Reaper,
Here is the problem getting information from some knifemakers. A number of us are using very high performance steels, the state of the art stuff ever produced on this planet (and if some of you guys have access to other stuff, pm me here. :D ) Our, ok MY, opinion is going to be a little biased and I'm trying to keep the bias out of this. That said...this isn't going to be a perfect comparison but here goes:

If we compare knives to NASCAR, I'm used to building cars that do 220 MPH all day long on the track. Your D-2 steel only does 200 because of some limitations on blade geometry and ultimate strength imposed by grain structure. Your D-2 also doesn't have rain tires.


On the street, 200 mph capability is damn hot performance.

The average day to day pocket knife user needs a "steel" that can do 60, top speed and are satisfied with the job it performs because they know it's limitations (don't pry the split rim off the farm truck wheel with it...) and can probably do the basic work of sharpening to keep it cutting.
All knife steels will need sharpening at some point.

The potiential life critical tasks demanded of a knife by those who would be in tactical or emergency situations is the reason good knifemakers use the best steel possible

Amazing knives have and are being built from D-2 but the grain size and carbide saturation present some limitations in some areas of performance.
Yes D-2 is a little hard to polish but there are others that are tougher to fine finish.

If all my knife making got limited to D-2, right now, I'd still make very good knives but no filet knives at Rockwell "C" scale 60 that can bend near 90 degrees are going to be made from it.

I also know the maker of your D-2 knives and he has the process down to a science for best possible results.

Very cool on the scholarship from Latrobe.

Stainless
 

What makes a knife stainless?

Can a tool steel be stainless?

10-12% or more Chromium (Cr) content generally defines a "stainless" steel, though Cr content can run as high as 30%. Not sure how knife steel is defined versus normal metallurgical steel definitions.

IMHO, D2, at 11-13% Cr, is technically a high-carbon, high-chromium cold work tool steel. Depending on the exact amount of Cr, it could be stainless, or it might be very nearly stainless.

A little metallurgical poem, from one of my favorites.

"Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all."
-Rudyard Kipling

TR

If this question has already been covered, please ignore.

What about Cryogenics, is there a serious usage in cutting steel?

Terry

Do you refer to the sub-zero quench used in the heat treat process?

I haven't given up on the stainless question yet...Reaper has good answer but there is more.

Bill:

This process. http://www.nitrofreeze.com/

Terry

Terry, Much to this.
I always use liquid nitrogen (-320 F) as an integral step during the heat treat of the steels I use here, so does Chris Reeve. This is critical to the ultimate performance of the blade steels we use but is only good if integrated at the correct time during the hardening and tempering process.

There is much discussion about how much good a cryogenic treatment does after the part has concluded it's heat treat and has been made into a finished part.

Interesting!

Good thread, Bill!

Terry

I'm just venturing a guess on the Stainless/ Tool steel question. Tool steels have higher carbide content which gives them their hardness. (here comes the guessing) Stainless has a higher chromium content which increases corrosion resistance but limits the hardness.

BTW, great thread.

For the stainless tool steel question: My answer is yes, you can have a stainless tool steel.

Reasoning: It may have to be a precipitation-hardened, nonstandard chromium steel, AISI types 632-635. I chose the precip-hardened steel since the Martensitic grade is heat treatable, while the Austenitic grade allows you to add an array of elements to change formability (Cr-Ni), intergranular corrosion resistance (Mo), hardness (C), etc.

TR probably answered most of it; I don't have the numbers in front of me to compare the aforementioned steels to tool steels.

CPTAUSRET,
After main work hours, here's more answer to your question about cryogenic treatment of tool steels.

The reason we deep freeze tool steels is to force retained austenite produced during the high temperature phase to convert to martensite.
This happens because the freezing increases the mechanical driving force in the steel to complete this transformation.
This must be done during the initial heat treat cycle or the steel tends to "set" and the freeze will have much less ability to do any good.

Retained austenite in the steel causes weakness and we don't like weakness around professionalsoldiers.com. Just ask the Team Sergeant.

Your more right than you know. There is an entire area on the "tool steel alloy composition chart" where tool steels are stainless because of the addition of chromium. You swerved into something here too, too much chromium displaces other alloys and isn't as hard of a carbide.

Maybe I should explain what knifemakers call stainless, tool steels containing 14% chromium are considered pretty stainless. 14% is the threshold of "stainless" in a tool steel. D-2 has about 12% chromium and has some stainless characteristics but is more prone to the surface discoloration some folks call rust. The D-2 certainly doesn't rust much compared to other non-chrome tool steels.

