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During the “BOF-LF-CC” process of producing low carbon Al-killed (LCAK) steel, Al in the molten steel will react with MgO in the ladle refractory or the refining slag to generate MgO-Al2O3 inclusions, which have a negative influence on the molten steel’s castability. To enhance the castability of molten steel, calcium treatment is typically required following LF refining to promote the transformation of inclusions MgO-Al2O3 to CaO-MgO-Al2O3 or CaO-Al2O3. However, calcium treatment has many drawbacks, such as low calcium yield, increased smelting cost, environmental pollution, etc. Thus, how to improve the castability of LCAK steel without calcium treatment is worth studying. In this research, laboratory studies were first carried out to clarify the source of MgO-Al2O3 inclusions in the molten steel. Thereafter, industrial trials were conducted with the refractory material of the ladle replaced by a MgO-free and Al2O3-riched refractory. The results show that when a MgO-based crucible is used at 1600℃, the inclusions in molten steel after 25 min are mainly MgO-Al2O3, even without refining slag. However, even with the refining slag (the basicity is less than 4.5) containing about 5% MgO, when an Al2O3-based crucible is employed, the inclusions in the molten steel are mainly CaO-Al2O3. Consequently, MgO in ladle refractories is the main source for the formation of inclusions ­MgO-Al2O3. The results of industrial trials using the “3 + 1” smelting pattern, in which the molten steel is cast directly without calcium treatment in the first three heats, treated with calcium in the next heat, and the process is repeated, show a significant improvement in the castability of molten steel.

Clogging of sub entry nozzle is a recurrent problem during continuous casting of low carbon aluminum deoxidized steel. Newly modernized SMS shop, producing mainly low carbon aluminum deoxidized steel through BOF-Twin LF-CC route was facing a major issue of nozzle clogging leading to abrupt abortion of sequence casting. The incidences of SEN clogging were very high leading to loss of shop productivity. Within a span of one month around 28 cases of casting abortion were reported due SEN clogging. Casting was getting stopped in 3–4 heat sequence even after calcium treatment practice was adopted in each heat. The process of steelmaking was studied in detail to find out the root cause of nozzle clogging. It was found that dendritic clusters of alumina originating as a result of deoxidation of steel and reoxidation of aluminum during secondary refining was probably causing SEN clogging. It was also found that optimization of Ca treatment practice was required for successful continuous casting of an aluminum-killed steel. The paper elaborates the technical issues faced related to clogging of SEN in a newly installed high speed single strand slab caster during continuous casting of low carbon steel deoxidized with aluminum. The paper covers the essential steps required to identify the root cause of nozzle clogging and various process interventions essential to eliminate the SEN clogging issues and streamline the production of low carbon aluminum-killed steel in higher sequence lengths.

To investigate the dynamic interaction between refining refractory and low‐carbon low‐silicon Al‐killed steel, the “refractory‐molten steel‐inclusion” system was analyzed using dynamic erosion experiments and the FactSage database. This study discussed the formation of interfacial layers between various refining refractories and molten steel, as well as the transformation of nonmetallic inclusions in steel. The findings indicate that the interaction between refractories and molten steel produces a distinct interface layer. The influence of various refining refractories on inclusions varies significantly. MgO‐C refractory promotes the formation of MgO·Al2O3 inclusions in steel, while Al2O3‐MgO refractory leads to the formation of SiO2‐MnO‐Al2O3 inclusions. Both Al2O3‐SiC refractory and Al2O3‐MgO‐C refractory result in Al2O3 inclusions with trace levels of MgO. Steel refined with Al2O3‐MgO‐C refractory has increased MgO content within Al2O3 inclusions but still does not reach the stoichiometric ratio of MgO·Al2O3. As the initial Al content increases, the influence of MgO‐C refractory inclusions becomes increasingly noticeable. The average MgO content within the inclusions rises with the reaction duration, achieving as high as 62.9%. The transition path of Al2O3 inclusions in molten steel follows “Al2O3→MgO·Al2O3→MgO.”

In this study, industrial trials were conducted on Si–Mn-killed steels to study the evolution of inclusions and their transformation in steel to meet stringent steel quality. It is observed that inclusions modify along the route of ‘‘MnO–SiO 2 -based inclusions to CaO–Al 2 O 3 -based inclusions after calcium treatment and further transformed to CaO–SiO 2 –Al 2 O 3 -based inclusions’’ in billet stage. As more dissolved oxygen is present in Si-killed steel compared to Al-killed steel; a new generation of SiO 2 is taking place during solidification that too adjacent to liquid oxide inclusions (in tundish samples) which are getting transformed to wollastonite and anorthite at the billet stage. The results obtained from industrial trails denoting calcium treatment in Si–Mn-killed steels has an efficient method to get better castability of liquid steel and also is affable to enhance deformation ability of inclusions in steel further during cold rolling process.

It is to reduce the performance variation of DCO3 aluminum killed steel be fluctuations caused by components that the smelting and rolling process was controlled and adopted a chemical composition design plan of low-carbon + micro-alloying elements.Research result shows that microstructure of the DCO3 aluminum killed steel plate is ferrite, Further more various mechanical properties of the steel plate are in correspondence with standard requirements.

Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al 2 O 3 -based inclusions during secondary refining. The results showed that Al 2 O 3 -based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition, [Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO–MgO–Al 2 O 3 multi-component inclusions. Thermodynamic analysis confirmed that the reaction between [Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3wt% and the temperature is higher than 1843 K.

Subsurface macro-inclusions and hooks are detrimental to the surface quality of deep-drawing steel sheets. However, little is known about the relationship between macro-inclusions and hooks. Thus, in this work, two ultralow carbon （ULC） steel slabs and two low carbon （LC） aluminum-killed steel slabs were sampled to study the relationship between hooks and subsurface macro-inclusions, which were detected on the cross-sections of steel samples with an area of 56058 mm2 using an automated scanning electron microscopy/energy-disper-sive X-ray spectroscopy system. Results show that subsurface inclusions larger than 200 μm were almost entrapped by hook structures, whereas the location of other inclusions smaller than 200μm had no obvious dependence on the location of solidified hooks. Furthermore, the number density （ND） of subsurface inclusions larger than 200μm decreased from 0.02 to 0 cm-2 in ULC steel as the mean hook depth decreased from 1.57 to 1.01 mm. Similar trends were also observed in LC steel. In addition, the detected inclusions larger than 200μm were concentrated in the region near the slab center （3/8 width-5/8 width）, where hook depths were also larger than those at any other locations. Therefore, minimizing the hook depth is an effective way to reduce inclusion-induced sliver defects in deep-drawing steels.

The effect of the annealing cycle on microstructure, mechanical properties and draw ability of aluminium killed steel sheets at three different heating rates and holding times were investigated. Tensile test, hardness test, optical microscope and transmission electron microscope (TEM) techniques were utilized. The results of samples for different times in laboratory experiments were compared with the production samples. The results for these experiments showed that lower heating rates (12 °C/h) occurred at a lower annealing temperature, increase draw ability. This effect is attributable to the longer time available to initiate nucleation at the lowest heating rate. However, for all three heating rates (12 °C/h, 24 °C/h and 36 °C/h), the aluminium and nitrogen combine to form atmospheres or pre-precipitation clusters at polygonised sub-grains and as rolled boundaries, modifying the development of the recrystallized structure. Different amounts of AlN were precipitated prior to recrystallization for each heating rate resulting in different final recrystallized grain sizes, mechanical properties and drawabilities. The heating rate strongly influences recrystallization and drawability with a lower heating rate reducing both the temperature of the start of recrystallization and the recrystallized grain size. It is inferred that the lower rate promotes nucleation of recrystallization overgrowth of recrystallized. The effect of holding time on mechanical properties was to: (i) decrease tensile strength, yield strength and hardness and (ii) increase drawability, elongation and grain size. Tensile strength and hardness results from laboratory experiments were lower than those for production samples, but the trends were similar.

In the current study, the nozzle clogging behavior and inclusion composition in Al-killed Ca-treated steels were observed to investigate the relationship between the liquid fraction of non-metallic inclusions and the clogging possibility of the submerged entry nozzle. Clogging materials were mainly MgO-Al2O3 with less than 20% liquid phases, while most of the inclusions were full liquid CaO-Al2O3-MgO in tundish at the casting temperature. Thus, it was proposed that the nozzle clogging can be effectively avoided by modification of solid inclusions to partial liquid ones rather than full liquid ones. There was a critical value of liquid fraction of inclusions causing the nozzle clogging. A critical condition of the inclusion attachment on the nozzle wall was a function of cosθN−S+cosθI−S<0. With the increase of T.Ca content in steel, the evolution route of inclusions was solid MgO-Al2O3→liquid CaO-Al2O3-MgO→solid CaS and CaO. To avoid the clogging of the submerged entry nozzle (SEN) under the current casting condition, the appropriate T.Ca concentration range in Al-killed Ca-treated steels can be enlarged from the 100% liquid inclusion zone of 10–14 ppm to the 20% liquid inclusion zone of 4–38 ppm.

In this work, Ti3C2 MXene, a novel two-dimensional nanosheet, was introduced to waterborne polyurethane (WPU) coatings to prepare a composite coating. First, MAX phase materials were in situ etched by HF acid and further intercalated by water molecules to obtain exfoliated single-layer MXene nanosheet. And then, composite coatings were prepared via solution-blending low addition (0–0.4 wt%) of MXene, self-prepared waterborne polyacrylate emulsion (PAE) and isocyanate hardener, applying on Q235 mild steel. Results of AFM, XRD SEM and SEM–EDS confirm that single-layer MXene nanosheets with large lateral-to-thickness ratio are successfully prepared and achieved homogenous distribution within WPU matrix. With 0.4 wt% MXene incorporated, the WPU/Ti3C2 MXene composite coatings reach a lowest corrosion current of 2.143 × 10–6 A/cm2, a decrease of one order of magnitude compared with blank WPU (1.599 × 10–5 A/cm2) and own an excellent UV-blocking property (almost block the whole UV light).