1095 Heat Treat Woes

C

claytonsmith

Joined
Jun 5, 2014
Messages
7
Hello all,

I'm Clayton, and I'm a new-ish knife maker. I'm having quite a bit of difficulty heat treating 1095 and, if I'm honest, it's making me feel a little stupid. Any suggestions or advice is greatly appreciated.

I'll list some pertinent info

Method: Stock Removal
Material: 1/8" NJSB 1095 ( two different batches. both seem...*seem* to be exhibiting the same undesirable result for me)
Blade: Chef knife. 7.5" edge length, 2" height at heel
Quenchant: Parks 50 at ambient temp, indoors.
Heat Treat: full 1/8" thickness 1095, start cold and full ramp to 1475, hold 5 mins, quench in Parks 50, temper in kitchen oven ( indicated 380 degrees, temp of surface of blade, as checked several times is 400f) for two 1 hr cycles. all bevel bevel grinding done post heat treat for the sake of mitigating the risk of warpage during quench.


It seems as though I'm not getting even/through hardening. I've been using this HT method since I started using this steel and making this knife shape. I made several knives that have been through testing in pro kitchens and did great with regard to edge retention, toughness etc. I'm shooting for ~61-62 rockwell and the use seems to indicate that's where I am ( or was?) hitting. They hold a usable edge for weeks in a pro kitchen, they're very thin behind the edge (.005" before sharpening) and act, cut, last very well.

Here's the pickle: Out of the blue ( so it seems) I'm not getting fully hardened blades. I noticed "hamon-esque" lines running in blob/cloud patterns on a couple of blades recently that were most certainly fully quenched and intended to be fully hardened blades. These were not surface issues, as they were present after grinding down to something like .050" edge thickness, post full-thickness .125" heat treat. The previous knives that seemed to do well in testing had a variety of surface finishes. One was ferric etched, one was hand pulled to 1K grit and another had a surface conditioning belt finish. I would think ( maybe foolishly) that these variety of finishes would show any areas of questionable hardness. Especially the ferric etched knife. I'm aware of 1095 tending to be a shallow hardening steel, but I was under the impression that it was of little issue at thicknesses around 1/8" when using a fast oil. Am I wrong about that?

What's blowing my mind is that my success seems to have changed for no apparent reason, with no change in variables. Ambient temp ( oil temp) hasn't changed much, the steel hasn't changed, my method hasn't changed, my evenheat oven hasn't changed ( that I'm aware of), my temp and soak time haven't changed.

Did I just get really lucky on the first few knives and have them through harden? Am I missing something? I'm assuming the blob/cloud patters I'm seeing are a line of demarcation between soft/hard (pearlite/bainite and martensite or whatever it were) material. I'm pulling what little hair I have left out!

Any ideas, comments, suggestions, general genius-ness is appreciated.
 
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I had a similar problem a few months back heat treating in my even heat kiln. Once with some 1075 and another with some white steel #2. what it came down to is needing a longer soak time and a tiny bit higher temp.

Turns out my even heat is off by about 40°F. So when I was shooting for 1450° And a 5min hold, it was just hot enough to only harden the very edge of the steel.

I bumped the temp up to 1480° and held for 10min instead and got the results I was looking for. Very common for your kiln to be reading a bit off from what it says.

Try increasing the temp by 20° and see if you notice a difference, if not then add on another 20°. Shoot for a 10min hold as well, the steel is going to need a little extra time to even out it’s temp. If you watch your temperature reading as you get to your hold temp you’ll see that it bounces up and down for maybe a min or two. So always add on an extra few min to acomidate for that, 8-10min is usually good enough.

Hope this helps a bit,
Kevin
 
That certainly is good info. I did notice that it hunts for it's target temp for a bit. the 5 min soak was just a guess, really, as there is so much conflicting information that I've found around HT. I've read " short soak" so I figured 5 mins was "short." hah. It seemed to work for me so i kept with it. The oven was brand new, though, when I started this procedure. several blades later, it's entirely possible that the thermocouple has maybe settled in or lost some accuracy. I'll give 20 deg higher and 10 min soak a shot. Thanks for the reply!
 
I recommend you put a piece of kiln shelf in the bottom of the furnace to help hold heat better.

Adjust the set point to 1500f on the furnace and preheat the furnace for a bit before putting the blade in. Put blade in and then adjust temp to 1475f. Soak for 7-8 minutes total, quench, making sure oil is close.

1095 does not do well staying in the furnace while ramping.

