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- Apr 7, 2006
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When I first got into knives about 8 years ago I was also starting my career at a small machine design and building company. As one of the designers, I participate in a lot of metal selection and have always noticed how we never used any really amazing steels, even when we make blades and other hardened tooling. We tend to stick to 4140, 5160, 1085/1095, and sometimes O1 for our heat treated, high wear parts. If we need stainless blades that will cut all day, it's either 416 or 440C if we are feeling very ambitious. I always wondered why the fancier steels never applied to our applications (sometimes we make very small parts and material cost is not a factor).
I am currently toward the end of my engineering degree an have had a few metallurgy classes so already. I am half way through a fairly advanced Metals Selection course and a lot of what we deal with is the molecular makeup of steels. I am finding out that a lot of what knife/steel companies tell us is total bullcrap. As far as most of the industry is concerned, 99% of alloys are added to steel for two things: corrosion resistance or depth of hardness. You see, pure carbon steel (anything that starts with a 10XX such as 1095) has to be brought past its eutectoid temperature (around 1600 F) and quenched within 6 seconds after removal from the heat source otherwise it will not harden all the way. Most alloys are added to basic steel to give you more time to quench (A-2 which is an air hardening tool can wait so long that it can simply be cooled with air). The benefit is you get a better heat treat and you crack less steel because you are cooling slower. A lot of the strength in hardened steel comes from simply tempering the steel which removes some of the carbon form the hard BCC structures which relieves stress in the structure and slightly softens the steel. Steels with lower carbon content (420, 440A/B, 1045, etc.) don't have enough carbon to bond with all the iron atoms and therefore are automatically "tempered" of sorts and can only achieve 50-55 Rc even with perfect heat treat.
Therefore, with properly heat treated and tempered plain old 1095 steel you have a strong hard edge. Sure, some alloys do add additional stress to the lattice structure which can slightly increase strength on a molecular level (edge retention against cardboard), but these also increase brittleness on a large scale (edge chipping when a staple is hit). Heck, stainless steel has a reputation for brittleness because of their high alloy content. For the most part, it's good old carbon and heat treat that does almost EVERYTHING for the edge, good or bad.
Steel companies put out a lot of literature that makes it seem like the newest steels are vastly better, but for the most part I think it's in our heads. Think about it: 1095 is usually heat treated and tempered back to around 58-60 Rc. 1095 can be heat treated to 66 Rc and have awesome edge holding with the cost of increased brittleness. Now ZDP-189 is hardened to 65-66 Rc. It holds a great edge, but what do you know: IT'S BRITTLE! It took me a lot of science to realize that steels aren't really getting much better, the heat treat and metallurgy are simply getting more precise and allowing us to achieve higher hardness.
Let's take a walk down history lane:
5000BC-3000BC: Flint tools are very hard, but very brittle. Does not apply to this rant.
1700-1980's: Old knives and Chinese knives tend to be heat treated to around 50-55 Rc (420, 440A, etc.) and they could bend all day long and be hammered back to straight.
1980's-1990's: The last few decades saw a big jump up to the 58-60 Rc level (154CM, S30V, VG-10, etc.) but we started to see edge chipping and broken blades. This may be a result of increased brittleness or maybe just ninjanitis.
2000-present: Now we are seeing super steals up to 66 Rc (ZDP-189, M2, etc.) but these knives are usually quite brittle and suffer from edge chipping whenever they encounter resistance.
Future: Light Saber technology is finally refined enough to make pocket sized light daggers viable. Law's immediately ban concealed light sabers.
That's odd: Hardness = edge retention (who wudda thunk it)
The last myth: powdered metals. Crucible Metals wants us to believe their cutting edge metal mixing technology is the Mutt's Nuts because alloys and carbon are perfectly distributed in a steel AFTER heat treat. I hate to tell you this, but when you heat ANY steel up to its Austenitic temperature, the alloys and carbon move around to fill all the open spaces in the steel crystalline structure, and by move, I mean measurable distances. All that powered metals do is decrease the amount of time you must leave a steel in the furnace at it's Austenitic state. If a heat treat engineer knows what he's doing, the steel will be allowed to soak for the proper amount of time, coming out of heat treat the exact same as if it was a powdered metal in the first place.
Wow, long post. The moral of my story is: If you buy a knife from a reputable company and the steel is in the hardness range you desire: don't fret over what percentage of what alloy is in your steel. Some alloys do funky stuff to steel, and a couple of steels are starting to stand out as being able to be very hard and not quite so brittle, but their reputation has a lot to do with proper heat treat on every sample (you don't see a lot of BudK knives in M4 do you). The classic steels have been around for a while and have had lots of chances to be screwed up in the oven, resulting in scores of negative reviews of perfectly good steels. Don't expect a 55 Rc 420 blade to hold the edge of a 66 Rc ZDP-189 blade, but also don't expect to be able to bend the ZDP-189 blade and not end up with two knives.
