Recommendation? Cooling rate for tempering 1095

[The_Iron_Joe]

So, I've looked through the relevant stickies, and couldn't find anything through Google searching or within BF; I just want to ask what you guys do.

When you're tempering a high carbon steel like 1095, do you cool your knives in open air, either by removing the knives or just opening the kiln door (for those of you that work with kilns), or do you keep the knife where it is, and just remove your heat? Do you find it makes much difference?

 

[Karl B. Andersen]

Remove it from the oven and quench it in a bucket of water.
When it's cool, return it to the oven for the second temper.

 

[mete]

When tempering is done , it's done .Playing with slow cooling can produce unwanted microstructures.
In a similar way many times I see to VERY slowly cool from austenitic when annealing a high carbon steel like 1095. This can produce dangerous structures like continuous carbide in the grain boundaries - VERY brittle !

 

[Stacy E. Apelt - Bladesmith]

You used to hear to air cool between the tempers. This was due to most info being from blacksmith types and other non-metallurgist people. Other folks and I started recommending ,"Remove from the first temper, quench in running cold water, dry off, and return immediately to the temper oven. When done with the second temper, cool again in water, dry and finish the blade." a while back. Now most all the metallurgical bladesmiths use that as the accepted procedure.

 

[The_Iron_Joe]

Thank you very much for the information, everyone!

Would cooling with water between tempers be acceptable practice for steels like 154CM as well? Or does stainless behave much differently?

 

[Stacy E. Apelt - Bladesmith]

All steel should be cooled fairly rapidly between tempers. The only cooling that is type specific is the cooling curve from austenitization in HT ( the quench).

 

[The_Iron_Joe]

Thanks for the clarification and followup, Stacy! I'll be putting it to good use later this week.

 

[kuraki]

Stacy E. Apelt - Bladesmith can you explain why it should be water cooled after temper?

I ask because in industrial toolmaking my experience is that after temper cooling is always in still air or under a draft blower (for no other reason than to speed up the cooling) and never in water. In fact the only time I ever was instructed to water cool was when torch tempering and that was more to stop the heat from soaking up to a point where you don't want it, for example a punch you wanted softer on the striking end than the point.

But I've learned here there are many aspects of heat treatment that are wildly different from what I learned in industry to optimize blade performance, so I'm curious what the reason is for water cooling after temper.