440B hardness

M

Mac an sealgair

Joined
Apr 7, 2020
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Hi all, looking for a bit of advice. I’m making a small knife with 440B, an ornamental sgian dubh style knife. It’s my first attempt using stainless and I’m only set up for oil quenching. I bought the 440B because they didn’t have 440C and the carbon content of this particular steel is .93%, not far off the .95% of 440C and good enough for my needs. I’ve just finished heat treating it and after tempering for 2hrs at 150C my 65hrc hardness file is skating over it and doesn’t even leave light scratches. I know the hardness of this steel is meant to be 59hrc max so what’s going on?
If my temper has failed in some way, how hard does 440B get before tempering? I would have thought that given 59hrc max at such a low temper temperature it would be softer than 65hrc straight after quenching. I didn’t bother checking at the time because the final hardness wasn’t critical, anywhere mid 50’s would be fine. The problem is if it is too hard it will be brittle.
My heat treat in a gas forge with thermocouples fitted was heat to 800C and hold for a few mins to let the blade heat up then raise the temp to 1025 and hold for 10 mins before quenching in warmed Rye oil 32. Knife was coated in ATP 641 prior to heat treat. After cleaning it up I clamped it between two steel plates then put it in the freezer fo 20mins, (every little helps), then straight into the oven. First cycle was an hour and a half to give it time to warm up. Took it out and quenched/cooled then back into the oven for another hour.
Did it need more time due to the steel plates, both 6mm thick or am I missing something 🤷🏻‍♂️
I use the same steel plates for my carbo knifes to prevent warping with no problems but that’s at higher temperatures.
 
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Welcome to Shop talk.

440B is a stainless steel. It is heated to 1020-1050°C and held for 20 minutes at a controlled temperature. Quenching in oil is fine. It needs to be in a sealed stainless foil packet and in a HT oven. A forge won't work.

As-quenched if properly HTed it is Rc 59-60/ A temper of 150ÜC will drop it to Rc58. 200°C will take it down to Rc56.

Chech the local chaps. I bet someone in Perth does stainless HT. Many machine shops can do it. There are a reasonable number of knifemakers out your way, so see if you can get in touch with one.
 
Thank you Stacy, and good to be here.
My problem isn’t achieving the desired hrc but I seem to have mysteriously overshot it by a country mile at 65hrc plus. You said it should be Rc 59-60 after quench, that’s the piece of info I couldn’t find. If my bit of steel is so hard that might indicate it’s not 440B.
I cooled it after temper to about room temp before checking hardness. Would that affect the results I got? Could that hardness drop now that it’s rested overnight? I have to go to work so won’t be able to check until tonight and just picking brains. I’m doubting everything at the moment, my readings, the steel and even if it’s stainless.
I get your advice about sending it out and for most stainless types I’d agree which is why I’ve never worked with it before. With my forge setup I can achieve the desired temps and hold them by tweaking when required to. Time consuming yes, fun most definitely and the end results are self satisfying, mostly 🥴. Would an oil quenching stainless still need a foil wrap as opposed to a coating such as ATP 641? The point is an oxygen free environment to prevent carbonisation, my blade looks clean enough, no scale.
I’m not arguing or doubting, just asking and learning.
Thanks again for the speedy reply 👍🏻
 
DevinT said:
Data sheets are conservative on hardness, my guess is that you are in the 61-62 hrc range. Surface grind it and get a proper hrc test done.

Hoss
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Agree about the data sheets but with 440B every data sheet Ive read is consistent with the 58-59hrc after temper. Im way above that. I’ll have another look at it tonight after work and try tempering again.
I get whats being said about sending it out for heat treat and testing but in this case, as an ornamental piece, I dont think thats worth doing. Plus its a prototype, its not going anywhere. Achieving hardness isnt the issue, Im confused as to why Im getting such a high hardness.
I know 440B isnt a popular steel to use for knives with better options out there but I was hoping some of you might have used it at some point and been able to pass on some clues as to what might be going on.
Thanks for the advice though.
 
