Showing papers by "Fujio Abe published in 2023"
TL;DR: The role of BN, AlN and MnS particles on the degradation in creep life and rupture ductility has been investigated for 9 to 12Cr martensitic steels and 1Cr bainitic steel mainly at 550 to 650 oC as discussed by the authors .
Abstract: ABSTRACT The role of BN, AlN and MnS particles on the degradation in creep life and rupture ductility has been investigated for 9 to 12Cr martensitic steels and 1Cr bainitic steel mainly at 550 to 650 oC. The BN particles form in Gr.92 and Gr.122 during normalising at around 1100 oC. The BN particles have nothing to do with the degradation in creep life. The AlN particles precipitate in the high-Al heats of 12Cr-1Mo-1 W-0.3 V steel during creep, reducing dissolved nitrogen and fine nitrides beneficial for the creep strength and degrading the creep life. The MnS particles have nothing to do with the degradation in creep life of 1Cr-1Mo-0.25 V steel. The BN, AlN and MnS particles are responsible for the degradation in reduction of area of the steels by accelerating the formation of creep voids at interfaces between the particles and alloy matrix.
TL;DR: The degradation of the long-term rupture strength of ASME Grade 122 steel occurs earlier than that of Grade 92 steel as mentioned in this paper , and the authors investigate the reasons for this phenomenon by applying an exponential law to the temperature, stress, and time parameters.
Abstract: The degradation of the long-term rupture strength of ASME Grade 122 steel occurs earlier than that of Grade 92 steel. To investigate the reasons for this phenomenon, the long-term creep curves of Grade 122 steel pipe, plate, and tube product forms were analyzed by applying an exponential law to the temperature, stress, and time parameters. The activation energy (Q), activation volume (V), and Larson–Miller constant (C) were obtained as functions of creep strain. All Q, V, and C (QVC) decreased simultaneously with an increase in creep strain during the transient creep in a data group (Gr.IIIa), where an unexpected drop in the long-term rupture strength was experienced. Metallurgical considerations of the variations in QVC meant that “heterogeneous recovery and heterogeneous deformation” (HRHD) should occur during the simultaneous decreases in QVC. The Z-phase is easily formed by the consumption of the strengthening particles of MX in the HRHD zone, which causes the degradation of the long-term strength of Grade 122 steel. The higher hardness of Grade 122 steels promotes the coarsening of the Laves phase particles and, in addition to this, the amount of MX inside the subgrains is estimated to be less than Grade 92 steel, which cause severe HRHD and the resultant degradation in rupture strength compared to Grade 92 steel. In a data group subjected to lower stresses than those of Gr.IIIa, the degradation rate is mitigated, and a deformation mechanism was proposed. The improvement in the long-term rupture strength of Grade 122 steel was also discussed.
TL;DR: In this paper , a modified Monkman-Grant equation was used to predict the creep life of Gr.92 using creep data in the NIMS Creep Data Sheets at 550 to 750°C.
Abstract: ABSTRACT A modified Monkman-Grant equation, which can provide a more accurate means of predicting creep rupture life than the standard Monkman-Grant formula, has been investigated for Gr.92 using creep data in the NIMS Creep Data Sheets at 550 to 750°C. The t r versus minimum creep rate min plot, which is called the Monkman-Grant relation, deviates downward at low stresses and long times. Better correlation of the t r with the min is obtained by the replacement of t r with (t r /ε r), where ε r is the total or rupture strain. The (t r /ε r) is inversely proportional to the min over a wide range of stress, temperature and test duration, and the magnitude of data scattering is only a little bit even at low stresses and long times. The creep life of Gr.92 can be predicted by evaluating the min, together with the ε r evaluated from the stress and or min dependence.