What
Is the Best Blade Steel?
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What
Is the Best Blade Steel?
FOREWORD
What is the best blade steel? I get this question a LOT, and I'm afraid it's one I can't answer... well, not with a simple, definitive winner anyways. There are a lot of great alloys out there, and none are "the best", no matter what the marketing wonks of some knife company say. Truth is, most knife companies don't care nearly as much about producing quality blades as they do about coming up with better marketing campaigns. They also like to make up fancy "tech" sounding names for common steel alloys that have been around for many, many years. They LOVE to make you think they've invented something new. V-this, CPM that, S-whatever. None of these steels started out with the name that the blade companies give them!
Where Do These Steel Designations Come From?
Here's a little factoid for you blade aficionados out there... and I'm going to get a lot of crap-filled emails protesting this point, but here goes... There's not a blade company in existence today that ever came up with a new type of steel.
I know that may be a bit surprising to many blade enthusiasts, but it's true. All of them buy their steel from commercial steel suppliers. They're not in the back room smelting iron ore, and adding bits of this and that like some witches brew. Most don't even have a metallurgist on their staff. They buy the steel from large steel companies like everyone else, and then their marketing geeks go to work on the gullible and unsuspecting blade market. *More on this point*
The Problem With Picking the "Perfect" Blade Steel
As for the various blade alloys, each has
it's benefits and each has it's drawbacks. Let's explore what properties of
steel are beneficial, and what properties constitute potential drawbacks. When a
metallurgist looks at the "strength" of a steel alloy, he is interested
primarily in two properties... "hardness" and "toughness". Hardness allows a
blade to hold it's edge. Toughness allows it to absorb impact and flex without
breaking.
One would love to have a blade that is both very hard AND very tough, but the
problem is that these two factors tend to fight each other. As one increases,
the other decreases. Some alloys can be
taken to incredible hardness levels, but can literally shatter if you drop them
on the floor. An extremely "tough" alloy may have all manner of resilience, but a
child can bend it in half. Might as well make a blade from coat hanger wire. As
such, most blade companies make a tradeoff. They pick a point that's somewhere
between tough and hard, and make the whole blade at that level. Either they hold an edge really well, but can snap if
abused, or they don't hold an edge very well, but can take some stress and abuse.
Most commercial blades just accept the tradeoff, choose a hardness, and end up
not very good in either hardness or toughness.
What Is Steel?
"Basic" carbon steels are simple alloys of iron and carbon. Most are a little
over 99% iron, and a little less than 1% carbon. Some steels have small
percentages of
other elements (vanadium, chromium, etc), but most of the great properties of
steel come from the two chief components, iron and carbon. Most stainless steels
(typically containing over 1% carbon and anywhere from about 10%-20% chromium) tend to be brittle. There
are softer grades, but these don't hold an edge worth a shit.
These are only used for blades because they are easy to work with, and they
don't readily oxidize. If you're looking for a pocket knife for casual duty
(cleaning under your nails and picking at zits), go for stainless. If you're looking for a hard duty
blade that won't fail you, there's no stainless that I can see adding up to a
good carbon steel blade. Simply put... stainless is great for soup spoons... bad
for blades. I will
discuss stainless no further in this article.
How Are Blades Processed?
Hardening (and thus embrittlement) of blade
steel is done by bringing the steel to it's Austenitic point (around 1100
degrees), and then quenching (usually in oil, brine or water). The heating process takes the carbon out of solution,
and lets it remix in different crystalline structures with the iron. At the
austenitic temperature, the structures formed are called "carbides". Carbides
are extremely hard, carbon-rich structures. If you slowly cool the steel, the
carbon will not stay in this structure... it will quickly migrate back to a nearly
homogenous state within the iron. The quenching process cools the steel very
quickly, and essentially locks the structures before they can change back. The
more carbides, the harder the steel, the less carbides, the softer (and tougher)
it becomes.
Whereas carbides and iron have different expansion/contraction rates, the act of
quenching can also create micro-fracturing within the structure (embrittling the
whole). After quenching, most blades are tempered. The tempering process
involves taking the blades up to 300-400 degrees F for a set amount of time.
This relaxes the structure enough for some of the carbides to shed a little bit
of carbon back into the surrounding steel. This tends to mend some of the micro-fractures, and adds a
little toughness, but overall hardness must also drop. All of this is an issue for mass produced blades... because
it's a pain in their ass to do in bulk. They want a manufacturing process that
allows them to heat a bunch of blades at once and either air, brine or oil
quench them all at once. They avoid tempering if they can. Most use "air-quench"
grades of steel that allow them to simply heat en masse, and then move the rack
to a room to cool.
This is the reason why large blade companies are always looking for new grades
of
steel. Many alloys are designed for ease of processing. This makes their life
easier by widening the
process windows for heating, quenching and tempering. As mentioned, some alloys allow them to skip one or more steps completely. NONE of this is done to
give you a better blade. It's done to make their production processes simpler
and much cheaper. Yes... money is the bottom line. Are you surprised? Me
neither.
So What's a Good Blade Steel?
Now that you have a basic idea of the properties of blade steel, you may wonder what constitutes a good blade. As we've discussed, we want a "magic" steel that is both hard and tough, but it doesn't exist... or does it? There's no magic alloy... BUT, there are careful and detailed processes that can give a single piece of steel both an incredibly hard edge and a really tough overall structure. Let's discuss a few strategies that can accomplish this duality of toughness and hardness.
