I have a friend who would like a stainless steel gaff hook for fishing. I have never worked stainless and couldn't find a BP covering its properties. I'd appreciate some pointers on it's differences from mild. Thanks, Gary

Lots of differences, even amongst SS types. Some are not forgable at all, some are but not by human muscle power. Metal suppliers have spec lists that will let you know what to expect.

In general though, SS has a narrow work range, 2-300 degree or so, from hot enough to too cold and you don't want to get it too hot. SS doesn't conduct heat very well either so it'll spend more time in the fire soaking for less time on your anvil. It's not only harder to move it doesn't let you work it as long.

You'll probably be happiest using a 300 series, say 304. It's been a long time since I worked SS but as I recall 304 worked best at a high orange, just shy of yellow heat. 300 series SS is pretty common and not too expensive. Be sure to pick up enough to experiment with and make some mistakes with.

Once you're done you'll need to passivate it or have it passivated or it'll rust. This can be done at home if you don't mind handling nitric acid or want to set up an electropolishing machine.

If you're bidding this project; figure it'll take you about 5x as long to forge and finish, the SS will cost 3-4x as much as mild and shop around to see what passivation will cost.

SS will make you work for it but it's plenty forgable and the results are excellent.

Frosty

erm, gaff fishing? isn't that considered poaching?
I guess maybe he's just using one to land the fish he has caught by conventional "legal" methods..
anyway, I've done some work in stainless and have had it crumble.. crack, and work.. so I guess like Frosty said, get the right alloy.
you could also just plasma cut out a hook shape in some .25in bar and grind it to shape.. no hot work involved.

find some 304 SS in 1/2" round or less and forge it like regular steel. Let it air cool and it will be fine

I dont know what the alloy was that I bought, 3/8 sq. stock. But, a friend and I just about beat our brains out trying to forge steak turners out of it. He told me that he would throw rocks at me if I brought any more into his shop. YMMV

I make BBQ tools from 304SS sometimes if I'm not feeling frustrated enough by daily life. I agree with the thoughts about narrow working range, but it moves okay if you stay in the temp. window. The other strange thing from my experience, is it doesn't scale much at all, and therefore it's hard to see facets or flat planes while it's yellow hot, meaning it's difficult to work square, octagon, round consistantly.

narrow work range? check. cools quickly? check, 304? check I do lots of hooks and camping equipment from stainless. Keep it hot hit it fast and don't hit it cold. Seems to me for a gaffing hook you could live with some 1/4 inch ss rod. Hope this isn't for a salt water guy as 304 will not hold up well to salt water. and (318?) is very pricey. real high orange works for me. gas forge makes working stainless a lot faster.

Gentlemen, thank you all, you've given me much to chew on and some good starting points. I'll see how interested he is after letting him know what I'll be dealing with and post results if and when I carry through the project.
RF- he just wants a landing hook that won't rust on him. No poaching as far as I know!
He does know a lot of other fishermen and maybe I can get some of their business too. Thanks again all.

BTW if you need to passivate it you can do it using citric acid found in the canning area of the local supermarket.

Thanks, Thomas!

stainless is tough stuff. it cools withing seconds, and fractures when drawn out too far. although this is just with the "unknown" stainless i've worked with. So you might want to look for some 304, or 430SS. i THINK those are fairly easy to forge. But it is night and day from mild steel. You'll hate it i guarentee :)