S7 Heat Treat problem

kuraki

kuraki

Fimbulvetr Knifeworks
Joined
Jun 17, 2016
Messages
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I bought 4 sticks of S7 through MSC to make some longer blades that I wanted to be as tough as possible. I've worked with S7 in the past building tooling and am familiar with it, so I thought this would go rather smoothly. But I can't get this stuff to reach full hardness out of the quench.

I've austentized a blank twice now and it's coming out of the quench at 54 RC both times. After tempering at 300F the first one was only 52 RC. The blank is tempering now again at 300F.

1st protocol:
Foil wrapped with a squirt of WD40, load into 1400 F furnace and equalize
Ramp to 1750F and hold for 30 minutes
Plate quench in foil

This came out straight as an arrow, no scale or decarb to speak of, and I was really happy at first because I hand sanded this to 320 grit prior to heat treat, so there would have been very little post HT work to do. I went right into the temper oven at 300 because it seemed to skate my file. Out of the temper it was 52 RC :confused:

So I tried again, 2nd protocol:
Foil wrapped with WD, 1400F and equalize
Ramp to 1800F this time, soak for 30 minutes
Then to quench, I wrapped it so I could easily and quickly pierce the foil with the tang, so I slipped it right out of the foil and quenched in oil.
This time I tested before temper and it's 55 RC :grumpy:

This MSC steel came from Precision Marshal Steel Co. I called them and they're faxing me their heat treat recipe but I doubt it's going to be much different.

I know S7 isn't going to get as hard as O1 or A2. But it should be 60 out of the quench, and 57 after temper is pretty common and what I was hoping to leave this knife at.

I'm probably going to try and get MSC to take the 3 sticks I haven't cut back and refund me, and buy some 3V instead. But this is frustrating, this blank I'm trying to harden was really nice :(

ETA: It's not my temperature, it's not my furnace. I hardened a Z Wear blade yesterday as well and it's exactly where it's supposed to be after plate quenching and 1000F temper.
 
Scott Gossman isn't on here really often, but I know he uses S7 a good bit. You may want to pm him. He's a good guy and had me to his shop before.
 
Thank you, I did so. Even if I return the 3 sticks I haven't cut I would really like to save the blade I've got if possible.
 
Have you tryied dropping the temp, I just had this issue with a bit of AEB-L. I would try dropping the temp 50° and trying again.
 
That's my next attempt. I'll try 1725 which is the lowest on any documentation I've seen.
 
Scott gave me his protocol which is also cooler (1735) so I'm definitely going to give it one more shot at the lower temps. Hoping it's not a grainy mess at this point. I should probably thermal cycle.
 
I know with AEBL it's is a rather tight window for temp. If you over shoot it by just a tad it comes out soft but if you go to low it is also soft. It's actually a good steel to test the temp of your oven. I had to use 1900° to get good hardness as 1950° gave me 55rc out of the quench and 1975 gave me 54°. I dropped it to 1900° and got 63rc out of quench and cryo bumped it to 64rc.

I have never worked with S7 in knife blades so I don't know if it is that picky or not but going hotter did not solve your problem so that's why I think try lower.
 
kuraki said:
Scott gave me his protocol which is also cooler (1735) so I'm definitely going to give it one more shot at the lower temps. Hoping it's not a grainy mess at this point. I should probably thermal cycle.
Click to expand...

Don't thermal cycle. I've done that with S7 and it was a disaster.
Scott
 
I will say this about S7, IMO it is one of the toughest steels available. Edge holding has been excellent for me. I have one customer who has had an S7 Big Boar Tusker for 2 or 3 years and has told me he has only had to strop the edge. I made a Bladesports comp knife out of S7 with an edge ground thin and have cut 2X4's, around 10 to 15 cuts, about a dozen golf balls, a dozen tennis balls, 9 foot of dowel rod and maybe 100 foot of rope. The edge was damn near the same as when I started. Hard to believe but a friend who is practicing for the Bladesports Mid-Atlantic school and competition I'm having at my shop in March was surprised at the performance he saw with that blade. S7 is very underrated as a knife steel.
Scott
 
JT and Scott thank you both. Going to 1725 got me 61 out of the quench. That should temper back right where I want it.
 
Nice! I'm also running about 1733 F and have excellent luck testing my S7... heat treated about 200 blades this way with great luck. I don't have a RC tester but a friend runs my same heat treat and is hitting 59 after temper with sub zero cycles.
 
Here is the blade in question. I shamelessly copied i4marc's pig sticker Bowie profile. When I saw it I had to make one.

dcKSG09.jpg
 
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Good looking blade
 
I think it's spectacular. I will definitely be buying more. It nailed the heat treat out of the gate, came out of my quench plates straighter than it went in to the furnace, easy to work when annealed but I'm very glad I finished it prior to heat treat because it's incredibly hard to sand after. I haven't done any edge testing yet but I fully expect it to meet my expectations there.
 
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