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15 pages, 5735 KiB

Open AccessArticle

Effect of CeO₂ Content on Melting Performance and Microstructure of CaO-Al₂O₃-SiO₂-MgO Refining Slag

by Bo Zhao, Wei Wu, Jianguo Zhi, Cheng Su and Tonglu Yao

Metals 2023, 13(1), 179; https://doi.org/10.3390/met13010179 - 16 Jan 2023

Cited by 3 | Viewed by 1947

CeO₂ can be applied to refining slag to minimize the size of inclusions, speed up the deoxidization process, and adsorb Al₂O₃ inclusions. The impact through which CeO₂ content affects slag’s melting efficiency is still uncertain. The thermal analyzer [...] Read more.

CeO₂ can be applied to refining slag to minimize the size of inclusions, speed up the deoxidization process, and adsorb Al₂O₃ inclusions. The impact through which CeO₂ content affects slag’s melting efficiency is still uncertain. The thermal analyzer was used to measure the thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) curves of the slag melting process. According to the study results, with the increase in CeO₂ content, the melting temperature of slag decreased first and then increased. The slag’s melting point fell from 1364 °C to 1324 °C and then rose to 1503 °C. XRD and SEM were used to analyze the CaO-Al₂O₃-SiO₂-MgO-CeO₂ slag’s microstructure. The mineral-phase structure of CeO₂-containing refining slag was primarily composed of Ca₂SiO₄ and 3CaO·Al₂O₃, MgO, SiO₂, CaO·Al₂O₃, and Ca₈Ce₆Al₆O₂₆. The proportion of 3CaO·Al₂O₃, CaO·Al₂O₃, and Ca₂SiO₄ decreased as the rare-earth-oxide content increased, while the proportion of Ca₈Ce₆Al₆O₂₆ increased. FactSage was used to estimate the equilibrium-phase compositions of slags with various compositions, and a model for predicting melting points was carried out by a linear regression model. Results were obtained through the analysis of equilibrium-phase composition and crystal structure transformation. The main reasons for the melting point decrease were the change of degree of polymerization and the decrease in contents and complete melting temperature of high-melting-point Ca₃Al₂O₆ and Ca₂SiO₄ compounds. The latter increase in melting point was due to the number of Ca₈Ce₆Al₆O₂₆ compounds and precipitation temperature increases and the complexity of the structural-network increases. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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15 pages, 7733 KiB

Open AccessArticle

Control of Bismuth and Manganese Sulfide Inclusions in Free-Cutting Steels of Different Classes

by Andrey Zhitenev, Anna Rovbo, Daniil Nechaev, Nikita Shaposhnikov, Sergey Ryaboshuk and Alexey Alkhimenko

Metals 2022, 12(12), 2076; https://doi.org/10.3390/met12122076 - 2 Dec 2022

Cited by 1 | Viewed by 1534

Abstract

The paper investigates the behavior of bismuth and sulfur in modern free-cutting steels. It is shown that today there are no mutually consistent thermodynamic data for calculating the solubility of bismuth in a multi-component steel system. Based on the processing of data from [...] Read more.

The paper investigates the behavior of bismuth and sulfur in modern free-cutting steels. It is shown that today there are no mutually consistent thermodynamic data for calculating the solubility of bismuth in a multi-component steel system. Based on the processing of data from separate works, mutually consistent dependences of the solubility of bismuth in pure iron, as well as Wagner interaction parameters for calculation for steels, were obtained. An attempt was made to model the formation of bismuth simultaneously with manganese sulfides during solidification based on the Ohnaka segregation model. Comparison with experimental data shows acceptable convergence of calculations and experiments. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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19 pages, 1874 KiB

Open AccessFeature PaperArticle

Thermal Effect and Metallurgical Characteristics of Hydrogen Bottom Blowing in Top–Bottom Combined Blowing Converter

by Jianhua Liu, Hongbo Peng, Yang He, Xiaodong Yang, Hao Xu, Yaobin Hou and Dali You

Metals 2022, 12(10), 1633; https://doi.org/10.3390/met12101633 - 29 Sep 2022

Cited by 1 | Viewed by 1745

Abstract

A new technology of hydrogen bottom blowing instead of traditional argon blowing in the current converter steelmaking process is proposed herein, in the aim of overcoming problems such as energy shortages caused by increased scrap charging, the low stirring intensity of bottom blowing, [...] Read more.

