Snap temper, compromise in quality?

[flatblackcapo]

Same ol situation, I only have one HT oven and it takes forever and a day for it to cool down enough to temper. Is there a compromise in quality when you snap temper? Also, Is it best to snap temper as close to the finish temper temperature as possible or does it matter? I am working with 1095 and my home oven just won't hit the desired temp. Thanks.

 

[Stacy E. Apelt - Bladesmith]

A snap temper is to slightly relieve any stress from the quench before cryo. It isn't a temper as-such. Once out of the cryo, the steel needs to be tempered.

All hardened blades need a temper cycle at around 400°F to convert the brittle martensite to tempered martensite. If the steel is a type that could have retained austenite, a second temper is needed. A second temper does no harm, so it is a good practice to always do double tempers, with a cooling to room temp between them. One hour is a minimum time for each temper, two hours being wise for higher alloy steels.
​

Tempering as soon after quench as possible is metallurgically wise. It doesn't have to be within minutes, but within a couple hours is smart. Once the first temper is done, you can delay the second temper for a day with no harm.

If your home oven won't hit 400°, you are in bad need of a new oven.
A toaster oven will work for a first temper while the HT oven is dropping to 400°F. Since toaster ovens can be a bit off in temp control, I would do a 375° temper in it, then wait until the HT oven reaches your temper point and do a second two hour temper.​

You may have noticed that I used 400°F as the start of the tempering range. Tempering below this is done for a few blades that need near as-quenched hardness, but for the best toughness and edge life, tempering between 400°F and 500°F will yield the best blades.
People seem to think that tempering above 400° will drop the hardness greatly. In actuality, most knife steels will still be well above Rc60 with a 450° temper.
1095 tempered at 450° comes out at Rc62, which is what I recommend doing it at.

 

[flatblackcapo]

A snap temper is to slightly relieve any stress from the quench before cryo. It isn't a temper as-such. Once out of the cryo, the steel needs to be tempered.

All hardened blades need a temper cycle at around 400°F to convert the brittle martensite to tempered martensite. If the steel is a type that could have retained austenite, a second temper is needed. A second temper does no harm, so it is a good practice to always do double tempers, with a cooling to room temp between them. One hour is a minimum time for each temper, two hours being wise for higher alloy steels.
​

Tempering as soon after quench as possible is metallurgically wise. It doesn't have to be within minutes, but within a couple hours is smart. Once the first temper is done, you can delay the second temper for a day with no harm.

If your home oven won't hit 400°, you are in bad need of a new oven.
A toaster oven will work for a first temper while the HT oven is dropping to 400°F. Since toaster ovens can be a bit off in temp control, I would do a 375° temper in it, then wait until the HT oven reaches your temper point and do a second two hour temper.​

You may have noticed that I used 400°F as the start of the tempering range. Tempering below this is done for a few blades that need near as-quenched hardness, but for the best toughness and edge life, tempering between 400°F and 500°F will yield the best blades.
People seem to think that tempering above 400° will drop the hardness greatly. In actuality, most knife steels will still be well above Rc60 with a 450° temper.
1095 tempered at 450° comes out at Rc62, which is what I recommend doing it at.

Thanks, Stacy
I appreciate the help. Do you recommend 2 hour temper cycles for 1095?
Also, so I am completely clear on this, Is there any negative consequences to doing a snap temper before a full temper cycle?

 

[benjamin.sellers]

Great question. I've been wondering about this too. So would it be a good practice to temper in the kitchen oven at 400 while the evenheat is cooling and the do a 450 degree (for 1095) temper once the evenheat is ready. I don't like the idea of waiting overnight for the ht oven to come down to temp.

 

[shqxk]

Snap temper is basically a short tempering that immediatly perform as-quenched to reduce any possibly problem due go the internal stress of the as quenched steel, mostly use in heat treat industry due to steel oftenly need to queue in line before having a real tempering to desired hardness. For custom heat treat in small batch you better skip snap tempering.

 

[Natlek]

Great question. I've been wondering about this too. So would it be a good practice to temper in the kitchen oven at 400 while the evenheat is cooling and the do a 450 degree (for 1095) temper once the evenheat is ready. I don't like the idea of waiting overnight for the ht oven to come down to temp.

