Cast Iron Knife

[Andrew Garrett]

I'm pretty sure I just made a knife from cast iron.
I aquired an old Fairbanks Morse & Co double open-end wrench--most likely a 1920s vintage.
I hammered it out, ground it, heat treated it, finish ground it, and etched it. It felt like I was working tool steel the whole time, but the etched finish looks different than I expected.
It hardened fine--easily passing the file test.
I know they made cast iron wrenches a century ago, so I'm fairly convinced that's what I have here.

I just made a brittle knife, didn't I?

[Andrew Garrett]

Ok. I worked it out.
I called my buddy Steve Culver ABS-MS, and we talked about it. I sent him some pics and it was decided that it could not be cast iron, as cast iron cannot ne forged--it would just crumble. Furthermore, it wouldn't make a good wrench. However, it does have a random grain structure without the linear properties of rolled foundery steel.
Since it heat-treated the same as most other simple carbon steels I've used, we concluded (he concluded--I agreed) that it is cast steel.
I may even get a bit of a dendritic edge when I sharpen it--just guessing on that one.

[Doug Lester]

Doubtful. Cast iron does not forge all that well from what I understand.

Doug

[jimmontg]

Cast steel would be a better term. In my old job as a T.I.G. welder and welding all kinds of cast steels I can tell you the carbon content varies quite a bit, but if the cast iron is running .50 to .70% it will forge just fine and many old tools were made of cast steel in that range. Higher carbon is the stuff you can't forge and if you break one of those high carbon castings note how large the grain is on some of them. No kidding some castings were 4% carbon, impossible to weld.

I have welded pure cast iron and it welds like regular low carbon steel. It's the doggone carbon that causes problems. Your typical exhaust manifold is 2% carbon and welding it is nigh on next to impossible, so we'd use Ni-rod or nickel or silicon bronze to braze cracks. If you preheat it to 1200 degrees and slow cool it you can weld it, but almost nobody does that.

[Andrew Garrett]

I put an edge on it and did the brass rod test all along the edge.
It's good.

Very happy with the blade. I hope to find some more such tools. Love the pattern when etched! Very 'wootz' like.