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Old 04-28-2013, 06:22 AM   #1
I am Carbon
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Default knife steel

Part 1
Articles in knife magazines and discussions on the Internet concerning knife blade steels are getting
pretty technical these days. The problem is that many terms are used with the assumption the reader
is familiar with them. This article will address the mechanical properties of blade steels in general.
Starting with that background we can apply the definitions outlined herein to illustrate how certain
properties pertain to the selection of blade materials for 3 different knife types. The following 6
properties are important for knife blade steel:
STRESS AND STRAIN, TOUGHNESS/DUCTILITY, STRENGTH, HARDNESS, RESISTANCE
TO WEAR, CORROSION RESISTANCE
STRESS AND STRAIN
All materials have a stress and strain relationship. Stress is the force applied to a member and
strain is the distance that the member moves (deformation) under the applied force. Imagine a
rubber band stretched between your two hands. The force applied to move your hands apart shows
up as a resistance force (stress) in the rubber band. The distance the band moves under the force is
the strain. If the stress and strain for the band are plotted on a graph a line is drawn representing
the behavior of the band from the initial load to the time it finally breaks. This is called a
stress/strain curve. This curve is unique for all materials and gives a vast amount of information
on how the material acts under applied force. Steel acts like a rubber band up to a certain point.
That is, it has an elastic range. An automobile spring, a folder spring, a skyscraper swaying in the
wind and a very flexible fillet knife all are working in the elastic range. If force is applied beyond
the elastic range then it enters the plastic range. In this area the material acts more like a soft
plastic, hence the name. The material will yield under the force applied but when the force is
removed it won't spring back completely. It has yielded or in the case of a knife blade, "bent".
Most knife blades are made from a grade of steel called cold work tool steel. This is the same
material used for dies, bearings, and some types of machining cutters. We all know from
experience that tool steels in general have a limited elastic range, and a narrow plastic range. They
will "flex", take a small permanent bend and then fracture suddenly. This property is called
bending fracture strength. We see an example of this every day in the knife shop working with
drill bits, taps and milling cutters.
TOUGHNESS/ DUCTILITY
When a material can absorb forces from many different load types with out breaking then it is very
tough or ductile. Tool steels tend to exhibit the opposite characteristics. That is they are elastic up
to a point but have a relatively narrow ductility range. The high alloy types, especially those with
carbon over about 1.0% and chrome above 5.0% at high hardness (over HRC 57) are moving out of
the ductile range and are approaching brittle behavior. This is most apparent under dynamic or
impact load conditions. Impact loads magnify the force that the steel feels and can cause large
failures very quickly. These steels are also notch sensitive. They will fracture at a much lower
load if an imperfection is present. This can be in the form of a deep scratch, corrosion spot, small
crack, or sudden change in cross section. Steel company data sheets refer to toughness in terms of
"Charpy C Notch" values. This is a measure of the ability of a notched test piece to resist
breaking under an impact load. An example of an impact load is a lawnmower blade spinning at
high RPM and hitting a rock, or worse yet, an ATS-34 blade (HRC 60) used to try to chop through
a bone. The lawn mower blade (low alloy and soft) is going to get a pretty good dent but the knife
blade is probably going to suffer a local break or "chip" out of the thin edge.
2
STRENGTH
From the above discussion you might say the knife blade was not very strong because it ended up
with damage. However the opposite is true. Tool steel heat-treated to the high hardness necessary
for a knife blade is very strong. It can be about 10 times stronger than mild steel. The ability of a
steel part to withstand force trying to pull it apart is called tensile strength. The ability of the part
to withstand force trying to push it together or compress it is called compressive strength. ASTM
