CruForge V temper issues

C

Cody Hofsommer

Well-Known Member
I tried a couple blades of CFV with a 1475 with a 15 min soak and quench in parks. I had a RhC of 68 as quenched. After several rounds of tempering, I am still at 62-63 and last temp was 515 degrees. Each tempering was at least an hour in my evenheat. Just keep upping the temp?
 
Well, I'm kinda just experimenting with this steel. I see that the specs call for higher temps, but i had read of some getting good results with a soak at 1475. I'm not an expert at this HT stuff, but I thought that you normally wanted the lowest temp that got the it fully hard. I would say RhC68 as quenched is fully hard. That and I had two blades of CFV and three 1084/15n20 Damascus.

As as far as testing, Christmas came early, and I am using my new grizzly hardness tester. I am getting consistent results, spot on, on my test blocks, and I am checking on clean, bare, flat steel. My Damascus stuff came out just as I had figgured it would.
 
Hey Cody. I'd try cutting some things just to verify, maybe some rope or cardboard. Then if that goes well, bump the temps up like you said and keep trying.

Sounds like your testing is pretty consistent. That stuff will be an absolute BEAR to finish at 62/63.
 
I think the MAIN concern with using 1475F vs higher aust temps is RA. Retained Austenite. When you stick with 1475F, the RA is minimal, and you put just enough carbon in solution to fully harden the matrix, and leaving the rest as vanadium carbides. As Karl mentioned elsewhere.....it's like 1084 with vanadium carbides. However, using higher temps such as 1530F, you are putting a bit more carbon in solution, increasing RA to some extent tho, and hand sanding is even harder it seemed to me. I tried 1475F with the longer soak and 1530F with shorter soak, and it was noticebly harder to hand finish the 1530F soaked blade. I personally think you should use the higher temps with steels like this, if the RA isn't too concerning. On knives that would see more impact use and maybe some abuse....DEFINITELY use that 1475F. Kitchen types and slicing machines, I would say use the higher temps. Cody, I am thinking you stated you did normalize and then thermal cycle this stuff a few times, right? I always do with CFV in spheroidized bar stock. (not forging yet).

Karl mentioned something elsewhere as well concerning the unusually high readings. The vanadium carbides may be the culprit. I have also had this theory before about unusually high readings being the result of carbides being "read", but it was shot down by others who know way more than me.
 
It would take very large carbides to give that kind of misleading hardness value. The small carbides in Cruforge V are not large enough to seriously change hardness readings. I'd say if you're looking for a certain hardness, just walk the temperatures up to it.
 
Me2...that is what I was told. I don't know enough to argue that...really! But here is what is swimming thru my head....it seems often I hear about a carbide bearing simple steel giving crazy high readings. I understand that carbides are small.....but Cr carbides can be quite large...VERY large. I understand that shouldn't be the case with CFV...just enough Cr to make the stuff role better for the factory. But besides the size of the carbides...we have their dispersion to consider. Is it so way out there to think that carbide structure in steel will not affect the diamond penetrator at all? That EVERY time, no matter HOW many times you try it, the reading will ONLY be on the cementite structure? That the carbide structure in the cementite would NOT affect the reading vs a pure cementite structure on each and every test?

The way I am seeing this right now (I can change my mind...I'm not dogmatic!)....No the "needle" is not going to land square on a vanadium carbide and give us the hardness of that carbide. How hard is VC anyway? But I would think that if nothing else, the carbide structure would influence how the cementite "moved"...or "gave way" when the needle hits.

Like the sand/concrete analogy. If I were to shove my hand in a bucket of sand...it would require a certain amount of force to displace the sand. If I shoved my hand in a bucket of sand and rocks....well...you get the idea. ouch!

I hope that I come off sounding like I am eager to learn. Not to argue.
 
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Think of it like this. Use clay instead of sand, and marbles instead of rocks. Now use just one finger instead of your whole hand. Do you notice any difference if you push a marble into the clay with one finger or just push your finger into it? That analogy applies when the carbides are similar in size to the diamond point, which is to say the carbides have to be comparable in size to the dimple left after the test, which is small to us, but huge to most carbides. For Cruforge V, a better analogy would be to mix sand into the clay, then try to pinpoint one with your finger when making an indention.

Now, if you have such large carbides, on the order of 0.5 mm or so, then if you hit one, it will definitely make a difference in the hardness readings. The very high carbide steels, with 20% by volume and up, may start to show some differences, but also think about how much carbide is in something like Stellite, yet it has a hardness below 50 or so HRc.