I am currently toward the end of my engineering degree an have had a few metallurgy classes so already. I am half way through a fairly advanced Metals Selection course and a lot of what we deal with is the molecular makeup of steels. I am finding out that a lot of what knife/steel companies tell us is total bullcrap. As far as most of the industry is concerned, 99% of alloys are added to steel for two things: corrosion resistance or depth of hardness. You see, pure carbon steel (anything that starts with a 10XX such as 1095) has to be brought past its eutectoid temperature (around 1600 F) and quenched within 6 seconds after removal from the heat source otherwise it will not harden all the way. Most alloys are added to basic steel to give you more time to quench (A-2 which is an air hardening tool can wait so long that it can simply be cooled with air). The benefit is you get a better heat treat and you crack less steel because you are cooling slower. A lot of the strength in hardened steel comes from simply tempering the steel which removes some of the carbon form the hard BCC structures which relieves stress in the structure and slightly softens the steel. Steels with lower carbon content (420, 440A/B, 1045, etc.) don't have enough carbon to bond with all the iron atoms and therefore are automatically "tempered" of sorts and can only achieve 50-55 Rc even with perfect heat treat.
Therefore, with properly heat treated and tempered plain old 1095 steel you have a strong hard edge. Sure, some alloys do add additional stress to the lattice structure which can slightly increase strength on a molecular level (edge retention against cardboard), but these also increase brittleness on a large scale (edge chipping when a staple is hit). Heck, stainless steel has a reputation for brittleness because of their high alloy content. For the most part, it's good old carbon and heat treat that does almost EVERYTHING for the edge, good or bad.
Steel companies put out a lot of literature that makes it seem like the newest steels are vastly better, but for the most part I think it's in our heads. Think about it: 1095 is usually heat treated and tempered back to around 58-60 Rc. 1095 can be heat treated to 66 Rc and have awesome edge holding with the cost of increased brittleness. Now ZDP-189 is hardened to 65-66 Rc. It holds a great edge, but what do you know: IT'S BRITTLE! It took me a lot of science to realize that steels aren't really getting much better, the heat treat and metallurgy are simply getting more precise and allowing us to achieve higher hardness.
Let's take a walk down history lane:
5000BC-3000BC: Flint tools are very hard, but very brittle. Does not apply to this rant.
1700-1980's: Old knives and Chinese knives tend to be heat treated to around 50-55 Rc (420, 440A, etc.) and they could bend all day long and be hammered back to straight.
1980's-1990's: The last few decades saw a big jump up to the 58-60 Rc level (154CM, S30V, VG-10, etc.) but we started to see edge chipping and broken blades. This may be a result of increased brittleness or maybe just ninjanitis.
2000-present: Now we are seeing super steals up to 66 Rc (ZDP-189, M2, etc.) but these knives are usually quite brittle and suffer from edge chipping whenever they encounter resistance.
Future: Light Saber technology is finally refined enough to make pocket sized light daggers viable. Law's immediately ban concealed light sabers.
That's odd: Hardness = edge retention (who wudda thunk it)
The last myth: powdered metals. Crucible Metals wants us to believe their cutting edge metal mixing technology is the Mutt's Nuts because alloys and carbon are perfectly distributed in a steel AFTER heat treat. I hate to tell you this, but when you heat ANY steel up to its Austenitic temperature, the alloys and carbon move around to fill all the open spaces in the steel crystalline structure, and by move, I mean measurable distances. All that powered metals do is decrease the amount of time you must leave a steel in the furnace at it's Austenitic state. If a heat treat engineer knows what he's doing, the steel will be allowed to soak for the proper amount of time, coming out of heat treat the exact same as if it was a powdered metal in the first place.
Wow, long post. The moral of my story is: If you buy a knife from a reputable company and the steel is in the hardness range you desire: don't fret over what percentage of what alloy is in your steel. Some alloys do funky stuff to steel, and a couple of steels are starting to stand out as being able to be very hard and not quite so brittle, but their reputation has a lot to do with proper heat treat on every sample (you don't see a lot of BudK knives in M4 do you). The classic steels have been around for a while and have had lots of chances to be screwed up in the oven, resulting in scores of negative reviews of perfectly good steels. Don't expect a 55 Rc 420 blade to hold the edge of a 66 Rc ZDP-189 blade, but also don't expect to be able to bend the ZDP-189 blade and not end up with two knives.
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