Steels with near 8% Cr and less than 1% C plus small amounts of many other metals

Cobalt

Cobalt

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I am asking about this because of another thread that was posted talking about INFI, and I will quote a post from there over here. My questions are not about INFI but more about the use of similar steels to INFI.

Here is one post:
Last Visible Canary said:
INFI's composition has been known to the public for nearly 10 years. It's not a modified A8. Given the degree of difference in number of elements present and percentage of those differing elements: they look nothing alike.

(this is from a 3rd party spectral analysis of INFI)
INFI
C 0.5% Carbon
V 0.36% Vanadium
Cr 8.25% Chrome
Mo 1.3% Molybdenum
Co 0.95% Cobalt
Ni 0.74% Nickel
N 0.11% Nitrogen
Fe 87.79% Iron

A8
Carbon - 0.55
chromium - 5.00
Molybdenum - 1.25
Tungsten - 1.25
Click to expand...

So Below is the actual A8M steel and 3V steel chem comp's. I know there is plenty of info on INFI and 3v. However, there is not much with A8M.
Latrobe A* Modified
C. - 0.5
Mn. - 0.45
Si. - 0.95
Cr. - 8.0
Mo. - 1.3
V. - 0.45

CPM 3V
C - 0.80%
Cr- 7.50%
V- 2.75%
Mo- 1.30%

The biggest thing in common all three of these steels have is the chrome content. Funny thing is that the original A8 chipper steel had 5% Cr and the Modified came out later and I think the only Knife maker to use A8 Mod was Tom Johanning. No one else has that I know of and I am not sure why as it is chemically a great steel and possibly as close to INFI as any steel has ever gotten.


So to those in here who use 3V, have any of you ever tried A8M and if so what kind of HT do you use? If no has tried A8M, then why? surely it appears to be a great steel.




Yushu_withwind said:
In my opinion,The propeties of steel depend on two factors: chemical composition and metallurgical quality.

in the alloy design of INFI,first the carbon is reduced to about 0.5%, it can get high toughness that will stiil provide sufficient hardness.second, about 0.18% nitrgen was introduced into the steel which can enhance not only corrosion resistance but also toughness . third, about 0.5~1% nickel was added and nickel is the most effective element to improve toughness. Fourth, because of nickel can lower MS critical point that may result in more residual austenite, 1% cobalt was introduced to fill in the gaps,because coblat is is one of the few elments that raise the MS critical point, and the tempered martensite turn more tough when nickel/coblat are added in steel together.Fifth,chrome was hold at 8% and molybdenum was hold at about 1%, than form a certain quantity of carbide to get wear resistance ,however the carbide is not too large to harm toughness.in conclusion,the alloy design of INFI is very clever .

Even so, alloy design is only one side,the metallurgical quality of steel is also very important which is determined by the technological process,but so far I still do not know the manufacturing process and equipment of INFI, so I have no comment.
Click to expand...

I also what to ask about this quote above. How does raising the MS critical point help and how does one go about learning which combinations of elements perform well together? In other words, it is great to know that Ni/Co combination works well together and brings a measure of toughness even at high temps, but how does one figure this out?

the original thread is here:
http://www.bladeforums.com/forums/showthread.php/963248-Infi-steel/page2
 
Cobalt said:
So to those in here who use 3V, have any of you ever tried A8M and if so what kind of HT do you use? If no has tried A8M, then why? surely it appears to be a great steel.
Click to expand...

I haven't tried A8M because A) I don't know where to get it, and mostly B) I'm a big fan of vanadium carbides. I believe the 0.45% V would serve to prevent grain enlargement during HT, (which is good) but that's about it. The 2.75% V in CPM-3V allows for lots of very hard, small carbides.

There's also the whole CPM process, which I also like. I just can't see any advantage of A8M over 3V, except maybe easier sharpening.
 
james terrio said:
I haven't tried A8M because A) I don't know where to get it, and mostly B) I'm a big fan of vanadium carbides. I believe the 0.45% V would serve to prevent grain enlargement during HT, (which is good) but that's about it. The 2.75% V in CPM-3V allows for lots of very hard, small carbides.

There's also the whole CPM process, which I also like. I just can't see any advantage of A8M over 3V, except maybe easier sharpening.
Click to expand...


Do you think that that much Vanadium creates a condition that simulates brittleness due to the very hard small carbides?
 