A new technology of hydrogen bottom blowing instead of traditional argon blowing in the current converter steelmaking process is proposed herein, in the aim of overcoming problems such as energy shortages caused by increased scrap charging, the low stirring intensity of bottom blowing, high CO₂ emissions, and endpoint carbon content control. The thermal effect and metallurgical characteristics of hydrogen bottom blowing were investigated based on the production data of a steelmaking converter in Pangang Group Xichang Steel & Vanadium Co., Ltd. This study shows that hydrogen bottom blowing at an intensity of 0.1–0.5 m³·min⁻¹·t⁻¹—rather than argon blowing at an intensity of 0.1 m³·min⁻¹·t⁻¹—can increase the smelting temperature by 16–73 K, increase the scrap charging ratio by 0.89–5.19%, and reduce CO₂ emissions by 19.79–115.96 kg per ton of steel. Intensive hydrogen blowing could significantly reduce the oxygen content of molten steel in the late stage of steelmaking and be beneficial to controlling oxygen at the endpoint. Hydrogen can also reduce the (FeO) content in slag, and the equilibrium partial pressure ratios of H₂O/H₂ for the reaction H₂ + (FeO) = H₂O + Fe in the middle and late periods are 0.41 and 0.11, respectively. Hydrogen can also slightly suppress the decarbonization reaction in the late period of steelmaking, and the equilibrium partial pressure ratio of H₂O/H₂ for the reaction H₂ + (CO) = [C] + H₂O in the late period is 9.65 × 10⁻², which means that hydrogen is beneficial in preventing the rapid decrease in [C] and, in turn, helps control the endpoint carbon content. By comparing the degree of the reaction (P₂O₅) + 5H₂ = P₂(g) + 5H₂O and the reaction (P₂O₅) + 5H₂ = 2[P] + 5H₂O, it can be seen that intensive bottom-blown hydrogen may have a slight positive effect on slag gasification dephosphorization. The FactSage simulation results further verify the conclusions of the above analysis. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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14 pages, 6066 KiB

Open AccessArticle

Effect of TiN on Sulfide Morphology of Non-Quenched and Tempered Steel

by Huajie Wu, Xin Li, Zhe Wang and Wei Liu

Metals 2022, 12(9), 1402; https://doi.org/10.3390/met12091402 - 24 Aug 2022

Cited by 4 | Viewed by 1684

Abstract

In this paper, non-quenched and tempered steel was selected to observe sulfide inclusions in as-cast and forged steel with different Ti and N contents, and analyzed the influence of TiN on the precipitation, morphology, distribution and composition of MnS. The precipitation of MnS [...] Read more.

In this paper, non-quenched and tempered steel was selected to observe sulfide inclusions in as-cast and forged steel with different Ti and N contents, and analyzed the influence of TiN on the precipitation, morphology, distribution and composition of MnS. The precipitation of MnS and TiN in liquid-phase, solid–liquid two-phase region and solid phase was comparatively analyzed from a thermodynamic perspective, and the effect of the thermodynamic precipitation sequence on composite sulfide was explored. It was found that the change in Ti content had little effect on the morphology of sulfide in its as-cast state, and the composite sulfide was more spindle-like in the forged state. The increase in Ti and N content will increase the content of composite sulfide containing TiN in the steel, especially the number of MnS with TiN as the nucleation core. The initial precipitation temperature of TiN is higher than that of MnS, which provides a thermodynamic explanation for the existence of composite manganese sulfide containing TiN. Titanium treatment provides a new way to improve sulfide morphology. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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15 pages, 6844 KiB

