CruForge V temper issues

[CliffStamp]

I understand that carbides are small.....but Cr carbides can be quite large...VERY large.

Think of this very simple fact, before hardening, there is much more carbide in the steel than after. The soaking removes a large portion of the carbide from the steel and ideally the quenching doesn't add it. However the blade gets much harder in the as-quenched state compared to after annealing or even normalizing yet it has a much lower fraction of and much smaller carbides.

Carbides do increase the hardness of a steel, in that if you took the same steel in the same micro-structure and then added/removed carbides it would change the hardness. However it is a much smaller effect than changes to the micro-structure directly due to phase differences (martensite vs austenite), carbon content of the phases, grain size and other factors.

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.

The first thing I would want to check is just use 1095 or similar and see if you get the same as-quenched hardness and the normal very low tempering resistance.

The only thing which stands out immediately is that walking up the tempering range and air cooling after tempering might be forming bainite which is temper resistant.

 

[scott.livesey]

back to original issue, how many points were checked during the hardness checks? when i get Rc readings that are not what i expect, i have done as many as 10 points at various spots on both side of the blade then used the average. i that if i do a ten point check, get 7 readings of 64 and 3 readings of 63.5, i am safe in saying the blade is Rc64. Rc62-63 should make a nice blade, wouldn't try to mirror polish.

 

[Cody Hofsommer]

I checked a half a dozen times and the reading was very consistent. Yesterday I ran a batch of 1084/15n20 and my as quenched hardness was about 66 RhC, and I also did some of the same with the CFV last time. I asked a MS what his as qunnched hardness is for similar mix, and he had about the same results.

 

[samuraistuart]

Those numbers are on the money. 68 as quenched CFV is right, too. Max, but realistic. But 63RC after 515F????

 

[jmforge]

Stuart, in thicker sections like 1/4 Parks seems to do okay. Take that down to say .85 and the blade will explode!!!!!!:sad: I bought some media fast oil after that.

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".

 

[samuraistuart]

Maybe you mean .085"??? JMforge, I have done two knives in CFV quenched in room temp Parks 50. (and two with canola a few years ago) Both were identical, 4" drop point hunters. .110" spine. Edge was at .020" before heat treat. On one I did a short soak at 1525F. The other got a 10 minute soak at 1475F. Both received the thermal cycle steps I outlined. No issues at all with the Parks 50 quench. The designers of the steel, I think Dan Farr being one, said "quench in oil...any oil". While CFV does NOT require a fast oil, it handles it quite well (in my shop).

Have you blown apart a blade quenching CFV in Parks 50?????