I have been cleaning up lots of old blades and what not using a material called Evaporust. There is a long thread on this process. However, not germane to that thread is an interesting thing I found on ALL of my stanley 45 cutters. When they come out of the solution, the lower 1/3 to 1/2 is darker grey than the rest.
Here’s the thing. Evaporust removes the iron molecules from iron oxide. The oxygen is freed. The carbon that was in the rusted steel stays behind in a film that is fairly easy to clean. The more carbon, the more film. SO it looks as though the Stanley cutters were made with two grades of steel. As they are not laminated, they must have been welded and then ground and polished.
Does this sound right to anyone who really knows about these cutters?
Joe
Replies
Joe, to the best of my knowledge those cutters are made from an oil hardening steel like O1. They will not be hardened from bottom to top-only the lower portion that does the work will be hardened. That would explain what you are seeing there.
As I say, I don't know that for a fact, but suspect it to be the case.
Interesting. I suppose that the hardened portions retained more carbon which wouls account for what I see. We are getting a bit beyond my understanding of metallurgy here.
If I can borrow a digital camera, I'll post some pix.
Joe, I will examine those on my Record 45- I would expect them to be the same as the Stanley.Philip Marcou
That makes sense in that wooden planes "cast steel" irons exhibit the same properties. It would not be right to harden the full length to cutting hardness because the top of the iron is hit in adjusting blade depth, and old irons bear evidence of this hitting. A hard top could splinter.
I think that you are looking at the colours from the tempering process.My Stanley planes show this .However It would seem that Record clean their irons afterwards
Jako -- these are not hardening colors. They are caused by a carbon residue that is a by-product of the derusting process. I have now detusted many tools and implements in that solution and find that the finer cutting tool steels have more carbon residue. In the case of these cutters, there is a very clear demarcation between dark carbon and lighter.
Joe
Not meaning to hijack this thread but more towards the next step following cleaning. I have just finished cleaning off the rust on my #45 cutters. I used vinegar. Now I am getting ready to flatten the backs and sharpen them for use. I've read several posts regarding sharpening of molding plane irons and am wondering if the same principals apply? Most suggest not sharpening the profile, just the flat edge, or did I misinterpret these posts?Regards,Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
The carbon content is the same. It is the same alloy for the entire length, but the crystal structure at the hardend end has more, but smaller, crystals. The austenitic form is a body centered cubic, with the carbon well distributed, the softer end would have a less uniform carbon distribution, but bigger clumps.
If asked, before this, I would have expected the surface carbon to be higher at the unhardened end of the blade. Is the carbon film on the soft end thicker, or fluffier when you first take it out of the bath?
Now I'm going to have to go dig out my materials and metalurgy books, read up on this, and figure out why you would see more carbon on the "hard" end.
There is less carbon residue on the soft end, and much more on the hard end. Thids is similar to the results when I derusted a very old smith-forged goose wing broad axe. The body of the axe showed layers of more and less carbon, but the cutting edge which extended into a plate covering most of the flat side of the axe were almost black with carbon.
Joe
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