Fundamental Properties of Long-term Creep Strength for Ferritic Heat Resistant Steels

Effects of Dislocation Substructure on Creep Deformation Behavior in 0.2%C-9%Cr Steel

“…For instance, under the lower stresses of 60 MPa, the creep rates reach first and second minimal values at the creep strains of around 3 × 10 − 3 and 5 × 10 , respectively. Similar fluctuation in creep rates under applied stress conditions have been recognized as to low alloy steels such as 2.25Cr-1Mo, [25][26][27][28] 1.25Cr-0.5Mo-Si, 29) 0.2C 30) and 1Cr-0.5Mo 31) steels but the 9Cr-1Mo steel boiler materials. 32,33) Some of the papers have discussed the reasons why complicated creep curves appear.…”

Precipitation Behavior of NbC in 9%Cr1%Mo0.2%VNb Steel.

“…1,2,[6][7][8][9][10][11] It has been reported that these elements along with carbon constitute the complex carbo-nitrides of Type NaCl (MX: M denotes Nb, V, Ta and Ti, and X denotes C or N) and that the average size of MX is about 150 nm for a high carbon 9Cr steel even after creep deformation at 650°C for 12 155 h 12) or 40 nm for a low carbon 9Cr steel after creep deformation at 600°C for 34 000 h. 13) In other words, MX is very fine and stable at high temperatures. However, the total amount of the precipitates does not exceed 0.15% in mass 11) and the value is much lower than the estimated value from the TEM observation of Mo 2 C 14) which is a main strengthening factor in 0.5Cr0.5Mo steel. Therefore, it is desirable to clarify the mechanism of high creep resistance of the high chromium heat resisting steels, but it has not been accomplished yet.…”

Method of Estimating the Long-term Rupture Strength of 11Cr-2W-0.4Mo-1Cu-Nb-V Steel

“…[5] Using these values, the values of R mtr at 673 K and 723 K (450°C and 400°C) after 100,000 hours are calculated as approximately 1.36 and 1.0, respectively. The values of R mtr of the carbon steel are close to unity because the microstructure of carbon steel generally changes slowly, [6][7][8] not because a higher-degree regression equation is used instead of Eq. [4].…”

“…IV data and the estimated maximum time-to-rupture ratio, R mtr , defined by Eq. [8] for Gr. IV is R mtr = 1.51, and this value is far inferior to R mtr = 1.04 obtained using the degradation data presented in Table I.…”

“…[5] This successful result is attributed to the fact that the microstructure of carbon steel is stable over a long period. [6][7][8] However, some high-Cr martensitic steels with high strength for use in ultra-super critical power stations have been reported to deteriorate unexpectedly in creep testing longer than several tens of thousands of hours. [9] The deterioration is attributed to localized regions near prior austenitic grain boundaries (PAGB) being preferentially recovered through the formation of Z phase at PAGB accompanying the disappearance of one of the main strengthening factors of the finely dispersed carbonitride (MX, where M denotes metallic elements preferentially forming carbide and/or nitride, and X denotes carbon and/or nitrogen) particles, [10,11] besides the scavenging effect of solute elements of W and Mo owing to the grain boundary precipitation of Laves phase.…”