quench help please

Mike Davis

Mike Davis

Joined
Feb 7, 2006
Messages
1,327
i got my very first hand made blade finished today. the thing is when i heat treated it(o-1 by the way) and put it in the quenchant it got a hairline crack in it. i will still finish it just to sit on my shelf, but im puzzled why this happened. i heated it in myforge to non magnetic and tried my best to keep it at that temp to soak for about 15 min. i then quenched it in vegetable oil heated to 150 degrees. can you guys help to bring back my sanity?
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edited for spelling
 
15 min is a long time to maintain at critical with a propane forge. Are you heating inside a pipe? Where on the blade is the crack? Did it happen during quench or after? What are you quenching in, and at what temp?
 
I think I might see the problem....Large gringer marks going up and down on the blade....Rub them out on the next blade and sand length ways so the sanding is from end to end. This might be the answer.
 
Well, then it isn't a crack induced from hammering too cold.. ;)

I don't know where 150F veggie oil falls in the realm of quench speeds, but too fast can increase how many blades crack. O-1 only needs a medium quench speed.

My next best guess would be that perhaps there may have been a grinding scratch there that induced a stress point and allowed it to crack . One piece of advice I can offer is to always have the edge ground so the scratches run lengthwise. Leaving 60 grit scratches running across the egde is sometimes all it takes. I always hand sand the whole blade to 400grit so all the scratches run lengthwise.

Sometimes this just happens, Mike, and there's no reason we can see, but the steel/treatment "knows". It won't be the last blade you "ruin", that I can promise. :(

Edited to add: ah, Jim, you beat me to the scratch remark! Hiya!
 
:confused: the steel is annealed 0-1. the quenchant was veggie oil at 150 degrees. i didnt think to put it in a pipe.i really tried to keep it at a specific temp with a digital readout high temp thermometer for automotive use. i tried to get my forge as close to 1550 degrees as i could. it fluctuated between 1475 and 1575(outside air flow?). i had it sitting on its spine in the forge. btw the crack is on the spine about 1 1/2" from grind start line.im too poor to afford a heat treat oven right now(girlfriend has surgery tomorrow after just having it 3 weeks ago). i was just trying to do this on a budget.

1 had it sanded lengthwise to 320 grit
 
Mike Davis said:
:confused: the steel is annealed 0-1. the quenchant was veggie oil at 150 degrees. i didnt think to put it in a pipe.i really tried to keep it at a specific temp with a digital readout high temp thermometer for automotive use. i tried to get my forge as close to 1550 degrees as i could. it fluctuated between 1475 and 1575(outside air flow?). i had it sitting on its spine in the forge. btw the crack is on the spine about 1 1/2" from grind start line.im too poor to afford a heat treat oven right now(girlfriend has surgery tomorrow after just having it 3 weeks ago). i was just trying to do this on a budget.

1 had it sanded lengthwise to 320 grit
Click to expand...
I've used O1 a lot and and have used a lot of vegie oil to h/t in
your oil should be about 125-135 F I use either O/A for small blades and the
even heat oven for longer blades , I have never cracked o1 as of yet..knock on wood
the only thing I can think of is your quench heat ..
not knowing if your digital readout high temp thermometer used was calb corectly.
what did the decarb look like on the blade when it came out?
stuck to the blade ? flaking off? no decarb?
and what did you do right after the quench?
did you temper it? if so at what temp , was it warped and did you try to straighten it out? if so when?
 
1550 is too hot for O1. And if the temp was getting as hot as 1575, you probably have some grain growth, which will increase the risk of cracking, especially if you leave scratches like the other guys pointed out. if you decide not to finish it, break it and see how the grain looks.
 
I'm thinking if he was at max, 75deg over, that would not have caused the crack I'm thinking he was much hoter than that.
USA recommends 1450 for the low no higher than 1500 deg F
 
No mention yet of how thick that blade was...how thin did you let it go?

M guess is that the section was too hot. Judging by its location, was that area of the blade near the burner flare?
 
All good info.
Check thermometer.
Drop the temperature about 75 degrees - O-1 is HT at 1450-1500.
Soak for about 5 min.,10 max.
Stress relieve before quench.
Temper immediately after quench.
Get a good quenchant like Parks AAA,of a commercial medium quench.
Stacy
 
TikTock said:
No mention yet of how thick that blade was...how thin did you let it go?

