Mete - Preheat Question

[rlinger]

I am reading that the preheat should be reached at a rate of no greater than 400 F per hour. Is this a rather fast rule or can thinner parts such as our knife blades be brought to preheat faster than that? I understand it has to do with steel expansion and that the steel needs to equalize at preheat and that critical temperature metallurically causes a decrease in steel volume, therefore the advisablty of preheating.

As an example question to you: If I reach preheat at a rate of 800 F per hour for a hunter thick blade would that be to quick?

Thanks. RL

 

[mete]

There is no absolute here. Much of the advice is aimed at dies or other parts that have complex shapes where stresses develop between thin and thick sections that can crack or warp the part. The same is true for the snap temper before cryo.You shouldn't have too many problems with a simple shape such as a blade.

 

[rlinger]

Thank you Mete and I figured they have to write these things as a 'cover all'. I presume there is no harm in ramping slowly to preheat regardless of geometry but after equalizing critical should be reached rather quickly. Unless you advise otherwise I will continue to hold faith in that.

It seems obvious that the reason for ramping slowly to preheat is to allow the cross section to heat up uniformly so as to reduce stress caused by expansion.

RL