A-36, structural steel, or mild steel used for general construction has a tensile strength of 36,000
pounds per square inch. Tool steel at HRC 60 has a tensile strength of about 350,000 pounds per
square inch. Note that the ability to take load is related to the cross section area of the piece. The
more material the greater the load capacity. For example a two square inch (1 inch x 2 inch) bar of
mild steel will withstand 72,000 pounds in tension and a similar size piece of tool steel can
withstand about 700,000 pounds in tension. The two steels have a very different stress strain curve
(figure 1). Mild steel is very forgiving. It will plastically yield a large amount before breaking
therefore avoiding a catastrophic structural failure. Tool steel has to be very stiff and strong
because it must endure very high loads at the cutting interface between a tool and the part
machined. When it breaks the fracture is usually very sudden. To put it another way mild steel
would make a poor drill bit and tool steel would be a poor material to use for a highway bridge.
Strength is a very important consideration for a knife blade because we like to make the cutting
edge as thin as possible for cutting efficiency. A very high strength material like tool steel is
necessary to prevent the very thin edge from yielding under load. Good toughness is necessary to
prevent the thin edge from breaking off under bending or impact loads.
HARDNESS
The ability to work in the soft or annealed form and then to be hardened is one of the most
important properties of tool steels. Steels are delivered from the mill in the annealed form. This
allows the knife maker to cut, drill, file, bend and grind the steel. . In the annealed form it acts
somewhat like the mild steel described above. To exhibit the positive properties of tool steel it
must be heat treated so that the final crystal structure of the steel is changed. The tensile strength
of steel is proportional to its hardness. The harder it is the more is resists deformation forces. In
other words the edge will resist bending or breaking while cutting some very hard materials.
Hardness is the most critical property for a knife blade because it is an indication all the other
properties. It is the most convenient property to measure. A hardness tester forces a cone shaped
diamond penetrator into the sample. The depth of penetration is measured very precisely and is
read on a calibrated scale. Hardness for tool steels is usually given in reference to the Rockwell C
Scale, abbreviated as HRC. The normal range for knife blades is HRC 50-63. Knife making steels
have a "sweet spot" hardness range in which they will perform best. At this hardness all the
properties are balanced to provide the best overall performance. Very good steel that is heattreated
out side this range will not perform up to expectations.
WEAR RESISTANCE
Abrasive wear resistance (most important type for a knife blade) is a measure of the tool to resist
being worn away by contact with other materials. Wear resistance correlates with hardness of the
material in general. Even mild steel in contact with an abrasive surface will wear much longer than
brass for example. In that case mild steel will make a better knife blade than brass. It gets more
complicated with high alloy tool steels because of the carbides present in the material. Steels like
O-1, A-2, 52100 will all have about the same wear resistance at equal hardness. The addition of
chrome in steels like 440C, 154CM, ATS-34 and D-2 adds another dimension. During the initial
melt the chrome combines with carbon to form chrome carbides. These carbides are harder than
the iron carbides present in the lower alloy grades and will therefore add some abrasive wear
resistance to the cutting edge (see figure 3). Imagine the carbides as the aggregate (rocks) and the
3
surrounding steel matrix as the cement in a concrete road surface. The cement wears away over
time leaving the hard aggregate as the road wear surface. The harder the rocks the better the surface
will resist wear over time. The same thing is true for a knife edge. The harder the carbides and the
more densely they are packed the better the edge will resist wear. This is carried a step further with
the high vanadium, high carbon CPM (Crucible Particle Metallurgy) steels and to an extreme with
high-speed tool steels. High-speed tool steels like M2, M4, M42, and T15 will resist wear even
when subjected to the red-hot temperatures at the cutting edge of a metal cutting tool.


