The ductile-brittle transition temperature determined at an impact energy of 20 joules is -27°C for ASTM A36, 32°C for the longitudinal specimens made from the Titanic hull plate, and 56°C for the transverse specimens. It is apparent that the steel used for the hull was not suited for service at low temperatures. The seawater temperature at the time of the collision was -2°C.[1]

Ductile-brittle transition wasn't understood at all in 1912. Mass production of steel only goes back to 1886 or so. Before that, good steel was an exotic, expensive material, like titanium is today. The first scientific work on ductile-brittle transition is from the 1920s, years after the Titanic. The Charpy test for brittleness was developed in 1900, but this was before refrigeration, so running a Charpy test on chilled metal was tough unless you were in an very cold climate. One early metallurgist spent a year in a very cold climate to do just such research.

[1] http://www.tms.org/pubs/journals/jom/9801/felkins-9801.html

The last few videos have been much higher in production value, and go into much more depth on really fascinating topics.