Grain Growth Help Please!

[FlyingKiwi]

In anticipation of heat treating my first knife in my backyard heat treating forge (brick construction, burns charcoal etc.) I took a small rectangular off-cut of O1 and filed in a single bevel. This piece was to act as a tester, so I could learn a little about how the fire behaves, and how to control temperature. I decided to do a triple normalize, and a double quench, followed by a double temper for 40 mins each time at 390F. For the first normalize, I lost the steel in the forge and it sank to near where the air enters, needless to say it got cooked. It was bright yellow. :grumpy: :barf:

I progressed though, and the rest of my heat treatment process went better. However, for the final quench, my fire was a little low and not producing enough heat, so I had to introduce more air. This caused the fire to burn at a higher temp that what I wanted the steel to be at. I believe the edge region was over heated slightly (as it was thinner), and the body was not quite at critical temperature. This was shown when the body of the steel bent 90 degrees when hammered hard in a vice. I could also cut it easily with a hacksaw. The edge region chipped, after several strong hammer blows. I was surprised with it's strength.This brings us to the crystal structure. I am sure there was a lot of grain growth from the first normalize, but I hoped the rest of the thermal cycling reduced that. The grain does look fine to me, but I have never examined steel structure before.

It is possible that the steel DID NOT become non magnetic on one of the normalizing cycles. Also I aimed for a soak time at critical temp of 2 mins, but I didn't time myself. The steel WAS NOT forged.

I would appreciate any comments which may give me some idea as to how the structure looks. Is it fine or coarse? Thanks.

 

[Jason Fry]

Bonus points to you for practicing before you tried a blade. Temp control is one of the harder things to learn. Sounds like you followed the right process, just without enough control. Without control, it's a crapshoot. I haven't worked with o1, but that grain does look large to me. Should be gray and silky looking.

 

[LRB]

Break the tip off of a good quality file, and look at the grain. You should see a gray, almost smooth surface in the break. That is what you're after. Rather than 01, you should be experimenting with a simple steel. Most 01 contains vanadium which retards grain growth, and will give different results than you will get with simple steels. If you intend to heat treat 01 in a primitive type brick forge, it is not going to work very well as 01 requires a controlled temp heat soak in order to austenitize properly.

 

[FlyingKiwi]

Thanks for the replies. In what way does it not look smooth and grey, I know there are fracture lines, but the actual texture looks fine to my untrained eye. There are a couple of what look like 'lumps' in the steel, and I believe they are dust, as I cannot see them any more. Prior to the hammer test, I whacked into the hair-whittling edge and with the corner of a file, and it did deform in the impact areas, but no chipping, leading me to believe the grain size was on the smaller size, because of the toughness. I would estimate the hardness to be in the mid to upper 50's, because of how the edge performed in paper cutting.

Through an 8x loupe with illumination I can see small sparkles, would I be wrong the assume these are sparkles off the individual grains? They are too small to be seen with the naked eye.

Unfortunately a 10XX steel is not an option for me, as I already have a couple of O1 knives made, waiting for me to HT, plus some O1 sheet which I plan to use because I paid for it

 

[mete]

You got the fracture surface in focus but it would be better to have that surface parallel to the camera. I don' think there's a grain size problem .It looks like it's just softer ,that is in the 50 s .Harden for a bit more time , 5 minutes .

 

[FlyingKiwi]

You got the fracture surface in focus but it would be better to have that surface parallel to the camera. I don' think there's a grain size problem .It looks like it's just softer ,that is in the 50 s .Harden for a bit more time , 5 minutes .

I tried some parallel shots, but the narrow depth of field was prohibitive of any clear images. Grain size was a problem I anticipated, with what I expected to be large fluctuations in temperature. I will try for a longer soak next time, and hopefully that should give me hardness into the 60's. Is the problem with low hardness because the carbon wasn't distributed properly with the quick soak? I did see on another thread longer soak times gave higher harnesses. I really love the strive-for-perfection nature of doing you're own heat treatment and will definitely be more careful to soak next time.

 

[Don Hanson III]

Grain size looks OK in the pics.

 

[stevomiller]

You should put a pipe muffle in your forge. It's just a black iron pipe (or stainless, no plated pipe tho) big enough to accept the blade. It will help you get a more consistant heat on your blade and isolate it from excessive air blast, etc.
Best,
Steve

 

[stezann]

The grain look quite fine with me too... the lumps could be the result with messing with uneven persistence of heat in the forge; something you could handle with muffle pipe and proper normalizing cycles. If you are doing it for hobbie don't be discouraged if you have only o1 available...you'll get it quite fine today or tomorrow

 

[elementfe]

Wow, someone else does that?
I decided to wing it with some practice knives and heat them in my forge (440c) and built a stainless box with a hole just big enough for the blade to slide in and out, then kept some crumbs of coke going in there to soak up O2. Not saying it's a great setup, but the knives are holding up very well and they didn't pick up much scale at all. Yeah, I'm way out here in the sticks...sigh.

 

[mete]

SOAK -- do dissolve carbides and diffuse the carbon into the matrix to saturate the matrix with carbon and give it maximum properties.

 

[FlyingKiwi]

Ok, I have some pipe coming, thanks for the advice.

 

[Brian Ayres]

Ok, I have some pipe coming, thanks for the advice.

Tai Goo has some very helpful posts he's done on using a pipe muffle in a coal forge to even out the heat as well as putting wood etc in the back of the pipe muffle to help reduce the decarb on the blade. You should be able to search and find the posts. Have fun!