Hardening then Tempering Time Between Question

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cartierusm

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Feb 23, 2017
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Ok so all the reading I've done it seems as though most people say that you must temper as soon as the blade is at a temperature you can hold it with your hand. I understand the reasoning as a blade with that much stress in it can crack on it's own.

Here's my dilemma. I have a nice, used, evenheat KO18 and I want to use it for both. I tried my kitchen oven out last night and no buena it swings more than Ron Jeremy in the 70's.

So let me know what you guys/gals think. Heat blade to quench temp > quench > leave door of evenheat open with a small fan until it cools to around 400F > close door fire it back up to tempering temp and temper for 2 hours > rinse repeat etc...

Does that sounds reasonable? Not sure how long it will take to cool the oven down or if a fan blowing gently on it is bad.

Thoughts?
 
Tempering as soon as you reasonably can is the best idea. I don't see a problem with the method you describe and have done it myself that way. I've also cooled my furnace down with a fan when normalizing and thermal cycling. I don't believe it's caused any ill effect, but I do have the controller off when I do so, so it doesn't cycle unnecessarily.
 
I've heard cooling the oven fast is bad for the heating elements. I temper around 300 in my toaster oven and when the kiln cools I temper again to my target temperature. You can also straighten if needed on the second temper.
 
Ok part deux...I'm making some tooling with 01 and A2 and hardening guidelines recommend Stainless Steel Tool Wrap. So I bought some. I have also been reading about a paint like coating that keep the metal from decarburizing and scaling.

So since I've got 50' of tool wrap coming should I tool wrap my blades before hardening? If so should I use tool wrap for normalizing, hardening and tempering? AND if you recommend using the tool wrap should I cut it out of the wrap before quenching?
 
Just start with your kitchen oven.
Let your oven preheat to 350 °F and put your blades in for an hour. That simple "pre" tempering will avoid any risk of cracking.
As soon as your accurate kiln reaches your target tempering temperature use it for a complete tempering cycle.
 
The foil is good for A2 since it is air Quenching steel that requires higher temperature and soak. You would benefit from a set of aluminum quench plates that will keep your blade straight while dissipating the heat.

The O1 is oil quenching at a lower temperature and soak time is until the steel is soaked through. Foil for O1 is a hassle to remove and still have the full heat in the blade to get a good quench. I know the foil idea is to cut down the Decarb mess but trying to remove foil is worse and not worth possibly missing the hardening curve.
 
cartierusm said:
Ok so all the reading I've done it seems as though most people say that you must temper as soon as the blade is at a temperature you can hold it with your hand. I understand the reasoning as a blade with that much stress in it can crack on it's own.

Here's my dilemma. I have a nice, used, evenheat KO18 and I want to use it for both. I tried my kitchen oven out last night and no buena it swings more than Ron Jeremy in the 70's.

So let me know what you guys/gals think. Heat blade to quench temp > quench > leave door of evenheat open with a small fan until it cools to around 400F > close door fire it back up to tempering temp and temper for 2 hours > rinse repeat etc...

Does that sounds reasonable? Not sure how long it will take to cool the oven down or if a fan blowing gently on it is bad.

Thoughts?
Click to expand...
some of your metal websites say cool to 125F then temper immediately. I have tried two approaches, both work. one is after a quick check for straightness, return blade to quench oil. My oil is usually about 125F. the other is put the blades in ice water. I have a cooler in the shop with ice and water, out of quench into cooler. when all blades are done, wipe off the oil then into oven. final idea is heat kitchen oven to 275F to 300F, then put the blades in. If you are working with high carbon steel, having a swing of +/- 25F isn't going to make much difference
 
Yes , some good answers. Some things hate thermal cycling like ceramics [like ovens are made from ] and the heating elements .
The martensite conversions create very high stresses ,they must be relieved or the steel will do it !! As Stefano suggests partial tempering can be used to safely reduce stresses then more precise tempering can be done later.
 
Huh. I guess I'll quit doing that then. I need to build a PID forge I guess. It would take me all day to normalize, thermal cycle and then austenitize a couple blades just letting my electric cool off as it will.
 
All good suggestions.

S stezann , great idea. I'll put that into my repertoire.

Busto Busto , got it. I might then return the $100 roll of foil I just bought. Unless it has a good use for other heat treats. All I'll ever be doing is tool steel for making tools, 1095, 15N20, 1084 and things in that range for damascus and regular billets for knives. You think it's worth keeping?

@Nateman, why do you ask? The A2 I already have comes annealed and I've already fabricated what I need. I just need to harden it.

@Karl, heard. What about keeping the door open after quenching to let it cool off normally? Or should I keep the door closed as it cools?

The problem with a toaster oven is down the road I plan on doing swords, might be years, but if I build something I would put that money into make a 48" long tempering/hardening oven. Which I'm not willing to do now as I fabricate everything I use. SO the new shop, mostly fabricated started with a 20' shipping container. Grinder, tables, forge, vise stand...you get the point. All fabricated from scratch. Not hard just time consuming. I'd like to actually make a knife so making an oven will probably be in the future just not right now.
 
If you are currently focusing on tooling, but in the future plan on making knives I would keep the foil. At some point you will want to make knives from stainless steel or air hardening steels which you should wrap. The foil will preserve the steels that require High Temp/Long Soak times. I was assessing my current use of foil and I'm about a 70/30% split 70% stainless and 30% carbon steel so I go through foil pretty quick.
 
I guess I need a toaster oven in the shop, it's a 60 yard walk to house kitchen oven, my blade is completely cooled by the time I get it in the preheated oven. I have been wire brushing the decarb off just after quenching, before going into the preheated oven.

I should leave the decarb on, temper in oven and then clean off?

Thanks,
 
DanF said:
I guess I need a toaster oven in the shop, it's a 60 yard walk to house kitchen oven, my blade is completely cooled by the time I get it in the preheated oven. I have been wire brushing the decarb off just after quenching, before going into the preheated oven.

I should leave the decarb on, temper in oven and then clean off?

Thanks,
Click to expand...

I would remove the decarb layer down to clean steel that way you have some visual reference to the tempering colors and you might miss the cutting edge getting to soft in the blue temper range. I temper into the "Straw" color range with just a hint of light brown and remove dip in water to cool then back into the oven for the next temper. Times are only approximate it's about seeing the color changes that give better information on the actual tempering range.
 
I wipe the oil off the blade and into a 275F to 300F oven for at least an hour. the first blades done may be in the oven for 2 hours, but no harm done. cold water quench then I scrub, rinse, then into oven for final temper, usually 350F. If I don't have toaster oven in shop, blade goes into ice water bath until all are done. a brand new convection/toaster oven should cost less than $50. I put a tray above and below the knives so they don't get direct radiation from the heating element.
 
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