cpm440v is rockwell 56
- Thread starter memnoch
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Obviously, hardness isn't the last word in edge-holding, especially when you're comparing vastly different steels.
In CPM-440V, the incredible edge-holding is due to the presence of well-distributed vanadium carbides. Those carbides are much harder than Rc 56, and their presence doesn't seem to be reflected in the standard hardness tests.
Joe
jat@cup.hp.com
In CPM-440V, the incredible edge-holding is due to the presence of well-distributed vanadium carbides. Those carbides are much harder than Rc 56, and their presence doesn't seem to be reflected in the standard hardness tests.
Joe
jat@cup.hp.com
Kodiak PA
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Good question-great answer....no wonder I love this place!
Joe, I was reading in Knives '99 that Bill Moran doesn't like to use stainless since he feels the additon of vanadium and/or moly makes it less malleable and less tough....my question is:
Steels like CPM440V and BG-42 seem to do an outstanding job in almost all daily knife applications. Do Bill's concerns about stainless really matter as much nowadays with such good stainless steel available or are there still jobs for knives that you would prefer to use carbon & alloy steels (non-stainless). Obviously I have a lot of respect for Mr. Moran but I was wondering what the practical application thoughts were.
Thanks
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~Greg~
Kodiak Alaska
KnifeKnutt@aol.com
Joe, I was reading in Knives '99 that Bill Moran doesn't like to use stainless since he feels the additon of vanadium and/or moly makes it less malleable and less tough....my question is:
Steels like CPM440V and BG-42 seem to do an outstanding job in almost all daily knife applications. Do Bill's concerns about stainless really matter as much nowadays with such good stainless steel available or are there still jobs for knives that you would prefer to use carbon & alloy steels (non-stainless). Obviously I have a lot of respect for Mr. Moran but I was wondering what the practical application thoughts were.
Thanks
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~Greg~
Kodiak Alaska
KnifeKnutt@aol.com
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It seems to be generally true that as you load a steel up with alloying elements, you often lose toughness. That doesn't mean that tomorrow someone won't create a supertough steel loaded with alloying elements, but for now I do think you often lose toughness.
BG-42 and 440V are nowhere near as tough as, say, 5160 at the same hardness. Some non-stainless steels can be differentially tempered, which can be another advantage. Overall, I'd say there are definitely times when I'd rather use a carbon or non-stainless alloy steel over stainless.
Joe
jat@cup.hp.com
BG-42 and 440V are nowhere near as tough as, say, 5160 at the same hardness. Some non-stainless steels can be differentially tempered, which can be another advantage. Overall, I'd say there are definitely times when I'd rather use a carbon or non-stainless alloy steel over stainless.
Joe
jat@cup.hp.com
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To add to what Joe said..
I have spoken to Phil Wilson, who is one of the knifemakers most familiar with the CPM Steels, and he said that in order to keep the toughness, it has to be the lower Rockwell.
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Marion David Poff fka Eye, one can msg me at mdpoff@hotmail.com
Patiently waiting for the Spyderco SpydeRench, Lum Chinese Chopper Folder, Rolling Lock, Benchmade M2 Axis, M2 Axis AFCK, M2 Pinnacle and the REKAT Escalator and Pat Crawford Design.
"The victorious Warrior wins first and then goes to war, while the defeated Warrior goes to war and then seeks to win" Sun-Tzu
I have spoken to Phil Wilson, who is one of the knifemakers most familiar with the CPM Steels, and he said that in order to keep the toughness, it has to be the lower Rockwell.
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Marion David Poff fka Eye, one can msg me at mdpoff@hotmail.com
Patiently waiting for the Spyderco SpydeRench, Lum Chinese Chopper Folder, Rolling Lock, Benchmade M2 Axis, M2 Axis AFCK, M2 Pinnacle and the REKAT Escalator and Pat Crawford Design.
"The victorious Warrior wins first and then goes to war, while the defeated Warrior goes to war and then seeks to win" Sun-Tzu
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Memnoch; if you were to post your questions somewhat more lucidly, it would make (at least my) answering them easier.