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Old 04-28-2013, 06:23 AM   #2
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Default Re: knife steel

Part 2
CORROSION
Plain carbon steel has very little corrosion resistance. We all know that a bar of steel out side in
the weather will soon form a coating of rust. To prevent this surface must be separated from the
elements with a barrier of some type (paint, plating act). Low alloy tool steels act pretty much act
the same way. A very fine “non-stain resistant” edge can get dull just due to atmospheric effects
over time if it is not protected. A tool steel rifle that has been blued (chemical oxide coating) and
oiled will withstand the weather very nicely. The addition of about 12% chromium to steel will
improve the corrosion resistance to a point that it can be called stainless. Other elements like
molybdenum also contribute to limit surface pitting. 154Cm for example has 14% chrome and 4%
molybdenum. Chromium can be too much of a good thing because amounts higher than about
14% in 1.0 % carbon steel tend to increase the brittle behavior at higher hardness.
IT ALL COMES TOGETHER AT THE CUTTING EDGE
Given the back ground in the preceding discussion we now should have enough information to
specify a range of steels for a knife blade. To illustrate all this lets pick a material for a Chef's knife,
a fillet knife and a utility hunter. The first step is to establish the criteria for the knife. It is going
to be somewhat different for all three. My criteria may be entirely different from yours but it's a
place to start
CHEF'S KNIFE CRITERIA
Excellent corrosion resistance for sanitary reasons as well as appearance- At least 14% chrome
content for stain resistance. Very good ductility -Because it will most likely see some chopping
action in the kitchen. The hardness should be in the 53 to 58 HRC range. Higher hardness could
lead to edge chipping and poor traction on sharpening steel. Good edge holding-Should have some
chrome carbides for wear resistance. Good edge strength to prevent edge from rolling over or
rippling under normal use against a cutting board-Hardness in the 53 to 55 range should provide
high enough tensile and compressive strength to accomplish this. Easy to grind and polish to keep
cost reasonable.
Steels like AISI420 modified (0.5% C), AEBL and 440A will make an excellent Chef's knife. They
have the right amount of chrome for stain resistance and chrome carbides for wear resistance.
These steels hardened to HRC 55 (310,000 psi) have outstanding toughness and are relatively easy
to grind and polish. If stain resistance is not a concern then A-2, O1, and 52100 (all with carbon at
1.0%) can be used at HRC 58. This will make for a blade with good toughness and a little better
edge holding. Edge strength will also be improved (325,000 psi) which will allow for a little
thinner grind and easy cutting ability. 154CM/ATS34 at HRC 58/59 (340,000 psi) will make for a
stain resistant blade that has improved edge holding, but will have less ductility because of the
added alloy. A little more edge thickness and caution during use will offset both of these factors.
These steels are more difficult to grind and finish so the final knife will be more costly. In addition
they will require abrasive stone sharpening since the additional hardness will preclude effective use
on a sharpening steel.
4
FILLET KNIFE CRITERIA
Excellent corrosion resistance since the knife will be subjected to salt water environments- At least
14% chrome and some molybdenum to prevent pitting. Reasonable ductility- Knife will not be
subjected to chopping so hardness could be as high as HRC 61 depending on the steel. Flexibility
will be fine at HRC 61 if heat-treating is correct. Very good edge holding- knife will be used
where sharpening is not convenient so should have high wear resistance provided by chrome
carbides. Hardness should be HRC 60/61 for edge holding. High edge strength is necessary to
prevent roll over. Ease of polishing and grinding will be compromised in favor of high strength,
edge holding and corrosion resistance.
These blades will be used in a much more severe environment than the Chef's knife above. 440C
and154CM/ATS34/BG42 are probably the best overall choices for a fillet blade. The 440C blade
would have to be a little softer (HRC 56/57) to offset the brittle effect of the high chrome at high
