Heat treat question

A

Andre V

Joined
Oct 6, 2005
Messages
268
Hi guys,

I have been making knives for about 4/5 months. This is my first post on this forum.

I live in South Africa. We use a lot of Sandvik 12c27 stainless steel here and i am picking up a problem.

After heat treatment i am still able to bend my blades.:(

What i have noticed is that after heat treat and tempering i am able to put a blade in a vice and bend it so that the knife bends and stays bent. sometimes they break but they always bend first. As far as i know the blade should flex a bit and then break rather than bend/ deform.

I am sure this is not right. My knives are getting hard, i cannot drill into them at all, so i am sure they are hard.

I have tried different heat treat temps including the makers specification, with the same result. I dont know if anyone here uses 12c27 but is this "bending" normal for the steel??

My heat treatment procedure is as folows :

-Wrap knife is a stainless foil
-Bring kiln upto 1080 deg C
-soak blade at temp for 15 mins
-Quench in mineral oil
-cool to room temp
-temper @ 180 deg C for 1 hour
-put in freezer for 1 hour.

I hve also tried this method

-Wrap knife is a stainless foil
-Bring kiln upto 1060 deg C
-soak blade at temp for 17 mins
-Quench in mineral oil
-cool to room temp
-put in freezer for overnight.
-temper at 180 deg C x 1 hour twice.

Anyway i hope that someone can help, i am sure i am doing something wrong or my kiln is not giving me accurate temps. I was hoping that someone has had a similar experience with stainless and might be able to point me in the right direction.

BTW great forum, lots of good info.

Thanks in advance,

Andre V
 
Stainless will bend unless it is left too hard.Your HT sounds OK and the bending results seem normal.Testing edge retention to determine if the blade is good is a better gague of HT quality.
 
how thick is your blade i have some SS knives that are real thin and have some flex in them but they spring back to true
 
I have tried various thickness. From 2.5 - 4mm. I spoke to a local guy here who suggested testing my kiln. I think thats the next logical step anyway. Thanks for the replies though.
 
Yes , always check your furnace temperature. You might increase your soaking time even though that steel doesn't have all that much carbon or high amounts of Mo, V or W. ...How do you get from foil to quench ? The most convenient way is to plate quench .Do a search here on "plate quench" . Taking it out of the foil or quenching in oil in the foil can lead to problems.
 
mete said:
Yes , always check your furnace temperature. You might increase your soaking time even though that steel doesn't have all that much carbon or high amounts of Mo, V or W. ...How do you get from foil to quench ? The most convenient way is to plate quench .Do a search here on "plate quench" . Taking it out of the foil or quenching in oil in the foil can lead to problems.
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My oven is cylindrical, my lid has a hook on it. I have a piece of wire attached to the tang of my knife i then wrap in foil, with a bit of toilet paper to burn oxygen and seal around the wire which then hangs from the lid , after hardening i lift the lid and pull off the foil with my other free hand and quench.

I have been doing some reading and see that i am doing quite a lot wrong. Firstly i am not heating my quench oil up.

I have also read about plate quenching. Some questions on that now.

When i remove my blade from the oven, do i put it in the plates in the foil?

Second question how much pressure do i apply to the plates?

Third question can i leave the blade to cool by itself or should i use a air compressor?

Lastly is it advisable to bring the blade up to hardening temperature slowly or is it fine to just drop it into a hot oven from room temp? For e.g put the blade in when the oven is cold and let the blade heat up with the oven and when i reach right temp, soak for the correct time.

Lots of questions, i know. Thanks in advance.
 
Do you have the afri-thipa kiln? Sounds very much like it. I just got one, its pretty nice but Its VERY annoying when you can only heat one blade at a time!
 
JohanB said:
Do you have the afri-thipa kiln? Sounds very much like it. I just got one, its pretty nice but Its VERY annoying when you can only heat one blade at a time!
Click to expand...

I think its probably the same.
 
