Primary Recrystallization of Grain Oriented Silicon Steel Strip Rolled by CSR and Annealed in Magnetic Field

The magnetic properties and textures of grain oriented silicon steel with different thickness rolled by cross shear rolling （CSR） of different mismatched speed ratio （MSR） and annealed in magnetic field under hydrogen were presented.Effects of the factors such as thickness and mismatched speed ratio on the magnetic properties and recrystallization texture were analyzed and the recrystallization principles in magnetic field annealing were discussed. The study would provide a new route for mass production of high quality ultra-thin grain oriented silicon steel strip.

Continuous Cooling Bainite Transformation Characteristics of a Low Carbon Microalloyed Steel under the Simulated Welding Thermal Cycle Process

Continuous cooling transformation of a low carbon microalloyed steel was investigated after it was subjected to the simulation welding thermal cycle process and the interrupted cooling test. Microstructure observation was performed by optical microscopy and transmission electron microscopy. On the basis of the dilatometric data and microstructure observation, the continuous cooling transformation （CCT） diagram was determined, which showed that the main microstructure changes from a mixture of lath martensite and bainitic ferrite to full granular bainite with the increase in the cooling time t8/5 from 10 to 600 s, accompanied with a decrease in the microhardness. The interrupted cooling test confirmed that the bainitic ferrite can form attached to grain boundaries at the beginning of transformation even if the final microstructure contains a mixture of granular bainite and bainitic ferrite.

Effect of boron addition on the microstructures and mechanical properties of thermomechanically processed and tempered low carbon bainitic steels

Thermomechanical process and tempering heat treatment were employed to produce the experimental steel plates. The effect of boron addition on the microstructure and mechanical properties of low carbon bainitic steels was studied in this paper. Microstructure observation and crystallographic features were conducted by using optical microscopy, SEM, TEM and electron back scattering diffraction （EBSD） analysis. The results showed that under the same rolling processes and heat treatment conditions, a substantial increase in strength is obtained by addition of boron into steel, but accompanied by an obvious drop in toughness. New martensite phase forms along the grain boundaries on tempering at 650℃ mainly due to boron segregation, which can further deteriorate impact toughness of the boron bearing steel. The EBSD analysis showed that high angle grain boundary, is not responsible for the deteriorated toughness of the boron bearing steel because it has relatively higher percentage of high angle grain boundary than the boron free steel. The low toughness of the boron bearing steel is mainly attributed to the coarse boride precipitated particles according to the results of fractograph observation.

Microstructural Evolution and Toughness in the HAZ of Submerged Arc Welded Low Welding Crack Susceptibility Steel

Microstructural characteristics of different sub-regions of heat affected zone （HAZ） of low welding crack susceptibility steel weldment were investigated by using optical microscopy and scanning electron microscopy equipped with electron backscattered diffraction system. And the focus was put on the correlation between microstructural characteristics and HAZ toughness of the weldment. The results reveal that the toughness of fusion line zone （FLZ） specimens is much lower than that of fine grained HAZ （FGHAZ） specimens. The coarse inclusions in the weld metal and the large martensite-austenite constituents in the coarse grained HAZ （CGHAZ） have an obvious negative effect on the crack initiation energy of FLZ. Meanwhile, the coarse granular bainite with large effective grain decreases the crack propagation energy seriously. By contrast, fine crystallographic grains in the FGHAZ play a key role in increasing toughness, especially in improving crack propagation energy.