hardness. 154CM/ATS34 (HRC 60) have good ductility as long as the heat-treating is correct. The
edge strength will be very high for slicing through fish bones (350,000 psi). The hardness and
presence of chrome carbides will provide very good edge holding. The addition of molybdenum
will off set pitting corrosion in salt-water use. CPM440V/420V at HRC 60 will provide additional
wear resistance at the edge with excellent corrosion resistance. The higher initial cost and
difficulty in grinding and finishing the CPM steels make for a much more expensive knife but may
be worth it for some applications.
CRITERIA FOR UTILITY HUNTER
Edge holding is the overriding criteria for this knife. No one wants to have to sharpen a blade in
the middle of field dressing an elk at night in a snowstorm. A hardness range of HRC 59-61 and
high carbide content is required. This will also provide very high edge strength (350,000 to
360,000 psi). Good corrosion resistance is desirable since the knife will be used in extreme
environments like Alaska and some times around saltwater- 14% chromium and some molybdenum
are desirable. Ductility should be adequate but can be compromised in the interest of edge holding
since an ax or saw will be used in lieu of chopping or prying with this knife. The primary use will
be field dressing, skinning, and boning and camp cooking. If very hard use is anticipated then the
edge can be left thicker at the expense of ease of cutting and slicing.
Ease of grinding and polishing is compromised in favor of high strength, high hardness, wear
resistance, and corrosion resistance. Cost of the blade steel is secondary to performance.
Edge holding is the most important factor in a hunting knife. 154CM/ATS34/BG42 and D-2 (all at
HRC 60 or higher) have the properties to accomplish very good edge holding while providing
adequate toughness and very good edge strength. The high edge strength allows the blade to be
ground relatively thin for ease of cutting. If corrosion resistance is not an overriding consideration
then 01, A2, 52100, 1095 and similar high carbon low alloy steels will do the job and provide
somewhat better toughness as a bonus. CPM420V (S90V) 440V (S60V) (HRC 60) will provide
increased edge holding with very good corrosion resistance and adequate toughness. CPM 10V
(HRC 62/63) offers, extremely high edge strength (375,000 psi). The combination of high hardness
and very high Vanadium Carbide content make for outstanding edge holding, but with minimum
corrosion resistance (5% chrome). If toughness is the overriding criteria then CPM 3V is a very
good choice. It offers twice the impact resistance of all the above grades plus good edge holding
and some stain resistance (7.0% chrome). The increased performance of the CPM steels is offset
by a higher knife cost due to the price of the material and difficulty in grinding and finishing. This
increased cost can usually be rationalized when considering the purchase of a custom knife.
Note:
5
The 5
The above article was written before the introduction of CPM S30V. 30V is a great addition to the
Crucible list of knife blade materials. At this point it is a favorite of mine for fillet knives and
hunters. Toughness is very good and edge holding is only topped by 90V and 10V. It is a little
easier to finish than 90V and 10V so fits in a category between 154CM and the alloys which have a
higher percentage of carbides.
The above criteria and steel selections are an examples of the many trade offs necessary to match
the right steel to a particular knife design and use. These examples also illustrate why some of the
more popular steels work so well. Forged and pattern welded blades add another dimension to all
of the above because certain of the properties can be modified for improved performance and
esthetics
A general knowledge of steel properties is an asset when specifying a particular blade. This can be
from the standpoint of a knife maker who is striving to match steel to his customer’s application or
from the point of view of a user who wants to get the most out of his knife and under stand the
limitations of its use.
The following are my current choices for knife blade materials. The steels are listed in order of
preference for each knife type. The preference is based on the best value for the user considering
utility and cost trade offs. These preferences are of course mine and can change based on
discussion with the user and his/her preferences.

