S7 Bowie

jhiggins

jhiggins

Joined
Jul 11, 2003
Messages
3,258
Hey Buds,

A friend just handed me a whopping-huge piece of 1/4" S-7 precision-ground. Its definitely bowie-sized. Anyone here had any experience with it? I know its an air-cooled steel, and from what I know it can get 60RC with no problems. Roger? Mete? Looking for some words of encouragement here. Its a dandy piece of steel, heheh. :p
 
S7 was popular in the 80's for awhile, but died out for some reason. I would guess lack of choice in popular sizes, but could be wrong.


I have no experience working with, or using the stuff though.:confused:
 
Higgy, The S-5 has .60 carbon, believe the S-7 has less. I still think it would make a dandy bowie.......

Mike, I just noticed your post, we must have been on at the sametime. I wonder if its the cost for the steel. Seems like the S serries is pretty spendy stuff.
 
Well according to the HT info I have S-7 needs to preheat 1200-1300 degrees, then 1725 for a 1-hour soak, then air quench in still air. Left alone, it'll be 59-60RC, a 400 degree temper will drag it down around 58RC, which may not be a bad place to wind up - especially for a big blade. Thoughts?

Oh and btw, looks like you are correct, Ray. S-7 is about .45-.50 on the carbon content.
 
According to the Crucible data sheet on S7, the only way you can get HRC 60 is as quenched.

http://www.crucibleservice.com/datash/dsS7v6.pdf

In practicality, you will probably end up in the mid 50s. A high impact steel used for things like jackhammer bits and as a matrix for carbide inserts in drill bits, S7 is for toughness and durability under high impacts. Great for choppers, but not for cutting edge holding.
 
jhiggins said:
...................

Oh and btw, looks like you are correct, Ray. S-7 is about .45-.50 on the carbon content.
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If memory serves correctly, that's about the carbon content of most Japanese Katana's, etc., of years gone by.

I think you should definitely do the tempering step.
 
I had Roger heat treat a 1/4 thick bowie of S7 for me. Even with a oil quench it only came out at 57 RC. It may be only 57 RC but it is very, very tough. I mean nail cutting, mild steel bar cutting tough. Takes a nice polish also. Maybe Roger will see this and tell what he did or drop him a line.
 
My data shows 1725F, air cooled ,tempered 400-800F will give you 53-58 Rc.In that hardness range it is very tough. The S steels are more likely to have decarburization so take precautions for that.You could do bainite but it's very tough as is.
 
At 57RC it come in at 125 ft-lbs Charpy C-Notch test. Which may not translate 100% in to knife toughness but it is a much higher score then I have been able to find for most other steels. A2, for example, has a high of about 41 ft-lbs but it can get that at 60RC. 3V comes close and can take a higher hardness but you would have a hard time making a shiny pretty 3V bowie ;). Just my 2 cents so forgive me.
 
I like Mike Fitzo's idea. Bainite may be the way to go. Can anyone think of a recipe for that right off? I was actually entertaining the idea of quenching it between two aluminum plates also. I'm wondering if that would set me up with about 57-58RC right off, and no need for the quench?

Mark, did Roger edge-quench that blade? I was actually thinking that low-carbon, and air-quenching steel may not show any transition-lines. Besides, I may carve this blade, not sure yet. Filework at the very least if no decent themes pop into my head.
 
mete, does that mean, then, that some steel is tough enough with tempered martensite there'd be little to gain for toughness by going to bainite?? Can you give me any other steel examples that would be in that same category, then?? Just adding data into the old thinktank!

Thanks, Robert!!
 
jhiggins said:
I like Mike Fitzo's idea. Bainite may be the way to go. Can anyone think of a recipe for that right off? I was actually entertaining the idea of quenching it between two aluminum plates also. I'm wondering if that would set me up with about 57-58RC right off, and no need for the quench?

Mark, did Roger edge-quench that blade? I was actually thinking that low-carbon, and air-quenching steel may not show any transition-lines. Besides, I may carve this blade, not sure yet. Filework at the very least if no decent themes pop into my head.
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No it was not a edge-quench. Looking at its make up I would be suprised if you could get any transition lines but that it without trying mind you so who knows and given its toughness I am not sure that you would have alot of advantages from it other then looks. Which I know is important, but I am just throwing that out there. I do know that Roger air quenched the blade (not sure if he used plates) and only got 54 or 55 RC (I know it was somewhere around that) and went to a oil quench and ended up with a 57 Rc, which is about what I wanted anyway. This was a thick convex grind so there was a lot of steel to try and cool quickly.
 
mete said:
My data shows 1725F, air cooled ,tempered 400-800F will give you 53-58 Rc.In that hardness range it is very tough. The S steels are more likely to have decarburization so take precautions for that.You could do bainite but it's very tough as is.
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What length of tempering time, Mete? One hour? Two? I know that of the so-called tool steels, S7 is not as wear-resistant as others, but is definitely very tough. Understandibly I wish to keep as much hardness as possible without compromising toughness. For the record, this will probably be a fancy knfe and will never be a "user" anyway. Still, when I make a knife I like to feel that its a REAL knife, not just a bauble to oooh an aaah over.
 
Jeff, I've been looking for a TTT online for S-7 for about an hour and can't find it. Sorry. I did find this one table for tempering:

http://www.artmetal.com/project/TOC/proces/S7tech.html

My feeble mind is thinking for bainite: very brief elevated temp oil quench to try and get it under whatever the nose of the curve is going to be, then toss it in a furnace at 550F for like 16 hours.

The "nose" has to give you a bit more time than a C10xx series, so you should be able to get it under 800F with just a brief dunk then get it right into a furnace.

Mind you, now, that is conjecture without any real data to back it up.

Could be a lot of PITA for something not worth it, after what Robert said about it being pretty tough anyway.
 
fitzo said:
Jeff, I've been looking for a TTT online for S-7 for about an hour and can't find it. Sorry. I did find this one table for tempering:

http://www.artmetal.com/project/TOC/proces/S7tech.html

My feeble mind is thinking for bainite: very brief elevated temp oil quench to try and get it under whatever the nose of the curve is going to be, then toss it in a furnace at 550F for like 16 hours.

The "nose" has to give you a bit more time than a C10xx series, so you should be able to get it under 800F with just a brief dunk then get it right into a furnace.

Mind you, now, that is conjecture without any real data to back it up.

Could be a lot of PITA for something not worth it, after what Robert said about it being pretty tough anyway.
Click to expand...

Thanks, Mike. The piece I have is 1/4" thick x 2.5" wide, by 18" long. Should be enough to experiment with once the bowie is profiled. I like the bainite idea. I think I'll go with the treating program on that url. Thanks!
 
Jeff,

I oil quenched Marks S7. Looks like it was back in the days I was vegi oil quenching.

I believe I did well to get a final hardness of 57 HRc by tempering at 400 F.

Here it is:

I stress relieved it at 1225 F / 1 Hour , still air cool

preheat: 1350 F / 7 min.
austenitize: 1725 F / 27 min. (seems long on soak but it turned out very tough)
oil quench: oil temp. 130 F. (120 F vegi oil should be fine, Tough-Quench should be much lower)
I see that I even cryo'ed the thing. (Doubt that helped at all though)
I snap tempered before deep cryo
Temper: 350 F / 1 hour
Temper: 400 F / 1 hour
Hardness testing resulted at 57 HRc, about as good as to be expected if properly tempered at 400 F.

EDIT: I remember that after looking the data sheet over I had decided 57 HRc would be my target. Also, I believe 2 hour tempers would have kept it faily close to that.
--------------------

RL
 
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