High-temperature mechanical properties of P91 weld metal

Increasing temperature is one of the key factors for improving the efficiency of steam power plants. Important metallurgical phenomena are activated at such high temperatures and creep resistance becomes a driving criterion for the material selection. Ferritic steels, including 2Cr, 9Cr, and 12Cr steels, are among the best candidates; their continuous development and optimization with the addition of Mo, V, Nb, and W have resulted in a significant improvement in creep strength together with a good weldability. This study investigates the high-temperature mechanical properties of two Grade 91 welded plates and focuses on the creep behavior, proposing a modified expression of the Larson-Miller parameter for the estimation of critical combinations of temperature, stress, and time, which could lead to rupture. The suggested parameter, which is highly sensitive to temperature, is able to outline the criticality of the welding and it is useful for predicting the duration of a creep test with the specimen rupture.