Abstract: The control of MnS inclusions in high strength IF steel containing phosphorus was analyzed. The inclusion statistics and two-dimensional morphologies of the samples at the slab thicknesses of 1/8, 1/2, and 7/8 and in hot rolling, cold rolling, and continuous annealing processes were observed and compared via an ASPEX scanning electron microscope (SEM). In addition, the three-dimensional morphologies of the inclusions extracted from the electrolysis of billet samples and inclusions extracted from the original rolling process samples were observed and compared. The results show that the amount distribution of MnS inclusions in the center of the slab is obviously larger than that near the surface of the slab. When a rare earth element is added, it is preferentially combined with the S in the steel and precipitates earlier than MnS in the solidification process, forming small spherical inclusions, which can significantly reduce the size and quantity of MnS inclusions at various positions of the slab. The size of MnS inclusions of the steel strip without a rare earth element addition is approximately 10 μm in each rolling process, which is inherited. During the rolling process, MnS inclusions become longer, but there is no fragmentation and dispersion. S–O–Ce inclusions are formed after adding a rare earth element. These inclusions are spherical, 2–5 μm in size, and distributed independently, which do not affect the structure continuity of the strip steel and benefit the relevant properties of the products.
Abstract: The effects of inclusions on the microstructure and toughness of the heat-affected zone (HAZ) in steel plates with Mg deoxidation after high-heat-input welding were investigated in the present study. The results indicate that the morphologies of MgO–MnS complex inclusions in steel are changed obviously with the addition of Al. When containing 0.001% Al (mass fraction), the inclusions consist of a central single MgO particle and an outside MnS phase. When containing 0.020% Al, they are comprised of several small MgO particles entrapped by the MnS phase. Because the former inclusion can nucleate intragranular acicular ferrites (IAFs) and the latter is non-nucleant, the main intragranular microstructures in the HAZs are ductile IAFs and brittle ferrite side plates, respectively. Therefore, the HAZ toughness of the steel plate without Al addition after a high-heat-input welding of 400 kJ·cm?1 is significantly better than that of the steel plate with Al addition.
Abstract: The typical inclusions in stainless steels were extracted by the anhydrous electrolysis method, the three-dimensional morphology of the inclusions was observed by scanning electron microscopy (SEM), the inclusions were classified and analyzed according to the element composition, and the inclusions with the same chemical composition but different three-dimensional morphology were characterized and summarized. The equilibrium states of the different inclusions were calculated by the thermodynamic software FactSage 7.0, the effects of temperature and molten steel composition on the equilibrium states of inclusions were studied, and the corresponding equilibrium phase diagrams were obtained. In the results, the inclusions in stainless steels can be extracted effectively by the anhydrous electrolysis method, avoiding the error caused by the metallographic method, and the three-dimensional morphology of inclusions can be observed more clearly; according to the SEM observation and measurement, the enrichment area of titanium is likely present at the larger alumina inclusion surface, and most of inclusions are spherical and polyhedral with smooth surface, whose diameters are generally no more than 5 μm. According to the thermodynamic calculation, the inclusions in steels are closely related to the mass fraction of elements in steels; the different mass fractions of Mg, Ti, and Si elements may lead to the different inclusions at 1873 K.
Abstract: As the preferred material for the first wall of fusion reactors, China’s low-activation martensitic (CLAM) steel has several advantages; however, its high-temperature (>550 ℃) strength is not enough, and the helium produced by fusion can easily form a thick helium bubble and gather at the boundary, which leads to helium embrittlement; thus, the low-activation ferrite/martensite steel cannot effectively function in the fusion reactor working environment. Previous studies have shown that adding nano-sized oxide strengthening phase into CLAM steel can significantly improve the high-temperature strength and irradiation resistance of the steel, and Y2O3, Al2O3, or ThO2 are commonly used as strengthening phases. Moreover, it has been found that adding Ti will result in a better strengthening effect. In this study, CLAM steel with the addition of Y2Ti2O7 nanoparticles was fabricated using a vacuum induction furnace. Afterward, the effect of Y2Ti2O7 nanoparticles on inclusions in CLAM steel was investigated via scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and a universal testing machine experiment; then, the mechanical properties of CLAM steel were analyzed. The results show that Y2Ti2O7+Fe nanoparticles are successfully added to CLAM steel. The inclusion size of CLAM steel is 0.5?1.5 μm. The inclusion morphology is near-spherical, and the inclusion composition is Y–Ti–O–Mn–C–Ta–W–V–Cr–Fe; thus, the inclusion is characterized as a compound inclusion, mainly because Ta and V are strong carbide-forming elements and some Y2Ti2O7 particles may agglomerate. When the Y2Ti2O7 content is 0.5%, the inclusions in the steel modify into composite inclusions of rare-earth oxides, and the steel strength is 1356 MPa, while the elongation and section shrinkage are 13.44% and 63.15%, respectively. Moreover, second-phase particles also exist in the fracture dimples. The particles are spherical, less than 1 μm and have a complex composition, mainly Y–Ti–O–C–Ta–W phase.