Fillet Knife 154CM, CPM S30V
Hunter/Utility CPM S30V, CPM S90V, CPM 10V
Chef’s Knife AISI 420HC, 154CM
Paring Knife CPMS30V, 154CM


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Old 04-28-2013, 01:13 PM   #3
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Default Re: knife steel

You're way over my head. I'm still using old files and car leaf springs for my knife building.
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Old 04-28-2013, 02:22 PM   #4
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Default Re: knife steel

Right On!
springs have made great knives for ever


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Old 04-28-2013, 03:03 PM   #5
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Default Re: knife steel

Hey carbon, thanx for the knife/tool steel alloy update.
What are your recommended grinding angles for these alloys, and any water-displacing oil suggestions?


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Old 04-28-2013, 03:48 PM   #6
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Choosing and angle to sharpen your knife is essentially a compromise between the sharpness and the durability of an edge. The most important factor when determining the angle comes down to how you will be using your knife. Will you be shaving your face, filleting a fish, cutting vegetables, carving or chopping wood? From these examples, it is easy to see how each case requires a different edge.
Under 10 Degree Angles
The lowest angles are reserved for edges that are typically cutting softer materials. In this case, the edges are not subject to abuse so the lower angle can be maintained without damage or edge failure. The lowest angles that we typically see are on straight edge razors. These are sharpened to an angle which is roughly 7 to 8 degrees (although the back of the blade is used as a guide so knowing the angle isnít important and nor is it adjustable). A straight razor has a very delicate edge that is very easy to damage. In proper usage, a straight razor would never see the type of use that would damage the edge.
10 to 17 Degrees Angles
A sharpening angle of 10 to 17 degrees is still quite low for most knives. With a total angle of 20 to 34 degrees, this is still a very fine edge. This edge is typically too weak for any knife that might be used in any type of chopping motion. Also consider that harder steels are also more susceptible to impact damage because they are more brittle. If your knife is used for cutting soft items or slicing meats, this lower angle can hold up and provide a very smooth cutting action.
17 to 22 Degree Angles
A 17 to 22 degree angle covers most kitchen knives. Some knives (typically Japanese manufacturers) will sharpen their knives to roughly 17 degrees. Most western knives are roughly 20 degrees. It is our experience that kitchen knives sharpened to 15 to 20 degrees cut very well and are still durable. These angles are still not highly durable as a total angle under 40 degrees will not respond well to rougher treatment in harder materials.
22 to 30 Degree Angles
In this range, the knife edges are considerably more durable. A pocket knife or a hunting knife will inevitably see abuse not seen by knives meant primarily for slicing or chopping softer materials. While the edge may not ultimately be cut as well (but you may not notice a difference) it will be considerably more durable.
Over 30 Degrees Angles
Any edged tool or knife that is sharpened past 30 degrees will be very durable. Its cutting ability will be noticeably reduced. This durability has an advantage because more force can be used to make the cut. While the majority of knives wonít benefit from this sharpening angle, an edged tool like a machete, cleaver or axe must be durable as the typical cutting action of these tools would damage other edges.

As far as oil goes i use air tool oil.

for sharping knives this is what I recommend
Your friends will think that you are a pro.
For the everyday guy this is a must tool.
I think they are around $70 on ebay

http://www.youtube.com/watch?v=F3MlkabgqYM


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Old 04-28-2013, 05:16 PM   #7
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Default Re: knife steel

Wow! Nice read... ive looked into making blades for a number of years... but the old pros seem to want to keep you out rather than share knowledge, and tend to make it sound so difficult that you just wont try.

Thanks Carbon, i'll have to give a go sometime real soon.

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Old 04-28-2013, 06:42 PM   #8
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Default Re: knife steel

You should give it a try



http://www.youtube.com/watch?v=IsNIhKRDg0E


http://www.youtube.com/watch?v=1C0spGxmggE


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Old 04-28-2013, 07:22 PM   #9
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Default Re: knife steel

Ever worked with bronze? Or is that something that requires forging? Ive been wanting to build a small forge for some time too... easy yes, but can never find the time.
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Old 04-28-2013, 07:37 PM   #10
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Default Re: knife steel

Thank you VERY much carbon. 'Work Sharp' on order...


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Old 04-28-2013, 08:16 PM   #11
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Your Welcome. TwoManyXS1Bs
shotgunjoe,No bronze the only forge work I've done is steel.
I get to use a forge at the metal shop I fill in when they need extra help. All though
I don't get any work any more after I trained the owners best friend to do what I was doing for them. go figure.


