Study On The Microstructure And Mechanical Properties And Forging Process Of11Cr10Co2W2MoReVNbNB Steel

Cr-Co-W-Mo steels possess very high hardness, strength, and high temperatureapplication properties, thus are widely used for manufacturing moving bladesworking at elevated temperature for ultra-super critical steam turbines. The newsteel,11Cr10Co2W2MoReVNbNB, has very good high temperature applicationproperties owning to adding refractory element such as Re, Nb, based onCr-Co-W-Mo steels. However, the blades do not meet the applicationrequirements due to the coarse and inhomogeneous grains, and the stress rupturetime under the condition of650℃and245MPa is only245hrs. Thus, reforging isdone for the the11Cr10Co2W2MoReVNbNB steel in order to make the grainsof the materials be fine, and quenching and tempering after reforging is done withthe purpose of making the structure and the properties be uniform and stable.This paper studies the deformation rules at high temperature for the11Cr10Co2W2MoReVNbNB steel using the hot compression test method, anddiscusses the correlation between the flow stress and flow velocity anddeformation during the high temperature deformation of the steel. The hotworking map is made using the data from the hot compression test, thus the bestworking region is gotten, i.e. deformation within1150～1210℃, and flowvelocity within0.1～0.6/s. Forging test within the best working region is done forthe steel. After forging, the grain of the steel is fine and equiaxed, the powerdissipation rate is within44%~47%. Heat treatment test is done for the new steel,and the best heat treatment process is defined, i.e. austenitizing at1120℃oilquenching, and tempering at680℃, air cooling. Furthermore, this paper observesthe microstructure of the11Cr10Co2W2MoReVNbNB after hot compression test,forging and heat treatment using optical microscopy, scanning electronicmicroscopy, and transmission electronic microscopy, and analyzes the grain size,dynamic recovery, dynamic recrystallization, the distribution of the dislocationand precipitate phases, and gives the theoretical analysis between the deformationstructure and the properties of the steel.After reforging and heat treatment both with the best process parameters, thegrain size of the11Cr10Co2W2MoReVNbNB steel is Grade4.5-5, the structureis uniform, the mechanical properties at room temperature are enhanced significantly, the stress rupture time is over300hrs, and the yield strength at630℃reaches450MPa, and all the properties meet the requirements for using asblade materials for the USC turbine.