Open AccessArticle

Effect of Temperature and Solidification Structure Evolution of S355 Slabs with Different Corner Shapes on Transverse Corner Cracks

by Minglin Wang, Hui Zhang, Heping Liu and Lijun Xu

Metals 2022, 12(8), 1383; https://doi.org/10.3390/met12081383 - 20 Aug 2022

Cited by 1 | Viewed by 1718

Abstract

The evolution process of corner temperatures for a typical micro-alloyed steel S355 is numerically simulated under various working conditions. The microstructure near the corner cracks of the S355 slab is experimentally examined, and the austenite/ferrite transformation temperatures of S355 steel during heating and [...] Read more.

The evolution process of corner temperatures for a typical micro-alloyed steel S355 is numerically simulated under various working conditions. The microstructure near the corner cracks of the S355 slab is experimentally examined, and the austenite/ferrite transformation temperatures of S355 steel during heating and cooling are measured. The results indicate that the right-angle slab corner temperature at the exit of the mould rapidly decreased to below Ar₃ under intensive cooling in the foot roller zone. The film-like ferrite began to precipitate along the austenite grain boundary at the slab corner. The transformation from ferrite to austenite cannot be fully realized because the corner temperature cannot be quickly returned to Ac₃ or higher. The slab transverse corner cracks occur along the film-like ferrite during the bending process. The chamfered slab, which modifies the original right angle of the slab into the 30° chamfered angle with a chamfered length of 60 mm, can significantly weaken the heat transfer and cooling effect of the slab corner. The chamfered slab corner temperature always remained above Ar₃ during the bending and straightening processes. Precipitation of the pro-eutectoid film-like ferrite along the grain boundary cannot occur during cooling for the chamfered slab. The chamfered slab can keep the corner temperature above Ar3 and effectively avoid the occurrence of transverse corner cracks caused by grain boundary embrittlement. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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10 pages, 5696 KiB

Open AccessFeature PaperArticle

Recrystallization Behavior of Warm Rolling and Cold Rolling Cr-Ti-B Steel during Annealing

by Ankang Huang, Zhigang Wang, Qiangqiang Yuan, Rongchun Chen, Jing Qin, Yinghui Zhang and Weizhen Liu

Metals 2022, 12(7), 1178; https://doi.org/10.3390/met12071178 - 11 Jul 2022

Viewed by 1997

Abstract

To study the nucleation and recrystallization behavior of deformation bands, shear bands and grain boundaries during the recrystallization process, a heat treatment test was carried out on Cr-Ti-B low-carbon steel after warm rolling and cold rolling. The results show that recrystallization occurs preferentially [...] Read more.

To study the nucleation and recrystallization behavior of deformation bands, shear bands and grain boundaries during the recrystallization process, a heat treatment test was carried out on Cr-Ti-B low-carbon steel after warm rolling and cold rolling. The results show that recrystallization occurs preferentially in shear bands and grain boundaries. The γ deformation texture can be enhanced and the Goss texture can be weakened during the warm rolling and subsequent cold rolling process. Recrystallization of the deformation bands was observed, but the nucleation time of recrystallization in the deformation band is much slower than that in the shear band and grain boundary. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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12 pages, 3156 KiB

Open AccessArticle

Thermodynamics Analysis and Pilot Study of Reusing Medium and High Alloy Steel Scrap Using Induction Melting and Electroslag Remelting Process

by Liushun Wu, Kunlong Liu, Haiqing Mei, Guangda Bao, Yun Zhou and Haichuan Wang

Metals 2022, 12(6), 944; https://doi.org/10.3390/met12060944 - 30 May 2022

Viewed by 2616

Abstract

The annual cumulative quantity of high and medium alloy steel scrap has exceeded 10 million tons. Using the traditional smelting process involving electric arc refining in a smelting furnace for these scraps causes high percentages of alloy losses, which decreases the value of [...] Read more.