Hoss
 
DevinT said:
I recommend you put a piece of kiln shelf in the bottom of the furnace to help hold heat better.

Adjust the set point to 1500f on the furnace and preheat the furnace for a bit before putting the blade in. Put blade in and then adjust temp to 1475f. Soak for 7-8 minutes total, quench, making sure oil is close.

1095 does not do well staying in the furnace while ramping.

Hoss
Click to expand...

Noted. Regarding 1095 not liking being in the oven during the ramp: why? Can you explain briefly, if that’s possible?

I don’t ask to sound combative or to cast doubt. I’m definitely not questioning your knowledge base, Devin. I’d just really like to understand what’s going on to the best of my ability. If that happens to resolve the issue I’d like to understand what’s happening.


I hardened the same blade again adjusting the oven temp up 20deg, to 1495, and doubled the soak time to 10 mins. Quenched and tempered one hour at 400. Ground it clean and looked. I can’t seem to catch any demarcation lines/shapes this go around, so I ran another temper cycle. It looks more promising this go around. The only variable here being that this HT was done on a blade that had bevels roughed in (because thats where I was at in the process). That certainly could have influenced likelihood of through hardening, I’d think. So I haven’t proven anything. I suppose I should do another full thickness blade with the higher/longer soak.
 
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claytonsmith said:
Noted. Regarding 1095 not liking being in the oven during the ramp: why? Can you explain briefly, if that’s possible?

I don’t ask to sound combative or to cast doubt. I’m definitely not questioning your knowledge base, Devin. I’d just really like to understand what’s going on to the best of my ability. If that happens to resolve the issue I’d like to understand what’s happening.


I hardened the same blade again adjusting the oven temp up 20deg, to 1495, and doubled the soak time to 10 mins. Quenched and tempered one hour at 400. Ground it clean and looked. I can’t seem to catch any demarcation lines/shapes this go around, so I ran another temper cycle. It looks more promising this go around. The only variable here being that this HT was done on a blade that had bevels roughed in (because thats where I was at in the process). That certainly could have influenced likelihood of through hardening, I’d think. So I haven’t proven anything. I suppose I should do another full thickness blade with the higher/longer soak.
Click to expand...

Grain growth.

Hoss
 
Exactly. Grain Growth. Besides that ....it’s possible your oven overshoots it’s target temp (almost certain it does).

There is ZERO reason to put a blade into a cold kiln and ramp the heat. If you’ve heard this from anyone, discard it. It is BAD practice. Get the oven to 1475f and then insert the blade. Soak 10 minutes and quench in fast oil.

If the knife was forged or the stee was sourced from the New Jersey Steel Baron, normalize it first at 1650f and air cool. Then thermal cycle 3x at 1500f air cool. Then harden at 1475f for a 10 minute soak and then quench.
 
samuraistuart said:
Exactly. Grain Growth. Besides that ....it’s possible your oven overshoots it’s target temp (almost certain it does).

There is ZERO reason to put a blade into a cold kiln and ramp the heat. If you’ve heard this from anyone, discard it. It is BAD practice. Get the oven to 1475f and then insert the blade. Soak 10 minutes and quench in fast oil.

If the knife was forged or the stee was sourced from the New Jersey Steel Baron, normalize it first at 1650f and air cool. Then thermal cycle 3x at 1500f air cool. Then harden at 1475f for a 10 minute soak and then quench.
Click to expand...


I didn't hear it as much as just assumed. That's what I get for assuming. Thanks for the info. I'll give it a shot, only putting the blade into a pre heated oven from this point forward. I have one blade I put through the thermal ringer, so it's a good candidate for normalization.

And this is, indeed, from NJSB. Is the reason for normalization the spheridized state their steel tends to come in or does it have a reputation for something else? I'm trying to grasp all this. I've been watching Kevin Cashen DVDs on repeat, but it's a lot at once. Like drinking from a fire hose.

Thank you, everyone, for the info an suggestions. It's much appreciated.
 
I've normalized two knives now and i've noticed that they warp pretty severely during the normalizing process. They're developing compound warps/waves in the length of the blade. Is that normal during normalizing/thermal cycling? I figured, because I had a controllable oven and good oil that 1095 wouldn't be much of an issue. I'm quickly learning how foolish I am haha.

Thanks everyone!
 
