Steel Getting Hot Before Heat Treat

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foxtrot delta

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Jun 24, 2014
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I have a question regarding my potentially flawed process for "roughing" out knife patterns. Currently I scribe my pattern, roughly cut out big pieces with an angle grinder w/ cut-off wheel, use a bench grinder to get close to my scribe lines and finally I use a series of files to reach my pattern and eventually smooth the metal. Everything is sanded with 220 grit wet/dry pre and post HT.

My question is this: cutting with the angle grinder and using the bench grinder obviously heat the metal pretty decently, enough to produce color changes. My thought process is that this is irrelevant because the entire piece will be heat treated at much hotter temperatures (normalizing and hardening.) Essentially, normalizing would wipe away any previous stressed or heated spots from roughing it out. Is this correct or am I doing myself a disservice by not using a hacksaw on the entire piece? I plan to get a metal band saw in the future when funds allow but I'm currently limited to what I have.

I've been working with 1095 and 1084 if that is relevant to the discussion.

Thanks in advance!
 
You are correct. The only disservice you are doing is to your lungs with the grinders.
 
I have some pretty solid half and full face respirators and I only work in my shop/garage. I'm really just concerned about the end product being diminished by the cut-off wheel/grinder approach.
 
foxtrot delta said:
I have some pretty solid half and full face respirators and I only work in my shop/garage. I'm really just concerned about the end product being diminished by the cut-off wheel/grinder approach.
Click to expand...
Like Bill said, you aren't hurting a thing. For the steel you're using the oxide coloration all occurs below 1000 degrees. As long as the steel isn't glowing red hot you haven't crossed the line so to speak. Even then, you are correct, a normalizing process would remedy any issues with the steel.

I used to use (and from time to time still do...) a cut-off wheel as well. But there is simply no substitute for a proper metal-cutting bandsaw though. You can have a reliable and efficient setup for under $100 if you go the Harbor Freight route... Not to mention they are also great for cutting other difficult stuff like G10, horn, carbon fiber, etc...

Edit: I think this is already in the stickies as a link... Nonetheless this is a good little reference for a color chart and phase conversion diagram. I have both printed and taped up in the shop...
http://www.m4040.com/Knifemaking/Steel2.htm

-Eric
 
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If you are normalizing, no problem. If you are going directly to final heat treat, then I would run a stress relieve cycle. Heat to 1250F(very dull red, still magnetic) a few times. This will help minimize warp if your shaping induced any stress.
 
Sorry to bring this back, I didn't realize I had more replies (which I thank you for.)

When using the cut-off it does get red/orange hot momentarily as I grind right on the edges but as soon as I stop it almost instantly stops. As I said, I have been normalizing. I've only made a couple knives so far but I'm normalizing 3 times (heat to red hot and then air cool.)

Is it possible at all to irreparably damage steel with a grinder? I've heard you can get the steel too hot, but people have always said "you would know it if you did." I'm assuming that's because it would warp or liquify?

That link was very helpful by the way Eric, thank you. I did read through most of the sticky although I must have missed that.
 
If you get steel hot enough to actually warp or liquify while you're grinding it, you're likely to have more serious problems than just a warped blade.

Normalizing or at least a stress relief cycle is of course a good idea as Rick said. It's pretty much mandatory when forging blades. But I wouldn't get too stressed (*groan*) about heating your steel just by cutting and grinding... your normalization procedure seems pretty reasonable to me.

If your blades are coming out of the quench straight or close to straight, don't sweat it.
 
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