The annual cumulative quantity of high and medium alloy steel scrap has exceeded 10 million tons. Using the traditional smelting process involving electric arc refining in a smelting furnace for these scraps causes high percentages of alloy losses, which decreases the value of the alloy steel scrap and poses environmental threats. Existing studies have rarely focused on separate smelting of the scrap and oxidation behaviors of the alloying elements. Therefore, this study proposes an induction melting and electroslag remelting scheme to process the scrap. Based on this scheme, the effects of the temperature, oxygen content, and element contents on the recovery percentages of the alloying elements were investigated using pilot experiment and thermodynamic analysis. The experimental results showed that the alloying elements (tungsten, chromium, nickel, molybdenum, and vanadium) exhibited recovery percentages of 97.36%, 94.62%, 97.63%, 95.09%, and 89.49%, respectively; furthermore, the impurity content did not increase during smelting. The thermodynamic analysis indicated that an increase in carbon content improved the oxidation resistance of the alloying elements except for nickel, whereas the increases in the contents of oxygen and alloying elements increase their oxidation. Steam partial pressure and air suction dramatically increase the concentrations of nitrogen, hydrogen and oxygen. This scheme is an alternative for smelting medium and high alloy steel scrap, and the thermodynamic analysis provides a theoretical understanding of the oxidation behaviors of the alloying elements in the steel scrap and the control of impurity. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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16 pages, 4140 KiB

Open AccessArticle

Primary Study on Medium and Low Carbon Ferromanganese Production by Blowing CO₂-O₂ Mixtures in Converter

by Yu Han, Cheng Li and Haijuan Wang

Metals 2022, 12(4), 682; https://doi.org/10.3390/met12040682 - 15 Apr 2022

Cited by 1 | Viewed by 2181

Abstract

The production of medium- and low-carbon ferromanganese (M-LCFeMn) using the converter method has not been industrialized to date in China due to the high manganese loss and serious erosion of the furnace lining. To solve the above problems and to improve the refining [...] Read more.

The production of medium- and low-carbon ferromanganese (M-LCFeMn) using the converter method has not been industrialized to date in China due to the high manganese loss and serious erosion of the furnace lining. To solve the above problems and to improve the refining technology of M-LCFeMn, the introduction of CO₂ gas into the traditional converter process is proposed. In this study, the oxidation behavior of C and Mn in various conditions was analyzed by blowing different proportions of CO₂-O₂ mixed gas into the high-carbon ferromanganese (HCFeMn) melt. The results showed that it is feasible to make M-CFeMn by blowing CO₂-O₂ mixtures, and the Mn loss can be effectively reduced during the decarburization process. It is considered that when the proportion of CO₂ reaches 25%, the mixed gas has the best effect on the decarburization and manganese preservation under current experimental situation. Two hypotheses and corresponding rate formulas of decarburization kinetics by using pure oxygen are put forward, and the effect of CO₂ on the kinetics of decarburization was studied according to different hypotheses. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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12 pages, 3160 KiB

Open AccessArticle

Image Processing Procedure to Evaluate Inclusion Dissolution in a Slag Observed by High-Temperature Confocal Scanning Laser Microscopy

by Shashank Ramesh Babu, Nikolaus Preisser and Susanne Katharina Michelic

Metals 2022, 12(4), 531; https://doi.org/10.3390/met12040531 - 22 Mar 2022

Cited by 4 | Viewed by 2293

Abstract

In situ study of the inclusion dissolution behavior in a slag utilizing high-temperature confocal scanning laser microscopy helps to understand the phenomenon of the removal of non-metallic inclusions from liquid steel before the casting process. The current work introduces an image processing procedure [...] Read more.

