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Temperature brittleness of 1018 steel

Temperature brittleness of 1018 steel

Temperature brittleness of 1018 steel

(OP)
Does anybody know the NDT (Nil-Ductility Transition) value for 1018 cold rolled steel.  I have an application at -65F with impact loads and I am concerned about brittle fracture.

RE: Temperature brittleness of 1018 steel

Unfortunately, I have no direct answer to your question as stated.  1018 steel has a max. carbon content of 0.20%, which is good as far as low carbon steels are concerned because lower carbon correlates to lower NDT temperatures.  Another important factor to consider is grain size.  You stated that the 1018 steel is cold worked, and that typically correlates to a smaller grain size.  Transition temperature varies linearly with ln(d^1/2)... (that is, the natural log of the inverse of grain size.)  Consequently, finer grain size means a lower transition temperature.  A final factor to consider is the microstructure that is in the steel you have and what practice was used to manufacture the steel.  As far as steels go, Tempered Martensite and Lower Bainite have lower transition temperatures (a good thing) while Ferrite and Pearlite have higher transition temperatures.  Also relevant is the deoxidation practice used in making the steel.  Rimmed and semi-killed steels have poorer notch toughness than fully killed steels; this is attributed to the levels of nitrogen and oxygen and the soundness of metal.  You should be concerned about brittle fracture of this steel at that temperature...I would choose something else if possible.

RE: Temperature brittleness of 1018 steel

(OP)
Thanks.  We won't change the material, I'll do some testing to find an acceptable range and limit the use of our product in extreme environments.

RE: Temperature brittleness of 1018 steel

Redpoint,
You may also want to have an FATT determination done on the material.  The FATT (Fracture Appearance Transition Temperature) determines the temperature where 50% shear fracture occurrs.

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