Yes, you are absolutely right. The carbide structure does influence how the matrix reacts to the hardness test. This is clearly seen in secondary hardening steels, where hardness increases as carbides start to precipitate at higher tempering temperatures. There is typically also some conversion of retained austenite during this high tempering, so the increases are not fully related to carbide precipitation, but it has an effect. Tempering carbides tend to be more coherent with the matrix, and strain it similarly to how the carbon trapped in the martensite strains it from a cubic structure to a tetragonal structure. Past a certain size, the coherency is lost and the strengthening effect and strain caused start to decrease. Check a tempering curve on M2 or M4 high speed steel and watch what happens when the tempering temperature exceeds 1100 degrees F.

Also, I think you were accidentally using cementite in place of martensite.
 
Oh, and to stay more directly on topic, I tend to view Cruforge V as vanadium based 52100, and would start by treating them similarly.
 
Thank you for the clarification on the needle penetrator. I see your point, and am not arguing it, just discussing, so I appreciate the help in understanding what is going on there. I am familiar with secondary hardening steels....but wasn't considering those even in the discussion. Just low alloy carbide bearing carbon steels such as Blue or CFV.

Yes....martensite instead of cementite. Thank you.

Still we are left with the question as to why Cody was getting crazy high readings after a 515F temper. And I have no idea. I would think with an as quenched hardness of 67 or 68, that 415F, not 515F, would drop it down to 63.

515F should be down to 57 or so. I would immediately suspect the equipment, but I believe him when he says it is spot on with test blocks and other steel.
 
Well, lets see. What hardness range are the calibration blocks and other steels? If they're in the same range, it looks like there's another issue. If he's using a 58 HRc cal block, it just might, might, be out of calibration in that high range. Or, his tempering oven could be off, or this steel might be different than other batches, or perhaps a couple other reasons. It could be a little of everything. I recently was discussing steel and the difference between non-magnetic and critical temperature. The maker said in his oven, non-magnetic temperature was around 1560 degrees F. Now, I think that's a little off, but as long as it's consistent, there isn't really an issue. However, there is an issue when that maker tells others what temperatures to use based off his oven, even if it's a starting point. There will also be an issue if his oven or thermocouple ever goes down and has to be replaced. The point is, if you are getting wonky data, it might be necessary to go back to square one and check a few things that may all be contributing a little bit. Honestly, personally, I'd give it a try at the higher hardness and see what happened. Of course you might not want to sell that blade. Cody may have resolved the issue, but hasn't said anything is a while. After a few more blades, it may be that it's ok to leave them like that, or he may decide to keep tempering until they're down to 60 or whatever hardness he wants. I'm a little backwards, as I tend to view tempering temperature as the target and hardness values as a by product. In other words, I probably wouldn't temper to a specific hardness on a knife, but use the tempering temperature I knew would give me the properties I wanted. For instance, I requested a relatively low draw on my A2 (375-400 F), and got a blade a little harder than most might want, but that's just how it ended up. Same thing with my S7 chopper. I knew the temperature I wanted, and a point or 2 either way won't be that big a difference.
 
It's mostly a reference to the fact that there are about a dozen ways to any given hardness value, but for blades, not all are equal. It particularly applies to the secondary hardening steels and complex stainless. I'm not really enthused about stainless steels treated in the higher tempering ranges, though the hardness will be the same in many cases. There are some subtle effects I'd rather avoid that happen at certain tempering ranges, but the hardness can sound dead on. If that's all the information you have, then you have to make due.
 
me2 said:
It's mostly a reference to the fact that there are about a dozen ways to any given hardness value, but for blades, not all are equal. It particularly applies to the secondary hardening steels and complex stainless. I'm not really enthused about stainless steels treated in the higher tempering ranges, though the hardness will be the same in many cases. There are some subtle effects I'd rather avoid that happen at certain tempering ranges, but the hardness can sound dead on. If that's all the information you have, then you have to make due.
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My limited understanding is that in those high alloy steels, the secondary hardening issues, loss of corrosion resistance, perhaps lost of impact srength are offset by ease of HT for the purpose the steels were intended. But we do not use them as intended, so we have to come up with interesting and sometimes crazy methods.
 
me2 said:
Oh, and to stay more directly on topic, I tend to view Cruforge V as vanadium based 52100, and would start by treating them similarly.
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That is a very interesting observation especially if the OP's readings are accurate. We know that 52100 reacts a bit differently to a long soak at say 1475. Seem to remember similar as quenched harness. With that said, CruForge V at 1500F with a soak supposedly hits spot on every time assuming use of good HT gear. The numbers you typically see listed are 61 or so at 400F temper and a drop to around 59 at 425.
 