As I understand it, you are comparing CPM440V in a Spyderco Military to a Cold Steel Voyager in AUS8-A, and your question is why does the CPM440V hold an edge better, despite a Rc of 56, compared with the Rc of 57 found in the CSV.
AUS8-A is an ingot steel (i.e. not CPM), and is a low alloy stainless: C 0.85-1.0, Mn 1.0, Cr 14, Ni 0.5, V 0.1-0.2, Mo 0.1-0.3, and W 0.4.
There are two things which are problematic with AUS8-A; one is the tendency of the carbides to separate out when the ingot cools, and the other is the type of carbides present. Cr carbide is only Rc 65-70, and since Cr is the primary alloy material in this steel, most carbides are Cr carbides, with a small amount of Mo carbide (Rc 75) and W carbide (Rc 75), if present (AUS8-A is supposed to have a small amount of W, but Spyderco's steel chart doesn't show any being present).
Basically, in AUS8-A, there are poorly dispersed, fairly soft carbides; since most of the carbides are on the surface, a somewhat misleading Rc is obtained. Remember Rc measures only the surface of the substance being tested.
With CPM440V, however, with the following composition, C 2.15, Mn 0.4, Cr 17, V 5.5, Mo 0.4, you have over twice the carbon to form carbides, and a better alloy component, vanadium, with which to form harder carbides. Vanadium carbides run 80-85 on the Rockwell C scale. In addition, the CPM process ensures uniformity throughout the alloy.
This means that the Rc is misleading, albeit in a different manner than AUS8-A. There are a lot of carbides in CPM440V, and hard ones at that, but since they are evenly dispersed, there are relatively fewer on the surface than with an ingot steel. Therefore, the Rc is not as high as it would otherwise be.
When you wear off the edge of CPM440V however, you reveal an area of blade which is every bit as hard as the edge was. THIS is what makes CPM440V a better edge holder than AUS8-A. It is a hard facing alloy, much like Stellite (r) and Talonite (r), which are cobalt alloys. Remember, 'tungsten carbide' is actually tungsten carbide suspended in a Co matrix (both alloys mentioned immediately above are Co alloys).
You may wish to peruse the Crucible Service website:http://www.crucibleservice.com/crumain2.htm be sure and read 'Heat Treatment and Fabrication of Tool Steels,'
Also read Selecting High Performance Tool Steels at this part of the website:
http://www.crucibleservice.com/crutool.htm
Hope this helps, Walt Welch
As I understand it, you are comparing CPM440V in a Spyderco Military to a Cold Steel Voyager in AUS8-A, and your question is why does the CPM440V hold an edge better, despite a Rc of 56, compared with the Rc of 57 found in the CSV.
AUS8-A is an ingot steel (i.e. not CPM), and is a low alloy stainless: C 0.85-1.0, Mn 1.0, Cr 14, Ni 0.5, V 0.1-0.2, Mo 0.1-0.3, and W 0.4.
There are two things which are problematic with AUS8-A; one is the tendency of the carbides to separate out when the ingot cools, and the other is the type of carbides present. Cr carbide is only Rc 65-70, and since Cr is the primary alloy material in this steel, most carbides are Cr carbides, with a small amount of Mo carbide (Rc 75) and W carbide (Rc 75), if present (AUS8-A is supposed to have a small amount of W, but Spyderco's steel chart doesn't show any being present).
Basically, in AUS8-A, there are poorly dispersed, fairly soft carbides; since most of the carbides are on the surface, a somewhat misleading Rc is obtained. Remember Rc measures only the surface of the substance being tested.
With CPM440V, however, with the following composition, C 2.15, Mn 0.4, Cr 17, V 5.5, Mo 0.4, you have over twice the carbon to form carbides, and a better alloy component, vanadium, with which to form harder carbides. Vanadium carbides run 80-85 on the Rockwell C scale. In addition, the CPM process ensures uniformity throughout the alloy.
This means that the Rc is misleading, albeit in a different manner than AUS8-A. There are a lot of carbides in CPM440V, and hard ones at that, but since they are evenly dispersed, there are relatively fewer on the surface than with an ingot steel. Therefore, the Rc is not as high as it would otherwise be.
