a good cooling curve and allow you to determine the heat transfer coefficients to be able to calculate the time for other sizes/thicknesses.
rp
RE: HEAT TREATMENT- AIR COOLING RATE
In theory, you can run fea to get an idea, but as redpicker, testing is still needed to confirm as fea can easily vary from testing by an order.
RE: HEAT TREATMENT- AIR COOLING RATE