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Old 05-05-2006, 16:36   #31
Bill Harsey
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Quote:
Originally Posted by Maytime
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.
Correctomundo Sir Maytime.


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Old 05-06-2006, 08:35   #32
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OK, back to work.
The significance of the hardness and toughness thing goes to not just what alloys are in a tool steel but how the steel is made because this is how carbide grain size is controlled. Carbide size has much to do with toughness, edgeholding and toughness. You will see this material again.

Here is something very important to know about knife steels. The hardness, usually stated in a Rockwell "C" Scale number, is not a direct indicator of blade quality or edge holding. In other words, the higher the indicated Rockwell hardness does NOT mean the knife holds a better edge
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Old 05-06-2006, 09:23   #33
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The first step would seem to be selecting an alloy that has the correct elements with the properties to produce the characteristics we are looking for. Beyond the iron and carbon that define steel, we could add varying quantities of chromium, nickel, cobalt, tungsten, vanadium, molybdenum, niobium, titanium, zirconium, manganese, silicon, or even copper. Each of these, in varying quantities, can give steel specific characteristics. The best known is the addition of chromium to make "stainless steel". Too much or too little, and you get something else.

Once we have the properties we are looking for in the chemical composition, the next step would be to properly harden it to develop the crystalline structure or grain that we are looking for in the various portions of the blade. Steel, even the same alloy, can be heated and cooled to produce everything from a useless paperweight to a superb cutting instrument.

I would think that the grain would be affected by the austenitizing or martensitizing. As noted, steel changes structure and therefore properties during heating and cooling. Some characteristics would be more desirable than others, but you might find both helpful in different areas of the knife. Look at a single-bit axe head with both a cutting edge and a hammering edge on opposite ends, each needs specific properties, yet both are part of the same piece of steel alloy. On a knife, you might want a tougher spine, and a harder edge.

Steel exists in a variety of crystallive forms, Austenite, Bainite, Martensite, Cementite, Ferrite, and Pearlite. Isn't the goal to try and produce more Bainite and Pearlite in the back of the blade and Martensite along the cutting edge? That would seem to be the solution to the toughness vs. hardness quandary. You could ruin a well-selected steel alloy for your knife by improperly heat treating it, or optimize a lesser steel for your purpose with a good heat treat.

Obviously, the knife cuts on its edge. You can use a knife for a pry bar, but it is not optimized for that. The edge of a well honed knife is not smooth, as most people think, but is very jagged. That is how it cuts. When the carbides and crystals at the edge are very hard, but the steel matrix is not, you get an optimized edge for cutting, yet is easily sharpened. The Crucible S30-V has the right carbides to work for this process. It is up to the knifemaker to expose them at the edge, and bring the hardness and toughness to the different parts of the blade, as required.

IIRC, the Japanese bladesmiths produced some very fine blades with little knowledge of metallurgy or chemistry by proper heat treating. They kept the spine softer and tougher, while creating the harder, better curtting Martensite along the edge by an advanced heat treat. As I understand it, the blades were generally straight prior to heat treating, and the curve of the Japanese sword occurred due to the properties and structure of the steel changing along the different parts of the blade durting their heat treat.

Just a few thoughts, probably in over my head, but I got that way by listening to smart people. Back to my cave.

TR
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Old 05-06-2006, 09:23   #34
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This question will likely show my ignorance but.....are there any blade makers doing the old Japanese techniques that we've heard about that give 'legendary' strength and edge to a blade...or is it all myth.

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Old 05-06-2006, 10:56   #35
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Reaper,
Highly simplified response to your comments and question.
Each type of tool steel has a range of hardnesses it can be hardened and tempered to and as you indicate with the example of the Axe, you can have two (or more) different hardnesses in the same finished tool.

Differential hardening is easier to do with water and oil quenching hardenable tool steels but does happen to some smaller degree with the air hardening tools steels which tend to be much more homogeneous in the heat treat because the quench time isn't quite so critical.

