Creep strengthening mechanism of Mo and W in 9% Cr heat resistant steels

In this paper, precise investigation on the 9 mass% chromium ferritic steels with up to 2 mass% molybdenum or 4 mass% tungsten extracts the contribution of molybdenum and tungsten to the strengthening mechanism. The creep rupture strengths of molybdenum containing steels increase with molybdenum content because of the molybdenum in solid solution and stabilized M23C6 by molybdenum. The extended transient creep stage implies the effective precipitation strengthening effect of the stabilized M23C6. Also, estimated creep rupture strength increases with tungsten content increases up to 2 mass%. But in case of tungsten containing steels, precipitation of Laves phase possibly contributes the lath structure stabilization. The resolution temperature difference between Fe2W type Laves phase and Fe2Mo type Laves phase explains the difference of precipitation strengthening effects for molybdenum and tungsten containing steels. (orig.)