S-1 is a medium shock-resisting steel combining moderate hardness with good toughness characteristics. It is a deep hardening, oil quenching steel designed for shock and impact applications as typified by chisels, pneumatic tools, shear knives, and punches. In recent years air hardening grades such as A-8 and other shock-resisting die steels have replaced S-1 in many applications because of their minimum size change during heat treatment, more specifically tailored properties and lower cost.

Preheating is not essential with S-1; however, it’s a good practice to warm the tools before hardening or to preheat at 1200-1400°F. Then heat to 1700-1750°F and after thorough soaking at temperature, quench into warm oil. If furnace hardening uses a soak time of 30 minutes for parts 1 inch thick or less, then add 15 minutes for each inch in thickness over 1 inch.

S-1 should be tempered for 2 hours per inch of thickness at the temperature that will yield the hardness desired. For hot work applications, temper at a temperature at least as high as the tools will reach in service.

Hardening happens between 1700-1750°F.

S-1 is an oversized material,