Temperature brittleness of 1018 steel

[Redpoint]

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.

 

[AJohnson]

Unfortunately, I have no direct answer to your question as stated.&nbsp;&nbsp;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.&nbsp;&nbsp;Another important factor to consider is grain size.&nbsp;&nbsp;You stated that the 1018 steel is cold worked, and that typically correlates to a smaller grain size.&nbsp;&nbsp;Transition temperature varies linearly with ln(d^1/2)... (that is, the natural log of the inverse of grain size.)&nbsp;&nbsp;Consequently, finer grain size means a lower transition temperature.&nbsp;&nbsp;A final factor to consider is the microstructure that is in the steel you have and what practice was used to manufacture the steel.&nbsp;&nbsp;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.&nbsp;&nbsp;Also relevant is the deoxidation practice used in making the steel.&nbsp;&nbsp;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.&nbsp;&nbsp;You <b>should</b> be concerned about brittle fracture of this steel at that temperature...I would choose something else if possible.

 

[Redpoint]

Thanks.&nbsp;&nbsp;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.

 

[rms1956]

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.