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Old 04-30-2006, 16:19   #16
Bill Harsey
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Quote:
Originally Posted by Ambush Master
And then there is passivation in the Stainless Steels!!!
I was gonna get here later but since you brought it up...

The trait exhibited by stainless steels not rusting is known as "passivity" and this refers to the material corroding to a point that a film is formed which acts as a barrier to further corrosion.

"Passivation" refers to a process where the stainless steel is, for example, placed in hot nitric acid to remove all surface contamination so nothing is left over from the manufacturing process that will act like a battery on the surface of the steel to set up corrosion. This is not a good process to do on the kitchen stove top.

The term stainless steel covers many types of alloys, the ones we are interested in are the hardenable or austenitizing steels.


Yes there are true tool steels that have good stainless abilities and these are also referred to as "stainless" even though they have little in common with non-hardening stainless steels.

Edited to add a footnote on stainless steels:
High temperature tempering of stainless tool steels can result in a loss of corrosion resistance because chromium carbides continue to form robbing the matrix of usable chromium. See next post.

Last edited by Bill Harsey; 05-01-2006 at 08:54.
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Old 05-01-2006, 08:50   #17
Bill Harsey
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tool steel basics

We all use tools made of one type of tool steel or another.

Entire libraries are dedicated to this topic and I'm not going to try and fill one up.

The tool steels we use are iron plus alloys carefully chosen by steel makers for certain performance characteristics combined with the ability to manufacture and cost considerations.

The metallurgists I work with call this "tool steel alloy design". They break this down into two basic parts, the matrix and the carbides.

Think of the matrix as the mortar and the carbides as the cobble stones.
Some alloys become the matrix, others produce carbides and some do either depending on the amount used or the type of heat treat.

This is the stuff that determines the traits we choose knives for, like edge holding (abrasion resistance), toughness (strength and ductility)and stain resistance

Last edited by Bill Harsey; 05-01-2006 at 09:51.
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Old 05-01-2006, 21:47   #18
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How a tool steel is made and heat treated determines the size of the individual carbides.

Anyone care to guess how this impacts knife blades for good or bad?


Not a test, just a conversation.

Last edited by Bill Harsey; 05-01-2006 at 21:49.
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Old 05-01-2006, 22:25   #19
gunnerjohn
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OH..OH.. I know!!!
Sorry, I took the class, so I will wait for other answers
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Old 05-02-2006, 07:59   #20
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John, Thanks for holding on.
Let's do this different to make it easier, maybe.

Please start naming the knife steels you've heard of or used.
Everyone is welcome to jump in.
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Old 05-02-2006, 08:12   #21
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Ok, I 'll jump.. My thoughts would be finer is better. Logic would be a more homogenous steel. But I am pretty much guessing. Isn't the difference being disccussed here, pretty small?
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Old 05-02-2006, 08:17   #22
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To name just a few I have seen, A2, O1, O2, D2, L6, W2, M2, 420, 440A, 440B, 440C, 154CM, ATS-34, 1045-1095, 5160, S-30V, and Damascus. Not steels, but also used for blades, Stellite, Talonite, Titanium.

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Old 05-02-2006, 08:19   #23
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Quote:
Originally Posted by HOLLiS
Ok, I 'll jump.. My thoughts would be finer is better. Logic would be a more homogenous steel. But I am pretty much guessing. Isn't the difference being disccussed here, pretty small?
Hollis,
Yes usually finer grain is better and your logic is correct but not always easy to do in tool steels.

I think the differences between tool steels are surprisingly large and are quite noticable to the user in terms of overall performance and sharpenability.

The performance thing gets important when the knife becomes a life critical tool in an emergency.

Last edited by Bill Harsey; 05-02-2006 at 08:22.
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Old 05-02-2006, 18:03   #24
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I have a book some where that is on heat treating metal. I have a decent size furnace, Nicked named "hades". I think I understand what you are saying. The difference of a small %, or how quickly the quench is, or heated too has a tremedous effect from brittle to too soft (as in not holding a edge).
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Old 05-02-2006, 19:18   #25
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Ok.. here is a list of familiar knife steels. The asterik next to some refer to those that are multi task steels, both carbon, alloy and stainless that are used if other applications than just knife steel.

O1*, O2*, A2*, D2*, S7*, W1*, W2*, 440series stainless' A,B,C *, AUS-8, CPM-S30V, CPM S90V, 154CM, ATS34, BG42, 4140*, 4142*, 4145*, 1095*, 1018*, 300 series stainless (303,304,305,316 are used in knife parts, but not blades because they do not heat treat but will work harden when you least expect it. Just ask Bill) A36 is a good carbon mild steel for making other parts, High Speed Steel used in tooling is sometimes used by some makers for it's hardness. Sandvik series 12C27 is an example of a designer steel that is easy to machine in the annealed state, but is tough as hell when hardened which explains the manufacture of machining tools using this material.
Those that like a challange there is also Inconel. This is one of those steels that will belittle the best machine.
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Old 05-03-2006, 12:53   #26
Bill Harsey
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Good list of various steels, I'll begin to categorize soon.


