What exactly is it in a blade that corresponds to how hard the blade is? Is it the carbon content? I'm assuming so, since Aus 6 is real easy to sharpen and it has a low carbon content, and something like vg10 is real hard to sharpen and it has a high content. But, the higher the carbon content, the higher the likelyhood that the blade will rust, right? What are some other key elements in steel that plays a critical role in it's performance?
just wondering,
thanks
randy
if anyone knows of some internet sites or anything that corresponds to this subject, id be happy to read it.
Bit of a steel question
-
Joe Talmadge
- Member
- Posts: 1077
- Joined: Fri Sep 24, 2004 10:33 am
Carbon is the primary, but not the sole, alloy that contributes to hardenability. But just because a steel has high carbon (and therefore good hardenability) doesn't mean it's going to be hard. By varying the heat treat, the maker can decide how hard to leave the steel. For example, Spyderco leaves their 440V at around 55 Rc, but 440V is quite capable of going to 58-60 Rc. The maker bases the final hardness on the tradeoffs he wants to make on strength, wear resistance, and toughness.
Also, how difficult a knife is to sharpen isn't strictly determined by how hard the blade is. Two other extremely important factors are: 1. the edge geometry, and 2. the type and distribution of carbides in the steel. As an example, Spyderco's 440V is around the same hardness as many AUS-6 knives. But even though they're at the same hardness, the presence of abundant vanadium carbides will make 440V more difficult to sharpen than blades made from other steels that are just as hard or even harder.
In addition, the amount of carbon doesn't strictly determine how quickly a steel will rust. It is an important factor, but there are more important factors as well. In stainless steels, it is the presence of free chromium (which forms an oxide on the blade surface) which fights rust. But, the more carbon that's added to the blade, the more chromium gets tied into carbides ... and the more chromium in carbides, the less free chromium available to fight rust. So, keeping everything else equal, what can happen as you add carbon is: you get more hardenability, and you get better wear resistance because of the presence of more chromium carbides, but less rust resistance because you have less free chromium.
An interesting case is CPM 420V. It has reasonable rust resistance, even though it's got incredibly high carbon (2.35%) and low-chromium for a stainless steel (14%). That's because of the presence of vanadium -- it's the vanadium that gets tied up in the carbides, so lots more chromium remains free than you would expect, and thus the steel is still nicely rust-resistant.
Joe
Edited by - Joe Talmadge on 4/30/2002 10:05:59 PM
Also, how difficult a knife is to sharpen isn't strictly determined by how hard the blade is. Two other extremely important factors are: 1. the edge geometry, and 2. the type and distribution of carbides in the steel. As an example, Spyderco's 440V is around the same hardness as many AUS-6 knives. But even though they're at the same hardness, the presence of abundant vanadium carbides will make 440V more difficult to sharpen than blades made from other steels that are just as hard or even harder.
In addition, the amount of carbon doesn't strictly determine how quickly a steel will rust. It is an important factor, but there are more important factors as well. In stainless steels, it is the presence of free chromium (which forms an oxide on the blade surface) which fights rust. But, the more carbon that's added to the blade, the more chromium gets tied into carbides ... and the more chromium in carbides, the less free chromium available to fight rust. So, keeping everything else equal, what can happen as you add carbon is: you get more hardenability, and you get better wear resistance because of the presence of more chromium carbides, but less rust resistance because you have less free chromium.
An interesting case is CPM 420V. It has reasonable rust resistance, even though it's got incredibly high carbon (2.35%) and low-chromium for a stainless steel (14%). That's because of the presence of vanadium -- it's the vanadium that gets tied up in the carbides, so lots more chromium remains free than you would expect, and thus the steel is still nicely rust-resistant.
Joe
Edited by - Joe Talmadge on 4/30/2002 10:05:59 PM