Also, you may be getting a lot of decarb from keeping the blade in the oven during ramp up. You start loosing carbon at around 1250F. One option is to use a thin coating to prevent this (ATP-641 or PBC) or foil. This may be why your ferric etches are variable as well.
 
claytonsmith said:
I didn't hear it as much as just assumed. That's what I get for assuming. Thanks for the info. I'll give it a shot, only putting the blade into a pre heated oven from this point forward. I have one blade I put through the thermal ringer, so it's a good candidate for normalization.

And this is, indeed, from NJSB. Is the reason for normalization the spheridized state their steel tends to come in or does it have a reputation for something else? I'm trying to grasp all this. I've been watching Kevin Cashen DVDs on repeat, but it's a lot at once. Like drinking from a fire hose.

Thank you, everyone, for the info an suggestions. It's much appreciated.
Click to expand...
I've been looking for this answer for a while, what do the color bars under the picture of steel on New Jersey Steel Baron mean?
 
Aldo's 1095 I have noticed heat treats much better if its forged . I was told to normalize . I think its because his is made more for hand forging and going through all the cycles it takes to get a blade just right by hand I am just totally guessing but it seems that way. I totally gave up on his W2 because I just cant consistently get it right for anything that is stock removal and for me I rather use something I can get 100% predictability. You will figure it out .
 
I'm shelfing this 1095 and moving on to something different. I don't have any faith in it. I did some "Scientific method" on it with several coupons and discovered that, through 4 bars of it, there are blobs of steel, sporadically, that won't harden. it took me a while to figure it out, but I saw the beginnings of it several months ago with a knife that etched weird, with blobs in it. I assumed I made an error, so I made several more knives. Every once in a while I'd notice what appeared to be an auto hamon, but in an odd, blob shape. I tested a knife and The tip was hard at 61, a random spot in the middle of the blade was hrc40, immediately next to that was hrc 61 and the heel was 61. The soft spot was at the edge, middle of the blade. Same inconsistencies on a blade that was normalized. I finally got aggravated enough to approach it with Scientific Method. I tested three test pieces, on two different rockwell testers, both verified accurate with test blocks, and came to the conclusion that there are blobs of steel dispersed through these sticks of flat bar that REFUSE to harden past low 40s. I have etched pieces that show amoeba shaped areas that are HRC40-42 surrounded by areas that are 61-62 ( which is what I was shooting for.) There isn't anything that leads me to believe it was an error on my part. It doesn't appear as if it auto-hamon'd with any sort of traceable logic. I'm definitely no expert, so it's possible that I did err, but I don't think that's the case. In a batch of three test coupons, I had two test coupons that completely hardened to my target of 61-62, and then one with a giant soft blob in it (42 rockwell) that ran from the edge of the steel to the middle point of the coupon. If I apply logic, with the only variable being which piece of steel I had in my hand while testing, I don't see how its a procedural error. My ignorant opinion says this steel isn't homogeneous.
 
claytonsmith said:
I'm shelfing this 1095 and moving on to something different. I don't have any faith in it. I did some "Scientific method" on it with several coupons and discovered that, through 4 bars of it, there are blobs of steel, sporadically, that won't harden. it took me a while to figure it out, but I saw the beginnings of it several months ago with a knife that etched weird, with blobs in it. I assumed I made an error, so I made several more knives. Every once in a while I'd notice what appeared to be an auto hamon, but in an odd, blob shape. I tested a knife and The tip was hard at 61, a random spot in the middle of the blade was hrc40, immediately next to that was hrc 61 and the heel was 61. The soft spot was at the edge, middle of the blade. Same inconsistencies on a blade that was normalized. I finally got aggravated enough to approach it with Scientific Method. I tested three test pieces, on two different rockwell testers, both verified accurate with test blocks, and came to the conclusion that there are blobs of steel dispersed through these sticks of flat bar that REFUSE to harden past low 40s. I have etched pieces that show amoeba shaped areas that are HRC40-42 surrounded by areas that are 61-62 ( which is what I was shooting for.) There isn't anything that leads me to believe it was an error on my part. It doesn't appear as if it auto-hamon'd with any sort of traceable logic. I'm definitely no expert, so it's possible that I did err, but I don't think that's the case. In a batch of three test coupons, I had two test coupons that completely hardened to my target of 61-62, and then one with a giant soft blob in it (42 rockwell) that ran from the edge of the steel to the middle point of the coupon. If I apply logic, with the only variable being which piece of steel I had in my hand while testing, I don't see how its a procedural error. My ignorant opinion says this steel isn't homogeneous.
Click to expand...

Ive seen it in his 1095, w2 and 1075
Its not your fault
-Trey
 
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