what steels and why

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DevinT

DevinT

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I've had many members ask me about steels that are used in knives so I've decided to start a thread that will explain why we use what we do.

Wear resistance, toughness, sharpenability, edge stablity, stain resistance are some of the main subjects that we will cover.

We've made knives out of O-1, 1065, 1075, 1095, 1084, 1086v, 52100, 440-C, AEB-L, mystery carbon, super wear resistant, PM stainless,154cm, cpm 154, D-2, spray form D-2, ATS-34, S-30V, L-3, 3-V, cpm M-4, vanadus 4 extra, niolox/SB1, L-6, O-2, 15n20, A-2, 19c27, 12c27, 425, spicy white, 5160, 9260, and several types of recycled steels such as chain saw bars, lawn mower blades, circular saw blades, coil and leaf springs, planer blades, etc. all come to mind. I'm sure that I've forgotten some.

We plan on trying several other steels in the future, to see if there is any thing better than what we are using.

The steels that we have settled on so far are; AEB-L, PM stainless (to remain nameless), super wear resistant (to remain nameless), and mystery carbon (also to remain nameless).

Some of the steels that we have tried have been a big disapointment, and some have been a big suprise.

More to come.

Hoss
 
This is great. I can only imagine how much time you burn on phone calls, emails, etc. trying to educate the great unwashed masses :O

There are bits and pieces spread through a handful of threads in your vendor forum, but it will be great having all the info consolidated.
 
DevinT said:
The steels that we have settled on so far are; AEB-L, PM stainless (to remain nameless), super wear resistant (to remain nameless), and mystery carbon (also to remain nameless).
Click to expand...

52100? Or is the super wear resistant carbon and mystery carbon taking over for 52100 in your lineup?
 
I still like 52100, 19c27, spicy white, niolox and a few others, however, I don't want to offer too many steels and the ones chosen may have a slight advantage.

Hoss
 
Have you all worked with W-2, i didnt see it on the list?
 
May I ask how your "PM stainless" and "Super wear resistant" compare to R2 (which Tanaka and Mr. Itou are using)? I absolutely have nothing but good to say about it.
 
Luke_G said:
May I ask how your "PM stainless" and "Super wear resistant" compare to R2 (which Tanaka and Mr. Itou are using)? I absolutely have nothing but good to say about it.
Click to expand...
I have the pm stainless and I will say that I would be very impressed if the R2 in either can match it. It's significantly nicer than SG series, SRS-15, zdp-189, etc.). I'm testing the DT-super now. So far, I can say it is nice to sharpen (just two trials so far) but not quite as nice as other DT steels (takes a little more time) and it gets very sharp but the DT-pm is one of those steels that really "likes" to be sharp. It is probably my favorite steel so far and definitely my favorite stainless. I've tried out knives made from many steels but not R2. Sorry. After the DT-pm, I might choose Niolox or AEB-L.
 
It's difficult to compare to R2 because there's little information available on the steel.
 
Wear resistance.

Does it "hold an edge" is the question I get more than any other. In custom knives it has more interest than any other subject. I've heard lots of tall tales and exaggerations about this over the years.

Edge holding is the ability for a knife to keep cutting well in service. A properly sharpened knife will have a diameter of .4 micron at the edge. With use the diameter gets larger until it does not cut well, usually > 1 micron diameter at the edge. There is no reason to buy a custom knife unless it has excellent or superior edge holding.

Most steels come in the annealed condition and require hardening and tempering. Annealed steels have very low wear resistance which allows them to be worked easily. There are two things in properly heat treated steel that contribute to wear resistance. The first is the hardened matrix (martensite), and the second are the carbides. The amount of carbide volume, size, hardness, and distribution of the carbides all affect wear resistance and edge holding. Vanadium and tungsten carbides are harder than chrome and iron carbides. Steels with more carbides are more wear resistant than those with less. A certain amount of the carbide dissolves in hardening putting alloy and carbon in to the matrix making it hard and wear resistant.

Hardness affects edge holding. An increase of 2 points in Rockwell hardness will generally increase edge holding by about 20%. Improperly hardened and tempered blades having retained austenite (incomplete hardening) will be softer and not as wear resistant. Retained austenite also affects how much of a burr is formed and how easy it is to remove from a knife's edge while sharpening.

Lastly, the keener the edge the faster a knife will become dull. The coarser the stone used in sharpening, the longer it will hold that edge. I think that in general most knife nuts over sharpen.

To summarize, the proper selection of steels given the correct heat treatment along with correct sharpening will produce a knife with superior edge holding, give years of service, and will be a joy to use.

More to come.

Hoss
 
Wear resistance contributes primarily to edge holding for slicing. This is where coarse edges also lead to longer edge holding. Coarse edges + high wear resistance + slicing = long edge retention. For push cutting/chopping wear resistance and coarse edges are not very helpful.