A lot of the Nexus knives by Molletta (this guy really knows his stuff) and the MCKF group used A8M,you may be able to find some opinions in the Lionsteel part of the forums,there is also some youtube stuff where they are pounding their knives into rocks,cutting rope,cutting nails with the help of a vise,that sort of thing of course most of it is in Italian -the steel was used in the Spartaco,Tito,Centurion versions of Nexus knives.
 
I have used about 50 lbs of A8mod with the addition of Ni 0.273 and a smattering of tungsten and cobalt. I like the steel but do not use it much because:

It is not super tough (compared to A-8, or my fav S-7)

Not super easy to get high hardness

Hard to find (all my stock is 0.625")

I still have lots and will not be throwing it into the recycling but probably not ordering more either.

Incidentally I do not use 3V yet because:

Fast quench required for full hardness (fine for small blades I can plate quench but fussy for 36" at the commercial HT)

Not comparable in toughness to S-7 at RC 57-58 I don't care what Crucible says it does not approach the toughness, even according to the numbers they publish themselves.

High austenitizing temperatures without corrosion resistance

Really though if you had top notch geometry and top notch HT you would be hard pressed to quantify the difference in hand between 3V and A-8mod... until you got out a hammer... then the powder metallurgy would probably shine in this case.
 
Interesting point about S7 and I have heard this from others. To be honest, I do think toughness is more than enough in any of these steels, I was just wondering why the 8% chrome steels just don't seem so popular with knifemakers these days. Aside from 3V of course which is very popular.

So when you HT something like A8M is there a std HT to follow? How about other Ax steels, such as A3, or A6, are there HT protocols for those? Just wondering how the elemental changes, change the way HT is done on these steels.
 
Cobalt said:
Do you think that that much Vanadium creates a condition that simulates brittleness due to the very hard small carbides?
Click to expand...

Nope. CPM-3V is very tough, both in terms of being able to beat on things, and in being able to hold a fine edge at high hardness without chipping. It's my understanding that the small size of V carbides helps this, as well as the generally small size and even distribution of all the carbides that comes from being a CPM steel.

Now on the other hand, if a steel has a lot of large carbides, and/or big, uneven clumps of them, that contributes to brittleness. Think D2... very good wear resistance, but not very high toughness.

Cobalt said:
Interesting point about S7 and I have heard this from others.
Click to expand...

I've heard that, too. The S-series is probably the way to go if one really wants super-toughness. But I also agree with you that any of these steels are plenty tough enough. Plain old O1 and A2 are honestly tough and resilient enough for most reasonable knife use... including "combat" or "survival" knives... but where's the fun in that? ;)
 
quite true, my concern has always been that when you get a steel with lots of alloying elements, the HT becomes a big unknown? The S steels are fairly simple, which should mean a very straightforward HT. Or even steels like O1 and L6 which are comparatively simple when put next to a lot of the A series steels. This is why I was wondering about steels that have lots of little alloying elements in them, not in great amounts but in small amounts, but yet, lots of them. Just wondering if lots of these elements make the HT a problem or not?
 
I wouldn't call the HT regimens unknown; most of the research on each alloy has been done by the folks that designed them. Of course, that's often tweaked for specific purposes.

Cobalt said:
Just wondering if lots of these elements make the HT a problem or not?
Click to expand...

Well, they certainly make the requirements different. Whether or not that's a problem depends on the heat-treater's experience and equipment. Speaking very generally, highly-alloyed steels require higher temperatures, more precise control of those temps, and longer soak times to get all the elements in solution.

Stacy wrote up a really helpful overview on this topic, here.
 
I think the reason the crowd doesn't run this way an that way every time a new steel is discussed or alloyed is that the steels we already have are there because they have been field tested thousands of times. Can a new steel get a little harder, tougher, etc.?...Sure, but will the difference be noticed buy a user, ....almost surely not. Occasionally a new blade steel comes along, but the steel is usually just a newer form of an existing steel.

The rather large list of commonly used blade steels, like the CPM alloys and the standard carbon steels will serve 99.9% of all knife making needs.
CPM 3V is a good example of a knife steel that gets overlooked by many. It is economical, readily available in many sizes, it has fine grain, has a fairly standard HT, and makes a truly tough and sharp blade. When I read threads about INFI or some other proprietary steel, I wonder what the folks want more than the great steels we already have. Maybe it is just the marketing of something being new and exotic sounding.

