Hot Deformation Behavior And Dynamic Recrystallization Mechanism Of Fe-Ni Based Alloys

Fe-Ni based corrosion resistant alloys are widely used in petroleum,chemical industry,metallurgy,nuclear energy,aerospace and other industrial fields,in view of the excellent corrosion resistance,mechanical properties and the 40-50% saving of Ni compared with Ni based alloys.However,due to the late research in our country,the core manufacturing technology has long been monopolized by foreign companies.In order to break the technical barriers of western countries and drive the development of domestic related industries,it is necessary to demonstrate the production process and microstructural evolution of the Fe-Ni-based corrosion-resistant alloys.In addtion,the hot working which is an essential and necessary step in production,has a significant impact on the material structure and performance.Therefore,to prepare corrosion resistant alloy products that meet the requirements,the comprehensive understanding of the impact of processing parameters on the hot deformation and the underlying mechanism scientifically and systematically are inevitable and provide theoretical guidance for controlling the microstructure and optimizing properties.On the basis,using the commonly used Incoloy 028 and Incoloy 825,we thoroughly investigated the flow stress curve and microstructure under a large deformation range,through a Gleeble 3500 thermomechanical simulator,electron backscattered diffraction(EBSD)and transmission electron microscopy(TEM).The dynamic softening mechanism of the Fe-Ni-based alloy during thermal deformation is revealed,and ta dynamic recrystallization kinetic model based on the physical mechanism is established,through the systematic analysis of the characteristic parameters of the flow stress curve and the typical microstructure,The main conclusions of this paper are as follows:(1)By characterizing the flow stress behavior and the typical microstructure,the mechanism of the typical dynamic recrystallization during hot deformation is clarified:discontinuous dynamic recrystallization(DDRX)involves nucleation and grain growth,and the nucleus is mainly generated at triple junctions;continuous dynamic recrystallization(CDRX)is completed along the microbands or the intersection of the microbands from the low angle grain boundary(LAGB)to the high angle grain boundary(HAGB);the necklace structure is controlled by the multi-layer nucleation and growth,and the first layer of grains is formed at the triple junctions and grain boundary bulging,and the subsequent layer nucleation mechanism is mainly produced at the triple junctions between recrystallization and deformed grains,and by twinning chains.(2)The role of twin boundaries in nucleation and growth during the formation of typical chain structures is clarified,by analyzing the evolution of the morphology and content of twin boundaries during the hot deformation of Fe-Ni-based alloys: the pre-existing twin boundaries transform into random HAGB,assisting the formation of the first layer grain;linear twin boundaries are formed behind the grain boundary migration,which promotes the boundary to further migrate to the deformed structure;parts of newly generated twinning chains at the front of the recrystallization zone converted into random HAGBs,providing sites for the following layer of nucleation.(3)The transition of the deformation mechanism and the dynamic softening mechanism of the alloy are revealed,by summarizing the deformation substructure evolution and grain boundary formation/migration law during the hot deformation of the alloy: with increasing temperature or decreasing strain rate(Z parameter decreases),the main deformation mechanism gradually converts from dislocation glide to cross/multiple slip,climb and grain boundary migration;the dynamic softening mechanism varies from continuous dynamic recrystallization(CDRX)to DDRX even dynamic normal/abnormal grain growth(DGG/DAGG),i.e.the transition from the formation to migration of HAGBs,resulting in ultra-fine,fine and coarse-grained structures,and thus proposed a method to prepare multi-scale microstructures.(4)A new physically-based model was proposed by considering the characteristics of grain size distribution,capillary effect of initial grain boundaries(GBs)and continuous consumption of GBs;the model can better describe the discontinuous dynamics of Fe-Ni-based alloys recrystallization process;classifying the linear relationship between thermodynamic driving force and kinetic energy barrier,making it possible to quantitatively control the thermal deformation process.