carbon and chromium and vanadium in solution

samuraistuart

samuraistuart

Joined
Dec 21, 2006
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For you metalheads out there, I have a question for you. If this has been answered in another post, or forum, please point me in the right direction. I hope I can formulate my thoughts well enough to convey what I am pondering. Let's take Cru Forge V as an example. Carbon:1.05 Cr:0.05 Mn:0.075 V:0.075. My question centers around time/temp and how to control what we want as an outcome. I hope this makes sense, and I'm not on Jupiter. Can we vary time and temp to dictate what we want a certain alloy to do? I'm pretty sure the answer is "of course", maybe more to the point is "how". And I don't know enough about carbides and all that to answer this question. To be honest, sometimes the stuff is over my head while reading posts from very knowledgeable sources.

If I wanted to make a knife with maximum edge holding abilities, and not concerned so much about overall strength (think White#1 vs 5160), is there a way to vary time/temp in order to control not only how much carbon comes into (out of?) solution, but how much Cr and V come into (out of?) solution? What is a chromium carbide and how does it act? How do we make them? What is a vanadium carbide? How do we make them? Is there such thing as a CrV carbide? Are there benefits of not tying up the Cr or V into carbides? Not even sure if I know what I'm talking about just trying to ask a question! Ever feel like you know so LITTLE about something, you can't even inquire into it? That's how I feel right now!

I don't think I am doing a good job translating my thoughts onto......keyboard. Maybe another way to ask it would be, "If a hyper-eut steel has Cr and V added, can we maximize the Cr and V for edge holding, and how is that done? Is there a process by which the Cr or V isn't combined with the carbon, and left to do other things?" Like Cr in D2. There is enough there to make it almost stainless. Do knifemakers vary their heat treat on D2 to either maximize edge holding vs maximizing toughness or corrosion resistance?

I really hope that made sense. Excited to hear your thoughts!!!
 
The general answer is that HT protocols are designed very much to get alloying elements into solution so they can be helpful to us. Purposely buying alloyed steel and messing with HT to not get stuff into solution is not going to add performance, and will probably cause other problems as well. At best it's a waste of time and expensive steel.

samuraistuart said:
Are there benefits of not tying up the Cr or V into carbides?
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Well... sort of... but not really, in the way you're thinking. Vanadium in small amounts contributes to fine and consistent grain structure. Having more V retains that benefit, but adds the wear-resistance benefit of V carbides. Chromium in small amounts increases steel's ability to harden through and not require a fast quench; larger amounts form carbides readily, and even more chrome that's not tied up with carbon adds stain-resistance. But having a whole lot of extra V or Cr that's simply not utilized doesn't do you any good.

One exception to this general rule is steel like AEB-L, which is specifically made to have barely enough carbon to get good and hard, leaving almost all the chrome free for stain-resistance while retaining the toughness/fine grain of a plain carbon steel - but that's accomplished by its chemistry, not by altering its HT regimen.
 
samuraistuart said:
Do knifemakers vary their heat treat on D2 to either maximize edge holding vs maximizing toughness or corrosion resistance?
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Indeed they do, but that typically has more to do with structural stuff like austenite vs. martensite than it does with carbide formation. Nathan the Machinist has studied this quite a bit with D2 in particular, and could explain it much better than I can.
 
Basicly, steel's compisition is design to meet specific properties, needed (mostly) in industry.
It is quite complicated science, based in huge part on experiments.
If steel is designes in a specific way in most cases you shall not try to design it another way.

Also, the same element in steel can have different properties, depending on its concentration.

For carbon and hardness and carbides. I would say(and books would say) that in simple carbon steels you do not need more than 0,5-06%C in solution to get maximum hardnes of steel martensite matrix. All aditional just increase briteness, without any benefit.
In case of cruV - Cr and Mn is for incresing hardenbility(lower quench speed), vanadium is for grain refirement, VC carbides should dissolve during austenitization. Vanadium will then precipitate as V2,4C during low temperature tempering.

Topic that you started is A GREAT topic to discuss next to a beer and a bookshelf full of metallugy books. One of my favourive hobbys :D

But to the point - CruV austenitize at high range of sugested temperatures, temper at 175-195°C - it will be peak of toughness at high hardness. You want your steel to be there.
 
"VC carbides should dissolve " Well you opened another ball of wax.The CM bonds are dirfferent for different metals .The weakest bonds are Fe and Cr carbide . [ maybe that's why many tool steels are based on Cr ???] Strong bonds ar found with V, Mo, W. These require much higher temps and longer times to dissolve the carbides !
Technically V doesn't "refine" grains but slows down grain growth. Only about 0.025 % is needed to do that. Higher amounts then are found in carbides. Just like cooking, it's the same as micro-alloying !
 
mete said:
"VC carbides should dissolve " Well you opened another ball of wax.The CM bonds are dirfferent for different metals .The weakest bonds are Fe and Cr carbide . [ maybe that's why many tool steels are based on Cr ???] Strong bonds ar found with V, Mo, W. These require much higher temps and longer times to dissolve the carbides !
Technically V doesn't "refine" grains but slows down grain growth. Only about 0.025 % is needed to do that. Higher amounts then are found in carbides. Just like cooking, it's the same as micro-alloying !
Click to expand...

