There is a thecnics "DISTENSIONE--STRESS RELIEVING"
1) HEATING RATE LESS THAN 200℃/h
2) FURNACE TEMPERATURE 630 TO 650℃
3) TIME SOAKING: 1h
4) COOLING RATE DOWN TO 300℃: 150℃/h
5) COOLING FROM 300℃ IN STILL AIR.
But the cruciai question is that---the furnace temperature is reduced so slowly,we can open the furnace door ,but the furnace temperature changes so fast that we can not control it.
You can use other cooling medium through the furnace,it can take away heat .control the cooling medium flow rate.we can control the furnace cooling rate.
if the furnace have not the cooling system, that will be hard to control it, in my opinion, you can add some the an air cooling equipment, control the cooling rate by control the air speed.
it is difficult to assure the cooling speed on your equipment .
i agree to remould the furnace, add a PLC and air pump to control the cooling and heating rate .
it's up to you chose what to cooling it,generally, at start youcan use of cooling air,when it reach 400 degree,cooling it with water,then the cooling rate is faster than norm.
150C/h from high temperature to 300,and according to the tyre of furnace ,I think cooling with the furnace while oopening the door !the cooling rate maybe middle of A and N.
just my own opinion ,maybe right maybe wrong !