... starts to decrease because of the higher hardiness resulting from higher carbon contents. A steel of optimum machinability—one ... 1215 and 12L14.Leaded Or UnleadedTo get the maximum production from automatic machines, additions of lead, bismuth, selenium and ... today. However, another “unleaded” steel, called 12T14, is available from Laurel Steel (Ontario, Canada). This steel uses tin as an addition ...