heat treating 9260

farmrbrnboy

Active Member
I picked up some 1/4"x1" 9260 steel and forged a semi-skinner. I was told to heat treat it the same as 5160. The pyrometer read around 1525 in the rear of the forge, but since the blower is located in the center and somewhat tangent to the tubular forge, it is hotter in the middle than the rear. I brought the blade to non-magnetic and let is soak for around 10 minutes, then quenched in 130 deg canola oil, moving the blade back and forth for a count of 7, then dopped the blade in the quenchant. Around 20 minutes latter, I took the blade out, cleaned the oil and tempered in the oven at 350 for 2 hours x 3. After tempering, I ground down the edge to sharp and tested it....deformed on a 1/4" brass rod. Could I have decarburized the edge because my forge was hotter in the middle than the rear? Is so, should I grind the edge down until I get to martensite? What else could it be?
 
Some of the hammer slingers may correct me but if you went straight from forging to hardening and tempering thats your problem. You need to normalize the steel between forging and hardening to refine the grain and make it smaller. I'm not sure about normalizing temps for 9260 but I'm guessing the first heat should be some where around 1600, the 2nd around 1550 and the 3rd around 1500. Bring the steel to these temps and soak for a few minutes and then air cool to black between heats. i hope this helps.
 
The temp and temper sound right but the 10 minute soak is suspect to me. You may have over heated it. Before I had the kiln, I'd go to non magnetic plus a 10-15 count and then dunk it. This seems to always have worked over the years. I'd heat it up again, normalize 3 times and give it a dunking before grinding on it and winding up with a completely different blade design.

Darrin is right on and beat me to it. (One finger typing slowly)

Rudy
 
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9260 is a hypoeutectic steel and the carbon in it will go into solution rather quickly so there is no reason to soak the blade longer than is necessary to heat all the way through. The pre-hardening temperature for wasn't bad for that alloy; you could have even gone a little hotter and you probably did. What I suspect is that you have some real grain growth in that blade.

The normalization temperatures that Darrin mentioned sounds good and you will need to re-normalize that blade to correct for grain growth, however, again, I would not let it soak any longer than to heat evenly all the way through. With normalization you are not concerned with getting carbon into solution as you are with hardening. All you need to do is trigger a phase change.

As to why the blade didn't harden I'm at a bit of a loss. It is a bit shallow hardening but nothing that you mentioned should have prevented it from forming martensite. The tempering temperature was a little low but not by much. I generally temper 9260 at 375° for three 2 hour cycles. My best guess on that is that you let it cool a bit too much in the forge trying not to overheat it as you soaked it and it wasn't as hot as you thought it was when you put it in the quenchant. It's an easy thing to do using a forge.

Go ahead and repeat the normalization as Darrin suggested to correct for any grain growth. Repeat the austinization for hardening with the forge running just a tad higher, maybe as hot as 1600° and keep the blade moving around to distribute the heat as evenly as possible and give it a soak after it has gone non-magnetic plus a little more and try to hold it at that color for only about a minute or two then quench. You could repeat the tempering at 350° if you want a harder blade. Of course you can always take it up by another 25° if that seems a little hard without having to re-harden it.

Doug
 
Some of the hammer slingers may correct me but if you went straight from forging to hardening and tempering thats your problem. You need to normalize the steel between forging and hardening to refine the grain and make it smaller. I'm not sure about normalizing temps for 9260 but I'm guessing the first heat should be some where around 1600, the 2nd around 1550 and the 3rd around 1500. Bring the steel to these temps and soak for a few minutes and then air cool to black between heats. i hope this helps.

I normalized 3 times prior to HT. I don't know about the exact temps. A HT oven may be next in order :) Thanks to all for the great input!!!
 
The hardening temperature of 9260 is higher than 5160. The stuff I found show up to 1650 F for hardening. Hypoeutectoid steels typically have higher hardening temperatures, and the high silicon content pushes it up more.
 
9260 is indeed a hypoeutectoid steel. Doug got bit by the spell checker bug that hates the “oid” because it only recognizes “eutectic” which is an entirely different thing, I have to retype the “oid” every time I write in MS Word. But being a hypoeutectoid it would not be my first choice for a skinner of any kind, but this is your knife and you get to choose the steel so let’s work with it.

9260 is more like a Mn rich 1060 with silicon added for toughness rather than resembling 5160 very much. It has around a full second to beat the pearlite nose, but then 5160 has around 5 seconds, so while I don’t think the problem is necessarily in your quench, it cannot be completely ruled out. I think I would look more at your heat. The specs for this steel recommend 1600F, and if this were a hypereutectoid I would say that we could adjust that down, but hypoeutectoid steels tend to need that extra heat to fully involve the extra iron (ferrite) in solution. Soak time is also helpful in doing this. So while you may be able to limit soak time or your temperature, you wouldn't wan to shortchange both. Although I think you could reduce the time a bit from 20 minutes. If you were making a camp knife this is not as problematic, but for a skinner you will need every last bit of maximum hardness you can squeeze out of this steel to maintain a fine edge.

I would also point to decarb except that a larger cross section of the blade deformed than should be accounted for in the .003-.005” that would be affected by normal carbon loss.

After forging get it hot (1650F) and let it air cool to normalize. Cycle it if you really want to but I wouldn’t go much lower than 1500F for this alloy. On your next hardening go more for 1550F for a little bit of a hold and then quench. Also be aware that this steel will only see a 58-63HRC maximum after the quench and tempering will soften it even more so be careful not to overdraw it.
 
The IT diagram that I have for 9260 lists that the steel was austinized at 1600° prior to hardening. It does not say why that temperature was chosen. With grain growth being a big concern, most recommend that the hardening temperature not be higher than what is needed to get the carbon into solution in the alloy. I think that it's pretty common to find the austinization temperatures for hardening recommended by knife makers is lower than what is often seen in these data sheets. Maybe it's overkill but we just seem to like a lower temperature to harden.

Doug
 
Ok, you got me there, Kevin. What's the difference between hypoeutectic and hypoeutectoid? Just one OCD technoweenie to another.:alien:
 
Not kevin, but hopefully my answer will do. Eutectic starts as a liquid and goes to a lamellar pearlite like structure while eutectoid starts as a solid (austenite) and goes to a lamellar structure, like pearlite.
 
I wish I read this before going to the shop. After normalizing x 3, I heat treated at 1525 deg. I tested a file on it and it bits into it. I was actually able to file on it fairly easily. Guess I'll try the forge at 1600 deg. BTW, I was looking for some 5160 for my hunting knife and all the shop had was 9260 in 1/4"x1".
 
That's a change, usually it's hard to find the 9260. Both the New Jersey Steel Baron, aka Aldo Bruno, and Admiral steel carry 5160. You can get a shorter length from Aldo. I think that Admiral sells it in 22 ft lengths. I had good luck tempering 9260 at 375°. You don't have to move much carbon out of the iron matrix to get it down to a usable hardness level. Something like 1080 or 1084 will give you a harder and more wear resistant blade and might, as Kevin suggested, be a better steel for a skinner. You could go to something like 1095 or the W series, with a higher carbon content, but then you are getting into the realm where you have to do a controlled soak at temperature to avoid forming excess retained austinite.

Doug
 
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