* (a) Maximum contents of sulfur and silicon for all grades: 0.050% S. 0.90% Si. * (b) Second and third digits of designation indicate minimum yield strength in ksi. Suffix “X” indicates that the steel contains niobium, vanadium, nitrogen or other alloying elements. A second suffix “K” indicates that the steel is produced fully killed using fine grain practice; otherwise, the steel is produced semi-killed. * Some key points provided by www.key-to-steel.com.