Creep strength

At room temperature a loaded component keeps its shape. At high temperature — from about 40% of the melting point — the metal starts to 'creep': it deforms slowly and permanently, even below the yield strength. Creep strength is the resistance to this. It determines the service life of steam boilers, turbines and pressure vessels that run hot and pressurised for decades. It is raised by molybdenum, chromium and vanadium — hence creep-resistant steels like 16Mo3 or P91.