Slab Casting Research Articles

Healing porosity cavities in a 300 mm thickness continuous casting slab by mechanical heavy reduction

This work conducted an exploring study to minimize porosity cavities in a 300 mm × 2000 mm slab by mechanical heavy reduction when it has solidified. Real density measurements of slab samples indicated that, with a heavy reduction of 20 mm to slab after behind its solidification end, slab center was much denser and much more consistent. Porosity volumes at 1/4 and 1/2 width regions of slab were minimized from 5.19 × 10−4 cm3/g to 1.29 × 10−4 cm3/g and from 2.27 × 10−4 cm3/g to 1.05 × 10−4 cm3/g, respectively. Original Position Statistical-Distribution Analysis (OPA) of larger sampled slabs indicated that the heavy reduction was efficiently penetrated from slab surface into center to heal porosity cavities. Obtained results indicated positive influences of heavy reduction in healing porosity holes in slab even after solidification, when the temperature gradient of slab surface and center was about 280 °C.

Transformation of inclusions in S32101 duplex stainless steel during continuous casting

In this study, the formation and characteristics of inclusions in S32101 duplex stainless steel (DSS) during continuous casting were investigated by analyzing inclusions in the tundish and continuous casting slabs. The composition of inclusions changed significantly during the continuous casting. The inclusion type in the tundish was primarily CaO-SiO2-Al2O3-MgO-MnO. There are two types of inclusions in the continuous casting slab: CaO-SiO2-Al2O3-MgO-MnO inclusions with dense Al2O3 and MnO, and Al2O3-MnO inclusions. TiN wraps the outer layers of both types of inclusions. The results obtained from thermodynamic calculations agreed with the experimental results. The weight percentage of Al2O3 and MnO in the inclusions increases significantly with the solidification process. In addition, the Al2O3-MnO inclusions were formed in the slab. TiN precipitates during the solidification of the S32101 DSS. The CaO-SiO2-Al2O3-MgO-MnO and Al2O3-MnO inclusions can be used as the nucleation sites of TiN.

Simulation of the fluid flow in continuous casting copper slab mold for different SEN design

The quality of continuously cast slabs largely depends on the processes taking place in the mold. In continuous casting of copper and its alloys the solidification process is almost completed within it. This paper presents a comprehensive optimization of the submerged entry nozzle design by combining physical and mathematical modeling with further comparison of obtained results with the actual process. The article studies the critical features of hydrodynamic processes in copper slab by physical and mathematical modeling during continuous casting. To ensure the efficiency of liquid pool homogenization, it seems appropriate to direct some metal upwards through openings in the SEN to the liquid meniscus. The optimal configuration of the SEN is the one where 35% of the liquid flows upwards to heat the melt meniscus and slab upper corner zones and 65% of liquid metal moves downward to the liquid pool bottom.

Investigation on the influence of fiber fraction and orientation on the mechanical properties of fiber‐reinforced concrete slabs

AbstractThe current work examines an experimental and numerical investigation into how steel fiber reinforced concrete (SFRC) slab failure behavior is influenced by fiber orientation by pouring concrete in slab elements. Double‐ended hooked steel fibers with an aspect ratio of 50 were used in varying percentages by volume. Fresh and hardened properties of SFRC were determined based on slump flow, V‐funnel, L‐box, J‐ring test, compression, and flexure tests. The effects of different pouring/casting locations (center and corner), fiber orientation, and fiber content (0, 0.5%, and 1.0%) on the crack pattern of the SFRC slab were observed. While casting, the concrete was allowed to flow through a 30° chute angle to enhance the flowability of concrete. The SFRC slabs without fiber reinforcement undergo brittle failure without forming any prior micro cracks. Slabs with fibers experience ductile failure and show significant post‐cracking strength. The concrete's pouring position only affects the failure crack's inclination for the given workability. In the case of the corner cast slab, the crack was propagated from one edge to the opposite edge of the slab in a straight line and split into two halves. This crack pattern suggested that the fiber distribution was concentrated in half of the slab part in which the pouring corner was located. Adding 0.5% and 1.0% fiber content increased the load‐carrying capacity of slabs by 1.31 and 2.15 times, respectively. In addition to fiber content, the pouring position of concrete also made a difference in the load‐carrying capacity of slabs. The concrete pouring in the slab from the center position with 0.5% and 1.0% fiber content has 17.2% and 40% more load‐carrying capacity compared to the concrete poured in the slab from the corner position with the same fiber content. The deflection and load‐carrying capacity obtained through finite element modeling (FEM) fit the experimental results well.

