Study On Applications Of Muti-Phase Separation Technology (MPST) To P92Steel

Recently, ultra supercritical (USC) boilers for fossil power plants have been applied for reduction of CO2gas emission in the world. Their steam condition is above600?with25MPa now. This requires new high Cr ferrite heat resistant steels with improved creep rupture strength and steam-oxidation resistance at elevated temperatures exceeding600?. Addition of W to the steel has been found to be effective to increase creep rupture strength at high temperature and been already used in some developed steels such as P92steel.In this paper, thermodynamic method and MPST method were applied to study the change of phase parameter of main phases in P92steel at as-received, aging, rupture conditions. The results revealed the transition and change of microstructure of P92and be help to develop the new generation heat resistant steels.With the help of MPST, as-received samples of P92coming from different manufacturers were studied. The composition and amount of the M23C6, as the main phase, was measured and calculated in this study. The results are helpful to evaluating quality of P92of different manufacturers and selecting reasonable heat treatment.Using the as-received P92steel pipe samples with/without5-ferrite as objects and EPMA-EDS+MPST (Multiphase Separation Technique), this work investigated the effects of ?-ferrite on the volume fraction and composition of M23C6and Laves phases precipitated in the ageing treatment at700?and750?for1000,3000and5000h, respectively. The results are as follows. The existence of ?-ferrite promoted aggregation and coarsening of M23C6and Laves particles precipitated along boundaries with its neighboring lath martensite at the expense of consuming Cr, Mo and W in ?-ferrite during the ageing treatments. With decreasing ageing temperature, the volume fraction of M23C6(Laves) increased in the samples without ?-ferrite (with ?-ferrite). Owing to a few amount of Laves formed at higher temperature, the volume fraction of M23C6increased in the samples with ?-ferrite. And increasing ageing temperature and time stimulated the coarsening of particles precipitated in the pipe samples investigated. It is expected that the related information from this study on the effects of existence of ?-ferrite on the microstructural stability and high temperature properties of P92can be used as a reference when needed.Characteristics of stress level multi-regions and the corresponding quantifications of M23C6and Laves phases are studied for P92steel samples subjected to625?-creep-rupture tests. The result reflects that the stress vs. rupture-time plot obtained from the test result can be divided into two regions (higher stress level and shorter rupture time region:180-150MPa/30-454h, and lower stress level and longer rupture time region:140-110MPa/2881-10122h) respectively, and accordingly the characteristic for the microstructural evolution is also shown as the two corresponding regions; The higher stress level and shorter rupture time region corresponds to the M23C6particle coarsening while the lower stress level and longer rupture time region to the coarsening of both M23C6and Laves phases; The composition, the amount and the elemental partitioning fraction of the alloy phases called phase parameters can be determined based on the creep-rupture test data through the application of the multiphase separation method developed.The studies suggested that MPST method was widely used in the analysis of microstructure of metal materials. The practicality and accuracy of this technology have been proved. Therefore, the MPST algorithm has been programmed to the dll files by COM connector of Matlab software. Then graphical interface developed by Visual Basic software, Microsoft Excel tables and the dll files were used to program to MPST software. The software realized the batch processing of MPST algorithm, simplified the calculation and improved the computational efficiency. So developing the software base on this method will promote the application of this technology. This technology must be more used in analysis of materials.