S99 Alloy Steel

S99 (W.Nr 1.6745) is a nickel-chromium-molybdenum low alloy steel used in the United Kingdom for the production of structural aerospace parts. S99 belongs to a group of British aerospace steels which also include alloys S156 and BS S106. S99 is a through-hardened steel characterized by high strength and toughness, thus being applicable for manufacturing structural parts where reliable mechanical properties are required.

As all the nickel-chromium-molybdenum alloy steels, S99 obtains its mechanical properties due to quench and temper heat treatment. Nickel imparts toughness and impact strength, chromium provides hardenability, while molybdenum increases strength and prevents temper brittleness. Thus, the same set of alloying elements determines special strength-toughness properties of this family of steels.

As any material S99 was approved specifically for some UK aerospace applications. Therefore, S99 is the only material which is required for some old projects. S99 is supplied by Dynamic Metals in bars, sheets and plates.