Physical modeling and numerical investigation of fluid flow and solidification behavior in a slab caster mold using hexa‐furcated nozzle

AbstractSlag entrapment from metal–slag interface during continuous casting operations has been a major area of concern for steelmakers globally. The presence of inactive regions in the upper region of the mold poses another challenge. Proper flow behavior of the molten metal coming out of the nozzle in the mold is required to overcome these challenges. Nozzle design greatly affects the flow pattern of the molten steel inside the mold. The present investigation is an attempt to study the flow and solidification behavior in a slab caster mold with the use of a novel‐designed hexa‐furcated nozzle using numerical investigation results. The casting speed and submerged entry nozzle (SEN) depth are varied to study the effect of these parameters on minimizing the inactive zones in the mold and the steel/slag interface fluctuations. The results show that the interface fluctuation increases at higher casting speed and lower SEN depth. The residence time distribution (RTD) analysis was also performed for different cases to investigate the flow behavior. The validation of the fluid flow and RTD curve inside the computational domain is carried out with the use of physical modeling.

Physical and Numerical Simulation Study on Structure Optimization of the Inner Wall of Submerged Entry Nozzle for Continuous Casting of Molten Steel

The submerged entry nozzle (SEN) plays an important role in the continuous casting production process. It is a cast refractory pipe fitting installed in the lower part of the tundish and inserted below the molten steel level of the mold. It not only affects the speed of molten steel flow, but is also prone to nodules and affects production. In the present work, the flow behavior of molten steel in a traditional nozzle and that in a new type of nozzle whose inner wall was distributed with arrays of hemispherical crowns were studied by means of both physical simulation (using a water model) and numerical simulation (using ANSYS CFX) based on the prototype of a production continuous casting slab mold. Both experimental and numerical simulation results show that, compared with the traditional nozzle, the impact depth generated by the new-type nozzle in the mold is reduced by 21.06–26.03 cm, the impact angle is reduced by 14–17 degrees, and swirl flow was generated inside the new-type nozzle, which not only improves the flow characteristics inside the submerged entry nozzle and changes the dead zone size in the submerged entry nozzle, but also improves the velocity distribution at the outlet of the nozzle and minimizes the possibility of nodulation. In addition, in contrast to the traditional nozzle that generates flat body-shaped jets of molten steel flow, the new-type nozzle produces baseball glove-shaped jets that penetrate shallower into the molten steel bath in the mold, which significantly reduces the outlet velocity and is conducive to the floating of inclusions.

Sigma‐Phase Distribution in 2507 Super Duplex Stainless Steel Continuous Casting Slabs

The sigma‐phase distribution in a 2507 super duplex stainless steel continuous casting slab is analyzed using microstructural analyses and thermodynamic calculations. The sigma phase contains high Cr and Mo contents, and precipitates along the phase boundary between austenite and ferrite and grows toward the interior of the ferrite phase in the continuously cast slab. The sigma‐phase fraction at the center of the width direction is higher than that in the one fourth width. Furthermore, the sigma‐phase fraction at the center of the thickness direction is higher than those at the upper and lower surfaces, which is due to the lower cooling rate at the center. The Brinell hardness (HB) at the center increases to 313 HB with an increasing sigma‐phase fraction. The sigma‐phase fraction at the one fourth thickness near the lower surface is higher than that at the one fourth thickness near the upper surface at the same cooling rate. Additionally, Mo and Ni are severely segregated in this zone. A higher Mo content influences the precipitation and stabilization of the sigma phase. Furthermore, Scheil–Gulliver calculations indicate that compositional segregation results in an increase in the sigma‐phase precipitation temperature range.

