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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 12-31-2015, 09:18 AM
WNC Goater WNC Goater is offline
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What are these marks, post heat treat?

Another newb question. Can anyone tell me what these small circles are? Not there prior to heat treating but there after sanding away the firescale. Small circles are approximately 1mm across. First two blades were of 1095 and each had 1-3 of these marks. Blade #3 in 1095 was clear. Last two blades were of 1084 and each had a couple of these marks. After the first two, I cleaned them with alcohol before heat treating to wipe off and remove any residual oil, thinking perhaps some speck of something was on there. Last two (1084)were carefully cleaned, laid on a paper towel while the oven heated and not touched on the blade area at all until after tempering.
So initially I thought some dust or something was on the blade but after carefully cleaning the last two I'm wondering if it is some impurity in the steel??

First blade, 1095 (scratches from using and testing)



1084 blade


1084 blade with large mark and "halo" circle


Last edited by WNC Goater; 12-31-2015 at 08:25 PM.
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  #2  
Old 01-01-2016, 06:14 AM
WBE WBE is offline
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Look like decarb and scale scars. Possibly from over heat, or lack of protection during upper heat level. All you can do with that is to sand it out best you can, and live with it.
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  #3  
Old 01-01-2016, 06:33 AM
WNC Goater WNC Goater is offline
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Originally Posted by WBE View Post
Look like decarb and scale scars. Possibly from over heat, or lack of protection during upper heat level. All you can do with that is to sand it out best you can, and live with it.
Lack of protection? Temperatures were 1095 steel @ 1450 and 1084 steel @ 1500 in a controlled oven.
But what is the "protection" you mention? Is there a coating that can be used to eliminate the firescale? (Jewelers dip gold into a solution of denatured alcohol and boric acid which prevents firescale when soldering.)
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  #4  
Old 01-01-2016, 07:42 AM
jmccustomknives jmccustomknives is offline
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I've never seen that before. How long were they in the oven? Were they sitting on something in the oven? What did you pick them up with?

Ask enough questions and sooner or later we'll figure it out.
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  #5  
Old 01-01-2016, 09:10 AM
WNC Goater WNC Goater is offline
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Originally Posted by jmccustomknives View Post
I've never seen that before. How long were they in the oven? Were they sitting on something in the oven? What did you pick them up with?

Ask enough questions and sooner or later we'll figure it out.
See, You're going down a road that I suspect, that is, something got on the steel.

The first 1095 steel I did, 1475? for about 20 minutes. When I pulled it out and quenched in canla @ 140-150?, I rubbed with a file and didn't feel the steel was hard enough. Laid the knives down and brought oven back up to temp to reheat. May have wiped off with a paper towel, not sure. They were handled somewhat before I put them back into the oven for reheat @ 1475?. There were two blades and both had these marks. Curious to me, they are perfect little circles.

The third 1095 blade I did, I carefully cleaned with alcohol and immediately put into the oven @ 1475?, of course, oven loses heat when the door is opened to insert the blade. So I started timing after temp comes back up, around 20-30 minute soak time then quench. This blade has no marks.

Next two blades were 1084 steel. I cleaned them with alcohol and laid them on a paper towel while oven heated. Into oven @ 1500? for 10-12 minutes. Then quench in canola at about 130?. Wipe off excess oil. Tempered at 375? for two, two hour cycles air cooling between.
Both of these had these funny little circle marks.

I did one yesterday, a skinner style blade with the last of the 1095 I have. Cleaned with alcohol, put into oven with tongs in position as *below. 1475? for 25 minutes +/- 3-4 minutes. Quenched in canola @ 130-140?. Two, two hour cycles @ 425? cooling between. This blade looks really good, clean, no marks or other "cooties" on the steel.

The black/fire scale on the 1095 seems to clean up much easier than the 1084 too, not sure if that is because of the steel type or the 25? difference in heat temps.

*When heat treating in the oven I stand the blades edge up, spine down, leaned against a little ceramic pad, and handle only the back of the tang with tongs.