Just with hrc testing files, rubbing them over the side of the blade. Not the most accurate but when the 65rc file skates with very light marks, no biting, you know your there or thereabouts.
 
Mac an sealgair said:
Just with hrc testing files, rubbing them over the side of the blade. Not the most accurate but when the 65rc file skates with very light marks, no biting, you know your there or thereabouts.
Click to expand...
You don’t know what the hardness is, you haven’t done anything special in the heat treatment.

Congratulations, you got a piece of 440B to harden, no big deal.

A forge is not the correct piece of equipment to heat treat high alloy steels, a hardness file is not the best way to test for hardness.

Don’t get too excited, there’s nothing special going on here.

Hoss
 
“A forge is not the correct piece of equipment…”

“Congratulations, you got a piece of 440B to harden, no big deal.”

🤔

Read the post before making silly replies snd if you cant be helpful why comment at all?
 
What help are you looking for? Do you want an award for heat treating 440B in a forge and quenching in rye oil?

Most cutlery grade stainless steels and some high alloy steels like D2 don’t harden to 65.

Every other week someone posts that they heat treated some steel in their forge and have spectacular results and want someone to tell them that they have discovered the secret to heat treating.

Buy a furnace, make some heat treat coupons, vary the austenitizing temperature, do it with and without cryo, check the hardness on an accurate hardness tester, send them out for charpy testing, do some metallography, report your findings and then we’ll have something to discuss.

I’m not trying to hurt your feelings but heat treating takes practice and the proper equipment.

You have a mediocre steel, the wrong equipment, a less than optimum quench oil, inaccurate testing methods and you want us to help.

Hoss
 
Mac an sealgair said:
“A forge is not the correct piece of equipment…”

“Congratulations, you got a piece of 440B to harden, no big deal.”

🤔

Read the post before making silly replies snd if you cant be helpful why comment at all?
Click to expand...
Devin might be blunt in his replies, but he is a top expert with loads of experience. Read his replies carefully as taken well they are very helpful.
 
Ok I know Devin and most other posters on here have more experience and expertise than I have, that’s why I’m on here asking the questions. What Devin is missing is that I’m not trying to say I’ve spectacularly made some shit steel into a super steel or reinvented the wheel. I’ve heat treated a piece of stainless for the first time using the equipment I’ve got, you’ve all been there, followed the suppliers heat treat schedule and got some unexpected results. My problem isn’t about the hardness but why it didn’t soften during temper. I expected mid fifties and got mid sixties instead. That’s not some kind of boast or bravado. I’m not trying to say I’ve achieved something nobody else can. I’m trying to work out why I failed in getting the knife soft enough.
If he’d read the post properly before shooting off he might have realised that.
I work with carbon steels, I’m not a complete noob. I have an understanding of heat treating. Stainless is different and new for me, but 440B, substandard as some may think, is absolutely fit for purpose for the use I want to use it in an ornamental piece that will never see any work or even have a properly sharpened edge. It’s a showpiece knife that hopefully won’t break if it’s dropped. That’s it, end off. No showing off no silly claims.
 
I’ve read all of the posts in this thread very carefully but we are coming at things from different perspectives.

People post things and have a specific answer that they want. If they don’t get the answer they want, they ask the question over and over until someone gives them the answer they want.

Hoss
 
I can't speak to the other stuff, but as to the hardness files, I've found that one can essentially get the results they want to get. For example, with the right touch, I can make a 65RC skate over a 62RC knife. When the teeth of the file dull, it only makes it easier to get misleading results.
 
And what’s the answer I want Devin?
But yeh my perspective was to try and have intelligent conversation with people who had used 440B in the past and share their experiences and maybe learn something. Your perspective has been to twist my words into something I wasn’t saying.
To the millions of guys out there with gas and coal forges, which covers almost all highly skilled professional blacksmiths, your knives are crap if you don’t have a heat treat oven or an HRC tester.
I’m obviously on the wrong site to learn anything.
Thank you Stacy, the only one I actually learned something from.
 