Investigation of Genesis of Internal Subsurface Crack in Continuous Cast Slabs and Finding Remedial Measures

Investigation of Genesis of Internal Subsurface Crack in Continuous Cast Slabs and Finding Remedial Measures

Effect of Nozzle Parameters on the Cooling Conditions in the Secondary Cooling Zone of a Slab Caster

The following contribution focuses on the secondary cooling zone of a slab caster, analyzing the effects of nozzle parameters on cooling conditions. The research group employs experimental measurements, including the Nozzle Measuring Stand (NMS), to determine local heat transfer coefficients (HTC) and water distribution. These measurements are crucial for accurately setting the boundary conditions in the simulation. The implementation of these boundary conditions is realized by an Exponential Gaussian Process Regression (EGPR) to predict HTC values. The results highlight the importance of an accurate HTC assessment in regions with overlapping sprays. The developed methodology aids in enhancing the precision of simulations for continuous casting processes, contributing to a better product quality and process efficiency using the non-commercial software platform “m2CAST”.

In situ measurement of austenite grain growth and recrystallization using laser ultrasonics

The development of next generation process models and advanced high-strength steel products for thin slab casting and direct rolling requires quantification of microstructure evolution during thermomechanical processing. Laser ultrasonics is a non-contact in-situ method to record grain growth, recrystallization and phase transformations in metals and alloys. Here, we will present an improved experimental design that facilitates a continuous microstructure measurement through the various stages of simulated hot rolling from reheating to runout table cooling using a Gleeble thermomechanical simulator equipped with a laser ultrasonics for metallurgy (LUMet) system. Austenite grain growth and static recrystallization after hot deformation are quantified based on attenuation of the ultrasound waves whereas austenite decomposition can be recorded with the changes in ultrasound velocity during the phase transformation. Further, the LUMet results for a microalloyed low carbon steel are validated with conventional techniques including optical and electron microscopy as well as double-hit tests. These experimental studies demonstrate the capabilities of laser ultrasonics in the identification of both normal and abnormal grain growth, non-recrystallization temperature, recrystallization, and austenite decomposition kinetics in a single test for a given processing path, as well as its potential for accelerated optimization of process control under industrial rolling conditions.

Binocular measurement method for a continuous casting slab based on the one-dimensional probabilistic Hough transform and local sub-pixel sifting.

Due to the low measurement accuracy of the continuous casting slab model caused by difficulty in detecting ideal corners, a binocular measurement method based on the one-dimensional probabilistic Hough transform and local sub-pixel sifting is proposed. First, the one-dimensional probabilistic Hough transform based on inclination angle voting and the Freeman chain code is used to detect the line segments of the exterior outline. Next, sub-pixel points are extracted in each region of interest (ROI) by using Zernike moments, and sifted in the overlapping area of adjacent ROIs. Then the orthogonal total least squares (TLS) method is applied to fitting sub-pixel edges. Finally, after the key points are matched, three-dimensional localization and measurement are completed according to the binocular vision measurement principle. The experimental results show that the minimum relative error and average relative error of length reach 0.3401% and 0.3945%, respectively, satisfying the measurement requirement. Compared with scale-invariant feature transform (SIFT) and the oriented FAST and rotated BRIEF (ORB), the measurement error of the proposed algorithm is reduced by 80.01% and 74.63%, respectively. Compared with another edge fitting method based on k-means clustering and least squares fitting, its measurement error is reduced by 34.11%, and the time consumption is shortened by 39.07%, verifying its excellent performance in accuracy and efficiency.

Mitigation of Corner Cracking in Continuously Cast Steel Slabs Through Strain Induced Crack Opening Test

Mitigation of Corner Cracking in Continuously Cast Steel Slabs Through Strain Induced Crack Opening Test

Designing mould fluxes to prevent longitudinal cracking for peritectic steel slab casting

ABSTRACT During continuous casting of hypo-peritectic steel slabs, control of horizontal heat transfer rate in mould is important to avoid longitudinal cracks. This rate can be manipulated by mould slag crystallization. From an industrial situation where the longitudinal cracking index was too high, a new mould flux was designed with appropriate crystallization kinetics. The mould flux crystallization process was analysed in laboratory through differential scanning calorimetry. The Friedman isoconversional method was applied to determine the activation energy of crystallization from melt. Besides, a new quick test was developed to evaluate crystallization kinetics. The industrial tests have shown that the new mould flux decreases the longitudinal cracking index, and this is related to the decrease of horizontal heat transfer rate during the continuous casting process, which in turn is related to crystallization from mould slag.