I use kitchen oven because that was I have. I borrowed very accurate instrument to measure temp in oven . I've marked where exactly was 400 and 450 degree and now it works excellent ..... This is last two I tempered in kitchen oven , 2 x 1 hours on 400 placed on the spine in middle of oven ............ pure gold
PS .Both are grind from very old file ..............they wait me more then 40 years to temper them

 

[kuraki]

The danger of a snap temper is with air hardening steels that require cryo to finish the quench. Snap tempering them before cryo stabilizes some of the retained austenite and makes the cryo less effective.

Shouldn't have any negative impact on 1095 but I don't really see a purpose either, unless you quenched and for some reason couldn't temper within the next couple hours. 30 minutes at 350 or whatever would be better than nothing but if you can do that I don't know why you could not do a full one.

 

[flatblackcapo]

The danger of a snap temper is with air hardening steels that require cryo to finish the quench. Snap tempering them before cryo stabilizes some of the retained austenite and makes the cryo less effective.

Shouldn't have any negative impact on 1095 but I don't really see a purpose either, unless you quenched and for some reason couldn't temper within the next couple hours. 30 minutes at 350 or whatever would be better than nothing but if you can do that I don't know why you could not do a full one.

My situation is that the friend that I am HT this 1095 blade for requested me to temper it back to 59-60 and my home oven has trouble holding 500*F with out fluctuating 20-25*F . I was told to always let my HT oven cool down with the door closed to prevent oxidizing the coils and shortening their life. Cooling the HT oven down with the door closed takes a lonnnng time. I wonder just how much faster the coils will need replacing if I cool the oven down with the door open.....10% , 50% ?
I almost forgot to say, thank you for your reply, it did answer my question.

 

[kuraki]

Oh. Just temper one time for 2 hours in your easy bake at 350 to 400 then again in your ht oven at 500 after it's cooled down. No sweat. No snap temper required.

 

[flatblackcapo]

Oh. Just temper one time for 2 hours in your easy bake at 350 to 400 then again in your ht oven at 500 after it's cooled down. No sweat. No snap temper required.

Thanks again, kuraki.
I am I using the term "snap temper" incorrectly.

 

[milkbaby]

Another thing you can do in your home oven is leave a bunch of cast iron pots and pans to act as a heat reservoir to avoid wild temperature swings. Just preheat it ahead of time so the temperature is stabilized by the time you're done with HT. Combine that with a 350-400°F initial temper then moving to your HT oven at 500°F would probably work fine.

 

[joedhiggins]

In a decent quality oven you probably are not getting wild temperature swings in the center of the oven. If you are worried about it, put the blade into some sort of heat sink. I have tested the three kitchen ovens I have owned since I started smithing with a digital thermometer that records history and the largest swing I saw was less than 10 F at the center of the oven during preheat. Said swing was quick (it was in a convection oven), so I doubt it would have translated into excessive tempering. That being said, maybe other ovens are worse.

I suspect that if there is anything to worry about it would be excessive radiant heat off exposed elements or open flame that could detemper an edge. A loose aluminum foil edge wrap would likely prevent this, though I doubt it is necessary if you just wait until the oven is preheated.

 

[Stacy E. Apelt - Bladesmith]

In your situation, I would oven temper at 350-400F ( doesn't need to be exact) then when the HT oven has dropped to 500F do the second temper. It is a personal preference, but I like two hour tempers. The extra hour does no harm, and will give a tiny increase in toughness. The second temper could be the next day on 1095.

 

[flatblackcapo]

Another thing you can do in your home oven is leave a bunch of cast iron pots and pans to act as a heat reservoir to avoid wild temperature swings. Just preheat it ahead of time so the temperature is stabilized by the time you're done with HT. Combine that with a 350-400°F initial temper then moving to your HT oven at 500°F would probably work fine.

In a decent quality oven you probably are not getting wild temperature swings in the center of the oven. If you are worried about it, put the blade into some sort of heat sink. I have tested the three kitchen ovens I have owned since I started smithing with a digital thermometer that records history and the largest swing I saw was less than 10 F at the center of the oven during preheat. Said swing was quick (it was in a convection oven), so I doubt it would have translated into excessive tempering. That being said, maybe other ovens are worse.

I suspect that if there is anything to worry about it would be excessive radiant heat off exposed elements or open flame that could detemper an edge. A loose aluminum foil edge wrap would likely prevent this, though I doubt it is necessary if you just wait until the oven is preheated.

In your situation, I would oven temper at 350-400F ( doesn't need to be exact) then when the HT oven has dropped to 500F do the second temper. It is a personal preference, but I like two hour tempers. The extra hour does no harm, and will give a tiny increase in toughness. The second temper could be the next day on 1095.

Thank you guys. It is in the HT oven right now.