Mac an sealgair said:
Just with hrc testing files, rubbing them over the side of the blade. Not the most accurate but when the 65rc file skates with very light marks, no biting, you know your there or thereabouts.
Click to expand...
I think your first step is you need to get accurate hardness testing before coming to any conclusions.

Perhaps somebody on the forum will offer to test it for you with a rockwell hardness tester.
 
Mac an sealgair said:
Ok I know Devin and most other posters on here have more experience and expertise than I have, that’s why I’m on here asking the questions. What Devin is missing is that I’m not trying to say I’ve spectacularly made some shit steel into a super steel or reinvented the wheel. I’ve heat treated a piece of stainless for the first time using the equipment I’ve got, you’ve all been there, followed the suppliers heat treat schedule and got some unexpected results. My problem isn’t about the hardness but why it didn’t soften during temper. I expected mid fifties and got mid sixties instead. That’s not some kind of boast or bravado. I’m not trying to say I’ve achieved something nobody else can. I’m trying to work out why I failed in getting the knife soft enough.
If he’d read the post properly before shooting off he might have realised that.
I work with carbon steels, I’m not a complete noob. I have an understanding of heat treating. Stainless is different and new for me, but 440B, substandard as some may think, is absolutely fit for purpose for the use I want to use it in an ornamental piece that will never see any work or even have a properly sharpened edge. It’s a showpiece knife that hopefully won’t break if it’s dropped. That’s it, end off. No showing off no silly claims.
Click to expand...


I think the problem is the temperatures that are being used can't be confirmed and are prone to error and the hardness testing method being used is also not very accurate and prone to error so the problem here is more likely measurement error in temperature and hardness than something unusual with the steel.
 
I am also based in Europe and it looks like most of the shops carrying knife steel have that high carbon 440b. With oven at 1060°, dry ice bath and temper at 180°C I am reaching about 61 HRC.

I doubt that it is in 65 HRC range, but it might be in 62-63 HRC range.

Hardness chisels with a narrower hardness range could give you a preciser results. Keep your eyes open for a used hardness tester in local classifieds and auction houses.
 
AISI440B is a dignified steel, nothing special but dignified. As for the rest of the discussion, what we are trying to tell you is that with files you do not have a certain measure of hardness, with forging you do not have a certainty of temperature, steels with a high chromium content are also sensitive to variations. of only 5 ° C. For this reason you should review your TT for stainless steels by following Devin's tips.
 
Mac an sealgair said:
Ok I know Devin and most other posters on here have more experience and expertise than I have, that’s why I’m on here asking the questions. What Devin is missing is that I’m not trying to say I’ve spectacularly made some shit steel into a super steel or reinvented the wheel. I’ve heat treated a piece of stainless for the first time using the equipment I’ve got, you’ve all been there, followed the suppliers heat treat schedule and got some unexpected results. My problem isn’t about the hardness but why it didn’t soften during temper. I expected mid fifties and got mid sixties instead. That’s not some kind of boast or bravado. I’m not trying to say I’ve achieved something nobody else can. I’m trying to work out why I failed in getting the knife soft enough.
If he’d read the post properly before shooting off he might have realised that.
I work with carbon steels, I’m not a complete noob. I have an understanding of heat treating. Stainless is different and new for me, but 440B, substandard as some may think, is absolutely fit for purpose for the use I want to use it in an ornamental piece that will never see any work or even have a properly sharpened edge. It’s a showpiece knife that hopefully won’t break if it’s dropped. That’s it, end off. No showing off no silly claims.
Click to expand...
I still use hrc files myself and find them very useful, but they also have a learning curve and can be very misleading at times. If any file skates over the blade, I’d say it is good to go for your intended use.
 
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