Experimental Investigation on the Impact of Micro-Steel Fibers on the Flat Slabs' Punching Shear Resistance

This research examined the effects of micro-straight steel fiber percentage and column form on the punching shear of SFRC slabs. Fibers made of micro steel with a diameter of 0.2 mm and a length of 13mm with an aspect ratio equal to 65 were used. The fiber content varied between 0.5%, 1%, and 1.5% by volume. Four different types of concrete mixes were adopted and tested. Experimental results showed that when the percentage of steel fibers in SFRC increased, its compressive strength, flexural strength, splitting tensile strength, and direct tensile strength improved. This investigation applied a monotonic load to eight cast slabs (two each of conventional concrete of square and circular column sections of the equivalent area while the other six slabs were made with steel fiber concrete. The dimensions of each slab were (920 x 920 x 80 ) mm. Each slab specimen had essential, edge-based support with square and round column sections. It has been demonstrated that slabs with square column sections endured a relatively higher ultimate load than slabs with circular column segments when the steel fiber dosage was 0.5% or 1.0%. Still, at a steel fiber dosage of 1.5%, circular column segment slabs approached the ultimate load of square column segment slabs. The heterogeneous behavior in concrete can be attributed to the random and unequal distribution of steel fibers throughout the material. There were only flexural fractures visible on the tensile face of the slab. New fractures emerged in the center of the slab as the load increased.

Effect of Cold Rolling Reduction Rate on the Microstructure and Properties of Q&P Steel with a Ferrite-Pearlite Initial Structure.

Quenching and partitioning (Q&P) steel has garnered attention as a promising third-generation automotive steel. While the conventional production (CP) method for Q&P steel involves a significant cumulative cold rolling reduction rate (CRRR) of 60-70%, the thin slab casting and rolling (TSCR) process has emerged as a potential alternative to reduce or eliminate the need for cold rolling, characterized with a streamline production chain, high-energy efficiency, mitigated CO2 emission and economical cost. However, the effect of the CRRR on the microstructure and properties of Q&P steel with an initial ferrite-pearlite microstructure has been overlooked, preventing the extensive application of TSCR in producing Q&P steel. In this work, investigations involving different degrees of CRRRs reveal a direct relationship between increased reduction and decreased yield strength and plasticity. Notably, changes in the microstructure were observed, including reduced size and proportion of martensite blocks, increased ferrite proportion and decreased retained austenite content. The decrease in yield strength was primarily attributed to the increased proportion of the softer ferrite phase, while the reduction in plasticity was primarily linked to the decrease in retained austenite content. This study provides valuable insights for optimizing the TSCR process of Q&P steel, facilitating its wider adoption in the automotive sector.

Flow and Heat Transfer on the Surface of Molten Steel Slag Layer in Continuous Casting Mold

Protective slag is coated on the surface of molten steel during continuous casting, the flow and heat transfer state of the protective slag is a decisive factor affecting the inflow and consumption of liquid slag and is also an important prerequisite for stabilizing and improving the quality of continuous casting billets. Based on the Navier Stokes fluid momentum conservation equation and energy equation, a two-dimensional longitudinal numerical model describing the flow/heat transfer of liquid protective slag on the surface of steel is established. The data comes from the equipment parameters and casting process of an arc shaped slab continuous casting machine in a domestic steel plant. The flow field and temperature field distribution of protective slag are calculated and analyzed, and the effects of factors such as slag layer thickness and shear speed on the flow and heat transfer status of the liquid slag layer are discussed. When the bottom shear velocity increases from 0.005 m/s to 0.2 m/s, the maximum flow velocity of liquid slag from the nozzle to the narrow surface in the center area of the model increases from 0.0012 m/s to 0.0617 m/s, and the average longitudinal flow velocity of liquid slag near the nozzle increases from 0.0012 m/s to 0.0627 m/s. The research results provide reference for investigating the complex metallurgical behavior of protective slag.