Thank you for that information, I allways tought that one need a little more of V, like 0,1% to slow grain growth. I will now look another way on some exotic steels.
 
This really helps me big time!!!! Basically, with a given steel, it has a set heat treat with the given alloying elements, and there is a specific heat treat for that steel. Messing with the heat treat in order to get this, remove that, balance this, balance that does no good. The alloys and their percentage dictate the heat treat. If we want something different...go with a different steel.

James, Idaho, and Mete, your posts helped a lot with what I've got swimming around in my head. Thank you.
 
mete said:
"VC carbides should dissolve " Well you opened another ball of wax.The CM bonds are dirfferent for different metals .The weakest bonds are Fe and Cr carbide . [ maybe that's why many tool steels are based on Cr ???] Strong bonds ar found with V, Mo, W. These require much higher temps and longer times to dissolve the carbides !
Technically V doesn't "refine" grains but slows down grain growth. Only about 0.025 % is needed to do that. Higher amounts then are found in carbides. Just like cooking, it's the same as micro-alloying !
Click to expand...
A little off topic but, so a steel like VG-10 (0.95% - 1.05% C) with its high Cr and other metals will still form vanadium carbides with just 0.1 - 0.3% V??
 
If you have a detailed FE-C Equilibrium diagram ,you will see a thin strip on the left where there is complete solubility of carbon in iron ! A bit more C and you have a two phase FE ,C structure .
Another factor is where does the V or VC go ? It likes to be in the grain bondaries.That is what slows grain growth - blocking grain boundary movement. A similar alloying element niobium, will tend tobe throughout the structure instead of Grain boundary concentration.
 
So, If I understand the phase diagram and your explaination, in the presence of excess carbon (hypereutectoid steel) the vanadium should form carbides in the grain boundaries. If the carbon binds with V preferentially over Cr then the Cr is left to do its anti corrosion duties in a steel like VG-10. So, given the correct sequence in the HT protocol, we would end up with a fine grain structure (the vanadium slowing grain growth), a high corrosion resistance (the chromium is free to help prevent the oxidation of the iron), and good edge retention due to the formation of small vanadium carbides and other metal carbides????
 
That's about right . BTW you can google phase diagrams - Fe-C, Fe-V, Fe-C-V ETC, ETC ! That'll get you confused.
 
Bo T and Mete, your recent exchange is tapping into what I have swimming in my head, and again thanks for your input! Idaho, I re-read your post because I thought you touched upon something I had come across recently and that is in simple carbon steels .6% carbon gives you the max hardness, and carbon content above that doesn't give you harder steel. That I do not understand yet. I was thinking that, for example, 1060 (I looked to find max hardness as quenched...really couldn't nail a number down) as quenched wouldn't be as hard as 1095 quenched. That the 1095 could be a point or two higher. Now, with alloying, I get that hardness becomes a factor of not only the carbon in solution, but the alloying as well (Mn and Cr to name a couple). But with 1095, there is little alloying in there to make it harder....so why choose 1095 over 1060, if all we can get is .6% or so? I hope that makes sense.
 
I think your data is based upon a quench to room temperature. Since the Mf (martensite final temperature) is quite a bit lower for 1095 than 1060, there will be quite a bit RA (retained austenite) in the 1095. This will keep the 1095 from developing its full hardness. There are tricks that will decrease the RA in 1095 quenched steel. One would be to quench to almost room temperature, then place the steel in a dry ice chamber. This will lower the temperature of the steel to Mf and attain a higher % of martensite (and a higher hardness).
 
BoT, thanks for trying to help me, but I'm afraid you're over my head. I am indeed talking about as quenched hardness. Am I wrong in my thinking that if we heat treat and quench 1095 at it's recommended temp, same with 1060 (it's recommended temp)....that out of the quench the 1095 will be maybe a point or two harder than the 1060? You're saying that, even in a thin cross section and quenched in fast oil or brine, 1095 will not be harder unless it goes through cryo? So why choose 1095 over 1060 (especially if we don't have access to cryo?). I'm using 1060 and 1096 as an example to compare the difference in carbon, and little alloying. What advantage would White # 1 have over, say 1060 or 1050. White # 1 doesn't get cryo treated, at least not that I've heard. Why would we want to spend the extra money to have all that extra carbon, if it's only going to get as hard as a blade with .6 points of carbon? Just for discussions sake. I appreciate you guys answering my questions.

,
 
From the information that I have seen, given a good quench, 1095 will be several points HRc above 1060 at the as quenched hardness. However, 1095 should have some iron carbides that, if I understand it correctly, should give better edge retention. So, after you temper your blades, your 1060 will be a little softer but tougher. And your 1095 will be harder with better edge retention. This is if you make blades that utilize the characteristics of the steel to the greatest effect. 1095 - great kitchen knives, cutters, etc. Mora carbon steel or Opinel carbone. Steel used for choppers, machetes, axes, is often 1055 or 5160. Designed so the edge will bend not chip and there is less likelihood of the tool fracturing in use.
 
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