| Grain-oriented silicon steel has abnormally large size grains of secondary recrystallization and presents a sharp Goss texture,so it has the excellent properties of high magnetic sensitivity and low iron loss parallel the rolling direction,and is widely used in transformer manufacturing.Using low-temperature slab reheating in hot rolling to manufacture grain-oriented silicon steel is a low carbon and energy saving production method at present.Due to the use of fewer inhibitors with lower solution temperatures,the ability of the so-called inherent inhibitors to control the growth of primary recrystallization is weakened,so nitriding is required to compensate for the amount of precipitates to control the abnormal growth of secondary recrystallization.Therefore,it is a hot topic in the R&D of grain silicon steel how to control the growth of primary grain effectively by low-temperature slab heating technology and improve magnetic properties after high temperature annealing.An improved approach is to add trace alloying element.Some microalloying elements can inhibit the normal growth of grains by segregation at boundaries,while others can improve the distribution of precipitates.The size of the precipitates containing Nb are small in size and well dispersed,and the low solution temperature is expected to further reduce the slab reheating temperature.On the other hand,there are still very limited studies on the effect of trace Cr on characteristic of primary recrystallization structure and magnetic properties of low-temperature reheating grain-oriented silicon steel,which is an urgent demand for improvement production in industry.In this study,the evolution of precipitates,microstructure and texture in grain oriented silicon steel manufactured by low-temperature slab reheating method with added trace Nb and Cr has been studied respectively,the effects of Nb and Cr on secondary recrystallization and magnetic properties of grain orientated silicon steel were discussed.The research contents and results are as follows:(1)The characteristics of inhibitor,microstructure and texture in primary recrystallization of low-temperature grain-oriented silicon steel with Nb content of 0.005wt%,0.010 wt% and 0.030 wt% were studied.The results show that the amount of precipitates increases with the growth of primary recrystallization during decarburization.The addition of Nb increased the proportion of the fine precipitates below 40 nm in primary recrystallization of grain orientated silicon steel,which increased from less than25% of the sample without Nb to more than 30% of the sample with Nb.Meanwhile,Nb can significantly reduce the size of primary recrystallization size of grain-oriented silicon steel.With the addition of 0.005 wt%,0.010 wt% and 0.030 wt% Nb,the average size of primary grain decreased from 31 μm to 23 μm,21 μm and 16 μm respectively and the size distribution of primary recrystallization became uniform.With the increase of Nb content,the texture content of {111}<112> increased while the content of {114}<481>decreased in the primary recrystallization,but the sum of texture content of {111}<112>and {114}<481> increased with the addition of more than 0.010 wt % Nb.(2)The effects of Nb content on the primary recrystallization texture and secondary recrystallization behavior of low-temperature grain-oriented silicon steel with Nb content of 0.005 wt%,0.010 wt% and 0.030 wt% were studied.In primary recrystallization texture,the texture with abnormal growth ability had a great influence on the magnetic properties.With the increase of Nb content,the contents of Goss texture,deviated Goss(deviation Angle ≤ 15°),{001}<110> and {110}<112> in primary recrystallization increased.More Goss grains in primary recrystallization can grow abnormally,leading to the decrease of the final grain size.However,the larger deflection Angle of Goss grains in the secondary recrystallization and the abnormal growth of {110}<112> grains led to the dispersion distribution of Goss texture in the final product texture,which would have an adverse effect on the magnetic properties.(3)Magnetic properties of low-temperature grain-oriented silicon steel with different Nb content showed that the sample containing 0.005 wt% Nb could obtain perfect secondary recrystallization,and its {110}<001> texture was the most sharp.With the best magnetic properties,its magnetic properties can be as follow: B800 = 1.873 T,P1.7/50 = 1.21 W/kg.Adding trace Nb can improve the magnetic properties of the product.(4)The microstructure and texture of normalized samples and decarburization samples with Cr addition were studied respectively.With 0.145 wt% Cr,the layer structure in normalized recrystallization is narrower,and the difference between the surface layer and the center layer is smaller.Texture of the normalized recrystallization is weak and becomes scattered in the direction of {001}<110>,{112}<110> and{110}<001>.The texture on the γ-line around {111}<112> direction also appears.The addition of Cr has little effect on the change of normalized recrystallization texture.The grain size of primary recrystallization with 0.145 wt% Cr is 29.1 μm,which is slightly smaller than that of the low-temperature grain orientated silicon steel without Cr which is31.5 μm.The addition of Cr contributes to smaller grain size,and {111}<112> and{111}<110> components of γ-fiber texture become stronger than those of Cr-free grain-oriented silicon steel.While the texture content of {110}<001> has little change by adding trace Cr,the Goss grains are more in quantity and smaller in size.(5)The characteristics of precipitates in low-temperature grain-oriented silicon steel with Cr addition and its effect on secondary recrystallization behavior were studied.In addition to the conventional precipitates,the composite precipitates(Si,Cr)N were found by adding 0.145 wt% Cr after nitriding,and the amount of precipitates also increased correspondingly.Two kinds of Cr-containing nitrides were formed after nitriding in grain-oriented silicon steel with 0.145 wt% Cr,a large amount of amorphous(Si,Cr)N and the crystalline face-centered cubic Cr N with a size below 50 nm.In the process of high temperature annealing,the precipitates containing Cr were smaller in size and larger in quantity.Due to the stronger pinning ability,the starting temperature of secondary recrystallization raised nearly 20 ℃ by adding 0.145 wt% Cr.(6)The effects of Cr on final grain,static magnetic domain and magnetic properties of low-temperature grain-oriented silicon steel were studied.The reduction of secondary recrystallization size by Cr led to the narrowing of magnetic domain width.By adding0.130 wt% Cr,the average iron loss reduced about by 5.1 % at 50 Hz,4.0 % at 100 Hz and 3.6 % at 200 Hz respectively.However,the size decrease of secondary recrystallization and the increase of grain boundaries in finished products had adverse effects on magnetic induction,therefore the magnetic induction B800 of Cr-containing low-temperature grain-oriented silicon steel also decreased.The addition of Cr can reduce the iron loss of low-temperature oriented silicon steel and thus improve the product grade,but it has an adverse effect on the improvement of magnetic induction. |
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