Explore the vast range of titles available.

Nonmetallic inclusions mixed into large forged metal objects destroy the continuity in the metal and affect the quality of the forged product. Research on how inclusions affect the plastic deformation of a matrix shows the significance of the formation mechanism of inclusion defects. For upset forging, the nonlinear finite element model was shown to be appropriate for the ingot hot-forging process by comparing the results with experiments involving plastic and hard inclusions inserted into the forged piece. The high-temperature stress-strain curves of MnS plastic inclusions were obtained experimentally. The results show how, during upsetting, the morphology of MnS plastic inclusions varies from spherical to ellipsoidal, until finally becoming flat in shape. The larger the inclusion is, the larger the degree of deformation of the inclusion is, and large inclusions enhance the risk of the final product failing to pass inspection for inclusion flaws. Strain significantly concentrates in the matrix near a hard inclusion. When the hard inclusion reaches a certain size, conical fractures form on both sides of the inclusion. To pass inclusion-flaw inspection and close hole defects to the extent possible, the flat-anvil upsetting is recommended. Finally, the inclusion-deformation state obtained by finite element simulation is verified experimentally.

A better understanding of droplet formation and dripping behavior would be useful in the efficient removal of impurity elements and nonmetallic inclusions from liquid metals. In the present work, we developed a transparent experimental apparatus to study the mechanisms of droplet formation and the effects of filling ratio on droplet behavior during the electroslag remelting（ESR） process. A high-speed camera was used to clearly observe, at small time scales, the droplet formation and dripping phenomenon at the slag/metal interface during a stable ESR process. The results illustrate that a two-stage process for droplet formation and dripping occurs during the ESR process and that the droplet diameter exhibits a parabolic distribution with increasing filling ratio because of the different shape and thermal state of the electrode tip. This work also confirms that a relatively large filling ratio reduces electricity consumption and improves ingot quality.

Nozzle blockage is a common problem during continuous casting of Al-killed steel, and calcium treatment is widely used to resolve it. In consideration of the production costs, the technology of nonmetallic inclusion control was studied to optimize the Ca consumption. The proposed process of slag washing was employed, and the refining slag composition, deoxidation conditions and alloying systems were optimized. Using these measures, the steel cleanliness before Ca addition was improved significantly, and the corresponding Ca consumption was reduced. Moreover, the continuous casting could be conducted smoothly.

The influence of calcium treatment on non-metallic inclusions had been studied when control technology of refining top slag in ladle furnace was used in ultra-low oxygen steelmaking. A sufficient amount aluminium was added to experimental heats for final deoxidizing during BOF tapping, and the refining top slag with strong reducibility, high basicity and high Al2O3 in ladle furnace was used to produce ultra-low oxygen steel and the transformation of nonmetallic inclusions in molten steel was compared by calcium treatment and no calcium treatment. The results show that the transformation of Al2O3--MgO - Al2O3 spinel-CaO-MgO-Al2O3 complex inclusions has been completed for aluminum deoxidation products and calcium treatment to molten steel is unnecessary when using the control technology of ladle furnace refining top slag to produce ultra-low oxygen steel, and the complex inclusions are liquid at the temperature of steelmaking and easily removable to obtain very high cleanliness steel by flotation. Further- more, the problems of nozzle clogging in casting operations do not happen and the remaining oxide inclusions in steel are the relatively lower melting point complex inclusions.

The effects of Mg addition on the formation of nonmetallic inclusions and solidification structure of Ti-sta- bilized ultra-pure ferritie stainless steels were investigated by experimentally casting ingots with different composi tions. Thermodynamic analyses on the formation of complex inclusions after adding Mg into steels were carried out combined with the scanning electron microscopy energy dispersive spectrometry （SEM EDS） analysis. And the EDS analysis showed that in steel samples with Mg addition, a new spinel crystal phase combined with AI2O3- TiOx formed. It was also found that after Mg addition, the proportions of equiaxed grain zone of 409L, 4003, 439 and 443NT steels increased from 10.2%, 21.8%, 13.4% and 18.6% to 84.3%, 92.3%, 91.1% and 100.0%, respec tively. Since the planar disregistry between spinel and TiN is 5. 1%0, spinel could promote the precipitation of TiN and increase the number density of TiN inclusions in steel melts. The mechanism of solidification structure refinement after adding Mg into steels supposed that the complex inclusions of spinel and TiN in high number density enhanced columnar-to-equiaxed transition, since the planer disregistry between δ phase and spinel is 1.4 %.

