Annealing a straight razor

R

ricaga

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Nov 3, 2021
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I thought I would try making a few wood carving knives from Straight razors. I had no idea how hard and I presume brittle the steel is. One is made from tungsteel which I might use as the blade is in remarkablely good shape. I don't have any trizact belts yet but I might have to bite the bullet. I spent 30 min on my 1x30 to do one profile and the spine? is still over 1/8 in thick. Is it possible to anneal and reharden at home. I'm using 36 grit belts and it's slow going
THX
 
Astonishing project.

I would not expect "brittle" to apply to a steel intended to take the thinnest possible edge, and then cut tough beard hairs with it with an absolute minimum of chipping.
 
They are likely to be brittle. It's not uncommon to see large chunks of a blade get broken out just by bumping the tap, or dropping one to a tile floor. A lot of the beard cutting strength comes from the geometry and the "feedback" that the blade gives the user, you are unlikely to continue shaving if you are pulling out hairs. You could easily apply enough sidewards pressure against wood to chip out a straight razor, some are also shockingly thin if they were double ground. The last I saw of anyone trying to hardness test vintage blades they were getting well above 60rc, but also typically struggling to not deform/shatter the blade, and many vintage razors were somewhat differentially tempered, even if unintentionally since the proportion of edge to spine is far from what you'd find on most knives.
I don't think you will get a good result, but if it's sacrificial steel anyway, and they are of no other value, then experiment away.
 
Yes it should be possible to anneal most straight razors fairly easily if you have the means. They need to be brought up to critical temperature and then cooled slowly. Critical temperature is commonly tested for by those without more proper means by the use of a magnet. When the steel no longer attracts a magnet it has usually been heated to critical or beyond. At that point it can be cooled slowly back down to room temperature. Ideally in a controlled manner with a furnace - but again, those without better means have accomplished the task by burying steel items in vermiculite, sand or even the embers of a small campfire.

What you may need to be wary of with the minimalized low-tech methods is heating the steel beyond critical, being that the blades are so very thin. This can burn the steel away so you'd be left with not much but the thicker spine remaining. This can easily be avoided in an inert gas or reducing furnace, but that isn't something that most will have. You could try bagging the blade in steel foil with a small slip of paper or covering it in boric acid paste to prevent that issue also.

Alternatively, if that wouldn't bother you, don't even worry about it. It may be that you'll forge the blade after it's annealed, in which case you probably don't want the thinner part of the blade anyway. And in which case you really don't even need to anneal first.

Basic hardening is accomplished much the same as annealing except after reaching critical temperature you'd need to rapidly cool the steel. Whether to use oil or water depends on the alloy in question and the cross section of the blade, as well as desired characteristics of the steel. You might try a small sample piece with water, and if the steel cracks, instead use oil.

After the steel is hardened you'll want to temper it as soon as possible. With an unidentified steel alloy you can only guess at the proper temperature and resulting hardness. I'd advise shooting for a light to middling yellow color at the edge as adequate. Either heat in an oven or use a torch lightly played on the spine of the knife to temper. The heat will come up VERY quickly on the thinner part of the blade, so if using a torch, it's critically important to apply the heat only to the thicker spine, and very slowly/gently until you get where you want to be.
 
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A straight razor is very hard to support the very fine edge & yes it's brittle.

You could simply soften it to a more acceptable "wood carving" hardness by tempering it in an oven, look up "tempering temperatures" & air on the hard side as you'll be guessing the steel, you can always soften it a little more but you can't harden it a little more, that'll require quenching to full hardness then tempering again.

You could also flame (or better still a very hot surface) temper it the old fashioned way which is probably what I'd do, look up "running the colours tempering" to get the technique & colour charts, same applies to air on the hard side & soften a bit more if necessary.

You can grind it after that as long as you don't overheat it doing so, obviously that'd soften it even more.

Good luck & let us know how you get on.
 
I’d suggest the above strategy of simply tempering the steel further instead of annealing depending on how much grinding you intend to do.

If you do anneal, a muffle would be advisable in addition to the foil wrap suggested by E eKretz further above.

(A muffle is just a piece of pipe, etc., [non-galvanized] that you heat up in the forge and insert the knife into. It will help protect the thin edge from overheating.)
 
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I'mSoSharp said:
A straight razor is very hard to support the very fine edge & yes it's brittle.

You could simply soften it to a more acceptable "wood carving" hardness by tempering it in an oven, look up "tempering temperatures" & air on the hard side as you'll be guessing the steel, you can always soften it a little more but you can't harden it a little more, that'll require quenching to full hardness then tempering again.

You could also flame (or better still a very hot surface) temper it the old fashioned way which is probably what I'd do, look up "running the colours tempering" to get the technique & colour charts, same applies to air on the hard side & soften a bit more if necessary.

You can grind it after that as long as you don't overheat it doing so, obviously that'd soften it even more.

Good luck & let us know how you get on.
Click to expand...
Sorry for the late replies, covid strikes again. I used a Norton blaze ceramic belt which worked fine on my razors. Constant water cooling resulted in final thickness. I found out that most users/makers used a flat grind on razors, so the work continues.
Cheers
 
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