Yuanxiang Zhang

EFFECT OF NANOCRYSTALLINE AND TWIN BOUNDARIES ON CORROSION BEHAVIOR OF 316L STAINLESS STEEL USING SMAT

By means of surface mechanical attrition treatment (SMAT), the grain size with a diameter of about 60nm formed at about 20μm depth and numerous mechanical twins at about 50μm depth from the treated surface were synthesized in 316L stainless steel because of the different distributions of strain and strain rate along depth orientation. For instance the maximum strain rate reached 103–104s−1 on the top surface. The relationship between the microstructure and the corrosion property was studied in 0.05M H2SO4+ 0.25M Na2SO4 aqueous solution, and the results show an extreme improvement of corrosion resistance owing to the appearance of twin boundaries and the obvious reduction in corrosion resistance attributed to the presence of nanocrystaline boundaries.

Precipitation Behavior of 1.3%Si Non-oriented Silicon Steels During Strip Casting Process

In this work, the precipitation behaviors of 1.3%Si non-oriented silicon steel during the sub-rapid solidification process under different melt superheat were investigated using scanning electron microscope and transmission electron microscope, based on strip casting process. The results showed that the precipitates of as-cast strips were dominated by coarse AlN, and MnS particles were seldom observed. The mean size of AlN particles rapidly increased from 75 to 1060 nm, and the volume fraction increased from 0.028 to 0.069%, when the melt superheat increased from 20 to 70 °C. Besides, the precipitation quantity in the center layer of as-cast strip was obviously more than the surface layer. According to the different solubility ability in the liquid and ferrite matrix, Al or N elements tend to segregate during the sub-rapid solidification process, which is attributed to the nucleation and coarsening of AlN. On the condition of low melt superheat, the solidified layers suffered from hot deformation from the solidification end point to the nip point, which provided additional nucleation sites for precipitates and can be attributed to fine particles size. In addition, different heat conductivity and hot deformation degree in various thickness layer resulted in inhomogeneous distribution of particles through the thickness of as-cast strips.

Evolution of Microstructures and Texture of 1.3%Si Non-Oriented Electrical Steel in the Twin-Roll Strip Casting Process

In this work, the influence of casting rollers which had different thermal abilities on microstructure and texture of 1.3%Si non-oriented electrical steel was investigated in a twin-roll strip casting process. The cooling capacity of copper rollers is stronger than that of steel ones, and the difference of heat transfer capacities had an obviously effect on the solidification structure and texture. The results show that the microstructures with an average grain size of ~60–200μm and ~120–320μm could be respectively obtained in strips under both copper rollers and steel rollers conditions when the melt superheats were in the range of 30 to 50°C There was a relatively random and diffuse texture in strips under copper rollers condition compared to the one under steel rollers condition, which lead to the occurrence of relatively weak Goss, Cube and γ-fiber in the annealed sheet.