Weird Stainless HT question

[Jamie G Lupole]

I don't work in SS often, but when I do I will send it out for HT and have always been satisfied with the results.
Recently I met another maker who heat treats stainless in a way I have never heard of. So, I figured I'd ask if anyone else does this or have heard of this.
The stainless steels I use are 440c, ATS-34 and CPM-154, all standards, this other maker also use these same steels, so his process intrigued me.
The maker wraps his SS blades in foil, heats to temp and holds the needed time. Then he quenches in plain water in the foil. He does not temper or draw the blade back. He says he gets RC 61-64 and has never had a blade break or be brittle.
So my question, do other makers use this process? And why?

 

[Richard338]

Ah, the dim sum tempering method...
That procedure has little in common with the recommended protocol. Look on Alpha Knife Supply to see the recommended procedure for various steels. I wouldn't be comfortable finishing a knife like that.

 

[Bühlmann]

Funny this came up. D DevinT just recommended doing exactly that in my thread about oil quenching AEB-L.

If you use foil, double fold all edges, quench blade with foil in water.

Hoss

Sometimes it gets really tough to choose who to believe around here!

 

[Richard338]

I doubt Devin skips tempering altogether.

 

[Bühlmann]

I doubt Devin skips tempering altogether.

Oh, I was referring to the water quenching in foil bit. I don’t know much of anything about SS, so that was what caught my attention.

 

[Blankblank]

Im guessing he's getting enough retained austenite by not tempering, or doing cryo using stainless steels to not end up with the blade breaking.

That said. I would bet money, that those blades still don't have good properties.

 

[Jamie G Lupole]

Ah, the dim sum tempering method...
That procedure has little in common with the recommended protocol. Look on Alpha Knife Supply to see the recommended procedure for various steels. I wouldn't be comfortable finishing a knife like that.

I know the recommended procedure, that's why I send my SS out. I was wondering about his method and this HT would make me uncomfortable also.

 

[DevinT]

Tempering is a must.

Hoss

 

[HSC ///]

I know the recommended procedure, that's why I send my SS out. I was wondering about his method and this HT would make me uncomfortable also.

Did he say why he doesn’t want to temper?

 

[Jamie G Lupole]

Did he say why he doesn’t want to temper?

When I asked he said it was a wasted step, he's never had a brittle blade or one break with RC 61-64. My main question still stands "Why quench in water?"

 

[Jamie G Lupole]

Tempering is a must.

Hoss

But why do you quench a stainless steel in water?

 

[Blankblank]

When I asked he said it was a wasted step, he's never had a brittle blade or one break with RC 61-64. My main question still stands "Why quench in water?"

 

[Blankblank]

But why do you quench a stainless steel in water?

Im guessing with the knife double wrapped in foil. The water quench, means the speed of cooling for the actual knife inside, is much much slower than it might be if you just did a normal quench in water.

So with an oil quench it could be even slower.

Thats just me guessing though.

 

[DevinT]

But why do you quench a stainless steel in water?

I don’t, it can be done if you leave it in a properly constructed envelope with double folded edges. The foil envelope insulates the blade and quenches at about the same speed as a blade directly in oil.

The OP of the other thread was asking about a way to quench without plates so I gave him a suggestion. I plate quench all high alloy steels.

It always surprises me that knife makers want to cut out important steps in heat treating. They think they have discovered something new and always use anecdotal evidence for their discovery. Sometimes they add lots of unnecessary steps also.

Use a good equipment, go through the proper steps, use cryo, do some testing, it’s not complicated.

Hoss

 

[Stuart Davenport Knives]

When I was starting to get into SS heat treating, I tried to read as much as I could (this was before the days of KSN and the info provided by the Thomas's). I read an article from Roman Landes who suggested oil quenching for SS. I won't quote him as I don't recall 100%, but something like oil quenching SS is faster than plate quenching, and reduces unwanted precipitates from forming during a slower cool down. I don't know what those precipitates are. But I went that route, using thick layers of ATP-641 for anti-decarb. I did not have much success. There were warping issues and the ATP-641 would put little divots all over some alloys, and then other alloys were spotless.

After buying a couple of large thick aluminum plates and looking at the cooling curves for SS, I'm not so sure that I agree that a medium or slow speed oil is a faster quench than plates. Especially chilled plates with compressed air in addition. And especially if the bevels had been ground a bit prior to HT. That edge goes from 2000°F to black VERY fast with plate/forced air.

 

[Seedy Lot]

Ok don't hate me but I could not help but try the foil wrapped stainless into water and no temper heat treat.

The AEBL blank ended up being 61-62 Rc.

I could see how a maker could pull this off and have no issues especially if the knife was obtuse sharpened and thicker behind the edge. My blank was 0.015 behind the 15 dps micro bevel. The blank sharpened up nicely and with normal tasks no issues so I started to find the limits of the steel. Scooping cuts into Western Larch firewood and still no issues so scooping cuts into the end grain of the firewood and still no issues that I could see under 100x magnification.

Moved onto an old, very dry, oak board. Scooping cuts along the board and edge was still holding up well so moved onto very aggressive scooping/prying cuts into the end grain of the oak and finally had the edge start crumbling.

I did not have another AEBL knife in the house to compare to but one in CD1 that was similar hardness and geometery. With same high energy scooping end grain cuts into the oak with the CD1 the knife took very slight damage along the thin edge but only could be seen under 100x compared to this visible issue with the AEBL.

https://imgur.com/a/VdCbvUQ

 

[JV Knives]

I think the real test is down the road. Can you get a water quenched blade at Rc62? Yes. Does the retained stress without temperlead to blade failure? Not in a safe but likely many other scenarios.