An extensive study has been made on the effect of rolling condition on recrystallization of austenite, dissolution behavior of alloying elements and mechanical properties of 9Cr-1Mo-V-Nb steel. Thereafter, metallurgical factors for improving mechanical properties have been investigated and a suitable rolling condition for thermo-mechanical control process was determined. The results obtained are as follows.
1) In the higher slab reheating temperature, especially above 1200°C, dissolution of Nb is accelerated and creep rupture strength increases.
2) The recrystallization in hot working occurs above 1 000°C, and makes fine grain structure, thereby improves toughness of the steel.
3) Recovery is mostly completed in the steel rolled at the non-recrystallizing region above 900°C. The steel shows higher resistance to the softening by tempering.
4) However, in the steel rolled at non-recrystallizing region below 900°C, there is a fear of decrease in tensile and creep rupture strength.
5) Suitable mechanical properties according to the required material specification can be obtained by thermo-mechanical control process through controlling precipitation behavior.