Gunnerjohn,
This is complicated enough without mentioning other materials not used for knives. My poor little knifemaking brain is going to get a stress fracture if you keep this up.

The Inconel type metals (high nickel, chromium, molybdenum and sometimes niobium alloy with very little iron) have no knife blade application that I've ever heard of.

These alloys are designed for being resistant to specific types of corrosion, like in nuclear power generating plants.

Back to knife steels.
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Old 05-03-2006, 14:38   #27
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Mr. H, how about laminates? Say, as are used in traditional puukkos, with the outer layers soft to allow for a more flexible blade, but the inner layer (the one with the edge profiled on it) being harder to maintain its edge? How does one manufacture them without running into delamination challenges during use?
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Old 05-03-2006, 15:09   #28
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Quote:
Originally Posted by Razor
Mr. H, how about laminates? Say, as are used in traditional puukkos, with the outer layers soft to allow for a more flexible blade, but the inner layer (the one with the edge profiled on it) being harder to maintain its edge? How does one manufacture them without running into delamination challenges during use?
Good question.

Laminated steels are among the oldest known existing artifacts of iron work ever found in the greater region we now call Syria. (IIRC, from Scientific American article, unkown date) . The oldest known smelted iron ore is said to come from the Sinai Peninsula found in and among ancient copper smelting sites and preceding all this is the near pre-historic use of found meteoric iron by ancient peoples to fashion into tools. This meteoric iron is distinguished by it's nickel content.

High carbon steel was very precious when hand smelting Iron because it either had to be very carefully sorted from the original cooled melt or forged in in a reducing fire of charcoal (source of carbon) to gain enough carbon from "carbon migration" while the steel was at heat. This was some very resource and labor intense work.

I also think that the technologies of making ceramic wares was the source of the technology to smelt the coppers, bronzes and then steels.

To use this hardenable carbon steel frugally, it was laminated or forge welded to another lower carbon steel body to make the entire tool.

The actual "weld" involves heating up both pieces of steel together to just under melting temperature and quickly hammering them together before they cool to the point of not sticking. Fluxes of glassy material are used to float the oxidized steel scale off the surfaces and get a good weld. Steel reacts very quickly with oxygen at high temps and this will prevent a clean strong weld.

When done well, the two types of steel become one piece and can take some very hard use without cracking because the softer outside iron supports the hardened high carbon core that makes up the edge.

The same principles apply to Japanese sword making as well as many carpenters and timber frame tools like old chisels and slicks that can still be found in second hand stores and occasionally estate sales.
Look for the two different colors of steel in the tool body.

If memory serves, we can still buy new laminated wood working tools from some sources, especially fine Japanese woodworking tools.

The traditional Puukkos are a good example of this being done well on a production basis. I think the Puukkos steel is roll forged together in the mill then manufactured into knives. They are famous for toughness.

We also have some custom makers of modern laminated steels that are doing amazing work. My friend www.devinthomas.com comes to mind, he makes some exotic stuff in the high order stainless tool steels.

Last edited by Bill Harsey; 05-03-2006 at 15:36.
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Old 05-05-2006, 09:30   #29
Bill Harsey
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All Those Steels

Some overview before we go into details later.
You kids see there are a lot of different types of tool steels used for knives.

Many of these tool steels were developed for some other hardened tool steel application than knives, some steels are further developed specifically for blade steels and not just for hand held knives but also stuff like wood chippers, wood milling, steel, plastic, paper and other material cutting blades and industrial scale food machinery as well as the entire range of tooling like drill bits and milling cutters and saws used to machine steel.

The reason we see so many different types of tools steels is that alloys are chosen for particular traits in specific applications or modified as some alloys become scarce or difficult to acquire because of world politics.

The first thing a knife blade has to do is be hard enough so the cutting edge doesn't roll over or break off when we try and cut something. Tool steels need enough carbon to form carbides when hardened.

Other alloys form different kinds of carbides and add to the strength of the matrix but the first and most important alloy of "high carbon" tool steel is carbon in carefully controlled amounts varying from .75% to well over 1% and in the class called "ultra high carbon" a steels carbon amounts can be from 1.25% to 2%.

(darn phone, have business call from Italy, be back later)

Edited to add, It's later:
The main areas of performance knifemakers and users are concerned with are:

Hardness
Toughness
abrasion resistance
stain resistance

These are all mechanical traits of a given tool steel that are both related to each other and quite seperate.

Anyone know the difference between hardness and toughness?

Last edited by Bill Harsey; 05-05-2006 at 13:47.
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Old 05-05-2006, 15:41   #30
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IIRC, hardness is the resistance to penetration of the surface of a material by a hard object. Toughness I believe is ductile or yield strength. Could be wrong.
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