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heating temperature was 690°C, the recrystallization process was basically finished, the deformed microstructure had been replaced by equiaxed ferrite grains.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.

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.

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 Al2O3sloping 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 Al2O3single 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 Al2O3single crystal plate is 24mm2.

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, SiO2and MgS, the heterogeneous inclusions of containing rare-earth MnO-MgO-SiO2-La2O3and MgS-LaS-SiO2-Al2O3-MgO , and the heterogeneous inclusions of non-rare earth SiO2-MnO-MgO-Al2O3in 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.

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.