Creep behaviour and microstructure changes of model cast Ni-Cr-W-C alloys

AbstractA comparative study of creep and microstructural properties of two model cast Ni-Cr-W-C alloys (Alloys A and B) resistant to high-temperature oxidation with different contents of Cr, W, Zr and Fe was performed. Uniaxial tensile creep tests were carried out at temperatures from 1023 to 1273K and at the applied stresses ranged from 20 to 250MPa. Creep tests were followed by microstructural and fractographic investigations. A mutual comparison between the creep characteristics of the alloys under comparable creep loading conditions shows that the alloy B with higher contents of tungsten and zirconium is more creep resistant as that of the Alloy A at lower temperatures. It is suggested that the alloy A and B earn their creep strength from the combination of solid solution hardening and precipitation hardening. However, it is difficult to quantify each contribution to the overall creep strength. Possible reason for the different consequence of strengthening effects is discussed

The Effect of Ultrafine-Grained Microstructure on Creep Behaviour of 9% Cr Steel

The effect of ultrafine-grained size on creep behaviour was investigated in P92 steel. Ultrafine-grained steel was prepared by one revolution of high-pressure torsion at room temperature. Creep tensile tests were performed at 873 K under the initially-applied stress range between 50 and 160 MPa. The microstructure was investigated using transmission electron microscopy and scanning electron microscopy equipped with an electron-back scatter detector. It was found that ultrafine-grained steel exhibits significantly faster minimum creep rates, and there was a decrease in the value of the stress exponent in comparison with coarse-grained P92 steel. Creep results also showed an abrupt decrease in the creep rate over time during the primary stage. The abrupt deceleration of the creep rate during the primary stage was shifted, with decreasing applied stress with longer creep times. The change in the decline of the creep rate during the primary stage was probably related to the enhanced precipitation of the Laves phase in the ultrafine-grained microstructure