An interesting thing to know about 14% chromium tool steels like 154CM (common good blade steel) is that the kind of heat treat can change the ability to not stain. Some of these steels have two distinct final temper ranges, high and low. When 154CM is tempered in the high temp range of over 900 F, the chromium carbides continue to form thus pulling usable chromium out of the matrix for stain resistance. The difference is noticable especially with 154CM knives used around salt water.

Correct.
The term "stainless steel" got a deservedly bad reputation back when manufacturers figured out that you don't have to use a good grade or do a good heat treat to sell knives. Hard use knife folks got it and the word was "stainless sucks".

Much has changed. For one the business of selling knives is very competitive and if quality slips, someone else gets your market share.
Steel companies are supplying good working grades of these steels on a regular basis to knife companies who are careful to get the heat treat right because reputation is everything.
We now have more metallurgists than ever before working directly with knife companies to keep this stuff sorted out.
(I keep my metal guys on speed dial.:D )

The knife buyer is the winner.

Now we have a grades of stainless tool steels with hardness, toughness and abrasive resistance properties that few tool steels could even dream about 20 years ago.

Bill:

Let's cut right to the chase.

If you had to build a fixed blade knife that was going to be your only tool to survive with out in the woods (in combat), and you could have any alloy you wanted, in the dimensions you wanted, what steel would you pick?

What would it be for a folder?

That is really what we want to know.:D

TR

The same stuff I'm using now, CPM S-30V for both.

Edited to add, some may be familiar with a few of the knives made with this steel.


Edited to continue: Reaper, as you probably know, we never stop testing new steels as we can get our hands on them. Yes there are a couple very exotic and difficult to work steels that can do a thing or two better than CPM S-30V and they are very cost prohibitive to manufacture and there will be huge downsides to the user.

These steels would defy re-sharpening in the field making them of little use to the soldier.


My answer remains CPM S-30V steel.

How we pick a knife steel...
 

As is beginning to be discussed here, tool steels are made from many different recipes of alloys.

The purpose of these choices is to try and combine multiple physical properties we want in a single piece of steel for a specific edged tool.

For a knife we want it to get sharp and stay sharp as long as possible while being able to use as a prybar if needed. These are two distinct and seperate physical properties.

Stain resistance is important to "sharp". We can lose the edge on a non-stainless knife without ever using it if your in the right geographic location like a warm marine or tropical climate.

If we pick any single steel designed for a single trait, there will be many other steels that do the other traits better.

These are some of the things we have to think about when choosing a tool steel for extreme use knives.

We haven't spoken about "particle metal steels" yet (CPM S-30V is one of them)... this stuff is gonna get like science fiction, only better. :lifter

Speaking of hardness and toughness. In the mid 70's I got a Puma Skinner. Still have it. Up the blade is the 'diamond punch mark' Did a quick search on the net. The design is like the top knife in that pic. However, There isn't any etching/writing on that side of my knife. It is on the opposite side and different. it is the 6393, serial # 56472.

http://www.foxridgeoutfitters.com/de...1&product=4109

Brad,
I'll assume your asking what steel this is and I don't know but I can ask the owner of Boker or his top knife designer over in Germany. Everyone knows what their competitor is doing.

The "diamond punch mark" is the impression left by the point on the Rockwell hardness tester. The diamond is gently preloaded onto the flat and parallel surface of the heat treated blade, while it rests on the machines anvil, then a known pre-set load is applied. The depth of this impression is carefully gauged by a large readable dial on the Rockwell hardness tester and the user reads off the hardness.
The less the penetration, the harder the steel.

A Rockwell Hardness test is that of testing a given steel or other materials ability to resist surface indentation.

In selecting steel, what we really need to do first is to determine what we want the blade to do.

The use of the item, and the characteristics we need will decide its optimal composition.

A soldier, a butcher, a surgeon and a gift-wrapper may all use knives, but what they are doing with them are completely different, as are their ability to maintain them. A surgeon may toss a multi-hundred dollar instrument, the soldier spend it reluctantly, but be unable to care for it and maintain it like the butcher, where the gift-wrapper will not spend over $10 for one, and will probably throw it out (or change blades) when dull.

The best steel is always going to be a compromise between multiple factors, only the user can decide whether a particular product is worth the price. For the soldier, I believe that the primary characteristic sought is toughness. For the butcher, it may be edge-holding, for the surgeon, it may be sharpness, for the gift-wrapper, it may be price.

Speaking of price, I know that steel prices are a portion of the finished product's costs, and that the time and abrasives it takes to prepare the steel is another portion of the cost. Clearly, CPM S-30V is a great steel for those serious users who can afford it, but is may not be the right steel for a knife going on the shelves at your local Wally-Mart.

Bill (or Mick, or any of the other makers here), can you elaborate at some point on the relative prices of the steel, the abrasives, the heat treat, and the time spent working it to the final cost of the knife?

Thanks much, great thread.