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Old 04-29-2013, 06:22 PM   #12
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hi guys ,,, years ago i did my time at vickers ruwolt in melbourne,,,, it was great ,,, in my spare time,,, i ,d find some old roller bearing and remove the outer shell ,,,take it to the blacksmith at the back of the foundrey,,, and throw the shells in the fire split them and then flatten them out they worked really well, it could be worth trying regards oldbiker
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Old 04-29-2013, 07:27 PM   #13
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Post some pics of you work carbon.
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Old 04-30-2013, 06:52 AM   #14
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Default Re: knife steel

It has been years sense I was making knives.
I am getting into it again.
Thats why I have been boning up on the subject.
I have no pix or knives at this time.
7 years ago dec 18 my home burned to the ground.
I lost everything but my 2 dogs and my wallet n keys.
But I will make one and shoot a video.
I make them completely by hand no power tools


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Old 04-30-2013, 01:05 PM   #15
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Quote:
Originally Posted by I am Carbon View Post
7 years ago dec 18 my home burned to the ground.
I lost everything but my 2 dogs and my wallet n keys.
damn... sorry for your loss man, one of my nightmares. At least you have your life, stuff can be replaced.

I'll be waiting patiently for the results...
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Old 04-30-2013, 01:23 PM   #16
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Default Re: knife steel

been doing alot of studies on metallurgy lately (went back to school to get my engineering degree), and howw you work and form the metals can be just as important as the choice of alloy. very interestig subject. the non-ferrous alloys get quite interesting too.
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Old 04-30-2013, 02:40 PM   #17
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Thanks shotgunjoe.
It was quite freaky.
those wood framed stilt houses go up quickly.
i found that I have some wonderful friends.
And you are right things can be replaced.
I now have fire safes and a safe deposit box


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Old 05-01-2013, 08:05 PM   #18
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Default Re: knife steel

Carbon, Since you are working things by hand, do you have any good advise on materials to quench with? Bloodmeal? Rendered goat fat? Blue clay from the north side of the riverbank on a cool spring night? I just love some of the old ideas of proper steel working. Lots more interesting than all the air/ oil hardening steels we can buy now. Some of that old knowledge is remarkably good. At my first real job back in the 60's, I watch as an old duffer made a center punch out of an old rat-tail file. Anealed it, heated and quenched it and handed it to me as a gift. I have used it for all these years and have never needed to sharpen it. I wish I had asked him a lot more questions before he died.
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Old 05-01-2013, 09:45 PM   #19
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Default Re: knife steel

Iowa Mark, yew fergot 'stump water', 'charred bone', and (*gasp*) japanese peons.
My dad did the same thing, tried to show me metalurgy stuff when I was 10, but dammit, he's gone now, and I sit here trying to remember what he said...


I think, therefore, I'm confused.

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Old 05-02-2013, 11:36 AM   #20
I am Carbon
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Default Re: knife steel

Iowa Mark. This a very complicated subject. I will just touch on it.
as far as I'm concerned Used motor oil is great to quench with. The dirtier the oil, the better as this is a rich source of carbon. I heat the steel to a cherry red and quench it in the carbon rich oil, maybe repeating the process several times until I have a good blackening much like the carbonizing on camshafts and other parts of an engine. This surface is reasonably hard, but more importantly, holds up under the 96 percent average humidity found in the Southwest Gulf Coast of Florida. It simply won’t rust.
Steel is hardened by heating the metal to a cherry red and quenching it by quickly dipping the redhot piece in either water brine or oil. The particular quenching liquid necessary depends on the type of steel.
When I don’t know the type of steel I am dealing with, I always try hardening the piece in an oil-quench bath first. If this doesn’t harden the metal sufficiently, I use water. A water quench is much more aggressive, than an oil quench and can make steels which should be quenched in oil very brittle and glass-like. It is often necessary to identify the approximate type of steel before deciding whether if would be best to harden the surface or harden it throughout.
Case hardening was often used in the past when the selection of steels was considerably more limited. In times past, it was more economical to harden only the surface of a relatively soft steel than to pay for a much more costly steel which could be hardened throughout. This fairly easy process was done in early times with fire and various powders—mainly bone. The bone supplied carbon and calcium which both hardened and colored the surface.
While case hardening is no longer used as much for economy, it makes sense in terms of obtaining a hard surface with a tough inner-structure. Conventional through-hardened steels must be used for parts which must undergo hammering or repeated impacts.
I found a some interesting videos on colonial Gunsmith that touch on this subject.
http://www.youtube.com/playlist?list...EJxHdphK3lqrxc


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