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CruForge V crumbling!


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Hello everyone,

 

I went over to kevin_k's place today and we did some forging--he had a big bar of round CruForge V that he wanted to break down into blade stock, so we stuck it in the forge and manned the sledgehammers. Well, for some odd reason as we were forging (not sparking, but at a yellow heat because MAN is that stuff hard to get moving under a hammer!) the bar just started to crumble once we had it down to about 1/2" thick. The crystals in the broken off pieces are quite a bit larger than the ones in the section that didn't get crumbly, but I was under the impression that the grain should be fine just by the nature of that steel. Kevin thinks the steel is red short--is that the case? Neither of us could think of any other reason for steel to crack and break apart when it is plenty hot. I'll post up a couple pictures when my fiancee gets off the other computer. Thanks!

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I seriously doubt it is really red short, as it was made by Crucible. Too hot for too long equals BIG grain, and with the carbon as high as it is in that material, there will be an inergranular network of carbide particles under the right (wrong for what you want) conditions.

 

The vanadium in the steel will help promote fine grain, but it cannot prevent grain growth if you get over the Acm temp., which you did, or this could not have happened. The grain will grow very rapidly if you dissolve all of the carbide into the austenite. I do not know at precisely what temp that happens with that steel, but it is going to be pretty high with the C, Mn and V at the levels they are. Likely 980C (1800F) or higher.

 

How big a bar are you breaking down ?

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I seriously doubt it is really red short, as it was made by Crucible. Too hot for too long equals BIG grain, and with the carbon as high as it is in that material, there will be an inergranular network of carbide particles under the right (wrong for what you want) conditions.

 

The vanadium in the steel will help promote fine grain, but it cannot prevent grain growth if you get over the Acm temp., which you did, or this could not have happened. The grain will grow very rapidly if you dissolve all of the carbide into the austenite. I do not know at precisely what temp that happens with that steel, but it is going to be pretty high with the C, Mn and V at the levels they are. Likely 980C (1800F) or higher.

 

How big a bar are you breaking down ?

 

We were breaking down a bar that was (I believe) 1-1/4" thick, round, so we let it soak in the heat to make sure it was hot all the way through, and it was yellow when we worked it. The stuff cooled off pretty fast, though, it seemed.

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Looks to have been wildly overheated. :( How's the lighting situation at your forge? It may have been hotter than it looked. That's the kind of garbage I get when I overheat file steel in tomahawk bits, and that's just running at welding heat which for files is in the yellow range.

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I sooooo wish I had a power hammer! Noah was kind enough to come over and give me a hand with breaking down some of the bar(ha ha) but I must say I'm still not used to the new forge. New steel and a new forge, oh well it was fun and a learning experience! Next time I'll have to try not to get so WILD :lol:

 

Kevin

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  • 1 month later...

I'm not familiar with the steel, but my guess is that there are two options:

 

1) it has a very high carbon content similar to wootz... 1.4 to 1.8% carbon by weight

 

2) it has a high alloy content similar to the D series

 

In option #1, the high temp and soak would put ALL of the carbon in solution (it would have started as a carbide of some kind to provide crazy wear-resistance) and this would lower the allowable forging temp. The large grain structure seems to support this concept, since most high alloy steels take a very long time to grow large grains. Was the bar ever dropping below critical during this forging, or were you pretty much just putting it back in the fire as soon as it dropped below yellow? If it was never dropping below critical, then even your sledge hammering was probably having little to no effect on the grain structure, and your soak time was effectively as long as the time you were forging.

 

In option #2, you might actually have failed to let it soak long enough. the high-alloy steels take a very long time to realize they are hot (this is why high speed steels take so long to soften in use), so it is possible that what you were doing was similar to forging 1095 with sledges at a black heat. If you can post the alloy contents that would certainly help with diagnosing the problem and coming up with a solution.

 

In a steel that is truly "hot short", the crumbling is caused by excessive sulfur, which combines with elements in the steel to create sulfides. The sulfides melt at a relatively low temp and essentially lubricate the steel from the inside. Hot short steels would not have lasted through even a single heat of your forging, but instead would have started coming apart under the hammer right away. In this case, I am guessing that you started getting micr-cracks early in the process, and these developed over time until they finally became visible to the eye. I have had the same experience with wootz ingots that I either mis-forged or had gotten the initial mix wrong... hours of forging and the bar just comes apart in the late stages of bar creating!