Hello Andre

I'm a newbie [to knife making and this forum] and a fellow South African.
I have only made a few knves so far, so I'm no expert and still have plenty to learn.
The 2nd heat treatment procedure is the same one tought to me, and the same procedure I used on one of my knives, though I admit I never tried to bend it. So it's very distressing to hear that you can bend the blade afterwards. Have you had your kiln checked out yet? The only other thing is to maybe let the blade soak for a few more minutes. The 17min is for 3.25mm blade thickness, 5min soak time should be added for every 1mm thicker, but I'm sure you have read the same data sheet I have. Please let me know how this turns out as my next knife will be from 12c27.
Best of luck
Garth
 
Hi Garth,

I am having my oven checked on monday. In a way i actually hope it is my oven, i have been racking my brains trying to figure this one out.

At least if its my oven, all thats needed is a quick repair and thats that. Hopefully.
 
Why is bending bad? It seems like a little warning before the blade breaks would be nice.
 
Andre

How about trading a bit of steel and cross practicing? I'll send you some Crucibl 154CM and you could send me some of the 12C27 (which I've never had the opportunity to use). Of course, the shipping might cost more than the steel, but it might be informative to try. It would also try your steel in a different oven.

I have one more suggestion - don't know if helps, but I have received steel from a major supplier which was labelle wrong. Isa all uyour steel from one purchase or one supplier?

Rob!
 
Rob! said:
Andre

How about trading a bit of steel and cross practicing? I'll send you some Crucibl 154CM and you could send me some of the 12C27 (which I've never had the opportunity to use). Of course, the shipping might cost more than the steel, but it might be informative to try. It would also try your steel in a different oven.

I have one more suggestion - don't know if helps, but I have received steel from a major supplier which was labelle wrong. Isa all uyour steel from one purchase or one supplier?

Rob!
Click to expand...

I have got all my steel from 1 supplier. If you want to trade a bit of steel just email me your details. I would be happy to send you some.

My email : andrevaladao@mweb.co.za

I will post the results of my oven test as soon as i know.

Me2 :I see what you are saying as to the bending being nice. The only thing is its not meant to happen the way i am performing HT. I would feel better about it if i HT to get that result. Another worry i have is that if its bending the steel is probably as a very low rockwell, which would result in poor edge holding.
 
Okay a update.

I took my oven for testing with a renowned local maker, Andre Thorburn.

There seems to be a lot of problems. First my oven at low temp (tempering temp) is almost 30 deg C out. At full temp its okay.

As far as my HT method. He recommends that i Soak at 1060 for 5 mins and quench for 4 mins. He said it doesn't really make a difference if the quench oil is hot or cold. After that the blade must go into the freezer for 3/4 hours and then i must temper t about 220.

He still has my oven, he is going to try a HT and see what happens.

As far as the bending of the steel it is not right, Andre thinks it may be a result of soaking for too long with a combination of incorrect temper. I tried bending some of the scrap blades in his workshop and they flex too a point and then break, but they dont stay bent.

Thanks for all the advice, as soon as i have some more info i will update.
 
Andre V said:
Okay a update.

I took my oven for testing with a renowned local maker, Andre Thorburn.

There seems to be a lot of problems. First my oven at low temp (tempering temp) is almost 30 deg C out. At full temp its okay.

As far as my HT method. He recommends that i Soak at 1060 for 5 mins and quench for 4 mins. He said it doesn't really make a difference if the quench oil is hot or cold. After that the blade must go into the freezer for 3/4 hours and then i must temper t about 220.

He still has my oven, he is going to try a HT and see what happens.

As far as the bending of the steel it is not right, Andre thinks it may be a result of soaking for too long with a combination of incorrect temper. I tried bending some of the scrap blades in his workshop and they flex too a point and then break, but they dont stay bent.

Thanks for all the advice, as soon as i have some more info i will update.
Click to expand...