So I'm kind of leaning toward something getting on the blade and burning into it.
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  #6  
Old 01-02-2016, 06:46 AM
WBE WBE is offline
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1095 does not require or need a soak for that long. 5 to 10 minutes at temp is plenty. It is a simple steel and not a high alloy. To soak a blade as long as you are doing you need a decarb protector, such as ATP-641, or something similar.
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Old 01-02-2016, 09:22 AM
jmccustomknives jmccustomknives is offline
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Originally Posted by WBE View Post
1095 does not require or need a soak for that long. 5 to 10 minutes at temp is plenty. It is a simple steel and not a high alloy. To soak a blade as long as you are doing you need a decarb protector, such as ATP-641, or something similar.
I agree, that soak time is a little long. Scale can build up, I'm thinking that's what's going on.
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Old 01-02-2016, 09:37 AM
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ATalley ATalley is offline
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Im not sure how others feel about this, but Ive been taught to put the knife in the oven at room temp and then run up to your target temp. Ive not heard of placing a cold knife blank in a hot oven thats at temp and letting it catch up during 'soak time', seems as if that would invite warpage and other problems. The steel isn't having enough time to get into solution and that could result in problems like what you are experiencing.

Its been explained to me that a soak time is when the environment inside the oven reaches the target temp and you the oven to stay at that temp for an amount of time to allow the carbon, iron and any other alloys in the steel to flow into solution and create solid bonds between the atoms. (10** series steels are only carbon and iron= so a long soak time isn't required) the equation Ive heard is 1 hour per inch. So if you have a 1/4" thick piece of steel the ideal soak time is 15 minutes.

Cant say as I've seen the embedded/etched/engraved circles before. Im sure there is a wise guru on here who may be able to advise.

The third photo looks like a boil youd get during the quench. if you are not moving the knife, or circulation the oil enough during the quench, the fluid near the knife takes too much heat and boils which create a bubble of gas and that part of the knife its touching doesn't get cooled properly resulting in that little circle in the steel.

Jut $.02 from this guy...good luck!

And Happy New Year! Auld Lang Syne!


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Old 01-02-2016, 10:34 AM
samuraistuart samuraistuart is offline
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I can say that at first glance, they do look like a few anomalies I have seen a few times on my own blades after heat treat. I have nailed down the culprit in my case, tho......it is some sort of flux inside ATP-641 anti scale compound that will do this. However, it seems you indicated you did NOT use any sort of decarb. Guys.....if you are using a kiln, you should be protecting blades from decarb. NOT to be confused with scale. Scale forms on the surface, it is the carbon that has leeched out near the surface of the blade. Scale is easy to deal with, but a layer of decarb needs to be sanded off on a finished knife.

That first pic of the circle...WOW. Not sure what can cause that. I've never had any sort of strange patterning on my blades until I started using ATP, but it isn't a huge issue. I've since learned how to mitigate it...and it's not something that others are seeing anyway.

Concerning soak time with 1095, 10-15 minutes is generally recommended. Sure, 1095 doesn't have alloying, but it DOES have extra carbon that comes into solution either one of two ways.....higher heat which will not make the blade harder, it will grow grain, and you'll have retained austenite. And number two, the correct way to heat treat 1095, is with a solid soak. 10 or 15 minutes is good.

Get the kiln to temp, 1475 to be exact, and THEN place the blade in. Do NOT put blade in when kiln is cold and then ramp up. You want to heat the blade very quickly, this helps keep aus grain small. ESPECIALLY if you are not protecting from decarb...put it in when the kiln has reached temp.

The soak begins when the kiln rebounds to its target temp, after placing the blade in. Doing this does NOT cause any warping. That happens during marteniste formation after quench, usually due to imperfect grinds, or improper quenching technique.
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Old 01-02-2016, 05:00 PM
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Andrew Garrett Andrew Garrett is offline
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That's strange!

I have been making knives from 1095 for a decade now and never seen that.