 

Peter

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The only time I have seen steel look like that is when it has been oxidized to hell .What is your forge environ like ?I have seen this problem when I had a forge blower slide that would open up as I worked the power hammer.

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Hello,

Peter, I think Cru forge V is 1%C.

I'll go with Owen, looks overheated and held at that temp for a long time too.

Maybe the burner's flame is directly on the steel?

 

Antoine

 

I guess I missed the part where I said it wasn't the result of either too much heat or too long at temp or both. However, I don't agree that this is the result of over-oxidation, because if he had "burned" the steel so badly that it broke during forging, then there is no way that they could have missed the shower of sparks coming out of the forge. Most steels that are ruined by over-temp or over-soak are having issues with massive grain growth and/or the development of a compound that has a lower melting temp. We are seeing so much oxidation on the broken end because it broke while at a yellow heat and therefore developed a lot of scale on the broken ends. It is also likely that the crack had been developing for some time and finally let go.

 

To my knowledge oxygen is not able to penetrate the steel to any great degree unless a portion of the material has become molten. In the solid state iron and steel oxidize and carburize from the outside in, and both processes take a huge amount of time. Also, I think there would be a visible transition indicating the leading edge of the oxidation and I don't see any evidence ofthis in the pictures. I think we have all gotten a piece of steel WAY too hot or forgotten it in the forge for a while, but unless it is a steel that has problems with heat (as I discussed in my original post), it should be just fine once the thick layer of scale is taken off. If it is a steel that has problems with heat (I've seen O1 do similar things if worked too hot), then it should still be fine if it is allowed to cool before forging, since it is the forging of the material combined with the elevated temp that causes the steel to fail.

 

I think they were just working it too hot and it finally caught up with them. In all hypereutectoid steels temperature is more of an issue than with the eutectoid and hypoeutectoid steels, and the further you get above the eutectoid the more finicky the steel gets. Since carbon content is never perfectly even throughout on a microscopic level (even from Crucible-made steels), the melting temp of some parts of the mixture will be much lower than the melting point of the whole. My guess is that the excessive heat and soak time allowed a molten component to develop, and this "wetted" the grains and made it hot short even though there is not enough sulfur present for standard hot shortness.

 

Peter

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I use the steel all the time, and I love it. Greater wear resistance by a considerable margin than most forging steels with no significant reduction in toughness. Not sure it's what I'd plan to use for swords, but works great for anything smaller, with WAY better edge holding than any of the simple steels.

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I also took a few minutes to look it up and had the immediate reaction that it seems like the same concept as W2... lots of carbon and a nice carbide-former to soak up a bunch of it. I was surprised that the forging specs specifically say "don't forge below 1600", since below 1600 is where the real carbide formation is going to happen. Above that point you are just re-dissolving your carbides all the time. I guess perhaps when they refer to "forging" they are talking about heavy forging rather than finish forging. For me, I like the lower temp forging for cleaning up the details and as a good opportunity to thermal-cycle the blade to refine the grain and develop my carbides. The thermal cycling would be particularly necessary if using this steel for a sword, since you would want to get as much carbon tied up in carbides as possible. A careful, low-end austenization to avoid dissolving those carbides should yield a relatively good and tough sword. I gotta say, though, that when I am looking for a tough sword steel I would go for L6 over most other steels in a heartbeat. Just a personal favorite, I suppose.

 

Peter

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The following images are tests which were performed by Crucible's metallurgists on a test blade which was forged and heat treated by Dan Farr. The blade was heat treated using a propane forge, and the spine temper was drawn back using an oxy/acetylene torch. The vanadium content was chosen to increase wear resistance and also pin the grain boundaries during proper forging practices.

 

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Edited by Matt Gregory
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That's essentially what it is. W-2 with more V and lots more Mn to make it harden in thicker pieces with a less radical quench.

 

Nice structure in those photomicrographs. Some of the carbides are bigger than I would have thought.

Edited by Howard Clark
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Thank's for the feedback and the pictures Matt!

 

I'm glad you jumped in Howard, you are the second person that told me about the cru forge/W2 thing...

What I find funny is that I posted a question over a european forum on Cru Forge just to see if the had an equivalent and some feedbacks on it.

Well this super new steel is very close in specs to one that has been around for years in europe! It is classified as a ball bearing steel over there.

A good steel but I guess I want to share my frustration in seeing europe filled with a amazing variety of steel; from the simplest of the simple to the most complex space age powdered super steels... :)

 

Antoine

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