M guess is that the section was too hot. Judging by its location, was that area of the blade near the burner flare?
Click to expand...

Tik
I believe he said it was the spine that cracked and it was setting on it's spine
in the oven.. this is odd to me to crack there. the heat would have been more stable right there I would think :confused:

thinking more about it I'm thinking you had more than one problem and they ganged up on you..
I'm still thinking over heated and with the veggie oil hotter that I would have used it , it could have convex heat a littler faster than I normally had experienced, along with stress points,
I don't know how I came up with all that my self :foot: :D
little things mean a lot,, when they all add up :)
 
Without getting all scientific like the rest of these guys, that blade looks pretty thinly ground for heat treating in oil. It almost looks like a finished blade(in edge thickness) in those pics.
 
the o-1 is 3/32 thick before i ground the basic shape. i left the cutting edge over 1/16 thick to finish the grind post heat treat. im sure the temp was off. the decarb came out dark grey and flaked off really easy. the blade warped just slightly(barely noticable), i did not try to straighten it. i tempered it at 400 degrees in the oven for 3 cycles(400 1 hour, let cool to room temp and repeat.) i know the temper heat is right on, i have a thermometer in the oven with a light so i can see it.i think i will send my h/t out until i can afford an oven. i know delbert ealy does h/t and its only $5.00 a blade. im not mad oddly enough im just puzzled why this happened,i guess it gives ke a good chance to check grain growth. thanks for all of your input guys, it really helps a newbie like me:thumbup:
 
Mike , I was looking at that photo again,and one thing came to mind (that's all my mind can hold at a time). You may have a bad piece of steel.It happens.
It looks like the crack does not run from the spine into the blade,but is on the blade near the spine.This is not a normal quench related crack. It may be from an impurity in the steel.
FWIW ,I would use thicker bar stock to start with.
Stacy
 
bladsmth said:
Mike , I was looking at that photo again,and one thing came to mind (that's all my mind can hold at a time). You may have a bad piece of steel.It happens.
It looks like the crack does not run from the spine into the blade,but is on the blade near the spine.This is not a normal quench related crack. It may be from an impurity in the steel.
FWIW ,I would use thicker bar stock to start with.
Stacy
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stacy look at this one
 

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In that last pic, is it a shadow or is there a dark halo around the crack? I know with my forge, I sometimes have to really keep a blade moving if not in a pipe...right in that area especially since my burner is offset towards the mouth of the forge....it would be closest to the ricasso, right where your crack appears...

I wouldnt give up yet on HTing! Break that blade and check the grain. Break it in multiple places and see if there is a difference in grain at the crack vs towards the tip.
 
This can of worms seems to go around a lot, but I like it. So I will ask:
Once the blade gets to heat ( non magnetic ) what is the value of heating it more? Or longer. Inside the spine may be the last place to get to heat, it would get there long before 10 min, would it not? Would it not be better to under heat the spine than over heat the cutting edge?
I have a small two brick forge with uneven heat and so I watch to focus on the cutting edge of the blade is at non magetic, at least, and only go maybe 30 seconds of heat after that. This in no way makes me practiced at this as the above questions point out.
Is 15 min a long time to soak?
Cheers Ron.
 
Mungo Park - An example of this might be to chug down four shots of Scotch.It won't make you drunk right away,but will in about 15 minutes.It has to get into your system first.
In steel just getting it hot is not what you are trying to do.The carbon,iron,and alloy elements (chromium,vanadium,etc.)need time to get into full solution and form up the carbides that you are shooting for.It takes only a few minutes in simple steels,longer in simple alloys,and a long time in complex stainless alloys.
Heat Treating is not a system of getting it hot fast and get it cold faster.Both will end in failure.
O-1 should soak for no less than 5 minutes,15 being preferred.
Also,non-magnetic is not the point where the full austenitization occurs.It is about 50-75 degrees above non-mag (Between Acm and Ac3).This is called the critical temperature.For O-1 that is from 1410 to 1470,so 1450 is a good target temperature.
Stacy
 
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