When you wear off the edge of CPM440V however, you reveal an area of blade which is every bit as hard as the edge was. THIS is what makes CPM440V a better edge holder than AUS8-A. It is a hard facing alloy, much like Stellite (r) and Talonite (r), which are cobalt alloys. Remember, 'tungsten carbide' is actually tungsten carbide suspended in a Co matrix (both alloys mentioned immediately above are Co alloys).
You may wish to peruse the Crucible Service website:http://www.crucibleservice.com/crumain2.htm be sure and read 'Heat Treatment and Fabrication of Tool Steels,'
Also read Selecting High Performance Tool Steels at this part of the website:
http://www.crucibleservice.com/crutool.htm
Hope this helps, Walt Welch
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Vanadium carbides are in the low 80's on the RC scale.
Check out CPM 3V at 58RC it has a charpy test level of 85 foot pounds.
To compare A2 at 60RC is 40 foot pounds.
At 58RC 3V has 300% more wear resistance than A2 at 60RC.
ED
Check out CPM 3V at 58RC it has a charpy test level of 85 foot pounds.
To compare A2 at 60RC is 40 foot pounds.
At 58RC 3V has 300% more wear resistance than A2 at 60RC.
ED
Greg,
The gang here has done their usual outstanding job in addressing the metallurigal aspects of selected stainless steels and carbon steel. Joe commented that there are applications where he'd much rather have a non-stainless blade than stainless, but didn't elaborate.
If I want a prybar or the sharpest edge I go with carbon steels. If I want a non maintenance intensive blade I go to stainless. Generally speaking, carbon steel blades, properly treated can be made to take a heck of a beating including bending at extreme angles before breaking. Stainless stuff will snap much quicker given the same abuse. My comment about the sharpest edges obtainable is one that has narrowed in recent years such that my view is probably nothing more than an old bias now.
Bill Moran is unquestionably an outstanding knifemaker who is a giant in the industry having been the groundbreaker in many areas. But he specializes in the heat and beat technique and tests his blades for flexibility bending some over 80 degrees and returning them to true. For these purposes, stainless simply won't do.
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-=[Bob]=-
Bald is beautiful! Rub a dome for luck today!
The gang here has done their usual outstanding job in addressing the metallurigal aspects of selected stainless steels and carbon steel. Joe commented that there are applications where he'd much rather have a non-stainless blade than stainless, but didn't elaborate.
If I want a prybar or the sharpest edge I go with carbon steels. If I want a non maintenance intensive blade I go to stainless. Generally speaking, carbon steel blades, properly treated can be made to take a heck of a beating including bending at extreme angles before breaking. Stainless stuff will snap much quicker given the same abuse. My comment about the sharpest edges obtainable is one that has narrowed in recent years such that my view is probably nothing more than an old bias now.
Bill Moran is unquestionably an outstanding knifemaker who is a giant in the industry having been the groundbreaker in many areas. But he specializes in the heat and beat technique and tests his blades for flexibility bending some over 80 degrees and returning them to true. For these purposes, stainless simply won't do.
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-=[Bob]=-
Bald is beautiful! Rub a dome for luck today!
Concerning ATS-34 as compared to the other steels mentioned above:
Besides weak lateral strength, a tendency to rust, and only fair edge holding, let's not forget my arch nemesis which is more fully applicable to daily use: Edge Chipping (to include Tip Breakage)!
Everyone say it with me now: "We don't want any more crappy ATS-34 blades when there are far better steels and methods now available!"
BG-42
CPM440/420V
Tool Steel with a coating
Etc.
adamantly,
thaddeus
Besides weak lateral strength, a tendency to rust, and only fair edge holding, let's not forget my arch nemesis which is more fully applicable to daily use: Edge Chipping (to include Tip Breakage)!
Everyone say it with me now: "We don't want any more crappy ATS-34 blades when there are far better steels and methods now available!"
BG-42
CPM440/420V
Tool Steel with a coating
Etc.
adamantly,
thaddeus
- Joined
- Oct 3, 1998
- Messages
- 94
Thad my friend,you are preaching to the choir as far as I am concerned.After spending
considerable time with 2nd gen. Military with
440v,ats 34 just won't cut it.I can't get
excited about any whiz-bang new fangled
locking mechanisms as long ats 34 is part of
the deal.
considerable time with 2nd gen. Military with
440v,ats 34 just won't cut it.I can't get
excited about any whiz-bang new fangled
locking mechanisms as long ats 34 is part of
the deal.
