Nozzle clogging is a common phenomenon in the continuous casting of steels, especially for aluminum killed steels, and has detrimental effects on the continuity of casting and the steel cleanliness. ...The formation and prevention of nozzle clogging during the continuous casting of steels was reviewed in the current study. The characterization of nozzle clogging was firstly summarized, finding that the composition, morphology, and structure of the nozzle clogging significantly depended on the steel grade, casting condition, and clogging degree. Then three factors affecting the formation of nozzle clogging was briefly summarized as the physical adhesion of high-melting-point inclusions, the temperature drop resulted from the insufficient preheating of nozzles and the temperature fluctuation of molten steel, and the chemical reactions occur during the continuous casting. The prevention methods of nozzle clogging could be roughly divided into 5 types, including the cleanliness improvement of steel, the liquid modification of inclusions, the fluid flow control inside the nozzle, the coating treatment on the inner surface of nozzles, and the external field treatment. Moreover, the challenge of the nozzle clogging control in the future was proposed. Multiple methods should be coordinated, especially the external field treatment should be developed to achieve a better inhibitory effect on the nozzle clogging.
In order to investigate the effect of Rare Earth La-Ce on the modification of inclusions in GCr15 bearing steel， ahigh-temperature tube furnace with a nominal capacity of 1 kg was used to smelt 6 ...heats of GCr15 bearing steel ingots withdifferent La-Ce contents. Characterization methods such as optical microscopy and scanning electron microscopy wereused， and the transformation law of inclusions in GCr15 steel at different La-Ce contents was studied using FactSage thermodynamic software. The results show that the typical inclusions in GCr15 bearing steel without adding La-Ce areAl2O3and MnS， and the addition of La-Ce will modify it to more complex Rare Earth inclusions. With the increase of La-Ce content， the transformation law of inclusions in steel at 1 600 ℃ is Al2O3→REAlO3→ RE2O3→ RE2O2S → RE2O2S + RExSy（RE is La、Ce）. With the increase of La-Ce content， the density of inclusions and the average aspect ratio in the steel bothdecrease first and then increase. When the La-Ce content is 96 ×10-6， Al2O3 and MnS
Nozzle clogging is a common phenomenon in the continuous casting of steels, especially for aluminum killed steels, and has detrimental effects on the continuity of casting and the steel cleanliness. ...The formation and prevention of nozzle clogging during the continuous casting of steels was reviewed in the current study. The characterization of nozzle clogging was firstly summarized, finding that the composition, morphology, and structure of the nozzle clogging significantly depended on the steel grade, casting condition, and clogging degree. Then three factors affecting the formation of nozzle clogging was briefly summarized as the physical adhesion of high-melting-point inclusions, the temperature drop resulted from the insufficient preheating of nozzles and the temperature fluctuation of molten steel, and the chemical reactions occur during the continuous casting. The prevention methods of nozzle clogging could be roughly divided into 5 types, including the cleanliness improvement of steel, the liquid modification of inclusions, the fluid flow control inside the nozzle, the coating treatment on the inner surface of nozzles, and the external field treatment. Moreover, the challenge of the nozzle clogging control in the future was proposed. Multiple methods should be coordinated, especially the external field treatment should be developed to achieve a better inhibitory effect on the nozzle clogging.
Pitting corrosion behavior of Ce treated HSLA steels induced by sulfide inclusions in 3.5 wt% NaCl solution was investigated with potentiodynamic polarization and immersion corrosion test. The ...results show that Ce added steels exhibit better pitting corrosion resistance with lower corrosion current density and bigger pitting potential compared with steel without Ce, which is mainly attributed to optimized characteristics of spherical Ce-oxysulfide inclusions with less number density, smaller average size and lower pitting corrosion susceptibility. The spherical Ce2O2S inclusions precipitated on the surface of CeAlO3 inclusions in the Ce added steels induce pits with bigger opening mouth and shallow depth, reducing their tendency of extension to go deeper due to occlusion corrosion battery in the pitting holes. Furthermore, corrosion inhibitor Ce(OH)3 generated by Ce2O2S hydration can weaken electrochemical corrosion of the matrix micro-region around the pits. To avoid harmful bigger inclusions, Ce content in steels should be regulated within reasonable range, 0.015 wt% Ce in present steels effectively modified inclusions to acquire the best pitting corrosion resistance of the steels.
