Thread: Cold forging

I am working on my first project: a cutting knife for my mother. I am going for something that resembles this:


I have a piece of O1 that I annealed and cut to size.
I experimented a bit, and discovered that it is soft enough to shape with a 2,5lb hammer without heating it.
Granted, I have to file away as well, and the shaping goes slow, but I actually like being able to work on that piece for 15 minutes when I have time and then put it away again without having to fire up the bbq.

My main concern is: does this have a negative effect on the steel in some way?

This is the forging equivalent of fixing thebigspendur's nasty warped razor with a Belgian blue...

As long as the steel is soft enough, I think you should be OK. Cold forging is a legit technique, from what I understand. It probably imparts stresses as you go, but you should do a stress-relief treatment before you harden it, anyway. (Grinding also stresses the steel, and it's not a big problem as long as you deal with it.) It might be a good idea to re-anneal it every once in a while to minimize the stress build up.

When you read about forging too cold, usually that means while the steel is hot but in the black range. There's a range where steel is "blue brittle"--I think that's the term. It's roughly between 400 and 800 degrees F. You can crack the blade if you hit it in that range.

At room temperature, it's pretty ductile, so you should be fine. The nice thing is you'll have plenty of time to correct mistakes.

Josh

No you can not cold forge a blade. The stress will shatter it when heat treating starts. I find O1 to forge terribly, I stick with simple high carbon steels W1 is a good one and comes in many shapes, it works and treats like 1095. Cold forging a blade steel is not a good idea at all.

Originally Posted by Twalsh341

No you can not cold forge a blade. The stress will shatter it when heat treating starts. I find O1 to forge terribly, I stick with simple high carbon steels W1 is a good one and comes in many shapes, it works and treats like 1095. Cold forging a blade steel is not a good idea at all.

Well, I guess we should all throw our O1 in the trash, since it comes from the mill after being cold-rolled to shape. That's cold forging, my friends. What's going to impart more stress, a 2 lb. ballpeen hammer or hundred-ton presses forcing the steel ever thinner?

Dealing with stress is a everyday part of making knives and razors. A simple normalizing routine will relieve any stresses that build up due to cold-forging, hot forging, grinding, machining...

A blade that is hot-forged at too low a temperature will develop stress cracks that will show up later when you heat-treat the blade. W1 is notorious for this.

O1 is a little stiffer under the hammer, but it moves well once you get it hot enough. The only reason I'm not forging blades from it is that it can be hard to drill after forging. Otherwise, it's great to work with.

Josh

I found that one end of the O1 was soft enough to use my files with ease, so atm I am trying to see how far that'll take me.

The advice about sticking to simple steels is well taken. I would disagree about forging O-1 though. I routinely reduce 1.5-2.0 round bar down to flat because it's a lot cheaper than buying flat bar. Never had a problem with any of the O-1 after the heavy work. Fascinatingly, even W-1 is considered a cold-working steel in the books I'm reading along with a bunch of others that might surprise folks.

O-1 will work harden when cold forged and that effect needs to be accounted for. As Josh mentions, he found out that it doesn't take much to harden it. It'll even air harden if you have a fan blowing nearby. It'll need to be annealed again, but that's not difficult.

Originally Posted by JoshEarl

The only reason I'm not forging blades from it is that it can be hard to drill after forging. Otherwise, it's great to work with.

Josh

Thats because O1 needs some interesting annealing cycles after its been worked above critical to reduce the grin size and carbide structures to soften it.

I'm not saying to trash all the O1 I love it for punches etc. there are just some ways you should handle a piece of steel. Risking developing fractures in a cold rolled steel, which has decreased ductility, doesn't make any sense to me.

Originally Posted by Twalsh341

Thats because O1 needs some interesting annealing cycles after its been worked above critical to reduce the grin size and carbide structures to soften it.

You've made a link between annealing and grain reduction that should be explained, please.

Originally Posted by Twalsh341

Thats because O1 needs some interesting annealing cycles after its been worked above critical to reduce the grin size and carbide structures to soften it.

Yeah, I don't have the equipment to spherodize anneal. O1 will be a stock removal steel for me.

Josh

When a metal is worked the grain structure is distorted, gaps form in the lattice, these stresses are what can cause a steel to break of develop fractures when quenching. Normalizing is letting a steel air cool after reaching CT, a full anneal is achieved when a steel is brought to the CT and cooled to a specific temperature at a certain rate.
When annealing the steel goes through several phases the first phase the defects are removed from the steel (dislocated atoms), then the grain structure redevelops. After this spherodizing occurs and the metal may become too soft for certain applications. O1 needs to be spherodized to machine easily after being worked.
When martensite is tempered or austenite cooled a laminated structure called pearlite is formed. Pearlite is layers of ferric carbide, a very hard material; which impairs machining and reduces ductility. Simply heating O1 to above critical and normalizing it allows the carbide to form and will not be sufficiently annealed. Further cold work of the steel will develop micro-fractures that can break it in the quench; or make it impossible to drill.