In situ study of the inclusion dissolution behavior in a slag utilizing high-temperature confocal scanning laser microscopy helps to understand the phenomenon of the removal of non-metallic inclusions from liquid steel before the casting process. The current work introduces an image processing procedure to automate and measure the inclusion diameter during its dissolution. Silica and alumina particle dissolution were considered as they appear differently when suspended in the slag (bubble-like transparent and solid-like opaque, respectively). The procedure consists of two parts: (1) morphological isolation and construction of the inclusion, and (2) inclusion diameter calculation. The inclusion diameters could be successfully measured over a series of images and showed good agreement with the manually measured diameters. The image processing procedure has the advantages of significant time saving and standardization compared to manual measurements. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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11 pages, 7333 KiB

Open AccessArticle

Three-Dimensional Morphology and Analysis of Widmanstätten Sideplates Ferrite

by Shengli Cao, Shaowen Wu, Caijun Zhang and Qingjun Zhang

Metals 2022, 12(3), 523; https://doi.org/10.3390/met12030523 - 21 Mar 2022

Cited by 1 | Viewed by 2547

Abstract

The three-dimensional (3D) morphology and crystal structure of Widmanstätten sideplate ferrite were simulated using a focused ion beam (FIB) scanning electron microscope equipped with electron backscatter diffraction (EBSD). The primary Widmanstätten sideplates nucleated and grew directly at the austenite grain boundary (GB). A [...] Read more.

The three-dimensional (3D) morphology and crystal structure of Widmanstätten sideplate ferrite were simulated using a focused ion beam (FIB) scanning electron microscope equipped with electron backscatter diffraction (EBSD). The primary Widmanstätten sideplates nucleated and grew directly at the austenite grain boundary (GB). A certain included angle between the sideplates and the austenite GB was observed. The sideplates grew approximately parallel to the grain, and were separated by a small-angle GB. The primary Widmanstätten sideplates are best described as “∃” shaped, with a long intermediate ferrite strip. The interface with the austenite GB was smooth and flat, and the sideplate surface contained pits and holes. The secondary Widmanstätten sideplates nucleated and grew on the surface of the proeutectoid GB ferrite, with the sideplates and GB ferrite perpendicular to each other. Sideplates parallel to one another grew into the grain, and were separated by small-angle GB. The 3D morphology was distinguished by its “comb” shape. The sideplates’ tail was clustered and its front end remained sharp. The contact side of the GB ferrite was smooth and flat. The surface contained several uneven pits and defects. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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14 pages, 4091 KiB

Open AccessArticle

The Effect of Aluminum Addition on the Evolution of Inclusions in an Aluminum-Killed Calcium-Treated Steel

by Xingle Fan, Lifeng Zhang, Ying Ren, Wen Yang and Songjie Wu

Metals 2022, 12(2), 181; https://doi.org/10.3390/met12020181 - 19 Jan 2022

Cited by 6 | Viewed by 3546

Abstract

In the current study, the reduction of CaO-Al₂O₃ inclusions in steel by the subsequent addition of aluminum is revealed through industrial trials, laboratory experiments, and thermodynamic calculations. During the industrial production of the Al-killed Ca-treated steel, the Al₂O [...] Read more.

In the current study, the reduction of CaO-Al₂O₃ inclusions in steel by the subsequent addition of aluminum is revealed through industrial trials, laboratory experiments, and thermodynamic calculations. During the industrial production of the Al-killed Ca-treated steel, the Al₂O₃ content in CaO-Al₂O₃ inclusions increased from 72.05% to 79.83%, after the aluminum addition. In laboratory experiments, the addition of aluminum increased the Al₂O₃ content, and meanwhile lowered the contents of CaS and CaO in the inclusions. The average diameter of the inclusions decreased and the number density increased after the Al addition in steel, due to the formation of tiny inclusions. Based on the thermodynamic consideration, the transformation of the inclusions was attributed to the re-equilibrium of the reaction between steel and the inclusions after aluminizing. The Al₂O₃-riched calcium aluminate with a high melting point increased the possibility of the nozzle clogging during the continuous casting process, reducing the effect of the calcium treatment. Therefore, the addition of aluminum after calcium treatment should be avoided as far as possible. Full article

(This article belongs to the Special Issue Advances in Refining, Solidification, and Casting of Steels and Alloys)

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