Effect of quenching temperature on the strengthening contributions due to the (V,Nb)X carbonitrides to the creep resistance of 9Cr-1W-1Mo steel

Abstract

The increase in quenching temperature from 1050 °C to 1150 °C favorably affects the creep behavior of the P911-type steel, which is expressed in the increase in the rupture time by a few times and the decrease in the minimum creep rate under the applied stresses ranging from 160 to 120 MPa. However, as the applied stresses decrease, such improvement disappears; the 100,000 h creep strength is 70–75 MPa regardless of quenching temperature. A higher quenching temperature stimulates the significant dissolution of (V,Nb)X carbonitrides in the austenite region and their precipitation during tempering and the primary creep stage. This reduces the interparticle spacing during the primary creep stage that provides a high value of the detachment stress due to the (V,Nb)X of 30…34 MPa, even with an increase in their average particle size by 1.5–2 times, and is considered to be the main reason for the improved creep resistance under the high applied stresses. However, the growth rate constants for VX carbonitrides and M₂₃C₆ carbides were found to be similar during creep, regardless of the heat treatment regimens. The elimination of the difference in the particle dispersions during creep leads to the disappearance of the increment in the rupture times under the low applied stresses.