Call for Charpy toughness samples

As a heat treat non-scientist: does stress relieving before hardening have any effect on toughness after hardening? In other words, should we have some samples that have been cut, ground, drilled, and generally abused. Then try them with and without a stress relief cycle.

Since that's what actually happens when constructing knives, it might be worth knowing if stress relief is helpful for final toughness. Or it doesn't matter?
 
Sando said:
As a heat treat non-scientist: does stress relieving before hardening have any effect on toughness after hardening? In other words, should we have some samples that have been cut, ground, drilled, and generally abused. Then try them with and without a stress relief cycle.

Since that's what actually happens when constructing knives, it might be worth knowing if stress relief is helpful for final toughness. Or it doesn't matter?
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That’s an interesting question. It probably depends a lot on how much “damage” was done, and if the subsequent heat cycles erases that “damage.”

With the m4 I was cutting on the band saw, the blade just skidded on the sheared edge, like a file skating on a hardened blade. I assume the edge of the steel work hardened, as the Rc# was below 40 on the bar. I didn’t write the number down, as it was low enough that I should have been able to cut it easily with the band saw. I did a 1200f subcritical anneal for 2h, and the m4 cut easier than the z-tuff I cut right after it.
 
Have we gotten any updates o the surface grinding of the batches sent to JT and AKS?
 
Willie71 said:
I’ve got M4 and z-tuff in the oven today. I’m doing lower temps for M4, 1975f and 2050f, and same with z-tuff to see how much toughness drops as hardness goes up. I’m also doing 1900f in z-tuff for a high toughness sample.

Storm W will do the over 2100f M4 heat treat. He’s been playing with M2 and M4 more than me, and offered to get some samples done.
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What were the hardness on those? I just got a new fill of LN last week so hopefully I'm back in business. I will try to get them done this week.
 
Storm W said:
What were the hardness on those? I just got a new fill of LN last week so hopefully I'm back in business. I will try to get them done this week.
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I’ll check when I get back home. I tested the z-tuff, but not the M4.

Z-tuff hardness was:

1900fx40min, cryo 1h, 400f temper, 2hx3. Rc58-60.
1975fx30min, cryo 1h, 400f temper, 2hx3. Rc60-63 (most readings were Rc61/62, but not all were consistent.)
2050fx20min, cryo 1h, 400f temper, 2hx3, Rc58-64.

I didn’t need the third temper on the 1900f sample, but I was doing the other samples with 3 tempers, and just ran them all. The 2050f sample had really inconsistent numbers. I thought there might have been decarb affecting the 1975f sample, as the samples were darker, but I ground the surface off, with no difference in numbers before and after. I suspect the 2050f sample has inconsistent structures, and possibly a carbon depleted matrix. Zapp doesn’t recommend going above 1950f. The 1975f/400f sample is only one Rc point higher than the 1925f/300f sample I did earlier. I should play with lower tempers rather than increasing austenitizing temps if we want higher hardness, assuming toughness doesn’t take a big hit.
 
Larrin said:
Have we gotten any updates o the surface grinding of the batches sent to JT and AKS?
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Last I heard from Chuck was that he was sent the wrong magnetic Chuck for his surface grinder, and had to exchange it.
 
Larrin said:
Have we gotten any updates o the surface grinding of the batches sent to JT and AKS?
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We have the new magnetic chuck. It is installed on the surface grinder and dressed. We ground some test coupons and decided to make a fixture to hold the coupons on the magnetic chuck. The fixture should be finished by this weekend.

Chuck
 
Keith Nix said:
Yes sir! I've been popping a gasket to get in on this!
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Heat treating the last two samples tomorrow, then off in the mail. I’ll post the list of everything going when I am ready, probably Sunday.

I spoke with Storm W today. He’s doing the higher temp M4 in high and low temp. We were discussing M2, and pushing the envelope in terms of hardness and thinness. Interesting stuff to ponder.
 
I was out of commission with too much fun from Friday night, then a massive head cold. Steel (a11) is in the oven today. I’ll post the list later. I have a day off after two cancellations today.
 
Oh dang. My S30V samples were undersized. :( I'll have to make a new batch.
 
Just a quick note on steel thickness for the sample coupons. 1/8" thick stock is about the thinnest that is workable after removing decarb and accounting for warp. The finished samples need to be 2.5 mm (.0984") thick, flat, parallel, and decarb-free.

Michael
 
Michael.Drinkwine said:
Just a quick note on steel thickness for the sample coupons. 1/8" thick stock is about the thinnest that is workable after removing decarb and accounting for warp. The finished samples need to be 2.5 mm (.0984") thick, flat, parallel, and decarb-free.

Michael
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DevinT suggested minimum 0.120”. We got away with 0.108” before but that cut it close.
 
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