Imperative to keep blade cool BEFORE heat treatment?

G

GrizzlyBear

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Dec 5, 2009
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Ok guys, help me out here...

Nearly every YouTube video and FaceBook answer I have seen concerning grinding before heat treating, 95% of these guys are adamant that you have to keep the blade cool or it will ruin the heat treat (or at the very least cause problems).

Can someone with some metalurgical knowledge help me out with this? Especially considering those guys who forge nearly to shape and do minimal finishing before heat treating. How is heating the blade while forging not MORE harmful than the few hundred degrees generated by grinding?

I understand that getting into a habit of cooling the blade while grinding leads to doing so after heat treating, where temperature maintenance is critical...and keeping the blade cool keeps you from burning your hands. But, is there any proof, scientifically speaking, that not keeping a blade cool while grinding, pre-HT, is harmful to the blade steel structure?

I'm in the group that says it doesn't matter. But there are long, drawn out arguments about this on facebook. The funny thing, is that no one can seem to generate ANY scientific data to back up their reasoning....yet they spout their answer off to some new guy like they've been putting steel to wheel for 40+ years.

Care to weigh in?

Thanks :)
 
I not a mastersmith by any means .. But the way I have been taught . Which is pretty much from this forum is when I forge I normalize after banging the steel around and heat treat as normal . As far as stock removal I really have no clue how hot I get it but I have never done anything other that straight into the oven. That's the way I see it. Any one got anything to add ?

Don't get to worked up about people bitching back and forth on the internet. If you need to find most any answer just go to the main search engine for blade forums and type away it really does help insulate yourself from useless bickering
 
I'm looking forward to this discussion.

There was a video of a maker that stated that he did testing that showed high edge temps when grinding after HT and that was the reason he does most of it prior to HT. He dipped but not after every pass after HT. He sharpened the blades on a Tormec water wheel and stropped on the other side of the machine on a leather wheel.
 
PT Doc said:
I'm looking forward to this discussion.

There was a video of a maker that stated that he did testing that showed high edge temps when grinding after HT and that was the reason he does most of it prior to HT. He dipped but not after every pass after HT. He sharpened the blades on a Tormec water wheel and stropped on the other side of the machine on a leather wheel.
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This was how I learned how to do things. When grinding after heat treat you have to be REAL careful grinding the edge. It's so much thinner than when grinding prior to HT and you can ruin a HT real quick. I just make quicker passes and dip the blade after each pass. Those Tormec wheels are cool, I'll probably get one some day.
 
I know the need to keep cool with finish grinding after heat treating. This discussion is on the subject of keeping the blade cool while doing the grinding before heat treating.

So many guys seem to harp on and on about keeping the blade cool while grinding...yet none can offer any evidence as to why they were taught that practice.
 
It doesn't matter at all how hot it gets before heat treating, as long as it is heat treated correctly
 
Tkrocky said:
It doesn't matter at all how hot it gets before heat treating, as long as it is heat treated correctly
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And there you go. Close the thread. That's the answer. Normalize after forging to relieve stress in the blade from beating it. Stock removal, all the molecular structure gets reset during ht, so no big deal other than you'll burn your fingers some getting it hot pre-ht.
 
For pure stock removal (no forging) ... If you're grinding by hand before HT and getting the steel anywhere near hot enough to change structure, you're going to a lot more damage to your fingers than you are to the steel. Don't sweat it.

Go ahead and run a stress relief cycle before ramping up to austenizing temperature if you're really concerned about it... but I strongly doubt that's necessary.
 
As James said, what happens to the steel in grinding will be erased in a proper HT. I sometimes get steel to glow red when hogging off the bevels . Cycling the steel to get it into pre-hardening condition as part of the HT regime solves any issues ( caused by you or by the steel manufacturing).
 
There is a lot of non-sense on U-Tube Videos. Some are good, but anyone can put up a video, and some are really, really, bad.
 
Just to clarify....pre-heat treat.....get it as hot as you want to....but you will need to normalize it during the heat treat to fix that. Post heat treat.....do not let it get so hot you can't hold on to it (bare hands only no gloves).
 
Well, let's not over-simplify it.

samuraistuart said:
Just to clarify....pre-heat treat.....get it as hot as you want to....
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No. If you get the whole blade glowing yellow and there are sparks leaping off it, yeah there's a serious problem. Makers who forge are very careful not to go that far.

samuraistuart said:
Post heat treat.....do not let it get so hot you can't hold on to it (bare hands only no gloves).
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Post HT don't let it get hot, period. If it feels warm to your fingertips, you should have already cooled it a few passes ago. Temps can rise several hundred degrees along a thin edge very quickly, and that can definitely be enough to blow your temper out the window - even before tell-tale blue or purple colors show up. It won't "ruin" the steel, it will just make the edge much softer (or even more brittle in the case of certain air-cooling steels).

Either way it won't hold an edge worth a hoot and you'll have to carefully sharpen past the over-tempered steel to get back down to the "good stuff". This happens with factory blades all the time... in fact, I suspect aggressive grinding/sharpening post-HT is the number-one culprit when people talk about certain blades or batches from certain manu's having a "bad HT".
 
Don Hanson III said:
I would Mark, but I'm not on Facebook.
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Heck I thought was the only one refusing to use willingly volunteer personal information to facebook and their ilk. :D

On the subject of heat pre-heat treat: Thank you James and Stacy for your authoritative responses, its too often that people deciminate their misinterpretations as fact (I too am guilty of course.)
 
I'm no "authority" :o I'm just a schmuck who does a lot of reading and has ruined a lot of blades... some on purpose, some by accident ;)

The info is out there for all of us to find, corroborate and share. :)
 
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What I said was an oversimplification...I understand that. Pre heat treat......yeah....don't get it so hot it melts on you and just falls apart as your grinding it. kinda obvious I thought....so I didn't think to say....don't get it to welding temperatures while grinding.
 
From what I gather....if grinding post heat treat....you don't want the blade to reach tempering temperature. I would say that is right at 300F. Do all you can to keep the blade from even warming up AT ALL....yes....that is the best. But.....the fact is after heat treat....for carbon steel......staying below 300 or technically your final tempering temperature is all that is required. Tempering colors will show if you get that hot....and sometimes you're OK even if say the tip reaches that light straw color...because the depth of "damage" may only have been skin deep, or it may have gone all the way through.

Pre heat treat. I would think that you could get the blade all the way up to red hot heat if you wanted to while grinding. Of course....I wouldn't say taking it to a yellow heat is good while grinding. I didn't think anyone would even attempt that. But after taking a blade that hot while grinding....it might be a grand idea to normalize and then stress relieve afterwards. "As hot as you want" was incorrect on my part, I was assuming you couldn't hold onto it for any length of time at a yellow heat, and it would probably plastic deform on you as you press against the platen. Just speculating on what would happen if one attempted such.

Does that sound right...or what am I missing?
 
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