Identify carbon steel in old slipjoints?

[Jon]

I was wondering if there's a "quick & easy" way to identify carbon steel blades in old dirty slipjoints? I've started cleaning & sharpening old slipjoints as a hobby/project to give away (I like to see a knife used) & prefer carbon steel blades because some of the old stainless couldn't be sharpened . Not looking for high end, just cheap ($1-$2)users from garage sales & flea markets.
Thanks.

 

[Railsplitter]

I have heard that a magnet will not stick to stainless steel but I have never tried it.

 

[Komitadjie]

That's SORT of true. Some will, some won't. Unfortunately, the Martensitic stainless that is usually used in knife blades *is* magnetic.

Shamelessly kyped from the rest of the internet:

Austenitic. Austenitic steels have austenite as their primary phase (face centered cubic crystal). These are alloys containing chromium and nickel (sometimes manganese and nitrogen), structured around the Type 302 composition of iron, 18% chromium, and 8% nickel. Austenitic steels are not magnetic and not hardenable by heat treatment. The most familiar stainless steel is 304 containing 18-20% chromium and 8-10% nickel.

Ferritic. Ferritic steels have ferrite (body centered cubic crystal) as their main phase. These steels contain iron and chromium. Ferritic steel is somewhat magnetic, less ductile than austenitic steel, and is not hardenable by heat treatment.

Martensitic. Martensitic steels have orthorhombic martensite as their main phase. Martensitic steels are low carbon steels. They are magnetic, and may be tempered and hardened. Martensite gives steel great hardness, but it also reduces its toughness and makes it brittle.

 

[rpttrsn]

I have heard that a magnet will not stick to stainless steel but I have never tried it.

There are several "types" of stainless steel. The 300 series (which contains nickel) is NOT magnetic. This is used for bolsters and liners on some knives. The 400 series (which just contains chromium and no nickel) are magnetic and can be hardened for knife blades. example 440 A ,B, C

 

[Obsessed with Edges]

It's very rare, with old knives especially, for carbon blades to show no evidence of rusting/pitting. If I were shopping old knives, looking for non-stainless blades, I'd bring a 10X or greater magnifier (preferably lighted), and look closely at the blades for evidence of pitting. Even if the blades had been sanded or otherwise 'cleaned up', chances are a few spots were missed. I'd also look at the backsprings for the same (especially the inside face of the springs, inside the handle). Although, it's no guarantee that some old knives won't have carbon springs and stainless blades (I have an example of this; a Buck 307 stockman). Under brightly lighted magnification, sometimes you'll even see some very tiny red/rust-colored spots on carbon steel, that otherwise won't be seen by the naked eye.

It IS possibe for occasional pits to be seen on stainless blades, especially in the less-finished areas (like the tang, close to the pivot). Usually, though, they exist one or two at a time, in stark contrast to the rest of the steel, which should look very clean & pit-free.

Edit:
AND, with most old carbon blades that've been USED, the vast majority will exhibit at least a little of that attractive, grey 'patina' that so many knife nuts like.

 

[Jon]

Thanks for the replies folks.