Soak time for 1095..., what's that?
I stick the cold steel (evenly ground to 120G usually about 1/8" thick) into the forge edge up, move it around as needed to evenly heat the blade under the downward blast of fire, when it get to be the right dull red color, I test it against the hanging magnet (sometimes I have to dip the very tip into oil a few times to prevent overheating, but mostly I just jam it into the Insulwool at the back of the forge to shield it a bit).
Quench in 120* peanut oil. Bam. It's a knife. It takes just a few minutes.
Most are clay backed with Satanite to create an attractive hamon.

I am sure that I am a poor example to follow, so consider this as 'educational, not instructional'.


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Old 01-02-2016, 07:54 PM
WNC Goater WNC Goater is offline
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Thanks guys for all the good info. I'm gonna shorten the soak time to around 10 minutes @ 1474 for the 1095 and check into some of that ATP-641. That stuff would save a ton of hand sanding after the heat treat.

Andy Garret, there's a lot of attractiveness to simplifying the whole process with a forge. Your knives look nice by the way. I like that finish. I assume thats what you acheive with the clay and satanite.
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Old 01-03-2016, 06:48 AM
WBE WBE is offline
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Originally Posted by WNC Goater View Post
Thanks guys for all the good info. I'm gonna shorten the soak time to around 10 minutes @ 1474 for the 1095 and check into some of that ATP-641. That stuff would save a ton of hand sanding after the heat treat.

Andy Garret, there's a lot of attractiveness to simplifying the whole process with a forge. Your knives look nice by the way. I like that finish. I assume thats what you acheive with the clay and satanite.
Two coats ATP on main blade. Tree coats at edge and point area.
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Old 01-03-2016, 01:25 PM
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Andrew Garrett Andrew Garrett is offline
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Goater, Thanks for the compliment.
Please don't misunderstand me. I'm not impugning your process, just contrasting it to mine. There are many paths to a functional blade and each maker has his preference.

I too have a digital oven, but I find using it to be too cumbersome unless I need to (stainless).

My little atmospheric forge that I bought on ebay years ago (made from an old insecticide bottle) is super fun and heat treats smalls knives like a champ! Having a cheap forge blowing fire in the shop makes me feel all 'smithy' anyway. I love the nostalia.

I've chosen a path that works for me, and I'm happy to share my experiences. It looks like you have done the same. Just be willing to adjust processes when the outcomes demand it.

Happy New Year!


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Old 01-04-2016, 05:52 AM
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If you are not forging your blades (which might impart these "artifacts" into the steel), what I'm seeing is defects in the steel itself. I've used a lot of 1095 in the past and have never had pitting like that caused by the heattreating process. If you look closely at the first pic there is evidence of sporadic lemon peel pitting. This would be a defect in the steel not caused by your process. Not all that common and most steel suppliers will replace that chunk of steel. I would have had to send it back. Each pic indicates to me that the imperfections were in the steel that usually occur near the beginning or end of a steel mill run. Normally these areas are cut off and returned to the mix for remelting.

Andrew - little concerned that you would have a forge running in your shop with loose (un-coated) K-wool inside. Everytime you fire up and/or disturb that wool, micro fibers are being blown out into your breathing air for you to suck down into your lungs. Not a good thing. Alternative is to make a small half tunnel from fire brick to place at the rear of your forge just big enough to protect the thinner tip. Make something easy to install/remove as needed.


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Last edited by Crex; 01-04-2016 at 05:54 AM.
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Old 01-06-2016, 11:07 AM
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Andrew Garrett Andrew Garrett is offline
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Carl. I have heard that concern before and I actually have Satanite on hand to coat it--just never have. I pull my little forge to the open garage door when I forge and I suppose I could even wear my respirator.

My father was diagnosed with Pulmonary Fibrosis recently, so perhaps I should be more diligent in my safety practices.

Thanks for the gut check brother.


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1084, 1095, acid, back, blade, blades, cleaning, dip, edge, file, fire, forge, heat, heat treat, knife, knives, post, quenched, sand, sanding, scale, skinner, small, steel, tang


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