I advise many newer makers to take a look at the steel suppliers like Aldo, USA Knifemakers, Jantz, etc. The steels they carry are the steels that make knives. Other steels may have this or that added for some metallurgical reason in aerospace industry or other non-knife area, but they probably aren't exactly perfect for knives.
Not wanting to plug Aldo, but if one looks at the list of steels available on his site, it is hard to see a normal need for any alloy other than the twenty or so he carries.
 
Given the money that is to be made or lost in an industrial situation it is likely that the HT is worked out fairly well. The A8mod I have is for log peeling lathes... they put a log on the lathe and peel it in one 12' width until the log is too small in diameter... massive forces involved and clean cuts essential to get smooth veneers. As for getting that HT info, that's another matter!

Speaking of HT the A series provide easier, slower quench and good dimensional stability... this is why industry is attracted to them for large or intricate pieces, even when a cheaper alloy might do the job (perhaps better) it's too expensive to straighten a 12 foot blade and do post HT machining. Meanwhile I have read design articles for fasteners where L6 was failing because it cracks in the quench. All this is to say that stuff like A8 and A8mod maybe are chosen not because they make the best blades but because they are better to make blades from!
 
bladsmth said:
I think the reason the crowd doesn't run this way an that way every time a new steel is discussed or alloyed is that the steels we already have are there because they have been field tested thousands of times. Can a new steel get a little harder, tougher, etc.?...Sure, but will the difference be noticed buy a user, ....almost surely not.
Click to expand...

We really are blessed with a lot of fantastic, well-proven steels. CPM-3V and INFI are good examples, and pertinent to this particular discussion, because it's clear that they're both really, really good for "heavy duty" knives. How much better could either of them get, performance-wise? Except for corrosion-resistance, probably not enough for most makers and users to tell the difference. Even between the two, it's hard to say which is really better than the other - read enough reviews and studies on them and they come out pretty much even.

Even fairly recent "super steels" like CTS-XHP and Elmax aren't vastly different chemically from much older alloys like D2 and 440C... much of the improvement comes from cleaner processes at the mill, which bring out the highest potential the chemistry offers.
 
and of course I am not trying to put down many of the fine steels with lots of elements, just trying to understand the complexity of getting the HT right on certain steels. Thanks for all the answers guys, very enlightening to me, though for you it is basic knowledge probably.

Looking at the steels below, all A series, some like A11, A9, A7 have a large variation in alloying elements, then it would be true that if the steel is created, that an HT protocol has likewise been established for the steel? I would assume this is based on it's usage and at a specific Rc for that usage. So if used in the wood milling industry, chipper, etc, the Rc may be set at say 56 and the HT is designed with that in mind, but if I want to make a knife of say 59 Rc with the same steel, that HT protocol is out the window?( I am going to go read that link now, by the way, may answer a lot of my questions)

AISI UNS. No. C Mn Si Cr V W Mo Co Ni
A2 T30102 1.00 5.00 1.00
A3 T30103 1.25 5.00 1.00 1.00
A4 T30104 1.00 2.00 1.00 1.00
A6 T30106 0.70 2.00 1.00 1.25
A7 T30107 2.25 5.25 4.75 1.00 (c) 1.00
A8 T30108 0.55 5.00 1.25 1.25
A9 T30109 0.50 5.00 1.00 1.40 1.50
A10 T30110 1.35 1.80 1.25 1.50 1.80
A11 T30111 2.45 0.50 0.90 5.25 9.75 1.30
 
Cobalt said:
...I would assume this is based on it's usage and at a specific Rc for that usage. So if used in the wood milling industry, chipper, etc, the Rc may be set at say 56 and the HT is designed with that in mind, but if I want to make a knife of say 59 Rc with the same steel, that HT protocol is out the window?
Click to expand...

Not out the window, just tweaked. There will be a range of austenitizing temps/times, quenching procedures, tempering regimens, etc for each steel that will all get the steel hard... but some are better or worse for specific applications. Even aiming at a certain Rockwell hardness is only a beginning point. Speaking very generally again, steel at 59Rc with a lot of retained austenite may be very wear-resistant, but "chippy". This is not a big deal in a 100# die. Convert that RA to martensite with a different tempering regimen and even at the same hardness, it will have better stability in a fine knife edge.

Cobalt said:
( I am going to go read that link now, by the way, may answer a lot of my questions)
Click to expand...

