ZF7B Annealing

H

HT_Super

New Member
We currently launched a new program in our shop that is hot forged with Gerdau ZF7B steel. We are having a real hard time getting the furnace (Surface Combustion Cast Belt) to run with an efficient temperature program. Currently we are running @ 1742° in front section, 1500° in the middle section, 1050° in the back section, all 3 zones have bottom burners with the same settings as well. The belt speed is @ 2.2 "/min, and loading with an electronic loader @ 1000 lbs/hr.

We have tried raising the temps in Zone 2 (Middle Section) to 1600°, however we lose our ability to control the cooling curve in Zone 3 and have had some spotty high harndess. Zone 2 and Zone 3 both have a control cool sytem built in. We only run the control cool in Zone 3, with the burner not hitting high fire under 1400° we must shut the gas off on Zone 3, so the control cool still allows us to manage the temp.

To my question...

Has anyone had any experience with heat treating this steel? We have had a metallurgist from an outside vendor give us some advice on how to process. They have suggested we ran as follows.

Z1 - 1742°
Z2 - 1600° Cooling On
Z3 - 1050° Cooling On
Belt Speed - 3.2"/min
Load Rate - 2000 lbs/hr

We are very concerned that we may not be able to hold the required tolerance in Zone 3 and lose our cooling curve and end up with parts with high hardness again. Upping the belt speed is going to drop the pre-heat temp down drastically, however it should in theory push the temps up in Zone 2, and most likely Zone 3 as well even with the cooling system on.

Any advice would be appreciated, i have been working with Heat Treat for 9 years now and have never struggled with any other steel the way we are with this mess.

Thanks in advance.
 
Based on what I know, that particular alloy is the same as AISI 5120. I'm assuming that you attempting to build blades/knives? If so, that particular steel simply is NOT suited to the purpose.

It's makeup is:

Carbon: 0.18, Si: max .040, Mn: 1.15, Cr: 1.15

The carbon content is too low for that alloy to harden to any usable level for blades/knives. "Heat Treating" that particular alloy for any type of hardness level is pretty much useless. With the levels of Cr and Mn, it would be very "red hard", but finished/treated hardness is going to be very low.

It might help if you stated the end product you're producing, and the characteristics desired in that end product.
 
Thank you for the reply. The program we are launching is a new program for 2", 4", 6", & 8" serated blades from a large US Hunting & Fishing Manufacturer. These parts are required to be between 79-86 HRB (Rockwell B), so no the heat treated hardness is not "low". I guess the question was really, has anyone else had experience running this steel and capable of "clean" microstructures? We are seeing a lot of grain growth (Baenite). As well as, the ability to produce at an effiecient rate? Other temp recipes on this furnace are pushing 2500 lbs/hr.

Thanks
 
Please provide us with the chemical composition of "ZF7B" steel. I cannot find it anywhere on the web, myself, much less a cross reference. We need to know chemical composition to be able to tell you anything.
 
Hey Stu.... Here's what I found on the steel..... confirms it is AISI 5120: http://www.oyalmetal.com/tablolar/359-zf7b.html

Unless I'm totally missing something, I can't imagine why anyone would attempt to make a functional blade from it. I also don't understand why the specs would call for a HRB of 79-86....... that equals BELOW dead soft on the Rc scale. ????? (am I missing something here?)

"has anyone else had experience running this steel and capable of "clean" microstructures? We are seeing a lot of grain growth (Baenite)."

With this particular steel, I can't see how you would achieve anything other than Banite.... It's makeup simply is not designed to do anything else.... and to do it at the rate that was mentioned..... I can't fathom how that would be achievable.

I'm gona go out on a limb here and say....... either there's some misinformation/miscommunication, or some total misunderstanding about the material/steel going on. ?????? UNLESS, these items/blades are just "trinkets" or "giveaways" perhaps ????

The chosen material for the intended use is just not making any sense to me.
 
Well, its out of my league to begin with but swung by before the first responce, since then it has been strangely silent! However something about it struck me as strange to begin with!!!!!

