stainless heat treat

[Teknition]

I did my first heat treat of stainless tonight (154CM) and I'm wondering if I am on the right track. Heres what I did:

Sanded Blade to 600 grit and gave it a quick buff.
Degreased blade and wrapped in stainless foil envelope with double folds (nothing in packet)
Set blades in oven standing up between 2 fire bricks (bricks about 2" apart) and ramped oven to 1500*F and held at 1500 for 10 minutes.
Ramped oven to 2030*F and held blades at 2030 for 20 minutes.
Pulled blade out and plate quenched between 1" thick aluminum plates (8"x18") and blew compressed air between the plates until blade was at room temperature.
Pulled out of foil and inspected blades for warpage (none)
Then right into the cryo (LN2) over night.
Thats where I am at this point- blades are in the LN2
I plan to leave the blades in the cryo until I'm done work tomorrow (20 hrs) then temper 2x at 400*F

I don't have access to a rockwell tester yet (saving after the oven and dewar purchase) but I did check the blade with a file and the tang section seems a bit harder than the bevels.

My main concern is, when I took the foil off, the full tang was multi colored but the blade section where the bevels are looked the same as when I put it in the foil. Is this normal or does it indicate one section didnt harden?

[mdagley]

Brad,

Check out Crucibles data on this steel at:

http://www.crucibleservice.com/datas...TOKEN=15828425

If I understand what the data sheet is telling me, it seems that 2030 deg. is a bit on the too hot side. 1950 deg. would probably be better.

-Mike-

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[Teknition]

Hi Mike,

I have the data sheet from crucible and I know I'm pushing the upper temps a bit but I'm basing my heat treat procedure from here:

http://www.seamountknifeworks.com/Article%201.htm

I was refered to him by another bladesmith I know that told me he has done alot of stainless.

We all have to start somewhere and from the researching I did on the net this was about the most informative directions I could find for blade size steels. From what I've read, most of the crucible data is aimed at thicker sections of steel.

Its somewhat confusing at this point because the crucible data doesn't cover plate quenching, and I'm told thats the best way to go with stainless.
Another confusing issue is which Austenitizing temp to go with. Some say use the high temp, some say the lower temp.

I'm hoping to get 61RC when Im done and I think I will have to temper between 400-500 to get there. Its just very difficult, if not impossible to know for sure without the rockwell tester. All I can do is test the blade for now and see if it is a good performer or not.

Thank you for the input Mike, I appreciate it.

[Larrin]

Phil has had a fair amount of success heat treating high alloy stainless steels, I can't argue with him, he's done his testing and his process works for him. I might be able to help you a little bit with your questions though.

With austenitizing temperatures, generally the lower you go the higher the toughness and wear resistance, even when at the same hardness, until the point where the temper is too low to get the same hardness you were getting at the higher austenitizing temperature. The wear resistance is greater because of less dissolved carbide, and the toughness is greater because of less carbon in the matrix and smaller grain size. Sometimes the grain size is not a factor or very little depending on which austenitizing temperatures and steels you're talking about. Higher austenitizing temperatures do give greater corrosion resistance, however, and of course to get the very highest hardness you have to use the higher austenization temperatures. Phil has done well with his higher austenitization temperatures, but if I heat treated a piece of 154CM I would probably use 1950F.

Generally plate quenching will give you similar numbers to the oil quenching numbers that Crucible gives you. Plate quenching is considered by many to be the best because it is very easy, not messy, and with stainless gives similar results to oil quenching.

I don't think you need to modify anything from what Crucible gives you, you might want to use the lower end of the time ranges given, but they are not giving recommendations for 5" thick steel or anything.

You don't necessarily need to make sure the blade is all the way to room temperature to check for warps, while it is a little hotter is the best and easiest time to straighten it. You also want to get it into cryo as soon as possible after quenching. Waiting until it's at room temperature, then straightening, then getting into cryo is wasting enough time to be a little less than optimal. You might not notice a difference, but then again you could.

I wouldn't tell yourself that you want to get 61 Rc, I think you should test the blade and find out where you get the best combination of toughness and edge retention. Start out with a low temper, test for toughness, and if you are not happy with it then raise the temperature a little on the temper.

[mete]

I would also stick to the 1950 F and I think most use that from comments I've seen. I wouldn't go less than 20 minutes for the soak . Color on the steel only means that there is some oxygen in the packet ,it will polish off easily.You shouldn't get any warping with plate quench and compressed air is not necessary. If you were to get warping do not attempt to straighten below 400 F !!!Cryo isn't necessary but will give you 1-2 points higher HRc.

