High temperature low cycle fatigue behaviour of P92 tungsten added 9Cr steel

Abstract

Modified 9Cr-1Mo steel is being used extensively as structural material for steam generator components of liquid metal cooled fast breeder reactor and fossil fired power plants. The selection of this material is primarily based on a good combination of mechanical properties, high thermal conductivity, low thermal expansion coefficient and good resistance to stress corrosion cracking in water-steam and sodium environment systems compared to austenitic stainless steels. A further improvement of the thermal efficiency of modern steam turbines can be achieved by increasing the steam operating temperature. It has been found that the substitution of W for Mo enhances the high temperature tensile strength, fracture toughness and creep strength. This had led to the development of P92 Steel.The components of the steam generators are often subjected to repeated thermal stresses as a result of temperature gradients that occur on heating and cooling during start-ups and shut-downs or during temperature transients. This leads to low cycle fatigue (LCF) damage in the component. However, the data on LCF properties of the W added 9Cr steel (designated as P92 steel) is scarce and this paper aims in understanding the high temperature low cycle fatigue behaviour of P92 Steel.Total axial strain controlled low cycle fatigue tests have been conducted in air in the temperature range 823 and 873 K to ascertain the influence of temperature on the LCF behaviour of the steel. A constant ramp rate of 3 × 10 -3 s -1 was employed for all the tests. The alloy exhibited a continuous softening before the final load drop that occurred due to the propagation of macro fatigue cracks. The softening rate is more for the tests conducted at higher strain amplitudes compared to that of lower strain amplitudes. Fatigue life decreased with increasing temperature and strain amplitude. In this paper the observed LCF results have been explained based on the detailed metallography and fractography conducted on the failed samples.

Designing P92 grade martensitic steel header pipes against creep–fatigue interaction loading condition: Damage micromechanisms

“…The cyclic softening results obtained by Kannna et al [10] also confirms to the present observation.…”

“…For P92 a substantial body of creep data was developed to enable code approval and further investigations have been carried out to obtain longer term properties and to evaluate the performance of welded joints. Also some work has been carried out to characterize the isothermal LCF [10] behaviour. Though the response of the microstructure to creep and fatigue loading conditions has been studied for P91 [11][12], it appears that work on the creep fatigue interaction in P92 is not extensive.…”

Cyclic behaviour of 12% Cr ferritic‐martensitic steel upon long‐term on‐site service in power plants

“…4 The X20CrMoV12.1 steel, typically 10 to 12% Cr, has been used as heat exchanger, steam pipes/tubes, boilers and turbine parts in Europe since the 1960s. 1-3 These characteristics permit to consider them being extensively used as structural materials for the steam generator components and fossil-fired power plants.…”

“…1-3 These characteristics permit to consider them being extensively used as structural materials for the steam generator components and fossil-fired power plants. 4 The X20CrMoV12.1 steel, typically 10 to 12% Cr, has been used as heat exchanger, steam pipes/tubes, boilers and turbine parts in Europe since the 1960s. 5 The alloy has typical strengthening possibilities such as solid solution by high content of Cr and Mo, refined grains by formation of tempered martensitic lath structure and precipitation of the uniform dispersion of M 23 C 6 carbides that were Cr enriched and fine MX-type carbides rich in V and Nb homogeneously.…”

Evaluation of the Effect of Dynamic Sodium on the Low Cycle Fatigue Properties of 316L(N) Stainless Steel Base and Weld Joints

“…Detailed investigations have been carried out on the room and elevated temperature properties of indigenously produced 316L(N) stainless steel [1][2][3] and weld joints [4][5][6][7]. Liquid sodium has been chosen as the heat transfer medium in Liquid Metal Fast Breeder Reactors (LMFBRs), because of its high thermal conductivity, heat capacity, and it remains in the liquid phase over a wide range of temperatures.…”