I'll start out first by saying that I'm not a stainless / high-tech sort of maker, but have succumbed to the demand for stainless knives. I like 440C so far because its easy to work with and the cost is reasonable here in Australia.

The pro HT-er's who do it vacuum HT, nitrogen gas quench (not the sub-zero type) and then temper. They test every blade. 440C generally comes out at 57-58Rockwell. That way, I'm happy with the blade, but the edge holding is not anywhere as good as I'd like. At a small added cost, they will sub-zero quench the blades and do a second tempering cycle. I think they get an extra Rockwell point from that. I intend to do a 3rd tempering cycle at 375-400F in my own oven at home.

So thats - quench, snap temper, cryo, temper and a 3rd temper at home. From what I've read and understand (sometimes a real problem for me) that gives gains in grain refinement, hardness values and toughness for 440C.

Will that process do the 440C any good, or am I barking up the wrong tree ? I'd appreciate any suggestions / opinions.

Many thanks in advance. Cheers.

All grades should be tempered at least twice, and triple tempering is usually recommended. Each temper should consist of holding for two hours at temperature, and cooling all the way down to room temperature between tempers. If there is any doubt about the proper temperature to use, simply use 25 to 50?F (14 to 23?C) below the tempering temperature used in the original heat treatment.
From Crucible,refers to all SS&HSS steels

440c will never be a great edge holder. But cyro treatment makes it very happy. you will see a noticeable difference.

steve

jason,

I'm a metallurgy student here in the U.S. and i use 440C for most of the customer blades that i am asked to make. i get 63 HRC. and I'll be glad to share with you my Heat Treat procedure. Here I will tell you and everyone else to get 63 i stress relieve i do not temper back. i temper at 250C for a couple of hour or more I remember to turn the oven off. no one has brought back to me a brocken blade because i tell people my knives are edge weapons not hatchets and treat them accordingly. a higher hardness will make that 440C steel hold an edge much longer than what you are experiencing at this time.

Nate, harder = better edge holding. 63HRc is quite high for 440C. Do you mean stress relieving at 250F, rather than 250C, because I think 250C will get almost a spring temper close to only 50HRC or so.

Unfortunately, I think that my clientele may be a bit different. I do tend to get asked to make a "durable knife". People I've worked with on design and "tolerance" ranges say that they often drop their knives, ding them against bone / teeth, chop lightly with their knives. I really in fact usually use O-1 carbon with the whole 9yards - differential HT, triple temper, drawing down the spine again x2 etc. They seem to "survive" better the sorts of light abuse that these guys throw at them.

The 440C and other stainless steels really come in for those guys working the really humid climates and near water a lot. I've never had expereince with any knife at that hardness (63HRC), nor with any of the exotics like CPMS60V S90V but I wonder if it'd be a bear to sharpen.

I'm not putting down your ideas, but not having gone there myself, I might need to do a bit of testing. The main problem for me is that I don't do the hardening on high-alloy steels and have to send it out - subject to the rules of that establishment.

PS.- my woodworking marking knife is O-1 carbon steel. Full hardened, also only stress relieved - miked out at 64HRC !! I've used it to score Micarta before bandsawing - I've now been using it for 14months, only the tip gets used and its never been resharpened or even touched up ! Same principle as your idea.

Cheers.

Rc63 is very high for 440C, and it will certainly be brittle at that hardness. I'm not sure about your numbers though. 250C is about 400F (I'm too lazy to do the arithmetic) and that should yield ~Rc60. 400F is what most folks use for 440C. What is your hardening temp?

Jason, you can get RWL-34 (a Swedish powder version of ATS-34, but with a pinch of Vanadium) there in Australia. It's a wonderful steel. It takes a fine edge, is tougher than its parent ATS-34, and polishes like no other steel I've ever seen. If it were more readily available here in the US I'd use a lot of it.

Jerry, Australian Knifemaking Supplies sells RWL-34 for only 15-20% more than 440C and a few dollars more than ATS-34. I've so far had very good results using it and it seems like the whole powdered metal technology thing is the way to go for that extra performance edge, literally. You mentioned that it polishes nicely - it is the only steel I've seen so far that has no visible grain structure (I mean the visible unevenness) that allows it to take such a beautiful polish or satin finish. I hear powdered 1084 is also around, so it would make sense to make billets with the 1084 also for that nice fine grain. I wonder if it would alter the "standard" practise of bladesmithing to improve grain distribution and refinement. I'm presuming that the CPM steels are similar in that respect.

But, I have enough 440C here to make 25-30medium-sized knives, so I'm trying to ensure that customers will be happy with the result. I'm keen to go the extra step needed if it helps along the performance of 440C. I find that it grinds a lot easier (anealed) than anything else in my inventory, so its perfect for all that extra grinding practise (I'm quite new to using high-alloys, so I'm still getting used to the quirks of grinding these steels - warpage, stressing that you've talked about elsewhere).

