low temperature suitability of steels
low temperature suitability of steels
(OP)
Can anybody help me. I am trying to determine the suitability of particular steels to low-temperature use (-40°c being low). As far as I know the normal way, to be on the safe side, is to look at the impact toughness of the material at the given temperature. If this lies above 27 Joule using the standard Charpy impact test. One can be sure that there is enough rest ductility in the part, that the part will survive at this reduce temperature.
Unfortunately this normally leads to additional cost and one starts to consider whether this is truly necessary. Bearing in mind that there is almost no chance of the part seeing a real impact and that any forces which the component meant see are introduced into the part at a relatively slow rate, is there not another way of defining this problem? The ASTM E812-91 describes a slow-bend test and shows that at slow loading rates the characteristics of steels are totally different to those seen in an impact test. Unfortunately the standard loading rate values used for this test are extremely small and do not compare with the loading rates I would expect to see on my component. I know that I will ultimately have to carry out some tests at reduced temperature on the component to verify this point. I just wanted to get some idea of the chance of success and what would be the best way of performing these tests.
Unfortunately this normally leads to additional cost and one starts to consider whether this is truly necessary. Bearing in mind that there is almost no chance of the part seeing a real impact and that any forces which the component meant see are introduced into the part at a relatively slow rate, is there not another way of defining this problem? The ASTM E812-91 describes a slow-bend test and shows that at slow loading rates the characteristics of steels are totally different to those seen in an impact test. Unfortunately the standard loading rate values used for this test are extremely small and do not compare with the loading rates I would expect to see on my component. I know that I will ultimately have to carry out some tests at reduced temperature on the component to verify this point. I just wanted to get some idea of the chance of success and what would be the best way of performing these tests.





RE: low temperature suitability of steels
You should post this question in the Metal and Metallurgy engineering forum (Forum330).
Best regards,
Matthew Ian Loew
"Luck is the residue of design."
Branch Rickey
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: low temperature suitability of steels
The Mainer...
RE: low temperature suitability of steels
Under identical loading conditions, a material that has poor toughness will suffer catastrophic fracture with a smaller flaw than a material that has good touchness. This being a perfect world, we do not have to worry about fatigue crack propagation while in service, undetected fabrication related weld defects or crevice corrosion/pitting that can instigate these flaws until they reach critical size. The critical flaw size is a function of applied load, crack geometry and (you guessed it) toughness. Designing a widget that is going to be exposed to temperatures below its ductile-brittle transition temperature (or nil ductility transition temperature, or 30 ft-lbs limit, or whatever spec you are using) is risky.
RE: low temperature suitability of steels
Best regards,
Matthew Ian Loew
"I don't grow up. In me is the small child of my early days" -- M.C. Escher
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: low temperature suitability of steels
TTFN