CPM 3v Destruction Testing and Etching results

Shane Wink

Shane Wink

Well-Known Member
I have been experimenting with 3v for the passed couple of months doing cutting test and working with the HT. I was done with most of the cutting test and decided to break the blade to see how the grain appeared and how it would break.

The blade I chose to break was a drop point hunter that speced at 8 3/4 long over all with a 4" blade 1/8th thick with distal taper along the blade and 1 1/4 wide. I mounted the blade in the vice 2"s from the tip. Wearing gloves, helmet and apron I began pulling on the blade but it was not easy to pull. I am a pretty stout firefighter and needed a cheater to bend the blade enough to where it finally snapped.

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Its returned too position after the above bending.
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Cross section showing where the tip was snapped off.
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The blade above preformed very well when compared to my 01 blades made the same way and with the HT I give them. I may need to refine the HT to make the 01 better or maybe the 3v is that much better but at any rate for me the 3v cut much longer than the 01. Another thing of not is when stropping the blades after grinding the bur on them it takes much longer to remove the bur from the 3v.

I was able to break the blade and it broke at about 45* which is past where it is in pic above. When it did break the knife snapped into 3 pieces, one piece at the jaws of the vice and the other in the middle of the tang. When looking at the cross section it has a ledge sticking out and not a clean break like most of the other steals I have broken. Is this an issue with my HT?

The current HT I am using soaks the double tool wrapped blade at 1450* for 20 min then ramps to 1980* and soaks for 30 min. Pull it out and using quench plates and compressed air to cool. Temper at 975* for 2hrs X3. The RC I am shooting for is a 60-61 as I make small skinning and utility blades and 3v has toughness to spare. The higher Rc also aids in better wear resistance at a slight trade off in toughness. The ht came from JHossom and Paul Bos.

I etched the pieces for different periods of time in a ferric chloride solution 4:1 and noticed several shiny specs in the thicker portion of the blade and on both sides. Is this indicative of not normalizing the steel or an issue with a poor HT and quench?

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Shane Wink said:
Another thing of not is when stropping the blades after grinding the bur on them it takes much longer to remove the bur from the 3v.
Click to expand...

I love your testing, Shane! I appreciate you taking the time to document it and begin these discussions. Regarding the above quote, I made the same observation after grinding the final edge & sharpening of my first couple of 3V blades. I just assumed it was attritbutable to the crazy toughness of the steel.
 
Thanks Shawn, I have made 8 blades from the 3v and all have preformed very well. I have been reading up on Jerry Hossons post about it and decided to start breaking a few to see what they will take and how my heat treat is. Honestly I enjoy working with the steel and like the satin finish.

Jerry etches his 3v to remove any iron oxides that are on the surface so when I began etching one of the blades and saw all the shiny specks I immediatly thought it may be my heat treat. I am sure Kevin can weigh in on the hows and whys.
 
My opinion, supported by no research or facts is, I think the break is pretty typical and normal for a hardened modern stainless steel. If it had rolled over and only cracked, I would say you did have a problem. While it's been proven it can be done, differentially hardened air hardening stainless steels are never hardened that way. It's hard to see in your picture, but the resulting break looks like nice and "sparkely" -- which to me, means you had a good heat treat through all the way. If you say different grain structure via light refracting differently across the face of the break, you might be concerned.
 
Naw, its sparklely Bossman. I used the hammer to snap another piece which was not easy either, and it too was clean with very fine grain. I have heard claims of being able to bend an air hardening steel 90* and back but I have not seen it nor experienced it. None of the knives have yet failed and all have the same blue look to them after HT and cut almost equally. I think the discrepancies are more geometry and edge thickness than the HT.

I still dont know about the shiny specks after etching. I think that more than anything had me wondering if I have done something wrong. I did not normalize the blade but did not forge this one either, however I do normalize the 01. I guess the reason I did not is I dont really have a definitive answer on the temp and soak as there are several listed. Jerry Hossman posted that he and Paul Boss proved their heat treating numbers produced a tougher steel for knives than did the Crucible data. He said that Crucible met them halfway. This also led to Jerry agreeing to a 600* temper over the 950* and having Paul do it this way.

Another concern I have only because its been mentioned to me is heating my oven up to 1950 for 30 min and tempering at 950* for x3 2 hour tempers is the stressing of the oven. I have one of the very last sugar creek 24" ovens that they sold through Tracy and I like it very much after I added the PID controller. Is stressing the oven like this an issue?
 
all coils in an oven will wear out, we have replacement coils now so you should be good on your oven. They were designed to go to 2300F so you are good.
 
The ledge on the break is probably due to the edge of your vise jaws cutting into the side of the blade during the flex. When i do a blade break, i use either hardwood blocks between the blade and the jaws or a set of angle iron holders that i made with the corners well rounded, and use a torque wrench on the tang so i know how much force is required to flex the blade. If you just log in your notes tough or easy, you dont know if you had a hard workout the day before or if you were fresh and feelin really strong that morning. With the torque wrench you get a number.

The spots on the etched blade look like contamination either in the etcheant or on the blade prior to etching. You can sand the blade back down, and without touching it put it in the etch for 1 minute, pull it out and if any spots are there, rub then with a cotton pad with etchant on it till they start to darken and then go back to etching and see if it comes out the same as before
 
I etched the 3v to aid in its corrosion resistance. It was suggested by Jerry Hossom to do so. Since I jade the pieces after breaking the blade I placed them in FC for differnt length of time to see what I liked. The 3v will get little specks of orange or red rust on the surface but under that speck it will pit out.
 
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