From the time I read the post before Ed even posted my mind said, "this is some kind of fishing expedition..... SPAM" who knows but if you are that into the thick of things you should basically have your own answers or least know enough knowledge to go to the manufacturer!! Just MHO!
 
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Good catch, Ed. I couldn't even find that reference myself.

HT_Super......2 things, just to support what Ed said earlier. 1. There is not enough carbon in that steel to harden it to any degree of what a knife should be. You would want at LEAST .4% carbon, preferably .7% - 1.5%. .18% carbon is like what is in structural steel, like A36/1018. You would never use it in a knife application. Not even serrated. 2. 86 on the Rockwell B scale is identical to 5 (yes.....that's FIVE) on the Rockwell C scale. Not sure who/where/what you're getting your info from.....but I wouldn't pay any attention to them. Fully annealed cutlery steel comes in at around 22 on the Rockwell C scale. 5? Seriously?
 
Trust me, i don't know much about this steel either...Every other program we've ever produced was either 420/420 HC or 440A/440C. My job is to burn them up, not design them.

However, we are indeed having luck with our new recipe change, although we had to have the steel mill put a tighter tolerance on the DI value. When discussing with them the application the steel was being used in, they couldn't believe it either. This steel is used alost exclusively in the manufacturing of transmission gears...We have suggested they look at changing material, but sounds like this was cheaper steel. Go figure!

As far as whether or not they are trinkets...no, it doesn't sound like it. According to our purchasing team this program is supposedly on contract for just over 8 million blades (each size) over the next 3 years.

Thanks for the constructive criticism...
 
samuraistuart said:
Good catch, Ed. I couldn't even find that reference myself.

HT_Super......2 things, just to support what Ed said earlier. 1. There is not enough carbon in that steel to harden it to any degree of what a knife should be. You would want at LEAST .4% carbon, preferably .7% - 1.5%. .18% carbon is like what is in structural steel, like A36/1018. You would never use it in a knife application. Not even serrated. 2. 86 on the Rockwell B scale is identical to 5 (yes.....that's FIVE) on the Rockwell C scale. Not sure who/where/what you're getting your info from.....but I wouldn't pay any attention to them. Fully annealed cutlery steel comes in at around 22 on the Rockwell C scale. 5? Seriously?
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sure. If the knife manufacter whose name starts with Cut and sells door to door can sell blades make of 410 and say they are made from the finest cutlery steel, why not. most of these knives will end up in tackle boxes or tool drawers and never get used. folks who use knives alot will just shake their heads, say "ripped off again", and not buy again from that provider.
 
Matthew Gregory said:
Scott, no argument on the quality side of this discussion, but I'm pretty sure Cutco uses 440a.
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they seem to use a little of everything. was sharpening a knife for a client and could never get a good edge. went to cutco website and this model knife used 410. they also had blades of 420. we all need to look and research before we buy.
 
More evidence that we live in the age of "Spec Manufacturing". Basically putting the cart before the horse... Rather then specify a material and work within it's boundaries, they specify what an item must do, then specify that it be made out of the cheapest material available (doesn't matter whether the material is suited to the item or not). This has been going on for about 20 years now.... it's the reason we can't count on recycled material being anything specific.... nobody specifies a particular steel type anymore.....it's always "Whatever the cheapest is that will meet the MINIMUM specifications. In this case it appears to have been taken to the extreme.
 
Matthew Gregory said:
Well, if the pros are using stuff like this, I think I'll lover my standards. Switching over to 12L14. No more time wasted hardening, or even rough grinding. Do it all with 120 grit followed by black compound on a buff. Such fools we've been, when all this time industry has had it all figured out...


o_O
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LOL!! A little lead never hurt nobody...unless it came out the end of a barrel...
 
Just wanted to revisit this thread after learning about how one particular knife maker is apparently making their blades. They are using A36/1018 steel for their knives. Yep. For real. However, they are carburizing the exterior layer (or maybe just the edge?), to allow for some edge holding. Still, about one of the worst ways I can think of to go about it.
 
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