While on the topic of hardnesses, they are many wrong ways to get the "correct" Rockwell hardness scale reading that result in a steel not being as good as it could be. Rockwell hardness is a test to be used in the shop under controlled heat treat conditions in order to be understood and used well.

The Japanese sword smiths, who mastered the craft well over 700 years ago, may not have understood the science of what they did but they fully understood the process that produced the best results and did it very well.

Remember, this is when all steel was "hand made" with charcoal fired melts and forges way before big power sources and mills.

Swatsurgeon, Yes we have modern makers of traditional sword making techniques that are doing very good work.

Yoshindo Yoshihara (check this next link out!) http://www.legacyswords.com/Yoshiharanihonto.htm from Japan comes to mind. My friend Bob Lum (knifemaker) met with him last week in New York City at the big knife show there.
Note the well defined differential hardening in the images.
Note the price the set of swords sold for at the end.

Last edited by Bill Harsey; 05-06-2006 at 11:04.
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Old 05-06-2006, 11:01   #36
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Bill:

Can you comment on forged blades, versus stock removal, and the effect of the forging on the steel grain and crystalline structure?

TR
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Old 05-06-2006, 11:24   #37
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Quote:
Originally Posted by The Reaper
Bill:

Can you comment on forged blades, versus stock removal, and the effect of the forging on the steel grain and crystalline structure?

TR
Good question.
Historically the only way to refine a steel was by hand hammer forging (drawing out), re-stacking the steel and forge welding solid then forging it again, repeat until good results which if you made swords meant making swords that didn't break or bend easily.

This concept for steel refining was done on a much larger scale in the big steel mills into the early 1900's. English Shear Steel was a good example we know about in Oregon because this was how the plate for really big circular saw blades used in the sawmills was made.

Forging breaks up the large crystal/grain structures that resulted during the original melt of steel cooling into an ingot. Alloys tend to gather together during the initial cooling and form large crystals that would be too large and brittle to make into strong steel.

Now we are using steels that are highly refined during the steel making and forging (rolling into usable bar stock or sheet) processes. I seriously doubt any positive change in the steels grain structure can be accomplished by forging many modern tool steels.
Many of the top metallurgists in the country will back me up on this.

With some of the steels we use forging can easily cause more damage than good and the best the bladesmith can hope for is not ruin the steel when they forge the exotic (highly alloyed) steels. This is because the temperature range at which the steel can be forged is both high and narrow. Forging the steel outside these heat ranges can/will cause damage like the grain tearing apart resulting in cracks that will propagate during heat treat or use.

We are lucky to have many accomplished bladesmiths working in the world today and I don't want them hunting me down for any perceived slight to their craft. Keep working guys!
Industry will never duplicate the fine craft of forge welded patterns and making steel into blades like these guys do using the straight high carbon steels and I have the highest respect for the work being done.
This is what Yoshindo Yoshihara and his brother are doing, keeping a fine craft alive. They do amazing work at the forge.

Edited to continue:
Stock removal is the shop practice of knifemakers (myself included) of purchasing a particular type of steel, chosen for a range of best possible performance characteristics, which is roll forged into a specific shape and thickness of either bar or sheet.

Upon arrival in the knife shop the steel is then formed into a knife blade by cutting, abrasive grinding, machining, heat treating and finishing.

These steels have undergone considerable forging processes under tightly controlled temperature and atmosphere conditions in the mills before they arrive in the shop. Optimum heat treat and control of manufacturing process is the key to good results with these steels, not forging in the knife shop.

Last edited by Bill Harsey; 05-06-2006 at 12:27.
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Old 05-07-2006, 09:26   #38
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Before this rodeo gets out of control with too much detail and I lose all interested readers, I'll try to explain why we are going into this detail.

A knife cuts well because of how the cross section of the blade is shaped or what knifemakers call blade and edge geometry.

The thinner the blade and acutely sharper the angle of the edge, the better it will cut.

The limiting factor on blade geometry is the strength of the steel and even the size of the carbides.