Weakening of electrochemical corrosion of pitting micro-regions in Ce treated steels is mainly attributed to optimized characteristics of spherical Ce oxysulfide inclusions with less number density and smaller average size, inducing fewer pitting holes with bigger opening mouth and shallow depth and therefore causing smaller catalytic corrosion of an occlusion corrosion battery in the pit holes. Display omitted
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•As S content increases from 0.002% to 0.008%, most oxides are covered by sulfides.•FCG resistance and fracture toughness are improved by the inclusion modification.•The reduction of tessellated ...stress results in improved FCG resistance at low ΔK.•The influence of inclusion tends to disappear with an increase in ΔK.•The thermal expansion mis-match affects FCG more than stiffness mis-match.
This study aims to investigate the fatigue crack growth (FCG) behavior of a railway wheel steel, which has undergone inclusion modification through sulfides enveloping oxides. It involves experimental and finite element (FE) investigations, including microstructural and inclusion analysis, mechanical testing (tensile, hardness, fracture toughness, and FCG tests), and FE analysis based on tessellated stress model and fracture mechanics method. The test results reveal that the microstructure of wheel steel remains almost unchanged as the sulfur content increases from 0.002% to 0.008%. However, the inclusion area fraction increases, the average inclusion size decreases, and most of the oxides are modified to be the duplex inclusions in the form of sulfide enveloping oxide. Moreover, the FCG resistance and fracture toughness are improved. The FE analysis results indicate that the tessellated stress around the inclusion, which is caused by the thermal expansion mis-match between inclusions and matrix material, can be reduced by the coverage of hard oxides by soft sulfides. This reduces the driving force of FCG at low ΔK ranges and results in improved FCG resistance. Furthermore, due to the lower driving force of FCG, fatigue cracks in the modified steel are more prone to deflect at cementite lamellas at low ΔK ranges, which leads to a rougher fracture surface. This further improves the FCG resistance by the mechanism of roughness-induced closure. As ΔK increases, FCG is gradually controlled by the remote applied loading, and the influence of the inclusion tends to disappear. In addition, the thermal expansion mis-match between inclusions and matrix material is found to have a more significant effect on FCG of wheel steel than the stiffness mis-match.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study focuses on purification and inclusion modification mechanism of equiatomic CoCrFeNiMn high entropy alloys with addition of various cerium (within the range of 0–0.0445 %) smelted by Vacuum ...Arc Melting (VAM), It was found that there are three types of inclusions in CoCrFeNiMn alloys: Mn(S, Se), AB2O4 spinel type, mixed type (Mn(S, Se) wraps AB2O4), and the average size of the three types of inclusions are 1.1 µm, 5.6 µm, and 4.8 µm, respectively. The addition of cerium can significantly reduce the oxygen content, as well as the sulfur content and selenium content are declined, the inclusions are refined and spheroidized simultaneously. The oxygen content, sulfur content and selenium content were reduced from 150 ppm, 46 ppm, and 105 ppm to 5–7 ppm, 22 ppm, and 80 ppm, respectively. When the cerium content is 0.0012 %, some of the inclusions are modified into three types of inclusions: Mn(S, Se) + Ce2O3, Mn(S, Se) + CeCrO3 and Mn(S, Se) + Ce2O3 + CeCrO3, while the average size of some unmodified AB2O4 spinel inclusions was reduced to 3.1 µm, and the average size of mixed inclusions was dropped to 2.6 µm. When the cerium content is 0.019 %, the inclusions in the alloy are completely modified into Ce2O2(S, Se) + Ce2(S, Se)3. Furthermore, the number density and area fraction of the inclusions are descended from 216.92 mm−2 and 0.1150 % of no cerium alloys to 121.64 mm−2 and 0.0602 %, the inclusions are well spheroidized, and the average size of cerium inclusions is 2.2 µm. Finally, the mechanism on the modification by cerium was discussed based on the composition evolution of inclusion during solidification with Factsage calculation and experimental results. The compositions of inclusions were also analyzed based on the inclusion evolution model.
