Stainless Steels vs. Carbon Steels

storyville · May 16, 2000

Some folks seem to be missing Tom "gimme extra" Mayo's point -- namely, that "high carbon" is simply a descriptive term about carbon content.

The distinction between "stainless steel" vs "carbon steel" is more for marketing hype than an indicator of performance quality. As Mayo Tom points out, modern steels are alot more complicated than that (thankfully!).

How many folks would really take well-treated 1095 over well-treated 420V, 440V, BG42, or even ATS-34? In all circumstances? Most?

1084 over "borderline stainless" D2?

1095 has nearly twice as much carbon as INFI, which has a "mere" .5% carbon content. In Cliff Stamp's test, INFI has also interesting proven to be highly corrosion resistant. Does INFI therefore suck?

Those who believe that "carbon steels" (all, most, some?) outperform "stainless steels" (all, most, some?) might want to check out developments in steels over the past, say, 30 years ...

Glen

dogboye · May 15, 2000

Originally posted by storyville:
How many folks would really take well-treated 1095 over well-treated...

.....420V? Dunno, no experience

.....440V? Tried it. 1095, no question

.....BG42? Dunno, jury's still out on that one, not enough experience with it

.....or even ATS-34? 1095, certainly.

.....In all circumstances? In all the applications that I have used a knife for.

But that's just me, and I'm ornery and like non-stainless steels better, in general. So far.....

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iktomi

tom mayo · May 15, 2000

I applaud Mr Storyville for actually reading my posts....but not for his racial slurs

...the bottom line is that there is NO such thing as stainless steel...not that is any good for a knife steel....and I will remind you again that we are in the 21st century...things have changed considerably in the last 15 years.....and yes....most tools are made out of the cheapest and most readily available resources....for profit. i will add something that i have said many a time...in front of you is a balance scale, whenever you put something on one side the other side goes up....we can try and balance out the various positive results of many different elements in many different steels, but it will always be left lopsided somehow.

[This message has been edited by tom mayo (edited 05-15-2000).]

tallwingedgoat · May 15, 2000

Cobalt,

I don't want this to become anything more heated than a friendly academic debate. So here's my arguement.

Charpy values are useful to a certain extent. But they refer to steel in bars and rods, or whatever shape useful in an industrial application, not a thin slice of blade steel.

You can differentially temper a piece of 5160 so that it can flex over 180 degrees without cracking. And yet as soon as a tool steel gets flexed to 45 degrees everyone declars it's the toughest steel ever.

Again, I have no problem with stainless steel for certain applications. But industrial product charts will only tell you one part of the story.

[This message has been edited by tallwingedgoat (edited 05-15-2000).]

Cobalt · May 15, 2000

Goat, I agree that this shouldn't become a heated discussion. After all, we're only talking personal preference here. I like 5160 and think it's one heck of a steel. But I would be surprised if you could get a 1/4 inch 5160 blade that can hold any kind of a reasonable edge to bend 180 degrees.

I disagree on charpy value being only good for certain shapes. It is a measure of the impact toughness of the steel, regardless of it's shape. All test samples are shaped the same and notched the same, and impact point and load is the same for all samples. The only difference is the material, so it is relevant to this discussion.

You also have to take into consideration bend strengths. What good is a steel that can flex 180 degrees when it's bend stregth is 4 times lower than a steel that only flexes 45 degrees. The point is that even though you can bend the softer steel further, you may not have enough strength to ever get the stronger steel to bend to the 45 degrees.

I doubt that you could flat grind 5160 in 1/4 inch stock and get the same performance as INFI or 3V. It would be interesting to test this though.

Roger Blake · May 15, 2000

Originally posted by Cobalt:
You also have to take into consideration bend strengths. What good is a steel that can flex 180 degrees when it's bend stregth is 4 times lower than a steel that only flexes 45 degrees. The point is that even though you can bend the softer steel further, you may not have enough strength to ever get the stronger steel to bend to the 45 degrees.
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I think this is wrong. All steel bends the same amount if it has same dimension and same force applied. In technical terms all steel has the same modulus of elasticity. Mild steel will go out of the elastic zone at lower stresses. They will deform sooner but not break at least at first. Harder steels will bend further and go to higher stresses but tend to break with less deformation, hence they are less tough. Still they make better knives. If I am wrong on this, educate me.

My experience as a woodworker and tool scrounger for 30 years is that manufactures are putting more chromium in chisels and plain blades mainly cause they look better on the shelf and resist rusting. They are also inferior to their older counter parts. Old chisels, especially forged ones seem much better.

