Michael, I have a bowie I am finishing up that is made from CruForge. I fully quenched the blade in Parks 50 and then heated the spine to a straw color with an oxy acetylene torch. The blade ended up about 53rc which is not bad for a big chopper. I have not tried a differential heat treat on a CruForge blade because I am out of CruForge. I went back to 5160 and 1084 when the company was sold.

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I have a 1" shaft of Cruforge V and have used it for just a few forged knives. As I made those knives I followed the guidelines set out by the manufacturer for proper forging and subsequent heat treating. After the hardening process I was not sure I had a hard knife. The knives performed well when finished but a file did not skid over the steel after hardening as it usually does when I have hardened other metals such as 52100, 5160, etc. I am looking for someone else that has forged Cruforge V and would like to know if they have had the same results as I and if different methods of heat treating are necessary to handle this steel properly. I am specifically interested in quench oil type, hardening method (mine is an edge quench in mobile medium quench oil at 125 to 150 degrees), number of hardenings, and number of temperings and temperature used. Any help would be greatly appreciated.

Michael, do you have any details on the heat treat you performed? You say a shaft of Cruforge, do you mean round stock, or an actual shaft off from equipment? If it is a shaft the chances are that you do not have Cruforge. Due to its chemistry the chances are very good that your problem is not in the oil you are using but in the heating. Cruforge is a deeper hardening steel that would make edge quenching kind of pointless, it is also rather picky about its higher end austenitizing temps due to its penchant for heavy carbides. Everybody has their own tastes and likes for a knife and so I try to carefully label things that are my preferences so in my shop a 53HRC for any blade would send it back to the salt pot for another hardening attempt, Cruforge should be capable of a nice 62HRC with the carbides doing most of the work in keeping the cut going. After a few years of studying optimum edge strengths 57HRC would be about as low as I personally would go for any knife.

Cruforge was pitched as a steel made specifically for bladesmiths but I have been very skeptical of that from the earliest stages of the project since bladesmiths have an affinity for very simple and straighforward heat treating, often done in a forge, and this steel needs a little more than this to live up to its billing. Many problems have been encountered by treating it like 1084 or 5160. You want an accurate soak in the 1500F - 1550F range and you may want to give it some time since a presoak is often specifically indicated. After this any oil should be more than capable of hardening the stuff.

I agree that 53rc is too low for a servicable blade. An axe maybe, since the geometry is more supportive.

Kevin said:

Cruforge is a deeper hardening steel that would make edge quenching kind of pointless, it is also rather picky about its higher end austenitizing temps due to its penchant for heavy carbides

Kevin, what type of quecnch would you suggest for this steel? And please offer comparisons so I might be a little bit more prepared when I use it. Thanks ahead of time. Lin

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I agree that 53rc is too low for a servicable blade. An axe maybe, since the geometry is more supportive.

Kevin said:

Kevin, what type of quecnch would you suggest for this steel? And please offer comparisons so I might be a little bit more prepared when I use it. Thanks ahead of time. Lin

Lin, I am mostly using the chemistry to draw from, due to my aforementioned concerns about what did indeed come to pass I backed away a bit from the Cruforge project shortly after getting one of the first prototype samples, so my experience with the final formulation is limited. Any medium speed oil good for O-1, L6 or 5160 should work, Parks AAA, Brownell's, McMaster Carr etc. Even some improvised substitutes may work, while the really fast oils like #50 would not be necessary.

I am glad I saw this again. This is why I love this forum. Thanks Kevin and Lin for the response and please correct me if I am wrong. I still have time to normalize the blade and quench it again and work toward 60 rc. Kevin, Lin, can you give me your high and low rc for a bowie and would you increase the rc on smaller blades? I have been making my smaller blades at least 60 rc but thought I should make the large bowie blades around 50 to 55 rc.

Thanks Lin, Dennis and Kevin for responding. The steel I have is round bar stock and is Cruforge V. That may be the only thing I am sure of! When I get to my shop today I am going to look back at notes I took when forgeing and so forth and see if I can get more specifics. I did talk to one other knifemaker that did a full quench and then a soft back draw. I do have a progamable kiln to work with so that should help me in this situation. I will check my notes and post back later.