Abstract: The marine environment significantly accelerates metal corrosion especially in underwater or undersea tunnels for high-speed rails, where the life of the metals will be shorter than normal life time; moreover, this type of corrosion critically affects the safety, promptness, and efficient operation of high-speed rails. Accordingly, this article systematically analyzes the behavior of inclusion-induced corrosion on steel by automatic scanning of inclusions, accelerated corrosion tests, and electrochemical testing. It focuses on the analysis of inclusions in steel used for high-rail signal connection equipment (Q235) and corrosive behavior in foggy environments. The results show that the types of inclusions in steel are oxides, sulfides, and composite inclusions, and each type of inclusion has different effects on pitting corrosion of the steel structure. Among the inclusions, the main types largely present are sulfide inclusions and oxygen-sulfur composite inclusions, which have a particle size smaller than 5 μm. The inclusions larger than 5 μm are oxide inclusions and they are present in small number. When components or steel structures are used in marine environment, sulfide inclusions in steel are easily dissolved and deformed to form pits, while oxide inclusions around the substrate get dissolved and fall off resulting in pitting corrosion. Composite inclusions also induce steel corrosion. Therefore, different types of inclusions induce corrosion in different ways. Sulfide inclusions and oxygen-sulfur composite inclusions have a greater impact on carbon steel. Electrochemical tests show that the self-corrosion potential is approximately ?0.1 V, and Q235 steel itself is not resistant to corrosion. As inclusions participate in corrosion process, they cause fluctuations in the anodic polarization curve and accelerate the corrosion of Q235 steel. The research results are of great significance for understanding and improving the corrosion resistance of steel, corrosion resistance of metal equipment in the undersea tunnel environment, and improving the safety and efficiency of high-speed railways.
Abstract: Nitrogen in the steel can either improve or weaken the performance, as well as reduce product. In the flow of producing steel, it is of paramount importance to adopt some measures to restrain or promote nitrogen dissolution in controlling the nitrogen content in the final product. The dissolution of nitrogen into molten iron in 1873 K has been measured by 15N-14N isotope exchange technology and online mass spectrometer. The results show that 600?800 mL·min?1 of gas flow rate removes the effect of gas transfer, and increasing the hydrogen content in shielding gas decreases the content of impurity element. A certain amount of C, Al or Si was added to the molten iron, and the three elements were inhibited from the nitrogen dissolution rate. Based on the values of the work and using the dissociation determining model, the reaction apparent rate constant, ka, was built the relationship with the content of oxygen, sulfur, carbon, aluminum and silicon. The adsorption coefficients were calculated to be KO=0.96, KS=9.32, KC=0.02, KAl=0.51 and KSi=1.16, respectively. The nitrogen dissolution reaction apparent rate constant in pure liquid iron is ka=4.8×10?6 mol?m?2?s?Pa.
Abstract: To realize the real-time prediction of slag composition in the smelting process and provide the assistance to the operations in electric arc furnace (EAF) steelmaking process such as charging, the influence factors on the slag composition in the furnace (furnace reaction, charging, and slag overflowing) were studied, and the real-time prediction model of slag composition in EAF steelmaking process was established. In the results, the model could predict the slag quality, the slag composition, and the oxidation status of Fe element in the furnace in real time, providing the guidance for the auxiliary material charging and the slag flowing in the smelting process. Compared with the slag sampling results, the average relative errors of CaO, SiO2, and FeO content in the slag between the actual measurement and the model predicted values were 12.66%, 11.17%, and 19.16%, respectively.