When we have a given blade steel with optimum heat treat and we need it to stand up to increasingly tougher jobs, the only way to make it stand up to the demands is to increase the thickness of the blade and the edge. Think of how swords are different than paring knives.

About carbide size
I've worked with the tool steel called D-2 for many years. It's a common planer blade steel used in my regions sawmills. People keep bringing me handfuls of used planers blades made of this stuff. I keep thinking it might be useful for something someday. The pile keeps growing.

Much of the D-2 I've actually made into knives and master drill/machining patterns was purchased new. Here is the thing with D-2, it has the largest carbide size of any tool steel i know about. This is a problem because you CANNOT place an extremely fine or acute edge on a blade made from this without having carbide chip-out on that edge.
Edges on D-2 have to be less acute of an angle.
The macro grain on this steel can be seen thru the grinding and buffing stages of finishing the blade.

There can be very large and discernible differences in how tool steels perform when made into knives.

Edited to add: D-2 is a legitimate knife blade steel. Some good knifemakers use it very successfully.
Here is the difference, you cannot grind D-2 into a super thin edge (like .015 to .007 thousandths of an inch thick before first sharpening) and expect it to hold up. It has to be left a bit thicker and I'd be comfortable with an edge thickness more like .035 thousandths of an inch thick for a folding knife or fixed blade hunter.
D-2, because of it's big carbide/grain structure does not have the transverse bend fracture strength of other tool steels so the edge will not stand up as well to prying or side load.

Last edited by Bill Harsey; 05-07-2006 at 09:44.
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Old 05-07-2006, 18:58   #39
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Carbide grain size can be measured and documented with a scanning electron micrscope. I do not have one of these in my shop but the metallurgists whose phone no.s I keep handy do.

One of the finest grain tool steels available (not stainless) is called 52100 and is made by Timken-Latrobe here in the USA. This is a bearing and bearing race steel and be gotten very hard by heat treat. This steel has gained favor among many bladesmiths.

Anyone care to guess how a steel testing softer on the Rockwell hardness scale can out perform the 52100 in edge holding type cutting tests?
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Old 05-07-2006, 19:20   #40
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Quote:
Originally Posted by Bill Harsey
Edited to add: D-2 is a legitimate knife blade steel. Some good knifemakers use it very successfully.
Here is the difference, you cannot grind D-2 into a super thin edge (like .015 to .007 thousandths of an inch thick before first sharpening) and expect it to hold up. It has to be left a bit thicker and I'd be comfortable with an edge thickness more like .035 thousandths of an inch thick for a folding knife or fixed blade hunter.
D-2, because of it's big carbide/grain structure does not have the transverse bend fracture strength of other tool steels so the edge will not stand up as well to prying or side load.
Does this acount for the joke about D2 taking a crappy edge and holding it forever?

I have also heard it has a rep for not polishing well due to the orange peel surface.

The D2 I have carried is superb.

BTW, I had a scholarship from Latrobe Steel, they were good people.

Timken is famous for their fine bearings. I had no idea they had merged.

TR
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Old 05-07-2006, 22:14   #41
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Quote:
Originally Posted by The Reaper
Does this acount for the joke about D2 taking a crappy edge and holding it forever?

I have also heard it has a rep for not polishing well due to the orange peel surface.

The D2 I have carried is superb.

BTW, I had a scholarship from Latrobe Steel, they were good people.

Timken is famous for their fine bearings. I had no idea they had merged.

TR
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. ) 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.

Last edited by Bill Harsey; 05-14-2006 at 19:17.
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Old 05-08-2006, 08:53   #42
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Stainless

What makes a knife stainless?

Can a tool steel be stainless?
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Old 05-08-2006, 09:36   #43
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Quote:
Originally Posted by Bill Harsey
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
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Old 05-08-2006, 10:43   #44
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If this question has already been covered, please ignore.

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

Terry
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Old 05-08-2006, 12:16   #45
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Quote:
Originally Posted by CPTAUSRET
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.
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