Problem with Tempering 01 - blade snapped off !

T

texasnewf

Joined
Sep 26, 2006
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Hi there, I am new to knife making and just noticed a problem tonight. I had a slight warp in the handle following heat treat and tempering. I tried to put it in a vise and apply a slight pressure on it to bend it towards me and it just snapped off - very brittle. The edge along where it broke appears to be very crystaline. I heat treat the 01 for 12 mins until non-magnetic and cool in motor oil. Then I tempered it for 2 hrs in a toaster oven wrapped in tin foil at a temp of 450F and then let cool normally.

Any ideas what I am doing wrong ?
 
If your quench from critical temperature is working as well as it should, a temper like that should have given you in the region of 60Rc.
Things to check for are cracks in the blade after quenching, possibly caused by stress risers in the transition between blade and tang (?), and that your toaster oven is actually getting to the temperature it says it is. I know that some of these little ovens make claims that they cannot live up to in terms of performance ;) Tempering at lower temperatutre will lead to harder (and therefore more brittle) blades.

If you spot a slight bend in a blade after quneching you can straighten it far more safely if you do it before the blade cools properly. It'll mean working it into a vice or between two surfaces to apply the pressure whilst it's still damned hot, but it's a better and safer time to do it than at any stage later on in the process.

Was your blade forged or stock-removed ? If stock removed you may have set up stresses within the steel by getting it too hot (Un-evenly) whilst grinding. This can be overcome by thermal cycling. Heat to just below critical then allow to cool to black before doing it all again, twice. Take it to critical and allow it to cool all the way to room temp afterwards and you should be assured of stress-free steel. Again, any bends that appear can best be 'mended' with the steel hot after one of these cycles, well prior to the quench.
 
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If the steel looked very crystalline it sounds like grain growth. To hot at some point. Did you forge it and if so did you normalize it after. What did you use to heat it for the hardening and is it possible that area got to hot. To get the idea of fine grain break an old file and look at the grain. Sorry about your blade. Chalk it uo as a learning experince. Jim
 
im with ib2v4u
if you can see grain it was too large
i had an O1 blade go sideways on me and i tried to take a bit of warp out and snapped it (let it get too cool) i have now broken it a few time jsut to see how it looks doen the blade
 
texasnewf said:
Hi there, I am new to knife making and just noticed a problem tonight. I had a slight warp in the handle following heat treat and tempering. I tried to put it in a vise and apply a slight pressure on it to bend it towards me and it just snapped off - very brittle. The edge along where it broke appears to be very crystaline. I heat treat the 01 for 12 mins until non-magnetic and cool in motor oil. Then I tempered it for 2 hrs in a toaster oven wrapped in tin foil at a temp of 450F and then let cool normally.

Any ideas what I am doing wrong ?
Click to expand...

I would start by reading Kevin Cashen's site info on O-1

http://www.cashenblades.com/Info/Steel/O1.html

You probably started your problems with your hardening
Steel becomes non-magnetic at the Curie point (1414 F or thereabouts) that tells you you're within spittin distance with simple (10xx) carbon steels. it doesn't indicate "critical" (austenization) has been achieved. With O-1 if you hit Curie point and it never got much hotter, you were too cold, soaking for 12 minutes, assumingyou actually got and held austenizing temperature will not let all the goodies get into solution to get the desired properties in the O-1.

That's a start.

-Page

P.S. Welcome to BF.
 
texasnewf said:
Hi there, I am new to knife making and just noticed a problem tonight. I had a slight warp in the handle following heat treat and tempering. I tried to put it in a vise and apply a slight pressure on it to bend it towards me and it just snapped off - very brittle. The edge along where it broke appears to be very crystaline. I heat treat the 01 for 12 mins until non-magnetic and cool in motor oil. Then I tempered it for 2 hrs in a toaster oven wrapped in tin foil at a temp of 450F and then let cool normally.

Any ideas what I am doing wrong ?
Click to expand...

What are you using as a heat source to heat before the quench? Unless you either have a good forge that you can control with a high-temperature thermometer or an electric heat-treating kiln, I would steer clear of O1 for now. Get yourself a different steel--preferably a simple carbon steel like 1080.

Soaking O1 for 12 minutes in an uncontrolled forge means you likely overshot your temperature by several hundred degrees, resulting in grain growth.

You are on the right track in terms of soaking, though. O1 does need to be held at temperature for a length of time to really get the most out of it. But it has to be the right temperature, too.

Chalk this one up to lessons learned... :)

Josh
 
That looks like a decent forge. Do you have a way to measure the temperature, or are you using a magnet or the ol' eyeball method?

Josh
 
No, I don't have any way of measuring the temperature. I'm just eyeballing it ... I ready somewhere that all you had to do was stick it in the forge for 12 mins and it would ne non-magnetic and then quench in oil.. so I thought that's all that there was to do. I did use a magnet after the 12 mins and found it wouldn't stick so I thought that was ok...
 
Time until critical temperature is reached is extremely variable. It can depend on if the forge is fully up to temperature, how high the gas is turned up, where the blade is in the forge, etc. Using curie point (non-magnetic) as an indicator is really close maybe for 1084 steel, but O1 needs to reach temperatures of 1450-1500 degrees which is above curie. Also, while overshooting temperature just a bit momentarily won't likely cause any significant trouble, grain growth happens rapidly once it starts, and it only starts when you overheat the steel. Holding at accurate temperatures for the steel will not cause grain growth, so you've likely overheated a good bit. FWIW, when heat treating O1 in my home built kiln, I have checked the blades and found them to be nonmagnetic in 5 minutes or less as long as the kiln was fully soaked at austenitizing (critical) temperature (1475F), so 12 minutes will put you way above that mark (thus overheated, thus grain growth) when using an unregulated forge that can be heated upwards of 2300+F.

For steels like O1, you really need a means to tell temperature. O1 benefits from a soak of 12-20 minutes AFTER austenitizing temperature has been reached and held. Relying on magnets isn't accurate as was stated above. Relying on color is a tough thing to learn, and while experienced smiths may have the knack, everything needs to be consistent (lighting, location, etc) for it to be anywhere near helpful. Purchase a kiln or furnace K-type thermocouple and a PID from ebay (they can be had fairly cheap). Consider using a stainless steel tube in the forge for a baffle with your blade inside the tube to equalize the temperatures and get more accurate temps for heat treating. If using a baffle, place the TC in the baffle with the blade to get a reading of temperature. The TC needs to be rated for 2300+ degrees.

Once you have a means of measuring temperature, you'll be able to get the most out of your steels and also be able to branch out in the future. It's all part of the process. I started out heat treating O1 blades in a one brick forge with no means of temperature reading/control except for magnets and my eye just like you. I never sold any of those blades, but they did help me figure things out. Once I was able to, I built my own oven and haven't looked back since. Chalk this one up to experience and learn from it the best you can.

--nathan
 
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If my forge is pre-heated, a piece of steel 1/8" thick to 1/4" thick will easily reach forging temperature (1800 F to over 2000 F) in way less than five minutes. I'm only running one burner, too. The temperature you probably hit was fine for forging, but it sounds like you overshot for heat treating.

The recommendation to get a decent thermocouple/pyrometer is a good one. I have an older model Fluke 51 with a K-type thermocouple. I think it cost me around $80 on eBay, and it was a great investment.

Keep at it! :)
Josh
 
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