•A new way to improve the quality of CoCrFeNiMn. high entropy alloy.•The inclusion evolution model of Ce modified high entropy alloy is proposed.•Ce-O-S data were supplemented in the Factsage software, the calculated inclusion precipitation and transformation process was consistent with the experimental results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To investigate the evolution of inclusions in high‐Al steel with addition of La, a series of laboratory experiments and thermodynamic calculations are performed, considering the reaction time and ...amount of La added. The main inclusions in the high‐Al steel without the addition of La are Al2O3, MnS, and Al2O3–MnS. The La treatment can efficiently modify Al2O3 to La–Al–O or La–O–S inclusions. For La additions less than 0.0041 wt%, the evolution route for the inclusion in high‐Al steel is Al2O3 → LaAl11O18 → LaAlO3 with an increase in reaction time. For high La additions, the evolution route for the Al2O3 inclusion is Al2O3 → LaAl11O18 → LaAlO3 → La2O2S → La2S3. The experimental results correlate with those of the thermodynamic analysis. Notably, excess La in high‐Al molten steel may consume O and S to form La oxysulfide and sulfide, respectively, which prevents the precipitation of MnS inclusion and promotes the formation of AlN inclusion during solidification.
Herein, the effect of rare‐earth lanthanum (La) on inclusion evolution in high‐Al steel is investigated. A low La content effectively modifies Al2O3 inclusion to LaAlO3, and a higher La content may promote the formation of AlN, La oxysulfide and sulfide. The recommended La content in high‐Al steel is in the range of 0.004–0.005 wt%.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
MnS inclusions in stainless steel can easily induce pitting corrosion, which seriously deteriorates the corrosion resistance of steel. Applying MnS inclusion control technology or modification ...technology is an effective way to improve the corrosion resistance of stainless steel. In this paper, the S32550 duplex stainless steel was taken as the research object, and the test steels with different Ce and Ti contents were smelted in a vacuum induction furnace under laboratory conditions. The modification effects of trace amounts of Ce and Ti on MnS inclusions in stainless steel and their effects on the corrosion resistance of stainless steel were studied by JSM - 6510 scanning electron microscope, periodic corrosion weight loss test, AC impedance test, Tafel polarization curve test and other test methods. Results showed that after adding 0.047% (mass fraction) Ce into the steel, the inclusions in S32550 steel changed from MnS into Mn - S - Ce - O composite ones, the size of the inclusions was decreased from about
The influence of minor Ce doping on the evolution mechanisms of microstructure and mechanical performances of EH47 grade HSLA steel for marine engineering was investigated by microstructure ...observation and analysis. In the present work, the chemical composition of steels with different Ce contents was designed, and the TMCP hot-rolling process was applied to obtain a portion of bainitic microstructure for the purpose of achieve the performance indicators. The microstructures, precipitates, and inclusions of Ce-free and Ce-containing steels were observed and analyzed by using scanning electron microscopy (SEM) equipped with electron backscatter diffraction (EBSD) detector and transmission electron microscope (TEM) equipped with energy dispersive X-ray spectrometers (EDS). The strength, plasticity, and impact toughness of the experimental steels was measured and evaluated. According to the results, after adding rare earth Ce, the microstructures including grains, M-A constituents, and inclusions of steel were refined and optimized significantly. Then, the influencing mechanisms of Ce doping on precipitates and inclusions formation were further discussed in detail. Simultaneously, a clear variation tendency of mechanical properties was presented by Ce addition. The strength and hardness enhanced significantly, and the total elongation declined slightly. Moreover, the impact absorbed energy enhanced from 56 J to 152 J.
•The microalloying effect of REM element Ce in steels was studied in detail.•Phase transformation driving force was raised to refine grains by adding Ce.•Increasing nucleation sites attributed to the inclusion modification of Ce.•Refined grains and M-A constituents enhanced mechanical properties significantly.
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GEOZS, IJS, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The effects of La-Ce rare earth treatment on inclusions， continuous casting castability and steel properties of Q345D structural steel were analyzed by field test. The results showed that the alloy ...yield of RE in Q345D structural steel was 21. 5%. Compared with the heats without RE addition， the desulfurization rate increased by 37. 5%， and the unit inclusion density decreased from 80. 16/mm2 to 60. 78/mm2 . The inclusions in molten steel before La-Ce rare earth treat ment were mainly MgO-Al2O3-CaO composite inclusions. The modification effect of La-Ce rare earth treatment on small size （ D≤5 μm ） inclusions was more obvious. Small size inclusions were modified into （La-Ce-S） and （La-Ce-Al-S-O） rare earth inclusions. La-Ce rare earth treatment can significantly reduce the aspect ratio of MnS inclusions in steel， so that the morphology of MnS inclusions after rolling was closer to ellipse without long linear， which was the main reason for the increase of transverse impact energy of Q345D structural steel by 20