- Joined
- Oct 3, 1998
- Messages
- 4,842
Continuing with what Bob started, why else might I choose stainless or not?
Obviously, the obvious reason for stainless is that it is, well, stainless. Or at least rust resistant, to put it more accurately. There's some subtleties in this. There have been reports of tests where a crappy stainless holds an edge longer than a high-performing carbon steel. These tests are often in meat or an acidic food, where the carbon steel's edge micro-rusts away quickly but the stainless doesn't have this problem. *POLISHING* the edge doesn't give the rust as much surface area to work with, and mitigates this factor somewhat. If you're doing more utility work and less food prep, this factor isn't seen, and you'll often get your non-stainless steel to take a sharper edge (and possibly keep it longer), besides the toughness benefits.
Another reason to think about stainless is that some of the new ones, like 420V, seem to have edge-holding that is unparalleled, even by the likes of 52100 and other great nonstainless edge-holding steels.
Joe
jat@cup.hp.com
Obviously, the obvious reason for stainless is that it is, well, stainless. Or at least rust resistant, to put it more accurately. There's some subtleties in this. There have been reports of tests where a crappy stainless holds an edge longer than a high-performing carbon steel. These tests are often in meat or an acidic food, where the carbon steel's edge micro-rusts away quickly but the stainless doesn't have this problem. *POLISHING* the edge doesn't give the rust as much surface area to work with, and mitigates this factor somewhat. If you're doing more utility work and less food prep, this factor isn't seen, and you'll often get your non-stainless steel to take a sharper edge (and possibly keep it longer), besides the toughness benefits.
Another reason to think about stainless is that some of the new ones, like 420V, seem to have edge-holding that is unparalleled, even by the likes of 52100 and other great nonstainless edge-holding steels.
Joe
jat@cup.hp.com
Sal Glesser
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Great stuff! Some good resource out there. I believe 440V to be superior in many ways but 440V has an optimum grain structure because of the method of manufacture. Comparing 440V with a non-particle steel may not be an "apples to apples" comparison? Much in the same way Mazda's Rotary is not measured or classified in the same manner as a piston engine. Just a thought to share.
In defense of AUS-8 (Austenitic steel with about .8% carbon. 8A is short for AUS-8. AUS-8A is redundant. AUS-6 (6A) = same but with about .6% carbon, etc.) Electron microscope photos of AUS-8 show a very even finely dispersed grain structure. Kind of like the right amount of stuff mixed with the right amount of stuff. a fine grain structure permits a steel to accept a very sharp edge (no really large secondary carbides breaking out at the edge). Also edge testing and Q fog corrosion testing indicate that AUS-8 is an excellent compromise in edge holding and corrosion resistance. There are some exceptions, but generaly speaking, the more carbon, the better edge holding and less resistance to corrosion. Chrome helps, but it is not foolproof. Cold Steel's Carbon 5 has a very fine grain structure but Carbon 5's structure is the result of controlling the processing at the steel mfg level, rather than the mix.
just mo input.
sal
In defense of AUS-8 (Austenitic steel with about .8% carbon. 8A is short for AUS-8. AUS-8A is redundant. AUS-6 (6A) = same but with about .6% carbon, etc.) Electron microscope photos of AUS-8 show a very even finely dispersed grain structure. Kind of like the right amount of stuff mixed with the right amount of stuff. a fine grain structure permits a steel to accept a very sharp edge (no really large secondary carbides breaking out at the edge). Also edge testing and Q fog corrosion testing indicate that AUS-8 is an excellent compromise in edge holding and corrosion resistance. There are some exceptions, but generaly speaking, the more carbon, the better edge holding and less resistance to corrosion. Chrome helps, but it is not foolproof. Cold Steel's Carbon 5 has a very fine grain structure but Carbon 5's structure is the result of controlling the processing at the steel mfg level, rather than the mix.
just mo input.
sal