The optimization of flow control devices in a single-slab continuous casting tundish was carried out by physical modeling, and the optimized scheme was presented. With the optimal tundish configuration, the minimum residence time of liquid steel was increased by 1.4 times, the peak concentration time was increased by 97%, and the dead volume fraction was decreased by 72%. A mathematical model for molten steel in the tundish was established by using the fluid dynamics package Fluent. The velocity field, concentration field, and the resi-dence time distribution （RTD） curves of molten steel flow before and after optimization were obtained. Experimental results showed that the reasonable configuration with flow control devices can improve the fluid flow characteristics in the tundish. The results of industrial applica-tion show that the nonmetallic inclusion area ratio in casting slabs is decreased by 32% with the optimal tundish configuration.

The fluid flow in tundish is a non-isothermal process and the temperature variation of stream from teeming ladle dominates the fluid flow and thermal distribution in tundish. A numerical model was established to investigate the effect of inlet cooling rate on fluid flow and temperature distribution in tundish based on a FTSC （Flexible Thin Slab Casting） tundish. The inlet cooling rate varies from 0. 5 to 0. 25 ~C/rain. Under the present calculation conditions, the following conclusions were made. When the stream temperature from teeming ladle drops seriously （for inlet cooling rate of 0.5℃/min）, there is a ＂backward flow＂ at the coming end of casting. The horizontal flow along the free surface turns to flow along the bottom of tundish. The bottom flow shortens the fluid flow route in tundish and deteriorates the removal effect of nonmetallic inclusions from molten steel. Nevertheless, when the inlet cooling rate decreases to 0.25℃/min, the horizontal flow is sustained during the whole casting period. The present research provides theoretical directions for temperature control in teeming ladle and continuous casting tundish during production of advanced steels.

The behavior of non-metallic inclusions in LCAK （low carbon aluminum killed） steel produced by BOF （basic oxygen furnace）-LF （ladle furnace） refining-FTSC （flexible thin slab continuous caster） production route was investigated. The results showed that, LF refining for LCAK steel could decrease the wT[o] significantly, and the inclusions were modified by Ca treatment, which prevented nozzle clogging efficiently. However, owing to the unstable casting condition in the earlier stage of casting, a severe reoxidation occurred, accompanied with mold slag entrapment. The transformation of non-metallic inclusions during the steelmaking process was Al2O3→MgO→Al2O3 type inclusion→MgO-Al2O3 O3-CaO type inclusion with a CaS ring, and the mechanism of the transformation was pro posed and discussed via thermodynamic and kinetic analysis. Besides, to avoid CaS precipitation, the product of W[Al] ×w3[S] in steel should be less than 2.0 × 10 10 at 1873 K, which remands higher desulfurization ratio during LF refining.

Alloying structural steel used for mechanical structures has a high requirement for cleanliness because its failures are greatly affected by non-metallic inclusions and total oxygen content in steel.It has been reported by some steelmaking plants to have some problems in controlling total oxygen content and inclusions during alloying structural steel production.For this purpose,cleanliness control in 0.2C-0.3Si-0.6Mn-1Cr-0.2Mo steel was investigated.Firstly,low melting temperature zone（≤1873 K） of CaO-Al2O3-MgO system and formation condition of low melting temperature inclusions were investigated through thermodynamic equilibrium calculation.On this basis,industrial tests were carried out.Through sampling at different stages,transformation of oxide inclusions and change of total oxygen content in steel were studied.The results show that：in order to form CaO-Al2O3-MgO system inclusions with low melting temperature,mass percent of Al2O3,MgO and CaO in inclusions should be controlled from 37.6% to 70.8%,0 to 17.4% and 25.5% to 60.6%;For the condition of 1873 K and 0.05%（mass percent） dissolved aluminum in steel,the activities of dissolved oxygen,magnesium and calcium should be controlled as 0.298×10-4-2×10-4,0.1×10-5-40×10-5 and 0.8×10-8-180×10-8 respectively.With secondary refining proceeding,average total oxygen content and inclusion amount decrease,the type of most inclusions changes from Al2O3 after tapping to Al2O3-MgO after top slag is formed during ladle furnace refining and finally to CaO-Al2O3-MgO after RH treatment.In the final products,average total oxygen content was 12.7×10-6 and most inclusions were in spherical shape with size less than 5 μm.

A detailed mathematical procedure of the optimization of the fluid flow in a tundish water model with and without flow control devices （weir and dam） was carried out using the commercial CFD eode FLUENT 6.0. The （k- ε） two-equation model was used to model turbulence. The residence time distribution （RTD） curves were used to analyze the behavior of the flow in tundish. The location of flow control devices in the tundish was studied. The results show that the flow modifiers play an important role in promoting the floatation of nonmetallic inclusions in steel. Comparing the three geometric configurations that are considered （bare tundish, weir, weir＋dam）, the tundish equipped with the arrangement （weir＋dam） is a best and optimal geometric configuration of tundish.