Papers by Keyword: Continuous Casting

Abstract: Non-metallic impurities in continuous cast billets are evaluated by a growth rate of edge point impurities. The first part of our research was devoted to a relationship between the growth rate of edge point impurities and other macrostructure defects. A correlation-regression analysis of steel macrostructure quality showed the relationship between the rate of edge point impurities and segregation cracks in general, as well as corner streaks. The second part of our research indicated that impurities in billets from conventional carbon steel were crucially influenced by a method of pouring steel from a tundish into a mould. By transferring from open stream casting to shrouded casting, the quantity of non-metallic impurities in billets decreases by 7 times. In case of open stream casting, prevailing inclusions are oxides resulting from secondary oxidation, while the growth rate of edge point impurities in billets increases with an increased content of sulphur and phosphorus in steel, and decreases with an increased manganese/sulphur ratio. In case of shrouded casting, non-metallic impurities are limited to casting temperature and speed: steel overheating in the tundish above the liquidus temperature and withdrawal speed of billets. Less non-metallic impurities in case of the shrouded casting are contributed by steel overheating in the tundish above the liquidus temperature over 30oС and withdrawal speed, not exceeding 2.5 m/min.

Abstract: A simple twin-wheel caster is proposed for casting thin bars. The lower wheel of this caster has a trapezoidal groove with an area of 25 mm2. A 1070 pure aluminum bar with a convex, not concave and trapezoidal, cross section could be cast at speeds ranging from 3 to 4 m/min. The area of the bar was 38 mm2 when the wheel speed was 3 m/min. The area decreased with increasing wheel speed.

Abstract: Corner cracks are very likely to occur in the slabs when peritectic steels, medium carbon steels, boron or niobium micro-alloyed steels are being produced by continuous slab caster, which will lead to edge upwarping and edge cracking of the finished products in the rolling process. To stop the slabs with corner cracks from going down to the rolling mills and affecting the finished rolled product quality, the slabs must be flame scarfed in the continuous casting process, thus causing increases in the operational cost. In 2013, Baosteel decided to relocate the two single-strand 2,300mm slab casters from Luojing of Shanghai to Zhanjiang of Guangdong. The slabs produced by the slab casters at Baosteel Luojing were observed with serious corner crack problem. To solve the problem of corner cracks, CISDI worked hard together with Baosteel to extensively optimize and improve the bender roller arrangement, segment roller gap accuracy control, secondary cooling zoning, secondary cooling width control, dynamic cooling control model, dynamic soft reduction model, etc., and eventually the conundrum of corner cracks which were frequent in the slab casters when at Luojing was solved and the presence of corner cracks in slabs of peritectic steels, medium carbon steels, boron or niobium micro-alloyed steels has been decreased from over 90% to less than 1%. The present article focuses on the work done specifically on solving the problem of corner cracks in the designing stage.

Abstract: A segmented 3-D coupled electromagnetic-thermal solute transportation model, aimed to better understand the macro-segregation formation in the strand during a popular continuous casting (CC) process, has been developed. Based on the model validation by industrial tests, the effect of M-EMS and F-EMS running parameters on the segregation distribution were subsequently carried out. It is shown that the simulated solute segregation profile in the W-shape along the casting thickness direction is in a good agreement with the measured profile. In the initial solidification shell with thickness in 0.020 m, the solute segregation degree changes from a positive value to a negative with the increasing distance from strand surface because of the washing effect induced by the impact flow from the nozzle side port and M-EMS. Here, the minimum degree of carbon segregation decreases from 0.976 to 0.875 with the increasing stirring current from 100A to 550A. As the stirring current of F-EMS decreases from 630A to 200A, the minimum segregation degree locating at 0.109 m distance from strand surface increases from 0.805 to 0.967. The carbon segregation degree at the strand center first decreases from 1.10 to the minimum value of 1.06 at the case of 350 A/4 Hz because of the concentration equilibrium for the local decreasing negative segregation induced by F-EMS, and then increases to 1.16 due to the local poor stirring.