Michael,

I got curious about the thread and the CruForge V. I was wondering if you had been able to make the time to look at your notes.

Mike

Dennis,

I dont vary the rockwell that much. I will try to have my big knives that will see chopping end up in the neighborhood of 58-59 and the smaller knives that will never see chopping to about 60-61.

I do want to stress that I pay close attention to edge geometry on every blade. As with rc, I consider the use of the knife and tailor it accordingly. The geometry has to support and work with the hardness level. Lin

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...I do want to stress that I pay close attention to edge geometry on every blade. As with rc, I consider the use of the knife and tailor it accordingly. The geometry has to support and work with the hardness level. Lin

As my friend Roman Landes is fond of saying- Geometry cuts, heat treat only determines how long.

Thank you Kevin. I will remember that quote.

I will look today and post tonight. Sorry life gets busy! I will looks at temps, etc. and some e mail replies that I have had and see if we can shed some light on this.

In review of my process followed to heat treat cru forge v I attempted to follow the cricteria outlined in the blade magazine from December 2009 page 43. In that article is a copy of what happens to be the companies recommendations for forging and heat treating. Forging was to be 1700 to 2000 degrees. Nothing below that. Annealing at 1450 long enough to make sure uniform heat and slow cooled. I used a programable kiln for this process and for hardening. Hardening was to be done at 1200 to 1250 degrees held for 10 minutes and then raised to 1500 to 1550 degrees. Here is where I am thinking my process was wrong. I diferentially hardened my blades, cooling the bottom 1/3 of the blade in 140 degree oil. I then tempered the blade double heating to 350 degees. I believe after some discussions that I have had that I will need to do a full quench and then if I want I will have to soft draw the spine with an acetelyn torch. I would like some feed back on the methods I have used and the conclusions I have drawn. Ultimately nothing short of me doing it the way I have described will prove my theory! But feedback is always helpful and maybe I have helped someone else who is up against the same challenge. If I full quench and soft draw is the soft draw done after hardening or after tempering? That sounds like a dumb question but like they always say, if you don't know the answer it's never a dumb question!

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I believe after some discussions that I have had that I will need to do a full quench and then if I want I will have to soft draw the spine with an acetelyn torch. If I full quench and soft draw is the soft draw done after hardening or after tempering? That sounds like a dumb question but like they always say, if you don't know the answer it's never a dumb question!

Differential tempering is done after tempering the entire blade... edge area is tempered to desired hardness, then spine area re-tempered to a lower hardness.(typically looking for spring-temper range).

Some folks differentially temper with just a small tip set with a very soft, neutral to reducing flame. Done slowly and carefully, heating as evenly as possible, the process is repeated three times (sometimes more). The blade is re-sanded to remove tempering colors before and between each tempering cycle with the torch.

Some folks run the blade edge in water in a shallow pan. The water keeps the edge from exceeding the boiling temperature of water, so from the surface of the water to the spine there is a 200-212F to spine-temp gradient... not a perfectly even gradient, though. I've been told 1/4" of water is enough, and rocking the edge to keep the section nearest the torch flame submerged may be necessary. The torch work here would be the same as without water... slow, and as even as possible.

The "slow, and even" part is about realities of tempering. Industry often tempers 2x's for two hours each. Though temperature is the primary driver of ending HRc, it does take a while for carbon atoms to move out of martensite crystals and for the entire piece to be entirely the same. Heating the spine three or more times helps the evenness of temper. A sanded-clean blade lets a person see how the heat is moving in the metal, which is evenness and temperature gaging from oxidizing colors on the blades surface.

I've heard/read discussion on whether differential tempering has useful applications... there are differing views, for sure. Right now I think, if I was going to make a knife blade (not sword, or machete, or ax) that would see hard whacking, I'd use a steel specifically designed to be extremely tough (L6, 6150, 5160), fully harden and temper to 57-58 HRc. I know that blade would be stronger than the same blade with the same edge hardness and a differentially tempered spine, but that's all I know for sure about the differences.

Mike