Thread: Crucible steel file

I've decided to try my hand at making a razor and before I start shelling out for steel bar I wanted to experiment with making one out if a file as I've seen on the forum is often done. I've started work on an old Sheffield file that is stamped 'crucible steel' and have got the rough shape down. I'm after a near wedge and have left the edge around 1.5mm thick.
I've done all the work so far with my angle grinder and bench grinder. I gave it a little polish too so I could see how the blade faces were looking in terms of flatness. I have read the posts regarding heat treating and am wondering what would be best for crucible steel regarding temps and times. Or more to the point if crucible steel is ok to heat treat. I know many old blades where made of crucible steel but I'm not sure on the ht process. Any help would be appreciated. Oh, and I'm going to drill the pivot hole in the morning. I'm currently looking to purchase a small knife forge to do the ht. not quite sure what's going to be best for quenching, canola oil isn't widely available here in the uk. Many thanks, Rob.

I know NOTHING of HT but I like the look of it so far!

Keep in mind that what is stamped on the file may very well be just marketing.
I suspect it is generic high carbon tool steel, not actual crucible steel, kinda like how razors are sometimes stamped with 'damascus', 'india steel', etc.
Crucible steel is expensive stuff, it would be pointless to use it for a file. It would be x times as expensive as a normal file, and not really have much if any benefit compared to simple tool steel. Files are not impact tools, and hardened crucible steel would not cut better than normal hardened steel.

I would heat treat is like generic tool steel and see how that turns out.

Yeah I would look up the ht for 1095 and us that. It's roughly heat as evenly as possible until non magnetic. Roughly 1450f. Try and keep it the same temp for 5-10 minutes. You can ball park it by color. Quench in warm oil or salt water with an up and down motion. Luke warm oil is preferred. Move it from the heat to the quench as quickly as possible. It should be really hard if everything went well. Temper in your regular oven to the desired final hardness. Final hardness is dependant on temp. I would not trust my ovens gauge and use a secondary. A couple of 1-2 hour bakes with a cool to room temp in between is the usual prescription.

Hope that helps. Almost any light oil works. I think people us canola because its cheap. Peanut, for that matter most of the vegetable oil family should do.

If you search around you should be able to find color charts for temp and temper charts pretty easy. I am curious what people think the right final hardness people think a razor should be. I've mainly made less specialize knives.

That depends. Most honers and makers go for 61HRc.
Personally, I think anything between 59 and 61 is great.

Brilliant, how many times would you recommend doing the ht from forge to warm oil? I think I'm going to invest in a pyrometer with ceramic sleeve too, does anyone know of any uk suppliers?

To be honest: don't overthink it.
The process is not anywhere near as sensitive that you would need a pyrometer or worry overly about the temperature of the oil. Just heat a bar of iron, quench it in the oil (watch out for flames) and stir it around.

Thanks Bruno, that's good to hear, I was just a bit worried having read specific temperatures and the like in recent threads. I'm a big fan of the trial and error method!!

You often read exact temperatures and times. That makes sense, because they measure those characteristics, and those temperatures / times are scientifically optimal. However, there is a relatively wide range which gives you comparable outcome. Sure, you cannot predict whether the exact hardness is 60.5 or 61.5. And the tensile strength might not be as high as physically possible. for industrial use in applications with specific requirements, this becomes important.

However, if the workpiece after heat treatment skates a file, there is no doubt it has been hardened successfully. You can do some experimenting, using break testing to see what works best for your setup. For the purpose of knives and razors, low tech can work perfectly.

Master blacksmiths have done this for centuries without pyrometers, vacuum ovens, salt baths or other modern equipment.

That's good, I'm on a budget ant those pyrometers are a bit expensive!! When quenching in oil how long do I need to leave in the oil? Long enough to cool down and handle? I'm unable to afford a forge at the minute so it will be a week or two before I can ht so I'm going to be making blade blanks with my spare time. I can see this getting addictive!