Hard carbides like Vanadium carbides in steels like S30V and 10V contribute more to edge holding than simple iron carbides in carbon steels or chromium carbides in simple stainless steels. However, they make it more difficult to sharpen, especially when the abrasive in the stones are softer than the carbide. The following is a chart of carbide hardness from Crucible:

HARDENED STEEL • 60/65 HRC
• CHROMIUM CARBIDES • 66/68 HRC
• MOLYBDENUM CARBIDES • 72/77 HRC
• TUNGSTEN CARBIDES • 72/77 HRC
• VANADIUM CARBIDES • 82/84 HRC

More carbides does the same thing. More carbides means more wear resistance, but more difficulty in sharpening. And of course there is the balance of wear resistance with toughness and edge stability that will be covered later.
 
Is there any difference in performance if the chromium carbides precipitate out as platelets rather than spheres and is that something that can even be controlled with the tempering or is it basically luck of the draw?

-AJ
 
Carbide precipitation in tempering goes through a series of stages. In the early stages of tempering (low temp), fine rows of transition carbides are precipitated within the plates/laths of martensite. They look a little like plates. They are usually not what is described when talking about plate-like carbides. Transition carbides are unlikely to b chromium carbides because chromium is a mch larger atom than carbon and so requires more temperature to precipitate out as transition carbides. At higher temperatures the carbides are spherical. Plate-like carbides are not generally created though tempering. They're more generally associated with certain primary carbides (created during solidification not tempering or other processes of precipitation) or upper bainite.
 
Mr. Tanaka's with R2 PM steel is the best performer out of all my knives.

It gets sharper and stays sharper longer then every knife I own.

My kikuichi VG 10's

My Murray Carter White steel

My Itou R2's

My Massakage AS's

My DT AEB-L

My Moritaka blue #2

My Ino white #2

VG 10 Hattori forum I use to own

Takeda AS i use to own

I love my Tanaka!
 
I thought Cr7C3 carbides were spheroidal and Cr23C6 carbides were platelet and that the spheroidal ones came first but I didn't know if that was solid state or during tempering. I may be completely lost though. Thanks.

-AJ
 
ajhuff said:
I thought Cr7C3 carbides were spheroidal and Cr23C6 carbides were platelet and that the spheroidal ones came first but I didn't know if that was solid state or during tempering. I may be completely lost though. Thanks.

-AJ
Click to expand...
It's a difference between primary vs secondary carbides rather than really the type of carbide, though the one type of chromium carbide is more likely to be a primary carbide. There's conflicting literature on which chromium carbide that is.
 
This is a fantastic thread!! Thank you Devin for starting it, and thank you to everyone contributing. I loves educating myself on metallurgy.
 
Toughness is the ability to absorb energy without fracture. (I called Larrin and gave me this definition) In use knives that are too soft will roll at the edge rendering them useless, and knives that are too hard will chip out at the edge or worse break all together and become useless. Proper heat treating is the best way to ensure the best balance of hardness and toughness.

Good toughness in properly heat treated steels will affect other things like edge stability, edge holding, and the sharpenability of the knife. To increase both the toughness and hardness of the steel correct forging and heat treating cycles must be used.

The amount of carbide in the steel and the size of those carbides along with the over all hardness of the steel has the biggest effect on toughness. Some elements added to steels will increase toughness.

Grains in steel are like soap bubbles in a jar. Grains are different than carbides. The smaller the grain and the smaller the carbides in the steel the tougher the steel will be. Correct forging and heat treating of the steel allows proper grain refinement and to a lesser extent smaller carbide size.

Powder metalurgy steels were developed to be able to increase both wear resistance and toughness by reducing both the grain size and the carbide size and by more even distribution of the carbides in the steel.

More to come.

Hoss
 
BTW Devin, I forgot to ask what steel that twist bar is made of?
 
Edge stablity, this is the ability for a knife to hold a very fine edge. A fine edge is one that is sharpened to a small angle and to a high grit.

Just like toughness edge stablility is affected most by grain size and carbide size and distribution. Steels with larger carbides and greater volume of carbides are not as stable as ones with smaller and fewer carbides. The smaller the grain the better the edge stability. Pm steels were made to improve edge stability.

There are 2 types of cutting, namely push cutting and slice cutting. Push cutting benefits from finer edges more than slice cutting. Too fine an edge will not work well slice cutting fiberous materials.

The thing that happens to edges that are not stable is that the larger carbides pull out from the edge while in service leaving a flat spot or a hole. This is called carbide pull out.

Kitchen knives, razors, scalpels, axes etc. benefit from greater edge stability.

Proper hardness and the elimination of retained austenite is also beneficial to edge stability.

More to come.

Hoss
 
I've read in several places this idea of "large" carbides falling out. It seems dubious to my mind. Is there anything out there to support this idea, particularly a photomicrograph?

Thanks,

-AJ
 
Larrin said:
This article on grinding and polishing of tool steels by Buehler mentions carbide pullout: http://www.azom.com/article.aspx?ArticleID=5289
Click to expand...

Hmmm.... kind of casually mentions it in passing. In the context of polishing a flat surface, not really the same as a knife edge.

Also, the context I have always read is the "large" carbides pulling out of the knife edge is the pull out is noticeable. How big is a "large" carbide? I still have my doubts.

What I'd like to see is some photomicrographs of a knife edge showing the missing carbides. Actually, I would love to see ANY photomicrographs of some knife edges, especially a transverse view. Are you aware of any Larrin?

Thanks,

-AJ
 
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