leaving mill scale on CPM154 going out for HT

R

Remyrw

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Jun 17, 2010
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I've got a batch of CPM154 about ready for mailing and was wondering if it matters whether I grind off the mill scale before or after the HT.
I'm going to be doing the bevels after HT on these so from that perspective I figure there's not much point if I don't need to. I've otherwise got them about ready in other respects, so if I'm not grinding the scale off I will just finish cleaning them and marking them with my name and the steel.

Does the scale get harder? Is there any issue doing it afterward rather than before? Obviously the steel underneath is going to be harder but I already planned on that.
 
I can't say I have ever had what I would call "Mill Scale" on CPM-154, but you can leave it on.
 
Hoo boy I've got it on mine! Better get it off beforehand unless you have a favorite relative in the sanding belt industry...easier to get off while annealed.
 
I wouldn't have thought the heat treating would matter on the scale, since it's already converted, what's left to change?

Stacy, I'm not sure it's actually mill scale, but my CPM154 came from Aldo with a rather tough layer of dark grey. I figure I'll try sticking one of the blades in some vinegar and see if it reacts like most scale. lol Didn't occur to me that it'd be anything else.
 
It's certainly not going to get any easier. Pickling the bars in mild acid will make the scale somewhat easier to grind off. Ordering precision-ground stock in the first place is by far my favorite option.
 
Besides being a bitch to grind, the scale can hide dings and dents that can cause stress cracks during heat treat.
 
hmmm, didn't even think of that. Could definitely have pits and such underneath, and better to find out before rather than later. I'd hate to be trying to grind down the flats far enough to get rid of that after HT.
Fair enough, they're in vinegar now, I'll flat grind them tomorrow.
 
I found this out the hard way on a stainless steel shaft many years ago. We decided to leave the bark on one end and hard turn it after heat treat. 3 out of 4 were fine. They were 27" long the fourth had a stress crack originating from the unturned area that was 15" long. Most likely it was where a forklift fork smacked it while unloading or maybe it was dropped on another piece. When turning large pieces you always order stock at least .125 to .250 bigger in diameter to remove any stress risers. I know this example is on a larger scale but the same theory applies.
 
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