Abstract: The formation mechanisms and characterization (distribution, size and morphology) of the inclusions during continuous casting process of steels were investigated in this study. Samples were took out from several steps of the process and then, fully characterized via metallographic techniques, microscopic investigations and elemental analysis. Results showed that the addition of ferroalloys can intensify the formation of inclusions in some steps of the steelmaking process. Also, it was confirmed that the total oxygen content of the samples can be considered as a criteria of the clarity (purity and inclusion-free) of the steels, if the samples prepared carefully.

Abstract: The influence of the St.3sp, 40 and 85 steel grades chemical composition, temperature of the metal in the tundish ladle, billet cross-sectional dimensions (150 × 150 and 152 × 170 mm), the sulfur content in the metal on the speed of withdrawal of the billets from the CCM mold has been investigated. It was established, that the change of the metal temperature in the tundish ladle of the CCM has the greatest effect on the billet withdrawal speed, the change of carbon content in the steel and the billet cross-sectional dimensions influence in less extend, and the sulfur content in the cast steel does not affect at all.

Abstract: The analysis of the production records on casting 150õ150mm billets at UMMC Steel LLC has made it possible to define the basic factors worsening the billet quality and increasing the rejection of the rolled materials: steel casting in case the sulfur and phosphorus content exceeds 0.015 % and overheat is more than 30°Ñ. In order to minimize the formation of local nonuniformity in the billets manufactured from low carbon and medium carbon steel, open cast by CCM, it is necessary to maintain a maximum [Mn]:[S] ratio with [Mn]:[Si] ratio at the level less than 2-3, which ensures the formation of fusible deoxidation products and prevents the formation of solid conglomerates in steel. In order to reduce the formation of axial porosity it is advisable to retain the carbon content at the lower limit for the steel grade and avoid overheating of steel above the specified values. In order to minimize the consequences of the overheated steel casting it is necessary to adjust the billet casting rate in accordance with the operating procedures.

Abstract: Crystallization of metallic materials occurs during their casting and following solidification. The influence of directional material solidification, the size of grains, chemical heterogeneity and existence of any non – compactness, can negatively affect properties of the final product. Microstructural analysis of its longitudinal section was performed to study heterogeneity in a continuously cast steel billet. Three typical areas of the cast structure of the billet were monitored (the chill zone, columnar crystals area and central area of equiaxed crystals). EDX microanalysis and micro-structural analysis were used for evaluation of chemical heterogeneity. Via X-ray microanalysis, concentrations of the following elements were observed: manganese, chromium, silicon, phosphorus, molybdenum and iron. The microanalytical measurements were completed by microhardness measurements in the investigated areas. Based on the measured data it was proven that central areas were enriched with all the substitutional elements including a considerable increase in phosphorus concentration.

Abstract: This paper focuses on the role played by the liquid metal management on the solidification microstructure in industrial solidification processes. In particular attention is paid to the elimination of solidification defects by governing the microstructure evolution through fluid-dynamics and heat and mass transport in the liquid. The formation of hot tearing and gas porosities as well as columnar and equiaxed microstructures and micro and macro segregation are analyzed to explain how the liquid management is used to avoid defects. Examples on continuous casting and welding are also included.A very powerful tool for dealing with the complex phenomena associated with the solidification process is numerical modeling. Its increasingly growing use contemplates fluid-dynamics of the liquid phase, mass transport of solutes and solid-liquid interface evolution. Models using phase field and volume-averaging techniques, as well as models integrating multi-physics and multi-scale phenomena, are described as their use is taking on increasing importance in the design of solidification processes.

Abstract: AZCa912, 8.8mass%Al-0.68mass%Zn-0.25mass%Mn-1.9mass%Ca-Bal.Mg, continuous casting bars with 50 mm in diameter were formed by a direct chill continuous casting method. AZCa912 alloy is a noncombustible magnesium alloy. The surfaces of the bars had excellent metallic luster. A dendrite structure with a DAS of around 11-23 μm and grain sizes of about 200 μm was observed. Samples with almost the same grain size and different DAS were measured at hot compression test at 250-350°C, 0.01-1/s. Crack on the side surfaces of the samples were not formed by compression at 350°C, 0.01-0.1/s. All samples had an unchanged casting structure after hot pressing, and the percent of the structure remaining unchanged decreased with low-temperature compression and wide DAS.