[Teknition]

Thank you Larrin and Mete for helping to remove some of the confusion.
It's very helpful to know that an oil quench is equivilent to a plate quench and that the crucible data is applicable to blade size steels.

I will use 1950* for my next blades as suggested. Mete mentions a soak time of no less than 20 minutes, is this long enough or is more time needed for a proper soak?

If I am understanding what I've read so far, once the blades hit 900 degrees they are commited to harden. So does that mean the the blade could be pulled from the plates at 7-800 degrees and it would still harden the same as if it was left between the plates till at room temperature? How you guys know what temp the blade is at in order to know when to pull it out of the plates.

Thanks again for the assistance.

[mete]

Try the 20 minutes , though more time won't hurt as long as you don't go above normal hardening temperature.....In general once you get below the 'pearlite nose' the steel can be cooled at a slower rate. I don't think there's much to gain in this case.

[Gary Mulkey]

I first started doing plate quenches when S30V came out and being as I was working with a new steel did a lot of experimenting. I found that I had much better success achieving full hardness by taking the heat out of the foil (or removing it) before plate quenching. I did this with a quick immersion in water of the foil package ( I was careful to make each packet water tight at the seams). I believe that I achieved better heat conduction of the blade this way.

Gary

[Larrin]

By the way, 30-60 minutes is plenty for cryo, you don't need to do it overnight.

[Teknition]

Thanks Guys,

Mete, The reason I asked about the comitment to harden at 900 is that I haven't figured out how to tell when the blade is 400 degrees so it can be pulled from the plates and straightened. I assume that window is between 900 and 400 degrees, so in fact the blade can be pulled at 600 degrees for example, and straightened without any hardening problems.

Gary, the idea of a quick water quench is interesting. This is the first time I've read anyone doing that. I will try that if I have hardening problems. With the 1" plates I have the steel seems to quench very rapidly.

Larrin, I knew the cryo time required was shorter then over night but by the time I was ready to do the cryo it was late. I had to work the next day, so I left the blades in until I got home from work. Is there any disadvantage to leaving them in this long?

[Larrin]

Originally Posted by Teknition

Larrin, I knew the cryo time required was shorter then over night but by the time I was ready to do the cryo it was late. I had to work the next day, so I left the blades in until I got home from work. Is there any disadvantage to leaving them in this long?

There is some carbide precipitation when using long-term cryo, which slightly raises wear resistance and slightly decreases toughness. It's up to you to decide if that's good or bad.

[Teknition]

Thanks Larrin. These 2 blades are slicers not choppers so the long cryo turned out to be good after all.

[Don Robinson]

I've always used 1920 For hardening 154CM and ATS 34.

As someone says above, using a hardening temp on the low side adds toughness. For a small blade 20 to 30 minutes soak is fine when hardening.

In heat treaters terms austenitizing at the low side of the range is called "under hardening". The term is misleading. You still reach the desired hardness after quenchand tempering.

I don't believe you mentioned a flash temper. If you went directly to the cryo after the quench you have a great risk of cracking. An as-quenched or as-quenched and cryo overnight cycle isn't advisable. Next time, quench, flash temper in an oven (kitchen) at 300 for 2 hrs., then cryo and temper again at a higher temp.to obtain your desired hardness. Counting the flash temper I temper 3 times 2 hrs. each.

It might be advisable to check for cracks and if none are noticeable, anneal the blade and start over.

By the way, the blade can be straightened any time after removing the blade from the furnace. Yes, straightening between 900 and 400 is good. The major thing here is not to try to straighten below 400.

[Teknition]

Thanks Don,

I checked both of the blades for cracks and found none, so I went ahead and finished sanding out the blades. I'm going to keep both blades for testing. One will be used and abused in the kitchen. The other will be tested outdoors and eventually be tested to destruction.

Im still a bit confused about the snap temper. Ive read in numerous places that the cryo should be part of the quench process and not to delay it with a snap temper. On the other hand, I've also read that the blades should be snap tempered before cryo.

Crucible's data sheet says:

"The freezing treatment is most effective right out of the quench, however complex
parts with sharp corners are more safely frozen between the two tempers."

I guess I'm still sitting on the fence in this debate. To me, it makes sense for the cryo to be an extension of the quench process. I also realize there is a significant thermal shock to the blade when going into cryo without the snap temper. I guess the real question is how big is the risk of cracking if going straight to cryo with a blade type cross section and careful preperation of the blade before beginning heat treatment.

As always, I look forward to, and appreciate the input and suggestions you guys provide.

[mete]

Brad, it all depends on whether you're the nervous type !! The choice is yours. Snap temper is done at 300 F because higher temperatures will stabilize the retained austenite and retard transformation.