Most often specified medium-carbon steel. Also available as special quality grades of proprietary steel compositions. Available in a variety of product forms, mainly as stock for forging. Excellent forgeability. Fair machinability. Responds readily to heat treatment. Available as an H-grade. As-quenched hardness of at least 55 HRC. Slightly higher, when carbon is near high side of the allowable range. Used extensively for parts to be furnace heated by induction prior to quenching.