The influence of intergranular oxidation on surface crack formation in continuous casting of steel

High-temperature oxidation phenomena play an important role in steel processing. What is mostly underrated is the importance of internal oxidation in casting processes, namely the continuous casting process. To investigate the impact of intergranular oxidation on surface defect formation, experiments for two cooling strategies and time sequences for a conventional slab caster were conducted. As the influence of silicon on high-temperature oxidation is well known and its effect on surface ductility is marginal silicon was chosen as an alloying element to provoke intergranular oxidation. The methods used were the In-Situ Material Characterization by Bending test (IMC-B), which provides the investigation of the susceptibility to surface crack formation by 3-point bending under oxidizing testing conditions and simultaneous thermal analysis for the well-controlled study of high-temperature oxidation phenomena. The results show that during a cooling cycle supporting highly oxidizing conditions, silicon favors the formation of a low-melting eutectic (FeO–Fe2SiO4) at the interface, infiltrating the steel along the austenite grain boundaries. The intergranular oxidation formed has a depth of less than 50 μm but leads to a stress concentration during a subsequent tensile deformation. In consequence, cracks may easily nucleate and propagate along austenite grain boundaries. A change in the steel composition by reducing the silicon content to almost zero or a less harmful temperature sequence reduces intergranular oxidation and subsequently the susceptibility to crack formation.

Behaviour of demountable steel‐concrete composite beams with bolts and headed studs

AbstractImplementation of demountable beams in steel‐concrete composite floors enables structure reuse during several life cycles, consequently leading to savings in material consumption and reduction of emissions, providing overall ecological benefits. The behaviour of the innovative demountable beam with a shear connection consisting of headed studs and bolts is analysed in this paper. The proposed beam is formed of a steel profile and a steel‐concrete composite slab cast in open trough profiled steel sheeting. Headed studs, welded to the additional steel angles, are placed in sheeting ribs, whereas bolts are installed between ribs, connecting the steel angles and profile flange. A numerical FE model of a full‐scale steel‐concrete composite beam has been developed to analyse the beam behaviour under service loads. Experimental results of push‐out tests have been used to describe the load‐slip behaviour of headed studs, whereas bolt response has been simulated according to the experimental investigations of lap joints with preloaded bolts and oversize holes. The parametric study has been conducted by varying the bolt diameter, grade and bolt hole size. The results have validated the applicability of the proposed system, confirming the fulfilment of serviceability limit state requirements.

Design of a submerged entry nozzle for optimizing continuous casting of stainless steel slab

Design of a submerged entry nozzle for optimizing continuous casting of stainless steel slab

Cooling Capacity Evolution of Steel Strip during Oscillatory Feeding Process in Slab Continuous Casting

To comprehensively understand the effect of oscillation on cooling capacity of steel strip, a mathematical model is proposed to investigate the distribution of temperature fields in continuous cast slabs, taking into account the oscillatory feeding process. Strip oscillation results in a periodic variation of nearby molten steel flow. It intensifies the turbulence of surrounding molten steel and enhances the interfacial heat transfer. During the feeding process, the morphology of strip undergoes three stages: upheaval, fluctuation, and disappearance. As the strip oscillation frequency increases, the maximum cross‐sectional area of the strip gradually decreases during the upheaval stage, the fluctuation stage gradually disappears, and the strip disappearance speed gradually increases during the disappearance stage. These observations suggest that an increase in the oscillation frequency accelerates the melting of the strip, which is caused by the enhanced heat transfer between the strip and molten steel. This results in a gradual growth of strip's cooling capacity and a decrement in the liquid fraction of molten steel surrounding the strip. In addition, feeding strip is advantageous in preventing the jet from impinging onto narrow surfaces of slab. The blocking effect initially increases and then remains almost unchanged as the strip oscillation frequency increases.