Shu Ying Chen

Control of Liquid-Drop Surface Shape in Melt

The carbon steel samples of great quality can not be melted using a high-temperature confocal scanning laser microscopy(HTCSLM). On account of only arc surface of the tiny liquid-drop top is observed, it is difficult to obtain distinct images. The shape variation of the tiny liquid-drop is studied experimentally in this article. The results show that the shape of the liquid-drop will be changed at 1600°C, when the carbon steel sample of 0.5g is laid on the Al2O3 sloping of 15 degrees. Though the radius of curvature of the liquid-drop top surface is obviously enlarged, the impact of improving the surface shape of liquid-drop through the gravity flow of tiny liquid-drop is finite. For the carbon steel sample of less than 0.8g, the hanging drop is automatically formed in the melting process under the condition that the gap between the solid sample and Al2O3 single crystal plate is 0.3mm, and the shape retains invariant when it is hold for 20 min at 1600°C. The contact surface between the sample and Al2O3 single crystal plate is 24mm2.

Influence of Carbon Content on the Solid-State Shrinkage and Expansion of Carbon Steel

The self-made device to test the shrinkage ratio and temperature of cast ingot is used to measure the shrinkage mass of Fe-0.1%C, Fe-0.15%C, Fe-0.33%C cast ingot with the dimension of 200×80×100mm. The results show that the total shrinkage mass of cast ingot is increased with the increase of carbon content. In the carbon content range of the experiment, the rate of shrinkage and expansion of Fe-0.15%C steel during, before and after eutectoid reaction is all the quickest. The solid-state shrinkage rate of Fe-0.15%C steel before eutectoid reaction is 288 μm•s-1. The shrinkage mass and rate of cast ingot after eutectoid reaction are 0.051 mm and 127 μm•s-1, respectively. The expansion mass and rate of cast ingot during eutectoid reaction are 0.016 mm and 53.3 μm•s-1, respectively.

Effects of Melt Superheating Holding Time on Solidification Structure and Mechanical Property of AZ31B Magnesium Alloy

Effects of melt superheating holding time on microstructure and mechanical properties of AZ31B magnesium alloy were studied. The results show that the grain size of AZ31B magnesium alloy is gradually increased with the elongation of holding time. The grain is the finest without insulation work, and the increase amplitude of grain size is the most when holding for 20 minutes in this experiment. The higher is the melt superheating temperature, the larger the increase amplitude of grain size when holding for 20 minutes is. The tensile strength, yield strength and elongation percentage of AZ31B magnesium alloy specimens are small declined with the elongation of holding time under lower melt temperature. At 850°C or 900°C, the mechanical properties are rapidly declined with the elongation of holding time when holding time is less than 20 minutes, whereas the mechanical properties are slight increased when holding time is more than 20 minutes. DSC analysis shows that the elongation of holding time causes the increase of solidification onset temperature and the augment of solidification range, so the undercooling degree and nucleation rate are decreased in the melt, which result in the grain coarsening and the mechanical properties decrease.

Crystal Growth during the Solidification Process of Continuous Casting Slab

Under the condition that the solid-liquid interface bends periodically in continuous casting, the expression of solid-phase growth rate adapting to continuous casting was set up, and then the growth rates were calculated. On this basis, the morphologic of crystal growth and the variation of primary dendrite spacing during continuous casting slabs were studied. The results show that the growth rate is the fastest when solid-phase moves to wave crest within a deformation periodicity, whereas the growth rate is the slowest when the crystal moves to wave hollow. The bigger the bulge size is, the greater the variation amplitude of the growth rate will become. The variation of the growth rate results in the S/L interface to develop towards a planar surface. Because the value is much smaller than the critical value of the transformation from cells to dendrites, and the crystals only grow in the fashion of dendrites. The primary dendrite spacing at wave crest is bigger than the primary dendrite spacing at wave hollow in early stage of columnar crystal growth, and the dendrite spacing at wave crest is basically equal with the dendrite spacing at wave hollow in the late stage of solidification, and they quickly simultaneous increase. Good correlation is obtained between the experimental results and the calculation results of the dendrite arm spacing.

Relationships between δ→γ Phase Transformation and the Crack Formation in Continuous Casting Slabs

The δ→γ phase transformation in the steel was studied in detail, and the relationship between δ→γ phase transformation and the crack formation in continuous casting slabs was discussed as well. The results indicate that the micropores are formed at the positions where δ-phase transformation terminates during the δ→γ phase transformation for low-carbon non-peritectic steel. The micropores will also be formed at the positions where the peritectic reaction of the steel terminates, then the pores are remained on the grain boundary of γ-phase when γ-phase becomes granulated. The micropores distributing on the grain boundary of γ-phase is one of the results for the crack formation of continuous casting slabs and the obvious plasticity decrease of δ-phase zone in the steel. The theoretical analysis results are basically consistent with the experimental results.

