Stainless/Non-stainless: How to Test ?

[btrwtr]

304 has a maximum Rockwell hardness of less than HRC 40. Hardly suitable for knife blades. It can be cold work hardened but is not hardened by heat treating. It is suitable for many applications and for knife components like bolsters, liners and handles but I do not think it is suitable for a knife blade. If it were used for a knife blade I don't think I would want the knife. 316 stainless like 304 is another great steel but again not suitable for a cutting, working knife. I have both 304 and 316 in my shop but would never think of using them to make a knife blade.

[terryl308]

I have to agree with most, 304 or 316 is not a good steel for blades, it wasn't intended to be either. If I use stainless for a knife blade , I like CPM 154. But I use mostly high carbon steel, O-1, 1095, 1080 and D-2. The metal people have come a long way in the alloys and they have some really good blade steels, the reason I don't use much is in the heat treating process, and most should be cryo treated after heat treating also, and I don't have the equipment for keeping liquid nitrogen. Just my two cents worth. Terry

[Steve Warden]

most should be cryo treated after heat treating also,

I'm a fan of "Forged in Fire" and I've learned quite a bit about knife making, though I do not make knives myself. Real or staged, I just find the show interesting.
What's the down and dirty on cryo treating?

[steve99f]

Nitrogen liquifies at around -320F Steve. That temp will burn you just like a flame or worse. With the right equipment (cost) and knowledge, it can be handled. Gun barrels are also said to benefit from cryo-freezing.

[Steve Warden]

Nitrogen liquifies at around -320F Steve. That temp will burn you just like a flame or worse. With the right equipment (cost) and knowledge, it can be handled. Gun barrels are also said to benefit from cryo-freezing.

I'm familiar with the precautions required around nitro. We used to have to fill the nitrogen tanks on the aircraft. Also extremely flammable to the point of explosive if it comes into contact with petroleum. Had to make sure the drip pan was in place in case any dribbled onto the ramp and onto a possible oil spot.

But what does it benefit in the knife making world? Is it used in lieu of quenching oil?

[Fisher]

Didn't read through all the posts, so forgive me if already answered. 300 series stainless is termed "austenitic" since the higher (approximately 8% nickel content) is an austenite retainer thus making the steel for the most part non-hardenable and used mostly for tableware like forks, spoons and butter knives. Being non-ferritic it's non-magnetic, but in some cases can show some magnetism if appreciably work hardened.

Ferritic stainless is the 400 series, magnetic and can be hardened and tempered.

How to test without staining is tough. I would try a test spot with a little vinegar which hopefully can be removed later with steel wool or Never Dull.

[ea42]

Nitrogen liquifies at around -320F Steve. That temp will burn you just like a flame or worse. With the right equipment (cost) and knowledge, it can be handled. Gun barrels are also said to benefit from cryo-freezing.

I'm familiar with the precautions required around nitro. We used to have to fill the nitrogen tanks on the aircraft. Also extremely flammable to the point of explosive if it comes into contact with petroleum. Had to make sure the drip pan was in place in case any dribbled onto the ramp and onto a possible oil spot.

But what does it benefit in the knife making world? Is it used in lieu of quenching oil?

Steve, cryo is used in addition to heat treating. It's done after all the heat treating steps, including the quench. Some steels still have some austenite present after heat treat. Cryo helps convert that to martensite along with making the steel more homogeneous. It's especially useful with steels like D2 that don't convert so readily by heat treat alone. The steel is generally heated up to a few hundred degrees before it's frozen, then heated up a final time. These temperatures, just like in heat treat, vary between materials so it's again a fairly precise process. The process tends to make the steel a bit harder but not necessarily tougher. What it eliminates is soft spots that might be prone to wear, chipping, or cracking. You can find a lot better explanations than mine if you google "steel cryo treatment" or something similar.

Eric

[Steve Warden]

Thanks Eric.

[Gunsil]

Emerson Case was one of the first to use " frozen heat" to temper blades back in the 1950s. The modern stainless German quality kitchen carvers and slicers like those by Henkels are marked "Friodor", German for cryo treating.

[kootenay joe]

Henckels introduced "Friodur" in 1937.
kj

[Mumbleypeg]

Nitrogen liquifies at around -320F Steve. That temp will burn you just like a flame or worse. With the right equipment (cost) and knowledge, it can be handled. Gun barrels are also said to benefit from cryo-freezing.

But what does it benefit in the knife making world? Is it used in lieu of quenching oil?

Some good answers already given, but here is a link to more. https://www.jayfisher.com/Heat_Treating ... Steels.htm

Probably more than you ever thought it possible to know on the subject.

Ken

[Steve Warden]

Thanks Ken. "Probably more than..." is an understatement!
I appreciate the link.

[Modern Slip Joints]

The D2 blades of my Queen made Robeson pocket knives are etched "frozen heat." Before reading this thread I thought it was a silly way to advertise the steel crystal structure was made permanent by heat treating. Now I understand Queen was advertising chilling them with nitrogen after heat treatment. I wonder if that was a standard last step in Queen's Philip's Heat treatment of D2. Queen routinely stamped their D-2 blades PH-D2.

I do not scuba dive but my brother has lived to dive for the last 55 years. Scuba diving knives have more in common with the bars sold to pry out nails than they have in common with cutting knives. They are mostly used to pry abalone and other stuff off rocks. Pry bars need to be softer than ordinary knives to keep the prying end from snapping off. The pommels are used to rap approaching sharks on the nose to drive them off but that's another story.

As a sailor on a ship and on my own sailboat I used carbon steel knives. On the ship I carried a Case 5265CV stag folding hunter. I had to cut drain holes in the bottom of its pouch to keep the tropical rains from filling the pouch to the brim. Even so, I only had to occasionally wipe the thinnest start of rust off it. When I did get splashed with salt water in storms the knife was underneath rain gear. It very seldom got any salt water on it. Today, decades later, there is no evidence of it ever having had rust on it. Sailors need sharp edges, not pry bars.

Getting back to the original question, I've found the spot left by cold blue on carbon blades does not wipe off with metal polish. That's the best way I know to test but use the tinniest drop on the least conspicuous place. The portion of the tang that is only exposed while a pocket knife blade swings through its opening or closing might be the best spot to test. Alternatively you could test the spine. That's an easy place to sand and polish.