blade materials

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blademan312

Joined
Jun 16, 2003
Messages
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why does it matter what the blade is made of? i've been reading up on the subject, and it seems that the hardness of a blade determines everyhting. that is, if the blade is harder, then it wont be as tough and will be brittle. and, i think you can harden any metal to any hardness and decrease it to any, so why does it matter the actual metal unless you want stainless ? thanks
 
Blade steel matters a lot when it comes to knife performance. Actually, it is a very broad topic.

Originally posted by blademan312
and, i think you can harden any metal to any hardness and decrease it to any
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No.
You can harden low quality steels to relatively high degrees of hardness, but they will become brittle.


I'd recommend reading Joe Talmadge's steel FAQ (.pdf).
 
could someone define hardness, strength, and toughness. also, what is the downside to blades with very high carbon, because i read carbon increases hardness and strength. thanks
 
Hardness tests were developed to give an approximate measure of tensile strength, when they are used for other things they may do poorly. Higher hardness usually means more brittle. You have to pick the properties that are most important for the particular knife and it's intended use.
 
Hardness = resistance to indentation/ compression ( this is the most common definition as this is what the Rockwell testers measure, hardness can also be defined as resistance to wear or the amount of rebound after a collision).

Strength = ability to resist applied forces. There are many types of strength including: tensile, compressive, bending, shear, torsion, bending and impact.

Toughness = impact strength.

Downsides to increasing carbon content include decreased rust resistance and increased brittleness.




- Frank
 
i have been reading the FAQ, and still have some questions. i understand hardness is tensile strength, and correct me if im wrong, but is toughness resistance to bending, or is somthing that will bend beefore break considered tough? thanks
 
blademan312 :

i understand hardness is tensile strength
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They are not the same thing, but are very closely related.

toughness resistance to bending, or is somthing that will bend beefore break considered tough?
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Resistance to bending, or stiffness is a measure of strength. Toughness is how the material responds to *sudden* impacts, like a smack with a hammer.

Ductility is how far the material can continue to bend, once it has taken a set. ductility is related to toughness in that as you increase one you tend to increase the other.

Strength and toughness are usually at odds with each other, in that as you increase one, you will decrease the other.

There are exceptions of course to these general relations.

The reason that the material is important is that some steels may be inhernetly far tougher, more ductile, or more wear resistant than others even when hardened to similar levels.

-Cliff
 
While the answers here might truly be on the FAQ list, the general implication here touches an interesting point.

As knuts, most of us want the latest thing, and we assume that this 'new thing' is lots better than that 'old thing.' I remember when ATS-34 was in all of the knife and gun rags. One of my favorite authors, Ross Seigfreid (sp?) opined that it was the 'best' steel for hunting knives, and he owned a few Loveless models.

Then, about two years later, some custom makers were returning to good old 440C. It worked better in their applications.

My own favorite brand, Strider, switched some of their line from BG-42 to S30V, and like most people I figured this was an upgrade. I'd read all of the press about S30V being invented to be primarily cutlery steel.

But let's face it, 440V, BG-42 and VG-10 are GREAT steels and any collector should be thrilled to have these tremendous products at his disposal. I think we should chose products that are best for us; if that means a knife made from 1095, then so be it. 'Best' should mean what's best for the individual.
 
A higher carbon content does increase the maximum hardness, but this is achieved at about 0.8%, at which a steel can get 66 HRC. As you add other alloy elements which form carbides more carbon is needed to bond with them. Yes in general (and loosely), adding carbon to a steel is used to increase strength and wear resistance, but will decrease impact toughness and ductility. For a complete picture you also need to look at the other elements, which can also effect strength, toughness and wear resistance. Some of the interactions can be quite complicated and while some of the properties can be predicted by the elemental compostion, the true performance is revealed by the various materials tests, charpy impact toughness, tensile strength, ductility, salt spray, wear resistance and so on.

-Cliff
 
Originally posted by blademan312
does having more carbon increase hardness or the ability to become hard and be tough? thanks
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Increasing the carbon content of steel increases hardenability (not hardness directly, since this depends on the heat treatment).

You need about 0.3 % carbon for a steel to be usefully hardenable using conventional heat treatments. Adding carbon increases hardenability until you get to about 0.8% carbon, at which point adding more dose very little to increase the hardenability of the steel matrix. Additional carbon tends to get used up in forming carbides which increase wear resistance. Carbides are generally harder and more brittle than the surrounding steel matrix, so they tend to lower the toughness of the steel. For maximum toughness, it is best to keep the carbon content under about 0.6%.





- Frank
 
what are carbides, and i thought wear resistence is hardness? also, if a steel is strong, it will resist bending, but then break. but if its tough , its softer and wont break as easily, but will bend easier. is that correct? i knoiw i have alot of questions and i appreciate eeryones help.
 
Generally knife steels will reach a maximum toughness at a specific hardness. For instance according to Crucible’s data, D2 is toughest at about 60 HRC (500 deg. F temper), increasing OR decreasing the hardness will reduce the toughness. Maximum bending strength should be at approximately the same hardness. Increasing the Rockwell hardness (a measure of compressive strength) will always increase the tensile strength of steel. All else being the same, generally harder steels will break when bent, while softer steels will tend to bend (although if you bend them to far they will take a permanent set).

Carbides are a chemical compound of carbon and another element (such as iron, chromium, molybdenum, tungsten or vanadium). The microscopic carbides in steel are generally much harder than the surrounding iron matrix (up to 84 HRC for Vanadium carbides), and increase wear resistance sort of like gravel in concrete. Carbides are brittle and tend to crumble when subjected to impact stress; this is why increasing the amount of carbides decreases toughness.

Hardness is most often quantified with a hardness tester which measures the resistance to indentation (compression), such as the Rockwell and Brinell testers. Since compressive and tensile strengths are nearly directly proportional in steel, these tests can be used to get a good estimate of the tensile strength.

Sometimes (but less commonly with steel) hardness is defined as wear resistance. Abrasive wear resistance is largely independent of compressive strength, so you can have two steels with the same Rockwell hardness but with very different wear resistance. Steels with a lot of carbides will do better than similar steels with less carbides at the same Rockwell hardness in wear testing.

Here is a link to general information on steels on Crucible’s site -


http://www.crucibleservice.com/eselector/general/generalpart1.html



- Frank
 
I should point out that steel itself does not make good blade, but treatment! Simpliest treatment is hardening. It may be also partial hardening - hard for edge then for blade (Lauri PT, Sissipuukko M95). Then there are laminated blades - Helle, Fallkniven, Sekicut Hiro. Then dmascus - real damascus makes blade really good. Then wootz/bulat -with sophisticated micro structure, I read about hardness more then 70HRC (V.Basov http://www.rusglobus.net/zlatoust/lib/Bulat_Basov.htm)
There is some modern technologies - embeding Nitrogen into blade, somehow. So steel itsalf - just starting point.
Thanks, Vassili.
 
so you want good blade material thats hardened to it sperfect level, not to hard or too soft so it will be tough ? and is that because if its harder it will be brittle and if softer it will rip easier? also, when there is no other alloying element in the ssteel besides carbon, where does the extra carbon go to if it cant form a carbide with anything? thanks
 
Originally posted by blademan312
so you want good blade material thats hardened to it sperfect level, not to hard or too soft so it will be tough ? and is that because if its harder it will be brittle and if softer it will rip easier?
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That is right.



also, when there is no other alloying element in the ssteel besides carbon, where does the extra carbon go to if it cant form a carbide with anything?
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Carbon not used in the matrix tends to form iron carbides known as cementite (Fe3C).





- Frank
 
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