Failed Heat Treat Due To AntiScale?

[ScarFoot]

I heat treated some blades last week and finally got them cleaned up and ready for hardness testing over the weekend. This was the first time I used an anti-scale compound (atp-641) and think it might have caused issues with the heat treat. I diluted it down somewhere around 3:1-4:1 water:atp and dipped the blades (sanded to 280 grit) after they had been heated to 190F. I left them submerged for 15-20 seconds and let them drip off once removed then dried them with a heat gun. After that they cured for 2 days until heat treat. I got complete coverage on all blades. The layer was so thin I really didn’t think it would survive until I heat treated. You could rub it off with your finger tip. I was heat treating 3 different types of steel: 1095, W2, & 80CrV2 all of which I have used before and all purchased from NJSB. While I was cleaning up the 1095 and W2 after heat treat I noticed an odd hamon effect on some of the blades. I assumed it to be decarb and ground a little more off to no avail. I took 0.025”-0.030” off of each side of one and it was still there. Hardness testing confirmed what I suspected which was that those two steels didn’t fully harden. I got anywhere from 39-64 HRC…on the same blade I ground until I was absolutely confident it wasn’t decarb. I etched it after I got home to make the areas in question stand out. A couple others tested all over the place so obviously I don’t trust any of the 1095 or W2 blades in their current state. The only thing I did different this time was the anti-scale. One thing that stood out was that everything I read said the anti-scale generally flakes off during quench but that didn’t happen on any of mine. It stayed on for the most part until I sanded it off.

My heat treat process for the 1095 and W2 is as follows and all blades were made via stock removal, none were forged:
1. Oven heated to 1465F confirmed with second thermocouple.
2. blade placed in oven and once temperature has come back to 1465 I soak for 10-15 minutes depending on thickness.
3. Quench in Parks 50 (leave blades completely submerged until cool enough to handle with work gloves.) Oil temp averages around 100F.
4. Straighten if needed.
5. Place in 300F oven for snap tempering.
6. Tempered at 405F for 2 hours then cooled to room temp then tempered again at 405F for 1.5 hours.
I normally get around 60-61 HRC with this recipe.

Cleanup for hardness testing was done with SGA. Ground at least 0.015” or more per side and went to 400 grit finish. Sanded some to 600 grit on surface plate and buffed them. All were flat and parallel to within 0.001”. I also checked the hardness tester against 3 test blocks and it measured within 0.1-0.2 HRC of each.

So the question is, could that thin layer of anti-scale have caused all this chaos or am I missing something? Had it only been only one of the steels I would have thought it was just an issue with that batch of steel but I had the same issue with 2 similar steels. The 80CrV2 came out to 60-61HRC on every blade and was probably the most consistent hardness measurements I’ve seen so far. I’m going to run the 1095 and W2 again minus the anti-scale and see what happens.

 

[DevinT]

What was your starting thickness?

Hoss

 

[DeadboxHero]

I taught a heat treatment class for 26C3, the ATP-641 reduced the hardenability. It's better just to grind off the decarb after austenitizing and quenching and to skip the coating and just use foil for thermal cycling.

P50 also is not as fast as water.

Vigorous agitation is crucial with P50 on shallow hardening steels. Pre grinding bevels may also be crucial depending on stock thickness.

 

[ScarFoot]

I forgot to add all blades were pre-ground 80%-90% and all skated a file easily along the edge when removed from quench. This is the first time I’ve ever had one fail to harden using my method and it looks like most of the 1095 and W2 failed. I’ve debated water quenching them but have been concerned it would be a little aggressive on a pre-ground blade.

 

[DeadboxHero]

I forgot to add all blades were pre-ground 80%-90% and all skated a file easily along the edge when removed from quench. This is the first time I’ve ever had one fail to harden using my method and it looks like most of the 1095 and W2 failed. I’ve debated water quenching them but have been concerned it would be a little aggressive on a pre-ground blade.

If you thermal cycled these shallow hardening steels with normalizing and annealing it also further reduces the hardenability.

Seems there's a lot to explore when it comes to doing deciding to do interrupted quench, what water temperature to quench with and using salt brine.

You'll have to do some testing.

I've currently settled for not using extremely shallow hardening steels and pre-grinding, selecting a proper austenitizing temperature and using very vigorous agitation in p50.

There are certainly some cases with some materials where water could be the only way to avoid very small colonies of pearlite hiding in the microstructure dropping the edge retention.

 

[ScarFoot]

If you thermal cycled these shallow hardening steels with normalizing and annealing it also further reduces the hardenability.