There seems to be a lot of problems. First my oven at low temp (tempering temp) is almost 30 deg C out. At full temp its okay.
Click to expand...
is the temp higher or lower then it's suppose to be? at your low temp..?
He said it doesn't really make a difference if the quench oil is hot or cold.
Click to expand...
it may not with that steel I can't comment on.. But with others it will make a difference, and make a difference on which oil you use..for what temp to have it..
After that the blade must go into the freezer for 3/4 hours
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if you are talking about a reg home freezer ,, it won't help to any point you'd ever see,, you need at the very least and it's argued about this at this temp. -90 deg F but is agreed that colder is better with LN ..and you'll see more benefits on higher carbon steel
there are many threads here confirming this..

you mentioned you temped at
-temper @ 180 deg C for 1 hour
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he says 220.... there is your 30 deg C ~ 10C + or - would not give you dead soft steel..spring temper maybe but not dead soft.
so you should have had close to the correct temper if your oven was reading low , right?
and if reading high the steel should have been a lot more brittle right?
reading from your unit
you've almost answered you're own question..
you have something else going on Right....time from the oven to the quench could be you problem as said before.. if you miss the nose of transfer you'll have steel the way you described here..

I'm not trying to bust any chops here just sorting fact from fiction..
 
Hi Dan.

Thanks for your input. I think the main part of the problem is the soaking time, i believe if you soak at heat for 2 long you might burn up the carbon..??

As far as quench time as i take from oven i pull off my SS foil and quench, the whole oven to oil procedure cant be more than 2/3 seconds.

I agree with you on the tempering thing, even if i temper at higher temps than 220 i should not be getting the results i am getting.

I cant wait to see what his Heat treat results will be, i am getting more and more certain that something i am doing in the procedure is wrong. I just cant put a finger on it. Thanks to the great input from you guys i am slowly getting there.

After learning to hollow grind i thought the hard part is over... I think its just starting.
 
Andre V said:
Hi Dan.

Thanks for your input. I think the main part of the problem is the soaking time, i believe if you soak at heat for 2 long you might burn up the carbon..??

As far as quench time as i take from oven i pull off my SS foil and quench, the whole oven to oil procedure cant be more than 2/3 seconds.

I agree with you on the tempering thing, even if i temper at higher temps than 220 i should not be getting the results i am getting.

I cant wait to see what his Heat treat results will be, i am getting more and more certain that something i am doing in the procedure is wrong. I just cant put a finger on it. Thanks to the great input from you guys i am slowly getting there.

After learning to hollow grind i thought the hard part is over... I think its just starting.
Click to expand...
to get full conversion of your steel you have to soak it for X amount of time
you'll need to find this out for your steel. at the proper temperature and time you need not worry about to much carbon burn off and plus you are using a foil pack...to stop this from happening anyway..
also you'll need to find out the amount of time you have to quench the steel you have some steels that if you take 3 sec's to get it from the oven to the quench it is way to slow.. these are some of the things you need to know about the steel you use..

it's sounding to me like you need a
bit more soak time
faster time to quench
and try a lower tempering temperature,

you can always redo the temper by increasing the temperature. each time,,, you can't hurt it this way
but you can't come back down form a too high a heat...with-out redoing the H/T
 
Well, time for an update.

My main problem was my soak time at full temp. I got back my oven and tried a blade using Andre Thorburns HT method and the knife broke as it should.

It seems i was just soaking the knife for too long. I am soaking at temp for 5 minutes now, and everything seems fine. One thing this whole episode has tought me is that there are a lot of factors which determine a good heat treat.

I will over the next few weeks try some different things and see if i can improve on what i am doing now. I am sure by a bit of experimintation i will be able to increase strength and durability of the 12C27 to what i have it at now.

Thanks for all your help.
 
Andre V said:
Well, time for an update.

My main problem was my soak time at full temp. I got back my oven and tried a blade using Andre Thorburns HT method and the knife broke as it should.

It seems i was just soaking the knife for too long. I am soaking at temp for 5 minutes now, and everything seems fine.

Thanks for all your help.
Click to expand...
Thanks for your input. I think the main part of the problem is the soaking time, i believe if you soak at heat for 2 long you might burn up the carbon..??
Click to expand...



I can't see that being the problem
maybe Mete will chime in here,, I don't use 12C27 so I can't coment on it all that much..
, normally the longer soak the harder the steel gets..if done at the right temp.. yes if you over heat it you can burn the carbon out of more than the skin of it..
I really think you're doing something else different,, the oven temp would be the first thing I'd suspect..
I'm glad what ever you're doing different is working better for you..
 
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