TR

Reaper,
Good overview, Your spot on about many things in your comments.

It is like trying to hit a moving target to find a tool steel that gives us the desirable performance traits in a knife and it does depend on the job your doing.

Let's stick to tactical knives and please remember:

"The biggest difference between knives is any knife over no knife at all"
(-Bob Loveless 1986, while I was his guest in his shop)

Yes we are guilty of trying to make the best possible knives with the best possible steel and it doesn't come cheap. The better the steel, the higher the price and we pay a premium for the steel alone and because of the properties we desire in the knife this correspondingly makes the manufacturing costs higher because of hardness and toughness to machine, grind and finish correctly .

CPM S-30V is running right at three to four times as expensive as other tool steels that knives could be made from. I haven't gone down the list of alloys and what they do yet so here is a start because it goes to "cost of making"..

CPM S-30V has, among other things, Vanadium in it, enough to form Vanadium carbides. Vanadium carbides are harder than the abrasive grit aluminum oxide. This is why this steel has some very good edge holding and abrasion resistance and it really sucks to grind and finish compared to other tool steels at the same hardness.

World markets are directly effecting the price we pay for steel. There is great competition for iron and all the other alloys that go in it. China is a huge factor in this situation. I'm seeing "surcharges" on my steel bill because of the added cost of getting particular alloys from various parts of the world.
This all goes to cost of manufacturing.

We also think the performance gained, as measured in toughness, edge holding and stain resistance, is worth it in life critical tools.

I would still take the knife forged out of a truck spring over no knife at all.

[QUOTE=Bill Harsey]Brad,
I'll assume your asking what steel this is and I don't know but I can ask the owner of Boker or his top knife designer over in Germany. Everyone knows what their competitor is doing.

I only knew the purpose of the Rockwell Hardness test, but now I know how it is done. Thanks. It would be interesting to know the type of steel but if it’s a hassle it’s don’t bother Bill. What I was trying to find out, while trying to sharpen it a few months ago, was whether it was a double or single bevel edge. I’ve had it for some three decades and don’t remember. Even looking through a magnifying glass it’s hard to tell. Reason for that is because I have tried sharpening both sides. I began wondering if maybe it was designed and made with a single edge.

Brad,
If memory serves, the Puma Skinner had a nearly sharpened top edge for bone breaking when working on big game. It was designed to be turned over and used like an axe.
My thought is concentrate on the main master bevel for hunting uses, the top edge doesn't have the geometery to get sharp easily.
I've worked on those knives before.

That it does Bill. I'm just not using the right nomenclature. I mean the edge. Whether it it sharpend on one side or both sides of the blade.
Brad, Bill here, let me answer within your post. Understand now, sharpen the blade from each side. If a blade has been sharpened unevenly it may be hard for you to see in order to figure that out.
Does this answer your question?

Caveman Status!
 

Hey Class! I almost forgot-
The Crucible Specialty Tool Steel metallurgists and management YEARS AGO named me the official "Caveman Testing Facility". Whenever they come up with something new, they send it to me for testing to see if it can be heat treated here, successfully. If it passes the "caveman test" they can go to market knowing virtually all machine shops can handle the steel well or have little excuse for not doing so.
Here's why I bring this up...
I'd thought I'd try and get "sooophisticated" on ya all and see if some research on alloying elements would be of any benefit to explaining this stuff to you here on this thread.
I quickly found so much empty or half complete information via Google that I came to my senses and we're gonna do it my way.

Next Installment: Tool Steel Alloys and what they do, caveman style :D

Yeah,,,,,,,,,,,,,, Caveman style, works for me, Let me go get my bigger hammer................

Thanks for the Thread BTW, Very enjoyable read..

The Good Stuff In Steel
 

Iron makes up most of "steel" but it is usually never mentioned in the chemical analysis or composition of added elements that make up tool steel alloys.

Tool steels are made and refined by several different processes but they all involve getting it very warm until liquid and then the alloys can be added to the melt.

This is done in amounts measured in tons at a time. I asked the Crucible steel guys if I could come help make steel sometime. They said no.

While a tool steel is molten samples are taken from the batch, cooled and tested for percentages of added elements. Adjustments are made on the fly.

Here are some of the alloys added to tool steels I know about, anyone notice anything a little unusual in the list?

Carbon
Chromium
Cobalt
Columbian(bium...:D, now called Niobium the last century or two)
Molybdenum
Manganese
Nickel
Nitrogen
Phosphorus
Sulfur
Silicon
Tungsten
Vanadium

Some of these strengthen the matrix, some make carbides and some do both.
There are other reasons that alloys are added to steel, like for example, improving the steels ability to cool down from the initial melt without massive segregation of alloys.

