effects of sub-zero temps on steel?

[Coty Handley]

I recently participated in an arctic survival school near Fairbanks, and the instructors there kept repeating something that bothered me. They said to be careful with knives and anything else metal because the cold would make the steel brittle and easy to break. I doubted even extreme temps (-60) would make an appriciable difference in a properly heat-treated blade, whether it was differentially treated or not, stainless or not. Has anybody done any cold temp testing, or have first hand knowledge?

 

[rlinger]

Sure, that would make steel brittle but only while at those temperatures. Cryogenic treatment is very good for steels but don't stress it until it warms out of the extreme low temperatures.

Roger

 

[RJ Martin]

That is why you want your blade cryo treated before you go there-Because cryo treatment, if performed properly, is followed by at least one temper.

 

[John Andrews]

Coty, I used to live in Fairbanks, out on Elkhorn. Folks up there always told me to be careful with knives when it was cold, but I never really had any problems with breaking blades. I am not in the habit of using a blade for a prybar,though, like some sorry people.

 

[satin]

For the sake of argument... what steels will do the best in sub-zero weather conditions?
I've been working on designs for a cold weather fighting knife, larger handle (longer, to accomidate gloved/mittened hands), hexagonal cross section to the handle, micarta or neoprene scales (dunno how neoprene would do in the cold?), accomidated forward and reverse grips of all types (edge up, in, down, or out), etc. etc. etc. But have been reluctant to progress, because I've been told what Coty has been told, but also been told some steels do better than others...

 

[Elwin]

Many metals exhibit what is known as a ductile to brittle transition as the temperature goes down. This is not linear and happens fairly suddenly in a pretty narrow temperature range. Above this temperarure range, the metal will bend before breaking and require a harder impact to break. Below this temperature range, there will be almost no bending before breakage, the broken surfaces are very clean, and less of an impact will cause breakage. Steel is one of the metals that suffers from this. I've never really heard of this being a problem w/ knives. It is a winter time problem w/ axe heads in the NC mountains, where I'm from. Of course, Fairbanks is a little bit colder. 300 series stainless steels do not have this property. They do get more brittle as temperature decreases, but its not a sudden and deep drop off, like that seen in carbon steel and hardenable stainless steels.
I sometimes do impact tests on bridge girder material at work. We occasionally get mild steel samples that can take 300 ft*lbs of energy and not completely break. This is at 40 degrees Farenheit. The same samples will snap and fly across the room at -40 degrees, and only absorb about 50 ft*lbs.

Satin, any steel that has a reputation of being tough, such as A-2 or 5160, should be fine. Axes are ground a little thicker toward the points of the edge than in the middle to deal w/ this problem. You may not be able to grind the edge as thin as you would like. Neoprene is an excellent insulator, and should work fine with respect to cold weather conditions. Its used in gloves and mittens. You'll have to look into its ability to deal w/ the stress of being a knife handle though. You may want to think about a way to isolate the tang from the hand, to prevent the user from touching ice cold (or colder) steel.

 

[Joss]

Don Fogg tells a story about a guy who needed a knife for the Arctic (or Antarctic?) Allthe knives that had been carried before had broken. Don made one out of L6, IIRC, which performed to satisfaction, and didn't break.

BTW, sub-0 quench or treatment is not useful for all the steels. On some steels, it serves no purpose whatsoever.

 

[Coty Handley]

Thanks for all the useful knowledge fellas.

 

[Don Powell]

This is a very interesting thread. I wonder if it is only a matter
of controlling the as heat treated hardness, on a very tough steel
like 5160, L6 or A2. So, the question is. At -60F what is the HRC of a steel that started out at a HRC of 60 at +60F. If we knew the difference, we could perhaps make an allowance and only have the cold
weather knife heat treated to, say, HRC 52. At -60F it might be HRC 59 or so. Wow, I don't know if I made my point, or even if this makes
sense. I don't really think this is practical, but it is fun to theorize.

 

[knightsteel]

Joss,

On what do you base your statement that cryo makes no difference whatsoever on some steels? The studies I have seen show at least double the wear resistance with blade steels.

Daniel

 

[Joss]

I'm just reporting something said by Howard Clark. He was mostly referring to 10XX steel. Which studies are you talking about?

 

[knightsteel]

Joss,

I believe that Howard may have based that unfavorable opinion on outdated information. Howard and I had facing tables a couple of weekends ago at the East Coast Custom Knife Show. Cryo was one of various subjects we talked about. After a bit of discussion, he accepted my offer to cryo one of his blades for him to do comparison.

If all that was happening was the conversion of retained austenite to martensite then Howard would be very correct. However the biggest benefits may be those of grain refinement and carbide precipitation.

The most widely publicized study was done by Dr. Robert F. Barron of Louisiana Polytech. The only 10XX series steel tested was 1020, which still showed approximately double the wear resistance.

I will post his entire results table on the "cryo testing" thread.

Daniel

 

[Joss]

Thanks - it seems my info might be erroneous. I appreciate the info.