Seems there's a lot to explore when it comes to doing deciding to do interrupted quench, what water temperature to quench with and using salt brine.

You'll have to do some testing.

I've currently settled for not using extremely shallow hardening steels and pre-grinding, selecting a proper austenitizing temperature and using very vigorous agitation in p50.

There are certainly some cases with some materials where water could be the only way to avoid very small colonies of pearlite hiding in the microstructure dropping the edge retention.

Being as they were stock removal I didn’t perform any thermal cycling. I try not to apply extreme heat to material any more than absolutely necessary. The reason I initially suspect the anti-scale is because of the visible hamon effect present on multiple blades during cleanup. Plus it was the only change to the process this time.

I did quite a bit of testing with W2 towards the end of last year and found that my 3/16” test coupons weren’t hardening all the way through with a 10 minute soak and quenching in Parks 50. The 1/8” stuff was fine. I tested more 3/16” coupons with some being soaked for 10 minutes and water quenched and others being soaked for 15-20 minutes and quenched in Parks 50 and got no significant difference in hardness results or grain structure in those scenarios. They all completely hardened and had a very fine grain structure. All of them were soaked at the same 1465F temperature. I hadn’t had any issues with 1095 until now so I’m scratching my head a little on that one. I’m confident in my oven/temp holding and the test equipment so I just have to figure out what part of the process broke down.
I might see if I can find some of the scraps of the stock I used and run a few test coupons with and without anti-scale to see if I can get a feel for what impact it might have had.

 

[Stacy E. Apelt - Bladesmith]

A few questions:
Did you thermal process the steel - Any cycling or normalizing?
What machine are you testing the hardness with?
What volume of oil and tank size?

Don't warm Parks #50. The stated range is 50-120°F, so 100°F should be OK, but ambient temperature always works best for me.

Best way to figure this out is to do several 2"X2" test coupons. Grind them clean and flat on both sides to 280 grit. HT half the batch with anti-scale and half without. Try and do quenching exactly the same. Hardness test all and see what you get. Only hold the corner when quenching.

You have proved why 80CrV is a good choice in steel. It has all the good properties of 1095 and W2 but has uch deeper hardening.

 

[Stuart Davenport Knives]

I have never had an issue at all with shallow hardening steels and ATP-641, or any steel for that matter. After the blade is degreased thoroughly, I just dip the tip of the knife in the ATP bucket and, using my wife's toothbrush, I just smear it back towards the handle. Also using my wife's hair dryer, it takes maybe a minute to dry, a little longer for longer blades. It almost always blows off in the quench. If it doesn't, I would suspect it to be applied too thick. Sometimes I will have the ATP remain on the blade after removed from the P50, but it wipes right off with your finger.

There is a few thousandths of decarb that is ground/sanded through very easily. I absolutely love the stuff. The only drawback is that you have to apply it to every cycle you do....normalizing, cycling, anneal, hardening.

If it's too thick, I can see that causing problems with such shallow hardeing steels.

Then there is the possiblity that the steel from NJSB is coarse spheroidized, and in that case really high normalizing heats are needed. I haven't used any shallow hardening steels from NJSB in quite some time, and was told that the mill they get their steel from has modified their annealing process for the better.

(p.s. I don't really use my wife's toothbrush)

 

[ScarFoot]

I read through my original post to make sure I covered everything since I was typing it past my bedtime. Full disclosure on something I missed, I was adding clay to the spine to force hamons which I have done successfully many times with both steels. I used the same clay as always, thin layer like always, stopped at least an inch from the tip, didn’t go past halfway to the edge or past the front pin hole with clay just like I always do. I also heat edge up on a kiln rack that makes minimal contact with the blade. When I pull the knives to quench I only grab the last 1/4”-1/2” of the blank. I generally test hardness around the middle pin hole or between the middle and back pin holes
My thought process has always been “repeat the process, repeat the results.” The only variable on this batch was the anti-scale but I’m not convinced there’s not something else going on. I might have to do some light science on this one.

 

[ak650]

While I'm new to knife making, I have heat treated oil and water hardening steels for tooling, etc...I find it a lot less hassle to simply quench and temper them unprotected, and then soak them overnight in vinegar to remove the scale. Carried that practice over to my introduction to knife blades. Here's my first blade ( 1095 ) after quench & temper.