So far, I've decided to use the 440C for kitchen knives, RWL-34 for hunters etc.

I also haven't done the math, but 250C comes up closer to 485F, 200C is around 390F or so.

Cheers.

Your math is probably better than mine but 485F should bring the Rc down even further.

It was something the HT guys said - 400F (actually closer to 375-380F) gets 60HRC, 500F gets 50HRC. Personally, for working knives I prefer the slightly higher "working" hardness. 58-59HRC for 440C seems ideal. I've noticed in some steels that its not entirely the hardness, but that particular quality of the edge that tells you the HT has hit the "sweet spot." (Bites better, takes a shaving sharpness that still rips well, etc.)

I can't really explain it, or if I'm just imagining it ... For some steels that seems perhaps a couple of Rockwell points lower than you'd expect. Maybe its got to do with grain structure rather than hardness and edge retention outright.

Jerry, just checked out your site again and everythings OK, I had some problems accessing it a couple of days ago, but looks like it was a temp thing.

My website's almost up and I'm putting a link to your site from there and just checking the connections.

Cheers.

For some reason, I saw somewhere that the highest obtainable hardness was 61 RC for 440C. Someone please correct me and show me their source of information. I had some old data sheets from Marmon Keystone somewhere which led me to think that.

Craig

Man, I am happy.

The guys are Hills Heat Treatment of Bayswater, Victoria. Of course thats in Australia, so this should be of interest to any of you in these parts.

They were more than happy to do the whole complex HT process for me. Obliging folks that they are. Even gave me an IOU when I forgot to bring cash when picking up the blades. They use a dry ice 24hour quench or thereabouts, as their cryo treatment. They took 5 days to do the whole thing, which is time well spent, it looks like.

They did the steels separately of course, then quench, temper #1, cryo, temper #2, temper #3. So everything got a cryo and triple temper.

The 440C - returned 59HRC !! (56-57HRC without the above).

RWL-34 (powdered version of ATS-34) - 60.5HRC !! (58-59HRC without the above)

BG-42 - 60HRC !! (58HRC without the above)

D-2 - 61HRC !! (58-59HRC without the above)

I was impressed. the 440C one I tested and found about double the edge holding of the 56-57HRC version and all survived some pine-chopping for toughness. The D-2 blade was too small to do that, but the edge holding is absolutely phenomenal.

All you local makers here should specify those things when getting them done by Hills HT, the cost is only a small addition to the price of HT compared to the great performance improvements.

Wow !! Cheers. Guys, thaks for all the input.

Will someone explain what the SNAP TEMPER

sorry about last post, hit wrong key.
Will someone explain what snap temper means and what is the procedure. When is it done during the cycle?.

Roland

This is what I've learnt 2nd hand, so please don't take it as gospel. I'll give you 440C as an example.

After the first quench from critical (hardneing phase), the steel is very hard and brittle (eg.- 63-64HRC). Usually with normal HT methods, the steel can be tempered now to the desired hardness (eg.- 57-58HRC). However, if you want a cryogenic quench cycle, there is debate as to whether or not you can do it from the fuly hardened phase. I have been told that the steel as it is heavily stressed by the first quenching stage. it can warp, crack or even break under the added stress of the cryogenic quench stage.

In order to reduced the stresses on the steel - the HT-er does what is sometijmes called a "snap temper" before doing the cryogenic quench stage. Depending on who you talk to and what they believe, there are perhaps 3 ways to do this, with different rationale.

1) Some people believe that doing a normal type of tempering cycle before cryo makes no difference to the outcome. So these folk may do a regular tempering, eg.- at 400F to produce 57-58HRC before doing the cryo.

2) Some other people believe that the first hardening quench needs to be followed by the cryo, but are worried about the stresses, so instead of doing the normal tempering as above, they temper with the intention of "destressing" only, eg.- at 300F or 325F, which produces a hardness of around 61-62HRC, too hard for use, but the steel crystalline structure has now "relaxed enough" to reduce the risks of the stresses of the cryo, as mentioned above.

3) Some others again believe so strongly in the value of cryo immediately, that they do not "snap temper" at all and cope with the consequences afterwards.

So to summarise, there are maybe 3 different ways (amongst many others) to do this -

1) Hardening quench, normal temper, cryo, normal temper, normal temper.

2) Hardening quench, snap temper(destress), cryo, normal temper, normal temper.

3) Hardening quench, cryo, normal temper, normal temper, normal temper.

Hope this makes sense. My HT-er does the 1) technique and gets 59HRC as we've found out. I'm very happy with the result but haven't been able to compare against other ways of doing it.

Cheers.

Thanks, Jason, I appreciate the info.
Roland

(non-knifemaker question) and what happens if you quench directly into cryo the first time?

Never tried it, but I would think the blade would shatter like glass from being cooled too fast. I have had blades snap into several pieces when I used to quench in water. I was just starting out and didn't know any better, but I learned fast.