Bill:

Don't want to ruin your alloying here, but if you put your Columbian in the steel, he (or she) is going to scream and flop about before ruining the steel.

I had no idea human sacrifice was a part of steel making any more.

You Oregon boys have all of the tricks.

TR

TR,
Our carbon comes from a different source and I don't think I've ever used a steel with Columbian in it.

Look at the list again, aren't alloys supposed to be a solid? :munchin

I am completely out of my lane here, but could the Nitrogen come from the Liquid Nitrogen that you referred to earlier in this thread?

Air.177, you have the correct stuff but not at that stage.

In some steels (like the ones we use) Nitrogen is injected into the melt and it reacts at the molecular level with the steel.

Anyone guess what it forms?

When nitrogen is heated, it combines directly with lithium, magnesium, and calcium, and when mixed with oxygen, it forms nitric acid then nitrogen dioxide. I believe large quantities of nitrogen are used to anneal stainless steel IIRC.

To the best of my knowledge there is no lithium, magnesium, calcium or oxygen in the melt when making the CPM steel that Nitrogen is used in.

Bill,
Are you talking about the use of a high pressure jet of N2 to produce the fine particles of extremely homogenious material that Crucible uses?!?!

That is in use too but I'm not sure that's how it gets in the mix.

The result of the nitrogen content are Nitrides which are like carbides.

Laying all my cards on the table face up for this one question, the process by which it's done is at the very least proprietary if not "classified" a little higher.

They won't tell me how it's done.:mad:

Bill,

I think that they are hiding it right out in the open!!!

Nitriding is a "Case Hardening" process, ie Surface, and if these nitrides are throughout the material, it is getting there during the atomization of the molten material. When the resultant particles are placed into the container, sealed, and then hot isostatically pressed, the N2 that is present in the droplets has no place to go and remains as an integral part of the mix!!!:munchin

Later
Martin

Not sure that we really want to get into the details here, even if we knew.

Some jerk in China is probably already trying to figuire out how to knock off a copy of CPM S-30V and make it for half the price.

Just my observation.

TR

Mr. Harsey,

Fascinating thread! I don't know much about materials science, but there's enough chemistry here for the topic to feel just a little familiar, and I've enjoyed learning more.

Speaking just as a fool chemist, I wasn't surprised by nitrogen, because I'd read that metal nitrides can be extraordinarily hard. If I were more timely I'd have offered phosphorus. (Since it's considerably larger than nitrogen, if you could take a metal nitride structure and substitute P for N, you'd disrupt the crystal lattice quite a bit.) From a quick Google search, most hits had to do with removing phosphorus that was present as an impurity, to avoid excessive brittleness. Are there instances where you'd want to add it on purpose? Or is it an element that tends to be present anyway, and you have to go to some effort to remove it? Sorry if this naive or off-topic.

Alchemist, It's an honor to have you here, thank you for reading.
I have someone hanging out in the shadows that may be more able than I to answer your question but yes I do use steels that try to minimize the phosphorus.

You have some (deep) background in organometallic chemistry, that sounds close enough to knifemaking for me, Sir. :D

How Steel Get's Hard
 

Here's a red-neck engineering attempt at tying up some of the loose ends about how tool steels harden.

We've already used the term Austenite or Austenitizing here without much of an explanation. If we get some understanding of this word, it will help us know what happens when heat treating tool steels for use as edged tools.

Austenite is the word used to describe the solid solution of Iron and carbon, when steel is heated above it's critical temperature (something like 1450 Degrees F for simple water or oil hardening tool steels, much higher like 1950-2150 F for air hardening steels).

When the steel is cooled quick enough this turns the carbon and other alloys which can form carbides into hard Carbides and that's called "Martensitic Transformation". All during this the steel remains the exact same chemical composition but it's a different shaped atomic structure because of where the carbon and Iron atoms freeze into place depending upon rate of cooling. Cementite (Iron Carbide) is produced in here somewhere too.


If the steel is cooled slowly, this hard carbide formation doesn't happen.

We control the rate of cooling from the austenitizing temperature to get a particular range of physical characteristics, like hardness, toughness and edge holding in the tool steel being made into knives.

Usually this "rate of cooling" is exactly as fast as we can get away with while not cracking the work piece. The thicker the work or more complex the shape, the more careful we have to be about cooling too fast.

The alloys and percentages of these alloys will determine the physical characteristics of the steel and how it is heat treated, that is quenched in water, oil or air OR a combination of oil/air interrupted quench etc.

For The Reaper and other scientifically distinguished company around here like Mr. Dick Barber and Alchemist:
Yes I left out the other good stuff in steels like pearlite, bainite and other phase changes in the steel structure and time/heat graph because quite simply, I can't explain them.

There's a whole lot of rockin' and rollin' going on at the atomic level when we heat treat this stuff.