Pits in my mirror finish

William Schrade

William Schrade

Joined
Jul 30, 2012
Messages
632
I find I'm getting very minute pits in my mirror finishes. Mostly in O1 and A2 steel. Not so much in 440C. Buffing wheels are dedicated for 1 compound only. I was wondering if it might be in the heat treat process. I use a local old timer who's trying to scratch out a living. 75 years old with 50 years experience. Anybody have this problem?
Thanks
 
Is the A2 ht'd in a foil packet or inert environment? I think it could be decarb.

How muc sanding are you doing post heat treat? Machine or by hand?

Do the blades sit for any time at low grit before being oiled? A blade left at 40 grit can pit quickly if left un-oiled.
 
Do you do grinding in the same room as the buffing wheels and do you cover them up if that is the case.
 
I know it's not heated in foil pouch and I don't know how much time before quench. These particular blades were ground to 60 grit before HT. Post HT I start with 120 > 240 > 400 > 600 > 1200 on a machine then buff.
 
It could be a lot of things, I'm still guessing deep decarb? In my opinion A2 and 440 need foil packets or an inert environment, they get too hot in ht.

O1 though.... I soak for 30 minutes with almost no visible decarb.

Hopefully more will chime in, I could very well be completely off track on this one...

If you can grind past it eventually I may be right.
 
My heat treater doesn't use foil. He's old school and I'm trying to share the wealth, what's left of it. Maybe it's time to use another.
 
I was just thinking I have scratched the heck out of a blade that I mirror finished and couldnt find out why then realized grit and metal was getting on the buffer wheels while I was grinding.

But I think it would mostly scratch and not pit more then likely. Dans probably right.
 
William Schrade said:
My heat treater doesn't use foil. He's old school and I'm trying to share the wealth, what's left of it. Maybe it's time to use another.
Click to expand...

I'd hate to see you stop using him, maybe we should send him some foil! He may be using a salt bath or nitrogen too.

Good luck with everything.
 
Keep those buffing wheels clean !! If they do get contamnated with dirt and grit they will leave scratches on the blade ! However 'pits' are from other sources. A free machining grade of steel with high sulphur for example.The soft manganese sulphide inclusions can be pulled out , leaving pits. Fresh compound and not to forcefull buffing will help. If it's 'dirty steel' ,that is high amounts of inclusions , They can be pulled out too sulphides or oxide inclusions.
 
William Schrade said:
These particular blades were ground to 60 grit before HT.
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That's very coarse. It's highly possible that your blades have lots of tiny belt grit and steel swarf in those deep 60-grit scratches, as well as scale from an unclean HT process. If so, they may be left behind or only get smeared around the blade during subsequent steps, and wherever they are, they'll trap moisture next to the blade and cause localized pitting. This can be prevented to a large degree by etching the blade in a mild acid to clean the gunk off before proceeding.

I feel pretty strongly that all steels benefit from as inert an environment as is practical during the hardening phase. Oxygen is the enemy. This allows one to do a lot more grinding and finishing work before HT without fear of contamination, decarb, etc. If I were you I'd invest $100 in a roll of SS tool-wrap for your current guy to use, or find a different HT guy who uses either a "vacuum" furnace or salt baths.
 
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