It's a great primer! It's part of the main HT sticky here. There is days if not weeks worth of fascinating reading material there :thumbup:
 
I think it is the heat treat process that brings out the "magic" in INFI. I think I read somewhere that it takes 40 hours to heat treat a blade. That is a huge time investment.
I remember at the machine shop I worked we made a part that needed extra toughness and spring action. We used plain 4140 for the parts and if we did not do the special HT that took about 14 hours the part would break in about two hours of use. Now when the part had the "magic" HT it would last for several thousand hours of use before needing replacement. Again I know some people hate to hear it, but the magic in some cases is in the heat treat.
 
I completely understand that HT is the magic, hence why it can be a closely guarded secret by a knifemaker using specific steels. Both Busse and Fehrman have proprietary HT's and I am sure they are not alone. I am sure this came with plenty of trial and error as well, it had to. I cannot imagine that someone could create an HT process and not have experimented with lots of failed blades before reaching the right recipe. So with Busse he used A2 for years before going to INFI. I am guessing he started his HT for INFI with a modified A2 HT schedule. How many blades did he go through before he got it perfect or satisfactory I should say? who knows. Likewise Fehrman started with the std 3V HT and modified it to suit his goals.

Aside from deep cryo as part of their process, do they just extend times for every part of the HT to assure transformations and do they do more than the std tempering cycles? And once they have this extended HT process, can they apply it to steels that change slightly in elements? So for example, if Busse, Fehrman, James Black, have this extended HT process that takes out any possibility of unknowns, can they slightly change their formula in steel from say INFI or 3V or A2 to something like A9 below and still use this very extended and conservative HT protocol?

AISI A9
C 0.50
Mn 0.50
Si 1
Cr 5
Ni 1.5
Mo 1.5
V 1.1
Cu 0.25

So if the high temp hold is typically 30 minutes, they push it to 45 minutes. If the cryo hold minimum is 2 hours, they hold it for 8-10 hours. If the cooling rate is 20F per hour, they do it at 10F per hour, etc. They make every part of the process more conservative and hence much longer. Have they not just taken out the unknown factor of the steel? within a certain range of course. If we stick to A# steels for this HT. or S# steels, etc. and use the std protocols for such a steel as the starting point and just extend all of it and go beyond it in every way, then have you not just made it possible to use that new process for a range of steels? or is this thinking to simplistic and it will not work.
 
I absolutely bridle at the term "magic" when it comes to heat-treating... but that's a personal thing and a topic best left alone. :)

Cobalt said:
So if the high temp hold is typically 30 minutes, they push it to 45 minutes. If the cryo hold minimum is 2 hours, they hold it for 8-10 hours.
Click to expand...

Well... maybe. Longer and hotter (or colder) is not necessarily better, and especially in terms of austenitizing temps, hotter can be very bad after a certain point. But within a certain range, there are a lot of factors to play around with. Pushing all of those factors to their limits is almost guaranteed to result in failure... and you wouldn't really know why you failed.

The guys with advanced degrees and folks like Stallsmith, Cashen and Bos who've been doing this for decades probably would have a pretty darn good idea where to start, just by looking at the chemistry of the steel. But I imagine you're right that to some extent it just takes trial and error and good old boring science. (Good record-keeping, accurate data measuring, corroboration, limiting the number of factors changed at a time, and so forth.)
 
Big Chris said:
I think it is the heat treat process that brings out the "magic" in INFI. I think I read somewhere that it takes 40 hours to heat treat a blade. That is a huge time investment.
I remember at the machine shop I worked we made a part that needed extra toughness and spring action. We used plain 4140 for the parts and if we did not do the special HT that took about 14 hours the part would break in about two hours of use. Now when the part had the "magic" HT it would last for several thousand hours of use before needing replacement. Again I know some people hate to hear it, but the magic in some cases is in the heat treat.
Click to expand...
That springs good old plain 1095 to mind..Take 1095 that has been heated to non-magnetic and quenched in transmission fluid and test it against a 1095 blade properly soaked for the proper ammount of time at the proper temp and then quenched in the proper quenchent like parks 50..Proper heat treat means better performance..When I moved from forge heat treating with wal mart quenchants to temp controlled heat treat and formulated quenchants I noticed a huge difference right off the bat.
 
I agree with Kentucky and the others that the thing that makes these "super" steels super is usually knowing how to do the HT right. Most home shop HTers don't have the skills or equipment to do these steels justice.
 
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