Medium carbon steels typically have between 0.3wt% and 0.5wt% carbon. They have higher strength than low carbon steels, but are less ductile. Medium carbon steels are often heat treated to obtain higher strength, such as by quenching and then tempering.
This steel has been normalised, which is a very common process applied to steels. The steel is heated to around 950°C (where it transforms to the austenite phase and the carbides dissolve), and then allowed to cool slowly (i.e. normally) in air. The relatively slow cooling rate gives a near-equilibrium microstructure of ferrite and pearlite, close to that predicted by the phase diagram.