Here it is, after an overnight soak in grocery store white vinegar. The scale wiped right off with a scotch-brite pot scrubbing pad with very little effort. For faster results, use "cleaning vinegar" which is a 30% acetic acid concentration, as opposed to the 5-6% in the grocery store stuff. It'll do the job in 4-6 hours. It also strips the mill scale off of hot rolled steel like nobodies business.

 

[ScarFoot]

A few questions:
Did you thermal process the steel - Any cycling or normalizing?
What machine are you testing the hardness with?
What volume of oil and tank size?

Don't warm Parks #50. The stated range is 50-120°F, so 100°F should be OK, but ambient temperature always works best for me.

Best way to figure this out is to do several 2"X2" test coupons. Grind them clean and flat on both sides to 280 grit. HT half the batch with anti-scale and half without. Try and do quenching exactly the same. Hardness test all and see what you get. Only hold the corner when quenching.

You have proved why 80CrV is a good choice in steel. It has all the good properties of 1095 and W2 but has uch deeper hardening.

No cycling or normalizing.
Not sure the brand of the machine. It’s a new bench top machine but one of the less expensive ones ($2000-$3000). We did check it against the test blocks and it hit the numbers on all 3.
My small quench tank holds a little under 2 gallons. It is a vertical tank and I had it almost completely full. I have a larger 3+ gallon tank but don’t use it for anything yet.

The oil was within the temp range the entire time. I start at ambient ~70F and check temps periodically to make sure I don’t exceed 120F.

I wrote another response before this. I forgot to mention I was claying the spines for hamons in my original post. I’ve done that with both steels many times, used the same clay and process and never had heat treat issues.

I do like the way the 80CrV2 steel turned out. I had an older piece I believe came from Jantz if memory serves me correctly that seemed to top out at 58-59 HRC. This new stick I got from NJSB behaves a little more to my liking.

Will definitely work up some coupons. I’ll probably have to order more steel to test all the variations I have in mind. Oddly enough I enjoy working through issues like this. Frustrating as it can be at times these are the things I like about this crazy hobby.

 

[ScarFoot]

While I'm new to knife making, I have heat treated oil and water hardening steels for tooling, etc...I find it a lot less hassle to simply quench and temper them unprotected, and then soak them overnight in vinegar to remove the scale. Carried that practice over to my introduction to knife blades. Here's my first blade ( 1095 ) after quench & temper.

Here it is, after an overnight soak in grocery store white vinegar. The scale wiped right off with a scotch-brite pot scrubbing pad with very little effort. For faster results, use "cleaning vinegar" which is a 30% acetic acid concentration, as opposed to the 5-6% in the grocery store stuff. It'll do the job in 4-6 hours. It also strips the mill scale off of hot rolled steel like nobodies business.

I don’t disagree with what you’re saying but the scale isn’t the problem so much as the decarb. The decarb will be soft and can be 0.015” or so deep and you really can’t see it well on bare metal. On a 80%-90% completed blank that can ruin the edge retention if you haven’t left enough thickness to grind it out. I left some on a test piece of W2 last year that was hardened to 64-65 HRC. I sanded the piece on my flat disc to 600 grit and polished it before hardness testing and it tested around 35 HRC. After it was surface ground removing around 0.020” per side it tested at the actual 64-65HRC. The anti-scale is more of an attempt to reduce the amount/depth of the decarb. I believe the larger heat treating services heat in inert atmospheres to achieve this but that’s harder to pull off in half a garage.

That’s a good looking blade profile. Welcome to the forum!

 

[ak650]

I don’t disagree with what you’re saying but the scale isn’t the problem so much as the decarb. The decarb will be soft and can be 0.015” or so deep and you really can’t see it well on bare metal. On a 80%-90% completed blank that can ruin the edge retention if you haven’t left enough thickness to grind it out. I left some on a test piece of W2 last year that was hardened to 64-65 HRC. I sanded the piece on my flat disc to 600 grit and polished it before hardness testing and it tested around 35 HRC. After it was surface ground removing around 0.020” per side it tested at the actual 64-65HRC. The anti-scale is more of an attempt to reduce the amount/depth of the decarb. I believe the larger heat treating services heat in inert atmospheres to achieve this but that’s harder to pull off in half a garage.

That’s a good looking blade profile. Welcome to the forum!

Gotcha. Got lucky on this one then. I didn't have my hardness tester at the time I did this one. All I had was a set of files, and spot checked it at several spots and they all felt the same. 55HRC skidded off, and the 60HRC just started to bite. Didn't notice any soft spots. Now, I have an Ames Model 1, but I've not done another 1095 blade to try it on. Forgot to note it on the previous post, but it was quenched in room temp Parks 50.