Huamei Duan

Hot Ductility of X70 Pipeline Steel in Continuous Casting

Transverse cracks in continuous cast steel may easily form if the hot ductility of the continuous cast steel is poor at the straightening stage. In this paper, the hot ductility of X70 pipeline steel was studied at various temperature from 600 to 1300 °C. The results show that the steel has a good hot ductility (RA above 70%) at 800–1000 and 600–650 °C. And the steel exhibits a hot ductility trough (RA below 80%) at 650–800 °C, which is mainly contributed to the austenite–ferrite transformation. For further understanding the low ductility, the fracture surface was examined by scanning electron microscope, and the second phase particles was examined by energy spectrum analysis. The results indicate that the low ductility of the steel is affected by the equiaxed (Fe, Mn)S precipitate as well as austenite transformation at the third brittle zone.

Manganese Influence on Equilibrium Partition Coefficient and Phase Transformation in Peritectic Steel

The equilibrium partition coefficient (k) affected by chemical component, phase constitution and temperature is a critical parameter related to solutes distribution during steel solidification. In this study, the effect of Mn on equilibrium partition coefficient and phase transformation was quantitatively analysed. A technique according to the relative amount of δ-Fe and γ-Fe to determine the equilibrium partition coefficients of solutes in L, δ-Fe, and γ-Fe three-phases coexistence zone was proposed. Results showed that Mn promotes the generation of γ-Fe and its effect on peritectic reaction zone is significant. The equilibrium partition coefficients were determined based on the phase change and relative amount of δ-Fe and γ-Fe according to the solidification paths which undergo difference phase coexistence zone. All of \( k_{C}^{\delta } \), \( k_{Si}^{\delta } \), \( k_{Si}^{\delta + \gamma } \), \( k_{P}^{\delta } \), \( k_{P}^{\delta + \gamma } \), \( k_{S}^{\delta } \), and \( k_{S}^{\delta + \gamma } \) decrease with Mn increasing, while \( k_{C}^{\delta + \gamma } \) increases due to solute Mn promote the generation of γ-Fe forming from peritectic reaction.

Study on the Formation and Control of TiN Inclusion in Mushy Zone for High Ti Microalloyed Steel

The coarse TiN inclusions can act as potential fracture initiation sites and deteriorate the impact toughness of steels. The experimental observation results indicated that CaS and TiN inclusions precipitated in solidification mushy zone. Meanwhile, it was found that CaS inclusions could act effectively a heterogeneous nucleation substrate for the precipitation of TiN inclusions, and the size of TiN inclusions with CaS core was obviously larger than those TiN inclusions without CaS core. Additionally, the thermodynamic calculation result showed that TiN inclusions began to precipitate at the end of solidification from the dendrites front; moreover, the preexisted CaS inclusions promoted the formation of TiN inclusions. Decreasing sulfur and nitrogen content could significantly reduce precipitation temperature and growth time of CaS and TiN inclusions in mushy zone. Furthermore, TiN inclusions could be prevented from precipitation at the surface of CaS inclusions when the S content of molten steel was below 0.0008 wt%.

Stress and Friction Distribution around Slab Corner in Continuous Casting Mold with Different Corner Structures

The non-uniform friction and thermal stress in the mold are important as causes of the transverse cracks around strand corner. To analyze the stress distribution features around strand corner, a three-dimensional thermo-elastoplastic finite-element mold model with different corner structures (right-angle, big-chamfer, multi-chamfer, and fillet) was established. The temperature field in the mold was indirectly coupled through a three-dimensional fluid flow and heat transfer model. In addition, the non-uniform mold friction stress loaded on the strand surface was calculated through a friction model. The results show that the stress distribution on the shell is similar to the temperature distribution. The stress concentration appears in the strand corner and the lower part of wide face. The friction stress enhances the corner stress around the edge of the air-gap. For chamfered molds, the stress around the corner between the wide face and chamfer face is larger than that between the narrow face and chamfer face. Around the corner region, both the stress peak and the area of the large stress zone of the right-angle strand are the largest, while those of big-chamfered, multi-chamfered, and fillet strands decrease in that order. The stress peak position of the chamfered strands is closer to the mold exit than that of the right-angle strand. Compared with the use of the right-angle mold, the application of chamfered molds is able to reduce the stress concentration around the strand corner.

Fluid flow and heat transfer behavior of liquid steel in slab mold with different corner structures. Part 2: Fluid flow, heat transfer, and solidification characteristics

ABSTRACT In this article, the complex transmission behavior was discussed in the slab mold with different corner structures. Results show that the up backflow is stronger than the down backflow. The cooling water temperature rise and heat flux through the wide face in the right-angle mold are the largest, while those through the narrow face in the multichamfered mold are larger than those in the big-chamfered mold. The corner temperature at mold exit of the right-angle, big-chamfered, and multichamfered strand increases. The shell thickness at the narrow face center in the chamfered mold is thinner than that in the right-angle mold.

Fluid flow and heat transfer behavior of liquid steel in slab mold with different corner structures. Part 1: Mathematical model and verification

ABSTRACT A three-dimensional model considering the fluid and temperature field of the liquid steel and cooling water, along with the copper plate temperature was established to study the fluid flow and heat transfer behavior of liquid steel in slab mold with different corner structures. Then, a two-dimensional stress–strain model was established to calculate the strand shrinkage. The two-dimensional stress and three-dimensional temperature were connected through the thermal resistance. The model was validated by the measured solidification shell, copper plate temperature, and cooling water temperature rise. Results show that this model is suitable to study the complex transmission behavior in slab mold.

Genetic Influence of Mold Corner Structure on the Strand Corner Temperature in Secondary Cooling Zone During Slab Continuous Casting

Mold corner structure will influence the strand corner temperature by changing fluid flow and heat transfer of liquid steel at mold corner. A three-dimensional model coupling fluid flow and heat transfer in the mold and a two-dimensional moving-slice heat transfer model in secondary cooling zone was established to investigate slab corner temperature under different mold corner structure: right-angle, big-chamfer, multi-chamfer and fillet. Results show that strand corner temperature increases obviously at mold exit through using chamfered mold. Compared with the corner temperature of right-angle strand, corner temperature of big-chamfered, multi-chamfered and fillet strand are promoted during the straightening process, which will avoid the low ductility temperature zone. When mold corner structure changed from right-angle to big-chamfer, the rise of corner temperature is much higher than that changed from big-chamfer to multi-chamfer or fillet.