In a lot of the secondary hardening steels, they are intended to be used in the temperature ranges just below the secondary hardening peak. They get tempered at say 1000 F for service temperatures in the 800 to 900 range. Also, many steels are listed or designed with coating in mind, and some modern coatings require temperatures in the range just below the secondary hardening range. As a last bonus, much of the secondary hardening comes from carbide precipitation, which will increase wear resistance, though at the expense of the other properties, as you listed. I once suggested, tongue in cheek, that a maker just use the proper quenchant to get O1 to the 58-60 hardness range he was after, and skip that pesky tempering step. I quickly retracted that, as I thought someone might actually follow that advice.
 
me2 said:
In a lot of the secondary hardening steels, they are intended to be used in the temperature ranges just below the secondary hardening peak. They get tempered at say 1000 F for service temperatures in the 800 to 900 range. Also, many steels are listed or designed with coating in mind, and some modern coatings require temperatures in the range just below the secondary hardening range. As a last bonus, much of the secondary hardening comes from carbide precipitation, which will increase wear resistance, though at the expense of the other properties, as you listed. I once suggested, tongue in cheek, that a maker just use the proper quenchant to get O1 to the 58-60 hardness range he was after, and skip that pesky tempering step. I quickly retracted that, as I thought someone might actually follow that advice.
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It would have to be something like molasses. Perhaps if it was 450F molasses you might get a sweet auto temper effect. :lol:
 
Hey guys, been away for awhile. I did some quick testing on he blade, and found it quite tough, so I left it as is. I stuck in in a pine board and pryed out the tip sideways a dozen times, chopped into pine knots as much as you can with a 4" blade and had no damage. These where 4" hunters, so that seemed about as rough use as should be expected.

As as far as test blocks, I was within a couple tens on the 63,45, and 26 blocks. My oven could be off, but I was getting appropriate readings on other steels.

Thanks for the tips and ideas. I have learn a few things.
 
Cody, I'm glad you're getting good performance. It's hard to screw up CFV I think, and that is why they made the stuff. To be easy to forge and heat treat, but give great performance! So go to town cutting!!!! I have done 1475, 1500, and 1530F hardening temps. The difference was difficulty in hand sanding. The higher the hardening temp, the more work it took to get to 600 grit. Not sure how much more wear resistance, if any, that translates to.

My recommendation with CFV is the following, if you have time/temp control. Well, temp control. Time is what it is!

Rough grind into shape (the stuff is seriously soft from Crucible)
Normalize at 1650F, just enough time to equalize the temp throughout the blade length, let it air cool
Thermal Cycle at 1550F, equalize, air cool
Thermal cycle at 1500F, equalize, air cool or quench
Thermal Cycle at 1450F, equalize, quench
Thermal Cycle at 1400F, equalize, quench
(you can skip one of those steps and just do three, don't skip the 1650F tho)
You can harden from here. If more grinding/drilling needs to be done... then hold at 1250F for two hours and either quench or air cool.
It's now ready to harden.
Get your oven up to 1475F (I don't do any 1200 pre heat at all), once the oven is stable, put blade in at 1475F.
Once the temp has rebounded up to 1475F, start your timer for 10 minutes.
Quench in 130F canola oil, or room temp Parks50 (no issues at all with P50).
Temper one hour at 350F and then quench in water.
Temper one hour at 375F and then quench in water.
Temper one hour at your final target hardness temp (400F or whatever), and then quench in water.

The reason for the 1475F is to put just enough carbon into solution to attain max hardness, and because of your normalization/thermal cycling that you did, it leaves the rest of the carbon to the carbide formation.



me2, you mentioned non magnetic in your friends oven is 1560F. I agree, consistency is more important than the numbers. But you and I know that with the carbon steels being discussed here, even allowing wiggle room because of grain size reduction, non magnetic starts around 1350F and ends more or less at 1414F. Not even close to what your friend is getting "in his oven".
 
The issue I have is that maker publishes the temperatures he uses without that tidbit of information regarding his oven. If he worked in isolation, it wouldn't really matter. The F, C, and K temperature scales just take known starting points and scale in between. The difference is there are millions sharing them and they have ways of making sure they are using synchronized measurements.

I am not aware of changes made by grain size in the Curie temperature (nonmagnetic). I am also not aware of it occuring over a range of temperatures. That said, I have been unsuccessful in trying to google a reference for how the different alloying elements change it. That they do change it I don't have much doubt, but I also don't think its more than a few degrees, if that much, for the steels knifemakers use. After all, it is constant across the iron-carbon phase diagram, and carbon certainly has different magnetic properties than iron. One wouldn't think it would be so hard to find information on, but it has proven frustrating. If you know of a source, let me in on the secret.
 
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