Recommendation? Mystery Steel Hardening Experiments

[Graham Taylor]

Hello,
First time on the forum. I've made a few stock removal knives but have a large stock of steel discs from a "discer" agriculture tool. I've read a lot on approaches to mystery steel on this blog but can't quite place the best hardening method.

I was able to track down the manufacturer and these would have been made in the '50s. I didn't do any forging or heating from the state I found it. I have access to a kiln and heated two test pieces to 1475F, held for about 10 min. I quenched one in canola oil heated to ~120F and the other in water at about 90F. Right after the quench, both snapped off with not a lot of effort on the edge of the anvil. Which seems to me to indicate that it hardened. A file "skated" over it without biting as well.

I tempered each at 400F for an hour, 3 times. When I put the water quenched steel in the vice and applied some pressure it snapped. The oil quenched piece was able to put up with a fair amount of pressure without snapping and rebounded to its original state (ie no permanent bending).

Now this is where my lack of experience comes in. I ground the oil quenched piece to have an edge (i made sure it never got too hot). If I hit the edge against another piece of steel, it doesn't a lot of force to dent the edge. Now I don't really know if this is an acceptable test for hardness or if its unreasonable to expect any blade hold up to this kind of treatment. I tried making another piece where I made an edge before heat treating with a similar outcome.

My questions are:
- How do I know if its "hard enough?"
- Would tempering at different temperatures/durations make it harder or softer? ie. 450F for 2hrs, twice etc.
- Can I toss my test pieces back in the kiln to do more tests in their current tempered state? Or do I need to treat it some other ways before attempting to re-heat treat?

I've tried to do a spark test on it, but to be honest, it all looks the same to me. I don't have a keen enough eye to discern any differences that would lead me to particular steel type.

 

[scott kozub]

This is a great video on the spark test. How does the grain look where it snapped? Dull grey fine grey is good. If you can see the grain it's bad. If the grain looks shiny it's really bad.

 

[Willie71]

If you have a kiln, test coupons from 1450 to 1550f, and the hardest sample out of quench is your ideal heat treat. Discs were simple carbin steel, between 1060 and 1090, but steel varies over the years, and good steel was less available during war time.

 

[Graham Taylor]

Hi,
The grain on the snapped piece is a dull type grey with a grainy/sandy type texture to it. I have a picture but can't seem to upload it. definitely not shiny. Again, with the lack of experience, I'm not sure what grain is supposed to look like or how to properly describe it.

 

[Graham Taylor]

Thanks Warren, how do you gauge smoke from the quench (assuming that's what you meant with "sam0ke")

 

[FredyCro]

If the file is skating it's good enough in my books. Mind you, I am a newbie and not selling. Why not do a more traditional edge test? Sharpen the blade razor sharp, hack through some 2x4, do a brass rod test, scrap some beef bone, cut though a nail...

 

[Willie71]

Thanks Warren, how do you gauge smoke from the quench (assuming that's what you meant with "sam0ke")

Sorry, fat fingers. That was sample. You will need to find someone with a hardness tester. IF this is a simple steel, you can approximate how much carbon is in the steel. If the hardest sample is less than 1475f, you have about 1% carbon, if the hardest sample is 1550f, you are down in the 0.6% range. This is a very loose generalization, as even small amounts of chromium or nickel will shift those temps up or down.

On the positive side, you have a kiln, so you can control your temps.