Nobody ever said you need to quench a whole blade, or even heat the whole
blade to the austenitic point. The Japanese figured this out hundreds of years
ago, and would mask the spine of their blades with heat resistant clays to protect
it from heating and quenching extremes. This gave them a very hard edge and a
tough, flexible blade that wouldn't shatter in battle. Today, we call this
differential heat treating. It's usually very labor intensive to do (especially in
quantity), so good luck finding a commercial blade that's differentially treated!
Another strategy involves layering different steel alloys, some harder and some
softer (usually with different amounts of carbon). When quenched, the lower carbon steel
layers remain tough, but relatively soft. The higher carbon layers form carbides
and get very hard. This is what is commonly called "damascus" steel today, and
when it's done right, it can be both very beautiful and very functional. Some
damascus steels have many hundreds or even thousands of layers.
Contrary to conventional wisdom, more layers are
NOT necessarily better. Too many layers, and you simply trade carbon across the
layers when you reach austenitic. Blades with a thousand or more layers
typically trade enough carbon across layers to become almost a single alloy again.
If this occurs, you lose the benefits of dual
hardness. Again, layered steel is labor intensive and most knife companies avoid
it. The main drawback to damascus steel is that it can delaminate if highly
stressed in tasks like heavy chopping or prying. This becomes particularly
noticeable in poorly made damascus where inclusions like oxides and residual
flux prevent proper layer adhesion, or where there was insufficient flux, heat
or pressure to create a good layer weld.
Then there are laminated steels like those found on some Swedish and Japanese
blades (San Mai). It's a simple 3 layer damascus. It's a sandwich consisting of a
single hard steel layer between
two softer flexible layers. These have come a long way in recent years, and tend
to make some really nice blades. The processes by which this is made are
automated and tightly controlled. So far, I haven't heard of any delaminations,
but I'm keeping my ears open.
Finally, there are methods by which you can make a blade from a very tough steel
with a relatively low carbon content, and then infuse carbon into the edge regions
and surfaces. This is done through
repeated heat cycling in a carbon rich environment. It is labor and time intensive
(and expensive) to infuse an appreciable carbon content, so almost
nobody does it. If a method were developed to make this practical, I would think
it ideal for blades. The ability to have a hard exterior and edge area, while
keeping a durable and tough interior would make for a hell of a nice knife!
Differentially Treated Carbon Steels
I do like the idea of San Mai steel, but it worries me to have a brittle core
running the full length and width of my blade. I've found that a differentially
heat treated blade with a decent carbon content (0.75% to about 0.95%) can
exhibit incredible strength and edge retention when properly treated.
These basic carbon steels are known as the "10 series" steels. 1075, 1080, 1085,
1090 and 1095 are all steels that are suitable for larger blades when properly
treated with a differential process. Some of the alloyed carbon steels with vanadium
and other elements can also exhibit great overall toughness (5160 and 6150 are
some of my favorites).
Final Thoughts
To be considered a master bladesmith in the American Bladesmith Society, you
have to submit a blade as a "final exam" of sorts. This involves one making a
large bowie style blade for the test. Then, while being observed by other
members, you essentially beat the hell out of it with no failures. Among other
tests, you must chop through multiple two by fours, and then shave your arm with
it. The ultimate test that most makers fear is when their blade is clamped in a
vise, and a long pipe is slid over the handle as a lever. The blade is then bent
sideways to 90 degrees. The blade must not snap, AND it must return to it's original
shape. Many a potential master nominee has failed due to a blade snap or bend on
this test.
I bring this test up for the following reasons:
- As far as I know, no commercially produced blade has ever passed the guild's test.
- As far as I know, none of the commercial "magic" steel alloys have ever passed it.
- As far as I know, no stainless steel blade has ever passed.
All of the knife companies, with all their personnel, all their expensive
equipment and all their "magic" steel alloys... cannot compare with a
knowledgeable bladesmith. There's no magic or mystery to the subject...
mankind's been at the blade game for a couple thousand years and the properties
of steel are well understood. All it takes is someone willing to take an iron-carbon alloy, take
some significant
time, put a lot of sweat (and quite often blood) into it, and make a blade the
right way.
Rather than worrying about whether your knife is made of magical supersteel, worry about who made it and what their heating, quenching, and tempering processes consisted of.
NOTES: Steel Designations - As mentioned at the start of this page, both steel companies and blade companies LOVE to come up with new and interesting names for common steel grades. You may think your blade is made from some brand new superalloy, but it's more likely just a creative marketing gimmick! Here's a few examples of common blade steels and some of the many marketing names they go by in the steel industry:
O-1 steel is also known under the
following designations depending on what steel company it is purchased from:
Saratoga, Keewatin, BTR, Kiski, Exldie / EXL-Die, Ketos, ManSil, Invaro 1, Tru-Form,
Badger, Teenax, Colonial # 6, , Wando, No. 6 Non-Shrink, and Hargus
A-2 tool steel is also known under the following
designations depending on what steel company it is purchased from: Sagamore,
Cr-Mo-Loy, AH-5, Airque, 484 & 484 FM, EZ-Die, Airkool, ClairMo, Airvan,
Windsor, Select B FM, Airtrue, Air Hard, Sparta, and Dumore
D-2 tool steel is also known under the following
designations depending on what steel company it is purchased from: Ontario,
F.N.S., Lehigh-H, Superior # 3, 610 & 610 FM, Atmodie, Airdi 150, Croloy,
Cromovan, CNS-1, Olympic F. M., CCM, Ohio Die, , Ultradie 2 & 3, Ohio Die,
Darwin #1
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