Ren Zhong-ming

Fabrication, Structural and Magnetic Properties for Aligned MnBi

MnBi compound is fabricated under a magnetic field of 1T, and the c-axis of hexagonal MnBi crystal is aligned parallel to the magnetic field direction. The saturation magnetization Ms decreases with the increase of temperature. At temperatures below 200 K, the coercive field Hc is about 150 Oe, while the coercive field Hc increases with temperature above 200K. From 200K to 300K, the remnant magnetization Mr and the Mr/Ms increase with the temperature. Below 200 K, Mr and Mr/Ms reach roughly a constant value. However, there is an abnormal increase at 100 K in Hc, Mr and Mr/Ms, which comes from a spin-reorientation in MnBi. Magnetization results show the spin-reorientation for MnBi at about 91 K due to the variations of the anisotropy constants.

Effect of distribution of magnetic flux density on purifying liquid metal by travelling magnetic field

The distribution of the magnetic flux density in the magnetic field generator which provided travelling magnetic field was determined. The experiments using liquid gallium and aluminum — silicon alloy to observe the turbulent flow or remove inclusions were performed to obtain the basic principles how the distribution of the magnetic flux density took effect on removing inclusions from molten metal by electromagnetic field. The suitable area in the field for purifying metal was suggested.

Grain Refinement During Directionally Solidifying GCr18Mo Steel at Low Pulling Speeds Under an Axial Static Magnetic Field

The present work investigates how axial static magnetic field affects the solidification structure and the solute distribution in directionally solidified GCr18Mo steel. Experimental results show that grain refinement and the columnar to equiaxed transition is enhanced with the increases in the magnetic field intensity (B) and temperature gradient (G) and the decrease in the growth speed. This phenomenon is simultaneously accompanied by more uniformly distributed alloying elements. The corresponding numerical simulations verify a thermoelectric (TE) magnetic convection pattern in the mushy zone due to the interaction between the magnetic field and TE current. The TE magnetic convection in the liquid should be responsible for the motion of dendrite fragments. The TE magnetic force acting on the dendrite is one of the driving forces trigging fragmentation.

PHYSICAL SIMULATION OF Ar BUBBLE BEHAVIOR IN THE SOLID/LIQUID INTERFACE OF CONTINUOUS CASTING BILLET

Ar gas was injected to the nozzle during continuous casting to prevent from nozzle clogging caused by solid inclusions,however,some gas bubbles were captured by the initial solidified billet shell,and subsequently billet defects were formed in final product.In present work,a physical model applying mold simulator was designed and used to investigate the bubble behavior in the solid/liquid interface.Different mold simulator angels and bubble diameters were considered,three typical behaviors were observed,some bubbles were captured by the solidified shell,several bubbles coalescence in the solid/liquid interface,and other bubbles stayed in the interface for a moment,and then left.The possible mechanism of gas bubble entrapped in solidified shell was analyzed.Besides, industrial billets were studied,many dendrites were found around the hole,it was considered to be a key factor for gas bubble engulfed in the solidification billets in the meniscus area.Further more,the effective technologies,such as electrical brake near the submerged entry nozzle and electrical stirring in the mold narrow face,can improve billet quality and reduce gas bubbles in solidified shell were imposed.

Crystalline and Magnetic Enhancement of Nanocrystalline MnZn Ferrites Fabricated under a High Magnetic Field

Nanocrystalline Mn0.6Zn0.4Fe2O4 particles are synthesized under magnetic fields of 0 and 6 T, and their structural and magnetic properties are investigated. The magnetic field enhances the grain size and the lattice strain. Magnetic measurements show that the majority of the 6 T nanoparticles are superparamagnetic nearly from 40 to 300 K. It is interesting that the saturation magnetization of the 6 T sample is about 18% and 16% higher than that of the 0 T sample at 120 and 300 K, respectively.

In-Situ Alignment of MnBi Crystals Induced by High Magnetic Field above Curie Temperature

Above Curie temperature, MnBi crystals are aligned in situ along the c-axis in a Bi matrix by a high fabrication magnetic field Hf of 10 T. Magnetic testing shows a pronounced anisotropy in magnetization in directions normal and parallel to the fabrication field, resulting from the alignment. The successful alignment may result from the fact that the easy magnetization direction is along the c-axis of MnBi and the high fabrication field of 10 T is large enough to rotate the MnBi crystal to this direction even though the temperature is above the Curie temperature.

Experimental investigation on solidification of GCr15 bearing steel by the simulated continuous casting

ABSTRACT An experimental apparatus for simulation of continuous casting process of GCr15 bearing steel billet is established. With the apparatus, the billets of diameter 140 mm are casted in various superheats and cooling conditions. The solidification macrostructure, dendrite morphology, segregation and carbide are investigated. It is shown that melting superheats and cooling conditions remarkably influence the microstructure and solute segregation. It is found that the secondary dendrite arm spacing of the steel increases with the increase of the superheat temperature, and with decrease of the cooling rate. Lower superheat with higher cooling rate promotes the refining of the microstructure. Refining equiaxed grains structure in the centre of the billet leads to lower segregation of carbon. Furthermore, with increasing cooling rates, the spacing of the pearlite laminar is refined and the precipitation of proeutectic carbides is suppressed.

EXPERIMENTAL STUDY ON FLOWIN SLAB MOLD CONTROLLED BY JET–PATTERN MAGNETIC FIELD

A mercury model was developed to investigate the control of the jet-pattern magnetic field on the flow in medium and heavy slab continuous casting mold.The velocities in mold with and without magnetic field was measured by ultrasonic Doppler velocimeter.The influences of the magnetic field on the flow discharged from the nozzle,the flow in the mold,the flow at the meniscus and washing intensity to wall were analyzed and studied.The results showed that the flow discharged from the nozzle is suppressed,and dissipated before impinging against wall,the flow in the upper eddy is strengthened,the flow in the lower eddy is weakened,and the flow at the meniscus is improved by jet-pattern magnetic field.Compared with electromagnetic braking(EMBr) ruler,the brake effect of the the jet pattern magnetic field on the flow discharged from the nozzle and the flow at the meniscus are the better.

Improvement of the structure and the electromagnetic characteristics of an induction ladle furnace

Based on a numerical analysis of the alternating electromagnetic field in the process of Steel refining with an induction ladle furnace (ILF), the optimization of the structure of ILF and the electromagnetic field for melting is realized in the present work. The optimization of the ILF by outward extension of inner yokes can decrease the magnitic flux leakage obviously, reduce the eddy current energy loss dramatically and then, decrease the total power consumption.