Zhu Miaoyong

Three-Dimensional Magnetohydrodynamic Calculation for Coupling Multiphase Flow in Round Billet Continuous Casting Mold With Electromagnetic Stirring

A 3-D combined finite element-finite volume for magnetohydrodynamic (MHD) calculation method considering the coupling flow field, heat transfer, and inclusion trajectory was developed, and the flow characteristics of molten steel and inclusion trajectory in round billet mold using electromagnetic stirring (EMS) were numerically investigated. The calculation results of magnetic field and temperature in the mold are in a good agreement with the measured data. The influence of EMS on the turbulent flow and temperature in the mold is estimated by the model, which shows that EMS has an obvious effect on the flow and temperature distribution of molten steel, and the macrostructure of the billet.

SIMULATION OF THERMAL BEHAVIOR DURING STEEL SOLIDIFICATION IN SLAB CONTINUOUS CASTING MOLD I. Mathematical Model

Thermal behavior of the solidifying shell in continuous casting mold is very important to final steel products. In the present work, one two-dimension transient thermal-mechanical coupling finite element model was developed to simulate the thermal behavior of steel solidifying in slab contin- uous casting mold by using the sequential coupling method. In this model, in order to get the physical properties of steel at high temperature, a microsegregation model which would give the relationship of phase fractions and temperature for acquiring the physical properties with �/ transformation in mushy zone was established. And the heat flux was obtained according to the displacement between the surface of solidifying shell and the hot face of mold as solidification contraction, the liquid/solid structure and distribution of mold flux, the temperature distribution of slab surface and mold hot face, and air gap distribution. In addition, the rate-dependent elastic-viscoplastic constitutive equation was applied to account for the evolution of shell stress in the mold.

SIMULATION OF THERMAL BEHAVIOR DURING STEEL SOLIDIFICATION IN SLAB CONTINUOUS CASTING MOLD II.Model Verification and Results Analysis

Based on the thermal-mechanical coupling finite element model described in PartⅠof present work,the thermal behavior of one high strength ship plate steel solidifying in slab continuous casting mold was simulated with the practical continuous casting conditions of a steel plant,and the availability of the model was verified by in-plant measurement temperature.With this model,the thickness distributions and thermal behavior of air gap,mold flux(including liquid flux and solidified flux),and the variation characteristics of heat flux and surface temperature,as well as the influence of casting speed,mold taper,and mold flux properties on thermal behavior of the steel solidifying in mold were investigated.

Evolution of Dynamically Recrystallized Grains in Steel SCM435

An MMS-200 high-temperature test complex is used to study dynamic recrystallization in steel SCM435. The effect of temperature and strain rate on recrystallized grain size is studied metallographically. Results show that strain parameters have a complicated effect on the number of average grain size, and also on the number of largest and smallest grains. The optimum deformation temperature providing formation of fine and uniform grains increases with an increase in strain rate. On the basis of analyzing the sizes of dynamically recrystallized grains in steel SCM435 a model is developed for calculating average grain size in the temperature range 850–1050°C.

Mechanical Properties and Corrosion Behavior of Bridge Weathering Steels Containing 3.5% Ni

Two types of steel specimens were prepared containing 3.5% Ni in order to study the mechanical and corrosion properties of bridge steels in a marine atmosphere. Corrosion depth was evaluated by measuring weight loss after accelerated corrosion tests by alternating cycles of immersion and drying. Steel microstructure, and corrosion layer characteristics of bridge steels with different Mn content in different stages of corrosion were studied by using methods of light, transmission, and scanning electron microscopy, and also Raman spectroscopy. Results show that the microstructure of the bridge weathering steels consists of quasi-polygonal ferrite, acicular ferrite and granular bainite. Strength and corrosion resistance are improved with an increase in Mn content. The distribution of Ni and Mn is uniform within corrosion product layers, although there is an increase in Cu content within cracks and pores of the corrosion product layer. Corrosion products mainly consist of α-FeOOH, γ-FeOOH, and Fe3O4, and their content through the corrosion layer differs insignificantly.

CORROSION BEHAVIOR OF BRIDGE WEATHERING STEELS IN ENVIRONMENT CONTAINING Cl

In order to understand the corrosion behavior of bridge weathering steels at marine atmosphere, three type steels containing 3.5% Ni were prepared for alternate wet-dry accelerated corrosion test. Microstructures, rust layer morphologies and characteristics of bridge weathering steels with different Mn and Cu contents at different stages were studied by using optical microscope, XRD and SEM. The results show microstructures of the bridge weathering steels are composed of quasi- polygonal ferrite, acicular ferrite and granular bainite. Corrosion resistance of the steels is improved with Mn content increasing. Distributions of Ni and Mn are uniform inside rust layers, but Cu is enriched at gaps and pores in rust layers. Crystal phases are mainly composed of Fe3O4, γ-FeOOH and α-FeOOH in rust layers, however, the compositions are somewhat different at different stages. The formation of γ-FeOOH and α-FeOOH is closely related to the change in corrosion rate. With increasing Mn content, the formation of γ-FeOOH and α-FeOOH are accelerated and their sizes are restrained.