Influence Of Niobium On Precipitates And Texture Of 3% Si Grain-oriented Silicon Steel

Grain-oriented silicon steel is a kind of functional material used in power system transformers,whose performance has an important influence on power system energy loss.There is an extremely strong Goss texture（{110}<001>texture）in the grain-oriented silicon steel and therefore excellent magnetic properties in the<001>direction.However,the production process of grain-oriented silicon steel is complicated.The mechanism of action of its inhibitor and secondary recrystallization is not clear,which restricts the simplification of its technology and the improvement of reliability.At the same time,it is the main direction for the world’s important silicon steel producers to adopt the energy-saving,environmentally friendly and economical low-temperature slab reheating technology to produce grain-oriented silicon steel with excellent magnetic properties under the current situation that the grain-oriented silicon steel performance is approaching the material limit.In order to further simplify the production process,reduce slab reheating temperature,and stabilize the product performance,the present study proposed the use of Nb as an inhibitor of grain-oriented silicon steel to form elements.The evolution of precipitates and microstructures after hot rolling and primary recrystallization was systematically studied.And comparison was made with the traditional orientation of silicon steel.The specific research contents and research results are as follows:（1）The hot-rolled plate in the precipitation and texture of the organization were studied.After the traditional oriented hot-rolled silicon steel,the inhibitor precipitation rate is very low,the particle size is coarse and sparsely distributed,the unit area of only 1.09×10⁵/mm²,the average diameter of 60.1nm.The main components to MnS and a small amount of MnS and AlN composite precipitates.After normalization,the traditional orientation of silicon steel precipitated part of the small inhibitor,the number increased greatly,the number of units per area of4.21×10⁶/mm²,the average diameter of 64.3nm.The texture of the conventional grain-oriented silicon steel after hot rolling mainly includes{110}<001>,{112}<111>and{001}<100>texture,and the initial Goss grain content is relatively high.While the hot rolled plate of Sample#2 has a certainγ-ray texture,such as{110}<001>,{111}<112>and{110}<112>texture with intensity of 3 to 4.（2）The precipitates and the structure of the plate are studied.After hot rolling of niobium-bearing grain-oriented silicon steel,the inhibitor precipitation ratio is high,the particle size is small and a large number of distributions,the number of unit area of 3.8×10⁷/mm²,the average diameter of 34.1nm.The main component is Nb（C,N）.After normalization,some of the inhibitors in the niobium-bearing grain-oriented silicon steel were re-solution dissolved to a lesser extent,with a unit area of9.08×10⁶/mm²and an average diameter of 67.5nm.Experimental results show that with niobium-bearing grain-oriented silicon steel after hot rolling inhibitor precipitation ratio is large enough,you can omit the normalization process.The main texture of the conventional grain-oriented silicon steel is{111}<112>and{111}<110>texture.<100>texture.Theγtextures of the two samples are all between 2 and 3,and the grain growth caused by the normalization has certain weakened effect on the texture.（3）Calibrate the lattice constant of the precipitates in the niobium-bearing grain-oriented silicon steel to prove its chemical composition.The lattice constant of Nb（C,N）shows that the lattice constant of Nb（C,N）is about 4.456?before the normalization and Nb（C,N）is Nb(C_0.85,N_0.15).The normalized Nb（C,N）lattice constant is about 4.431?,and the specific composition of Nb（C,N）is Nb(C_0.71,N_0.29).The Nb（C,N）precipitation temperature in the hot-rolled sheet is relatively low due to the relationship between the Nb（C,N）carbon and nitrogen atomic ratio and its precipitation temperature,probably because part of the Nb（C,N）Coiling between the cooling stage precipitation.Adjusting the post-hot rolling cooling conditions of the niobium-bearing grain-oriented silicon steel optimizes the precipitation of Nb（C,N）,thereby omitting the normalizing process.（4）The traditional grain-oriented silicon steel after nitriding precipitates were studied.After nitriding,the number of inhibitor particles in the conventional grain-oriented silicon steel further increases,but the particle distribution in the surface layer and the central part is not uniform.The average size of surface precipitates after nitriding is 35.97nm,the number of unit area is 5.57×10⁷/mm²,the average size of center layer precipitates is 46.85nm,the number of unit area is 1.32×10⁷/mm².Nitriding achieved the highest level of inhibitor of conventional grain-oriented silicon steel with an order of magnitude and unit area of Nb（C,N）after hot rolling.（5）The structure and texture of the initial recrystallization were studied.After the initial recrystallization,the uneven grain size distribution of the primary recrystallized grains due to the uneven distribution of the inhibitor particles in the conventional grain-oriented silicon steel.The average grain size of the center layer was 18.53μm,the average grain size of the surface layer was 6.47μm,and the average size of all grains was 11.56μm.The distribution of inhibitors in niobium-bearing grain-oriented silicon steel is homogenous.Grain size in the thickness direction of the samplehas novariation,the average grain size of 7.32μm.However,the（111）<112>textures of the niobium-containing samples are relatively stronger and more favorable to the Goss textures in the secondary recrystallization process grow up.