No abstract

In order to develop a third-generation automobile steel with powerful strength and elongation, we propose a method through high temperature quenching and two-phase region reverse-phase transformation annealing to develop such steel with 0.13% C and 5.4% Mn. To investigate the microstructure evolution and mechanical properties of manganese steel, SEM, XRD and TEM are employed in our experiments. Experimental results indicate that the microstructure after quenching is mainly lath martensite microstructure with average of lath width at 0.5 μm. The components of the steel after along with reverse-phase transformation annealing are ultra-fine grain ferrite, lath martensite and different forms of austenite microstructure. When the temperature at 625 °C, the components of the steel mainly includes lath martensite microstructure and ultra-fine grain ferrite and the fraction of austenite volume is only 5.09%. When the annealing temperature of reverse-phase transformation increase into 650 °C and 675 °C, the austenite appears in the boundary of the ferritic grain boundary and the boundary of lath martensite as the forms of bulk and lath. The phenomenon appears in the bulk of austenite, and the size of is 0.22 μm, 0.3 μm. The fraction of austenite volume is 22.34% at 675 °C and decreases into 9.32% at 700 °C. The components of austenite mainly includes ultra-fine grained ferrite and lath martensite. Furthermore, the density of decreases significantly, and the width of martensite increases into 0.32 μm. In such experimental settings, quenching at 930 °C with 20 min and at 675 °C with 30 min reverse-phase transformation annealing, the austenite volume fraction raises up to 22.34%.

The evolutions of microstructure and texture of ultra-thin high-grade non-oriented silicon steel for new energy vehicles were investigated in this paper, and the formation mechanism of typical recrystallized α*-fiber texture was described. The results show that: The microstructure of the hot rolled plate was inhomogeneous along the thickness direction because of the shear force and temperature gradient, resulting in the texture in each layer of the hot rolled plate appearing rotational distribution around the Goss orientation. After normalizing, the fully recrystallized microstructure was obtained, and α*-fiber texture was formed. Banded structure was obtained in the cold rolled sheet, with α-fiber texture {114}<110> dominated. The typical α*-fiber texture was formed after annealing recrystallization, which mainly consist of {114}<481> and {113}<361>. The {114}<481> oriented grains were mainly nucleated within the deformed {114}<110> grains and at the grain boundaries of α-fiber deformed grains, and without size, quantity and strength advantages. {111}<112> is dominated in the early stage of recrystallization, but {114}<481> became the main texture with size, strength and quantitative advantages in the late stage of recrystallization.

The grain-oriented silicon steel was produced by medium temperature reheating and two-stage cold rolling process, and the microstructure and texture of all metallurgical processes were studied. The results shown that the microstructure of the hot rolled strip was inhomogeneous in thickness direction, the surface layer was the recrystallized microstructures with average grain size of 42.29 µm, the center layer was fiber structure, and the Goss texture appeared at surface. The primary recrystallized microstructure with average grain size of 16 µm was obtained after decarburization annealing, which characterized by a strong γ-fiber texture and a weak Goss texture. The average size of inhibitors in hot rolled strip and decarburization annealed sheet were 9.078 and 21.691 nm respectively, they were mainly compound of nitride and sulfide with spherical or lump shapes. The coarse Goss grains with average size 17.57 mm were got after secondary recrystallization, and the magnetic induction B8 and iron loss P1.7/50 were 1.885 T and 1.10 W/Kg, respectively.

A grain-oriented silicon steel sheet was manufactured by slab reheated at “medium temperature” and two-stage cold rolling method. The function of heating rate on secondary recrystallization in grain-oriented silicon steel was investigated. The results show that: compared with 30 °C/h heating rate, the initial temperature of the secondary recrystallization can increase by 10 °C at the heating rate of 20 °C/h. Furthermore, the temperature region of secondary recrystallization also extended either with the increased heating rate. Even though the inhibitors maintain AlN, complex precipitation of AlN and sulphide in both heating rate, the average diameter and Zener factor of inhibitors are distinct. Inhibitors in the route of 20 °C/h heating rate express stronger inhibition than that of 30 °C/h, and the average diameter and Zener factor are 17.519 nm and 3.925 × 10−4 nm−1, respectively. In addition, more Goss texture component and less γ-fiber texture ({111}//ND) component form at the heating rate of 30 °C/h than 20 °C/h at 1000 °C, but the final Goss texture component of 20 °C/h is greater than 30 °C/h. The average grain size of the final annealing sheets increased with the heating rate decreasing from 30 °C/h to 20 °C/h, and iron loss reduced by 0.05 W/Kg, the magnetic induction intensity increased by 0.025 T.