Study on Inclusions in Ductile Cast Iron

The type, shape and distribution of inclusions in ductile cast iron were studied using a scanning electron microscopy (SEM) and the energy spectrum analysis, combining the thermodynamic calculation of inclusions formation. The results show that the oxides are most likely formed from the thermodynamics in ductile cast iron when the temperature is 1373~1873 K , followed by the sulfides, the carbides again. There exist the uniphase inclusions MgO, SiO2 and MgS, the heterogeneous inclusions of containing rare-earth MnO-MgO-SiO2-La2O3 and MgS-LaS-SiO2-Al2O3-MgO , and the heterogeneous inclusions of non-rare earth SiO2-MnO-MgO-Al2O3 in ductile cast iron. The shapes of the inclusions are mainly polygon, and the size variation is from 3 to 10 um. The inclusions are mainly distributed on the graphite ball surfaces, the ferrite grain boundaries and in the pearlites.

Effect of Pulse Electric Field on the Columnar Crystals Growth of Al-5.6 Wt.%Cu during Unidirectional Solidification

The influence of pulse electric field on the columnar crystals growth has been studied by employing pulse electric field vertically to the solid/liquid interface during unidirectional solidification. The results showed that the pulse electric field was favorable to columnar crystals growth with the increase of pulse electric field intensity when the liquid phase was the positive electrode of pulse electric field. The formation of equiaxed crystal was accelerated when the degree of composition supercooling in front edge of solid/liquid interface reached the degree of nucleation supercooling by pulse electric field. When the liquid phase was the negative electrode of pulse electric field, the growth of columnar crystals was hindered, and the formation of equiaxed crystal was accelerated by pulse electric field.

Measurement System of Contact Angle between Molten Steel Droplet and Refractory Material

The distinct images of molten steel droplets were obtained utilizing a home-made experimental equipment, and the method which measures the contact angle between the molten steel droplet and the refractory material using a computer image processing technology and Visual C++ language was represented, meanwhile the measurement system of the contact angle was developed. The results show that the maximum deviation of the measurement system is 0.13° comparing with the actual measurement results, the minimum deviation is 0.03°, and the mean deviation is 0.06°. Under this experiment conditions, the contact angle increases 1.2° when the quality of sample increases from 0.2g to 0.8g at 1550°C, and the contact angle increases 2.3° when the temperature increases from 1550°C to 1600°C for the sample of 0.2g.

Microstructure Evolution of Cold Rolled Hot Dip Galvanized Dual-Phase Steel during Continuous Heating Process

The annealing process of 800MPa grade hot dip galvanized DP steel was simulated on Gleeble-1500 thermo-mechanical simulator. The recovery and recrystallization of ferrite and the formation of austenite during the continuous heating process were studied in this paper. The results show that the fine equiaxed recrystallized nucleus started emerging nearby grain boundaries of deformed ferrites when the heating temperature was 630°C. With the increase of temperature, the recrystallized grain began to grow up, some new crystallized nucleus formed in other places with high stored energy of deformation. when the heating temperature was 690°C, the recrystallization process was basically finished, the deformed microstructure had been replaced by equiaxed ferrite grains. When the heating temperature was 730°C, the austenite nucleated on the carbide particles of the ferrite grain boundaries in the original pearlite area mainly. Some austenite also nucleated on the ferrite grain boundaries or the carbide particles within the ferrite grain. When the temperature was 750°C, the austenite began to grow along and parallel to ferrite grain boundaries.

In Situ Observation of Growth Process of δ Phase of 0.15% C Carbon Steel during Solidification

In situ observation of growth process of high temperature phase in 0.15% C carbon steel during solidification concerned with using Confocal Scanning Laser Microscope (CSLM), the growth rate of -phase has been measured. The results indicate that high temperature -phase grows at cell crystal way when the cooling speed reaches 2°C/min in 0.15% C carbon steel. The -phase of round or oval cross-sectional shaped may grow stably. The growth rate of -phase is gradually getting slow along with increasing of curvature radius. The variation of growth speed tends to be similar with different solid-liquid interface shapes of -phase. The growth rate of concave solid-liquid interface is faster than that of convex solid-liquid interface for phase. The smaller radius of curvature of phase is, the faster the growth rate reaches.