Strengthening mechanisms in heat-resistant martensitic 9Cr steels

Strengthening mechanisms of heat-resistant martensitic steels were discussed in terms of microstructural evolution and changes in hardness during creep deformation. In carbon-free 9%Cr steels, it was confirmed that the Mo or W addition improves creep properties of martensite through the solid solution strengthening. On the other hand, creep tests of low-carbon 9%Cr steels revealed the fact that carbide particles precipitated along lath boundaries markedly contribute to the retardation of the recovery of martensite, and this leads to an excellent creep properties. The addition of Mo or W to the low-carbon steels does not give a large effect to the retardation of recovery, but causes a large solid solution strengthening in the materials with the subgrain structure, which has been formed in the latter stage of creep deformation.