Carbon and low alloy steels have a huge range of nil-ductility temperatures depending on chemistry, melting, thermomechanical processing and heat treatment. Your question denotes a total lack of understanding of material toughness properties.
As an example of the nil ductility temp in API 5LX52 that we ran over 35 years ago, the nil ductility temp ranged from near 0 F to over 125 F.