440c Problem child or just misunderstood

Ed Fowler said:
Every batch of steel will vary, sometimes a lot, sometimes insignificantly. When I lucked into two steels developed to meet high quality control, tested the blades and noted the true joy of working with steel was close to the same or from the same pour I was very thankful for the lack of unknown variables we did not have to attempt to work with. This is the reason I mentioned quality control.
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That's what I was hinting at. :)
 
No one has even mentioned the times you order steel A and get a shipment of steel B.

42, that does not apply to all steels. Some are formulated specifically to avoid it. It is bad enough in some steels tha there is a range of strenths/hardnesses that should not be used due to the loss in toughness. 4340 low alloy steel is a common example. Toughness peaks at about 51-54 HRc in the tempering range of 400-450. It then bottoms out and doesnt recover the lost toughness until 650 to 700 degrees or maybe higher. The notion that toughness increases as hardness goes down is very general and many exceptions exist. This is another reason I would rather choose a different steel than just keep tempering softer. It may work or not, depending on the steel and temperatures involved.
 
me2 said:
No one has even mentioned the times you order steel A and get a shipment of steel B.

42, that does not apply to all steels. Some are formulated specifically to avoid it. It is bad enough in some steels tha there is a range of strenths/hardnesses that should not be used due to the loss in toughness. 4340 low alloy steel is a common example. Toughness peaks at about 51-54 HRc in the tempering range of 400-450. It then bottoms out and doesnt recover the lost toughness until 650 to 700 degrees or maybe higher. The notion that toughness increases as hardness goes down is very general and many exceptions exist. This is another reason I would rather choose a different steel than just keep tempering softer. It may work or not, depending on the steel and temperatures involved.
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Yup! I got that. Different steels all behave differently under heat treatment (and different kinds of heat treatment) so I wouldn't expect that behavior to be present in all steels. I just wasn't even aware of that effect at all, so thanks for making it known!
 
Read hardheart's link if you're interested further. It's quite good and it scratches the surface of several problem temperature ranges. Also, keep in mind they are not talking about knives, but structural steels and other high performance steels, which have toughnesses beyond comprehension relative to knife steels, and penalties for failure along the same magnitude.
 
Glad you guys brought mfg. concerns into this. I hadn't thought of that. I have some Uniloy 440C that was purchased 11yrs. ago. It grinds very clean, heat treats good and takes a great polish, every time I work with it. Could this batch been a good one. DM
 
I have a number of knives in 440C and have used them in the kitchen and for fishing. The knives are old Gerbers. In the kitchen, my Gerber knives require sharpening about 3X as often as a Spyderco kitchen knife in VG10. The kitchen use of 440C is OK, and edge retention is about comparable to some old carbon steel French chef's knives that I have.
In fishing, the knives in 440C never showed rust, but lost their edge faster than I would like. It is rough on an edge when you cut the heads off of fish. I have picked up some knives in VG10 for my next outing.
The 440C blades have excellent rust resistance, even in salt water fishing. Edge holding could be better under heavy use, but is fine in the kitchen.
 
I dont have a problem with properly heat treated 440C. I think it is misunderstood due to it being labelled on so many knives that are not really 440C. Years ago it was seen as the king of the crop. Just shows how far knife steels have come since then and our continued ambition to improve upon things.
 
I'm not sure Gerber's heat treat process entails a cryogenic soak. DM
 
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elkins45 said:
i get the feeling that most custom knives are never actually used, so the edge holding performance of the steel is probably irrelevant. I was under the impression that many custom makes took a very favorable view of 440c because it took such an exceptional polish. 440c can certainly make a pretty, shiny blade that resists corrosion well.
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*****winner*****:d
 
Gator97 said:
me2 - is 4340 steel used for knives?
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Not to my knowledge, though I've toyed with the notion a few times. I think similar alloys are used for axes and hatchets by a few makers. I chose it just as an example I've seen used to illustrate some of the embrittlement ranges. I have 2 texts and a heat treating video that use it for tempered martinsite embrittlement. It's so tough it is used with actual v-notches instead of of the un-notched or c-notch used for cutlery steels.

I dare say an un-notched piece of properly hardened (not in the toughness valley I'm referring to above) piece of 4340 would just bounce the hammer back on a 300 ft-lb Charpy machine. I know a couple of makers who have done that with 250 or 275 ft-lb capacity machines on L6, which is very similar, just with more carbon. That's why I considered it for large chopping type knives. I'll have to try it one day. Improperly hardened and it will go down to 1/5 or so if it's potential toughness, and at a lower hardness. I"m saying all this mostly for the benefit of other readers. I feel sure you're aware of this behavior.
 
I would think as long as a steel is mfg. AOD or double vaccum melted there should not be mfg. concerns.? Or powder metalurgy. DM
 
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Interesting. I shall have to review. Why would it be better than VAR (vacuum arc remelting)?
 
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