Steel Mixtures

Hi, I'm a fantasy and science fiction writer, and was recommended to this group for a technical question.
Well, maybe 'technical' is stretching things. I've written a bit where snaps and shackles were made of a steel. They tested well in normal temperatures, but shattered under load at about -40. I used manganese as a placeholder, but would like to use a correct alloying material to have my 'expert' character tell the journeyman to "try using a little less (or a little more) X" where X is my manganese placeholder.
Can anybody help me? Have I provided enough information?
Bill

Bill Swears wrote:
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Bill:
Try using more nickel in an alloy steel. See discussion in http://www.key-to-steel.com/Articles/Art136.htm
Pittsburgh Pete ---------------
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Bill Swears wrote:
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x = Nickel
Michael Dahms

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Nickel would increase toughness but might not be required, if you only want -40°C not -80°C. Phosphorous would be bad but would be an impurity not a deliberate addition. Vanadium or manganese might be good. Carbon might be bad. Finishing rolling or forging at too high a temperature might be bad.
The materials on page 24 (mainly plates?) are all pretty tough at -40°C. http://www.hse.gov.uk/research/rrpdf/rr105.pdf

David Deuchar wrote:
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I do need it to be able to withstand lower than -40, That's just the temp when the metal started shattering. Assumably what I'd want would survive down to at least -60C. It has to be able to handle extreme weather in an arctic environment...
Bill

Bill Swears wrote:
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Bill: Try adding a lot of nickel (3-1/2% to 9%). See the discussion of steels for cryogenic service: http://www.key-to-steel.com/Articles/Art61.htm
For more detail go to the nickel institute, www.nidi.org and look under toughness in their blizzard of thechnical lierature.
Pittsburgh Pete

snipped-for-privacy@hotmail.com wrote:
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I notice that Mn is up at 16% for the example steel in the article. That's higher even then the Ni. What effect comes of the Mn?
Bill

David Deuchar wrote:
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European low-temperature steels do all contain nickel, the lower the more.
Michael Dahms

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Sorry for the boring reply but:-
EN10025 and EN10028 include several steels charpy tested to as low as at -50°C with no minimum Ni and maximum Ni levels of between 0.35 and 0.85%.
The Low temperature Ni alloy steel parts of these standards include materials tested from -60°C to -196°C with as you say increasing levels of Ni being tougher at low temp.
Also thin material, particularly if not welded, can be used at lower temperatures than it has been charpy tested. For instance PD5500 Fig D.2.:- 4mm material tested at room temperature can be used down to -55°C, or EN1993-1-10 table 2.1:- S355JR tested at 20°C can be used at -50°C up to 10mm thick.
I have seen very few real fractures caused by temperature, (excluding overloads that just happened to be at cold times), probably due to the relatively mild winters we have. Those I have seen were very brittle materials often strain ageing, and very high nitrogen levels (poor casting technique/bad segregation/bad heat treatment/bad welding technique/poor material specification (low manganese & aluminium)).

David Deuchar wrote:
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I found an article in key-to-steel that showed a good steel for cryogenic uses. It contained 16 percent Mn and 5.8% nickel.
comparing that to a basic steel gave me enough information to work with, so I consider my problem solved.
Thanks everybody who contributed.
Bill

Bill Swears wrote:
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"A little more manganese" would actually be correct as it stands.
Or Nickel, nickel and manganese are the two main alloying components used for increasing cold toughness.
"A little less nitrogen" is another possibility.
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Agreed that Nitrogen is Bad. Also that Mn and Al are good, especially together - but are they needed? Afaik the 9% nickel steel traditionally used for cryo purposes has little of either.
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Low temperature (-40 to -100 C) and cryogenic (-200 C or so) steels are not quite the same - I know very little about low temperature steels, but from what I have learned here they do seem to be similar.
For cryogenic steels Nickel is more commonly used, but some newer (and some very old) cryo steels use manganese as well as or instead of nickel (and Al instead of chromium, Cr can reduce cold toughness).
9% nickel steel is "the standard" cryo steel, and the best-known, with afaik little Mn in it. Some other cryo steels have ~ 16% Mn with 6% Ni, some have ~22% Mn and virtually no Ni.
Manganese cryo steels are cheaper even than 9% nickel, which is "Approved" for more purposes - however unless they are using large quantities people often use 300 series stainless for cryo work, avoiding anything with an N at the end, as it is easily available.
Manganese cryo steels have been overshadowed by those for many years, though Manganese steels are being used more often recently, especially in LNG plant and pipelines.