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Roger Blake

Cobalt · May 15, 2000

Roger, you're wrong, all steels with the same dimensions, do not bend the same amount. Take 3 blades made from completely different steels and do you really think that they will all bend the same amount. Not! Take INFI, Carbon V and 1095. Do you think three exact knives made from these three steels will bend the same amount. Gee, Jerry Busse has been working hard on his steel for absolutely no reason. Crucible might as well close up shop since their 3V is no different than O-1.

johno · May 16, 2000

I think that Roger has it right. A hardened tool steel compared to a low carbon steel will have a similar modulus of elasticity, it will deflect a similar amount under a similar load given a similar configuration, but it will much higher resistance to deformation and will have a much higher yield strength, so that it can deflect more without displaying plastic deformation. Alhtough there are many tool steels there are a few types, such as hot work, cold work, high speed, high impact/spring, and such, in addition to plain and low alloy high carbon steel. With tools like drill bits, taps, saws, chisels, etc., people usually expect performance instead of shiny cosmetics, and although many different steels are used few are stainless.

tom mayo · May 16, 2000

in keeping with the friendly tones here...I SERIOUSLY DOUBT that anyone on this forum could bend ANY knife made out of .250" stock that isnt differentially heat treated (read soft all the way to the edge) without the aid of some serious levers. with that in mind....you would be a smoking pile of charred flesh before your knife was bent .125" in real life.....

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http://www.mayoknives.com

Cliff Stamp · May 16, 2000

Tom :

ATS 34 is considered a stainless steel and yet if properly heat treated it is one of the toughest steels on the market

ATS-34 is a very strong steel (as are most stailness blade alloys) - however this is not the same as having high toughness and ductility.

I SERIOUSLY DOUBT that anyone on this forum could bend ANY knife made out of .250" stock that isnt differentially heat treated (read soft all the way to the edge) without the aid of some serious levers

Since I have done it, I don't have much doubt about it. Why you keep saying this makes no sense to me as you also say knives should not be used as prybars. The two statements do not support each other well. You would either believe one or the other, not both.

As for charpy values, they give a good indication of high rate of strain toughness which is very important for a knife steel and as for bending, some steels are far stiffer than others, the elastic modulus is not constant for all steels and depends on composition and heat treatment. Steels with a low modului of elasticity are used for springs for example.

-Cliff

[This message has been edited by Cliff Stamp (edited 05-16-2000).]

storyville · May 17, 2000

Tom -- Racial slurs?!? Im not the one whos been calling on folks to HOLD the Mayo round here

Rockspyder -- Ah, the legendary staple incident! So you would really prefer a 1095 blade to 440V on your Spydie Native?

I, for one, am pleased that Chris Reeve has yet to decide on dumping BG42 switching to 1095 on the Sebenza...

Cobalt · May 16, 2000

Johno, you and roger should pull some strength of materials books from your local library and read them. I don't have my old engineering books with me since they are in storage so cannot give numbers right now, but have done so many times in the past.

It sounds to me like what you are saying is that all steels have the same % elongation and differ only in the force required to reach that elongation. I think it's pretty much obvious to anyone that a soft steel is going to have more elongation than a hard steel. If I am misunderstanding what you are saying then please let me know.

example; lets say that you have two identical steels with identical or nearly identical tensile and yield strengths and only differ in their rockwell hardness. The steel with the higher rockwell will have a lower % elongation usually.

Also, alloying elements are there to make steels stronger than a simple steel like O-1 or 1095. So how people deduce that a stainless steel is automatically going to be not as tough as a plain carbon steel is beyond me.

A while back we had several threads were we posted charpy values of some CPM steels and steels like A-2. This will give you an idea of how tough they are.

dogboye · May 16, 2000

Originally posted by storyville:
Rockspyder -- Ah, the legendary staple incident! So you would really prefer a 1095 blade to 440V on your Spydie Native?
I, for one, am pleased that Chris Reeve has yet to decide on dumping BG42 switching to 1095 on the Sebenza...

Storyville.... umm.... I don't think I really want to answer that. I might appear ungrateful for what I have, or worse yet, piss off even more people. I do like 1095. And, I'm starting to like my Military a lot more. It's easy to re-sharpen often...

I don't use the BF Native much at all anymore. Especially since I got my Standard, with ATS-55....

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iktomi

Roger Blake · May 16, 2000

Originally posted by Cobalt:
It sounds to me like what you are saying is that all steels have the same % elongation and differ only in the force required to reach that elongation. I think it's pretty much obvious to anyone that a soft steel is going to have more elongation than a hard steel. If I am misunderstanding what you are saying then please let me know.

example; lets say that you have two identical steels with identical or nearly identical tensile and yield strengths and only differ in their rockwell hardness. The steel with the higher rockwell will have a lower % elongation usually.

While both steels remain in the elastic range, this means no permanent deformation, they will elongate the same under the same force if their shape is the same. The harder steels can take more stress so they will stay in the elastic range longer so they can elongate further. The lower strength steels do elongate further but in the plastic range, which is to say they are tougher.

