Thread: Heat treating mucked up ?

How can I tell if I've mucked up the heat treating when (re)grinding a blade ?

And what, if anything, can I do to fix it ?

Barney

If there was any color change to the steel, the heat treat has been altered.

You can try to scratch it with another piece of hardened steel, to see just how soft it became. Or just hone it up and see if it still holds its edge like it used to.

There is probably nothing that can be done to save it if the steel has become unusably soft. You would have to reheat it to critical temp, ~1,600 degrees F, and quench it in an oil of some sort to regain the hardness it once had (which may warp or crack the thin edge).

Funny, I was just having a think about this; Do anyone soften the blade before regrinding... or do you risk warping it?

Originally Posted by mastermute

Funny, I was just having a think about this; Do anyone soften the blade before regrinding... or do you risk warping it?

Why would you want to do that? There is so little material removed in a regrind that it wouldn't be worth the extra procedure or risk in re-heat treatment.

You would have more risk of warping (or cracking) in the re-heat treating stage that would be necessary to return a softened blade to it's original condition. And a soft blade won't hold an edge.

Originally Posted by Russel Baldridge

Why would you want to do that?

I don't know, just popping the question!

Originally Posted by Russel Baldridge

You would have more risk of warping (or cracking) in the re-heat treating stage that would be necessary to return a softened blade to it's original condition. And a soft blade won't hold an edge.

Thanks, that answers my question...

Originally Posted by Russel Baldridge

Why would you want to do that? There is so little material removed in a regrind that it wouldn't be worth the extra procedure or risk in re-heat treatment.

You would have more risk of warping (or cracking) in the re-heat treating stage that would be necessary to return a softened blade to it's original condition. And a soft blade won't hold an edge.

The blade in question was a wapi that I'd tried to hone out a warp - this ended badly, ie still warped and major uneven hone wear.

I was going to even it out, make a narrower and shorter blade (you can see where this is going can't you ? ), experimenting to try and get my metal working skills back - its been a long long time.

In particular I had a couple of spots on the edge kinda flare and go black yet they were not to hot to touch if you know what I mean. These sections have since been ground away as the blade has got narrower so assuming this did damage the temper how localised would that damage be ?

Barney

I agree with Russel. Annealing and re-hardening most blades would be a lot more trouble than it's worth. For one thing, we don't know exactly what the steel is, so you'd be guessing at the proper heat-treatment recipie. Heat-treating damages the outer layer of the steel, so you'd have a lot of cleanup work to do on the tang, spine, etc. The chances of warpage or cracking are high.

Unfortunately, grinding the hardened steel is the most efficient thing to do.

Josh

Originally Posted by barneycg

The blade in question was a wapi that I'd tried to hone out a warp - this ended badly, ie still warped and major uneven hone wear.

I was going to even it out, make a narrower and shorter blade (you can see where this is going can't you ? ), experimenting to try and get my metal working skills back - its been a long long time.

In particular I had a couple of spots on the edge kinda flare and go black yet they were not to hot to touch if you know what I mean. These sections have since been ground away as the blade has got narrower so assuming this did damage the temper how localised would that damage be ?

Barney

At the risk of aiding and abbetting PCR....

Yikes, black is bad. If you have ground away all the discolored steel, you're probably OK. Trouble is, you can easily remove the surface oxidation (that's what makes the colors) long before you get rid of all the soft steel.

Josh

Originally Posted by JoshEarl

At the risk of aiding and abbetting PCR....

Yikes, black is bad. If you have ground away all the discolored steel, you're probably OK. Trouble is, you can easily remove the surface oxidation (that's what makes the colors) long before you get rid of all the soft steel.

Josh

Well it's not exactly PCR, it's for her legs - for the moment

I kinda thought black was bad ... what got me was that the blade wasn't too hot to hold - even in these areas. Unfortunately I'm not that well equipped at the moment and a cheap 6" bench grinder is all I have (a KMG style belt grinder is in the plans but it will be some time yet), I'd been moving the blade over the 1/2 inch grinding wheel at an even pace (about 2 seconds per pass tops) and this area on the blade about 3 mm long and about 1mm high just suddenly upped and turned black.

I think it is all ground away since the blade is now about 2-3 mm narrower than when I started and should get narrower still by the time I'm finished.

Cheers

Barney

about that warped wapi: You can sometimes fix this by clamping it in a vise with 2 pieces of wood at the toe and the heel on one side of the blade, and 1 piece of wood in the middle on the other side of the blade.
Then gently but firmly clamp it to bend it the other way.

How do you know how hard to clamp? It's easy. There are 2 ways. I prefer b).
a) turn the handle until the blade snaps, turn it a quarter of a turn back, and that is the ideal possition
b) turn until the blade is straight again, and then give it a tiny bit more.

If the blade snaps before the point where it is straight...
It wasn't that gret a blade anywa.