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Roger Blake

Cobalt · May 16, 2000

"While both steels remain in the elastic range, this means no permanent
deformation, they will elongate the same under the same force if their
shape is the same. "

--Roger, this is incorrect. The percent elongation will vary from steel to steel. A 420 steel will have a different % elongation than a 440 simply due to different microconstituents all other things being equal.

"The harder steels can take more stress so they will
stay in the elastic range longer so they can elongate further. "
---More stress? Not necesarily. That depends on How hard the steel is. I doubt that O-1 at Rc of 63 can take more stress than O-1 at 58. And the harder steel will not elongate further. Softer steels can elongate further than harder steels with everything else being equal.

"The lower strength steels do elongate further but in the plastic range, which is
to say they are tougher."
---Yes, the lower strength steels do elongate further. However, elasticity is not the only factor of toughness. In fact toughness is usually measured by impact testing not elongation. That's why Charpy values are a good indicator of how tough a steel is. I hope you are a little more clear on toughness measured.

Also, you continue to mention Modulous of elasticity. Well, since I do not have my books with me I cannot quote values, but, all the modulous of elasticity is, is the slope of the stress/strain diagram of a steel. Since most steels behave the same way, the slopes will be similar, but not exactly the same. They do differ, there is no doubt about that. I hope that modulous of elasticity is a little more clear for you also.

Additionally, you mention plastic range. However, if you put a steel in th plastic range, you have gone too far.

whitewinger · May 16, 2000

There is one brand new company that is using cpm3v exclusively right now. That company is Whitewing knives started by Bailey Bradshaw. I dont know much about steels but I do know that Bailey is a pretty good authority on steel, so it must be good stuff for him to decide to use it in his production knives.

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Chris http://www.members.tripod.com/ctexknife

Jerry Hossom · May 16, 2000

My head hurts... This is all too complicated.

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Jerry Hossom
www.hossom.com

Roger Blake · May 16, 2000

Originally posted by Cobalt:
"While both steels remain in the elastic range, this means no permanent
deformation, they will elongate the same under the same force if their
shape is the same. "

--Roger, this is incorrect. The percent elongation will vary from steel to steel. A 420 steel will have a different % elongation than a 440 simply due to different microconstituents all other things being equal."

Thats true but steel does not differ that much in elasticity from one carbon steel to another.

Originally posted by Cobalt:
"
"The harder steels can take more stress so they will
stay in the elastic range longer so they can elongate further. "
---More stress? Not necesarily. That depends on How hard the steel is. I doubt that O-1 at Rc of 63 can take more stress than O-1 at 58. And the harder steel will not elongate further. Softer steels can elongate further than harder steels with everything else being equal

"Also, you continue to mention Modulous of elasticity. Well, since I do not have my books with me I cannot quote values, but, all the modulous of elasticity is, is the slope of the stress/strain diagram of a steel. Since most steels behave the same way, the slopes will be similar, but not exactly the same. They do differ, there is no doubt about that. I hope that modulous of elasticity is a little more clear for you also.

Additionally, you mention plastic range. However, if you put a steel in th plastic range, you have gone too far.

I agree with your definition of the modulus of elasticity and that they do differ. But I doubt that they differ much. I do not have any books here to check how much but I would think its small. Given what you just said I can not think how would think soft steel deflects or elongates more before it goes plastic since as you say the modulus of elasticity is stress over strain. The more carbon the higher up the stress strain line and hence the more force and more elongation the steel can take.

I hope this quote thing came off right.

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Roger Blake

Cobalt · May 16, 2000

Roger, since you think that the hardness factor makes a steel elongate more. I want to make sure I am not misunderstanding what you are saying. Is the following what you mean: Take two pieces of 1095 steel , one hardened to Rc of 61 throughout and the other hardened to an Rc of 56 throughout. The Rc of 61 steel will elongate further under equal stress than the Rc 56 steel. Is this what you are trying to say? and if so, I would like to know where you got the information from since I have never heard of that before. I will learn something new today

johno · May 17, 2000

There are a number of sites that offer mechanical property values for various steels and as has been mentioned before the values for the modulus of elasticity don't vary much. From one the glossery at one site:

"Modulus of Elasticity - The number which represents the relative "springness" of a given type of metal. All steels have the same modulus of elasticity or "springiness" regardless of the tensile or yield strengths. That is, until the yield point is reached they all stretch the same amount for a given load. Aluminum, on the other hand, is more elastic than steel and thus will stretch more than steel under the same loading."

As was mentioned before increasing the tensile or yield strength allows a given item to remain elastic under higher loads. A common way to increase the strength is with alloying and hardening, but the failure modes will tend to change from one exhibiting a lot of plastic deformation, the item gets bent, to one of brittle failure. Common stainless steels used in knives are typically tempered to a softer condition than carbon steels as they are more brittle at a similar hardness level. Also, except for 440V and 420V the CPM steels are not considered stainless.