Abstract: Scrap is used as a basic raw material in an electric arc furnace (EAF) steelmaking process. During the process of melting, the phosphorus content fluctuates greatly, which is affected by various parameters such as the furnace structure and poor reaction dynamic conditions. Moreover, dephosphorization is very difficult to achieve. It is known that the carbon content of all melting scraps is low, C–O reaction in the molten pool is not sufficient, and number of bubbles is small; the FeO content in slag is high and molten steel is very easily oxidized by blowing oxygen and effective stirring. This study proposed a new process of submerged gas–solid injection and implemented it in EAF steelmaking, which effectively solved the aforementioned problems by delivering lime powder or carbon powder directly into the molten pool. In this study, the impact characteristics of submerged gas–solid injection in molten bath were investigated using numerical simulations and water model experiments. It is observed that when the gas flow rate was increased, the horizontal and vertical penetration distances were also increased. Meanwhile, when the installed angle of the nozzle was increased, the horizontal penetration distance was also increased, whereas, there was a decrease in vertical penetration distance. Further, the results obtained also show that both the kinetic energy of gas jet and impact penetration depth are increased by the proposed powder injection process.
Abstract: The blowing of oxygen at supersonic velocity through nozzles is a fundamental method and key technology for basic oxygen furnace process used in the steelmaking process. During the process, the high-speed oxygen jets penetrate the liquid slag leading to the formation of the impaction cavity on the surface of the molten bath. Further, the dynamic energy and mass transfer would occur at the three-phase (oxygen–liquid slag–molten steel) region. As a result, the impurity elements are removed, the temperature of molten bath is controlled, and the solid slag is melted faster. Moreover, many complex wave structures are formed in the traditional Laval nozzle depending on its gas flow field, resulting in suppression of the initial stirring ability of the oxygen jet. However, the new Laval nozzle designed by the characteristic-line method can solve this problem. Additionally, Mach number, dynamic pressure, and entrainment phenomenon of both traditional and new Laval nozzle structures were tested using various oxygen flow rates at the high-temperature ambition environment. The results prove that the new Laval nozzle structure prolongs the velocity core length of oxygen jet, increases the molten bath stirring effect, and improves the mass transfer process.
Abstract: The continuous scrap electric arc furnace adopts a long arc operation for a longer arc length and a larger discharge power. Although the long arc differs from the traditional welding short arc, few reports on long arc simulation research in the field of the electric arc furnace are available. As the main energy source in the electric arc furnace, the long arc is very important for the melting of scrap and heating of molten steel. Due to the complicated physical phenomena in the electric arc furnace, it is difficult to accurately obtain the distribution of various physical fields in the furnace. Therefore, numerical simulation is a frequently used method for studying the arc plasma in the electric arc furnace. In this paper, the magnetohydrodynamic method of the magnetic vector potential was used to establish the numerical model of an arc. Based on this numerical model, the electromagnetic field, temperature field, and flow field were coupled and solved. The effects of current and arc length on the temperature distribution, velocity distribution, arc force, and shear stress of the arc in the electric arc furnace were studied. The results show that the arc plasma in the electric arc furnace is distributed in a long bell shape, and the arc column is slender. As the current increases, the effective arc action range increases, and the arc pressure and shear stress on the anode surface increase. As the arc length increases, the effective arc action range decreases, and the arc pressure and shear stress on the anode surface decrease. The short arc operation has a strong effect on the molten pool, and the long arc operation is relatively stable. A reasonable control of the current and arc length effectively improves the thermal efficiency of the arc.
Abstract: This study proposes a model to increase the heating efficiency of tundish plasma heating and improve the flow of molten steel in a tundish during production. A physical model was simulated based on the tundish prototype of a steel plant, and the temperature field and flow field of molten steel in the tundish with and without plasma heating at different plasma heating positions were analyzed. The research results showed that in the tundish without plasma heating, the proportion of the dead zone was high, reaching 36%. Moreover, the dead zone was mainly concentrated in the upper area outside the weir in the tundish. When the heating position was located outside the weir, it was found that there was little difference in the proportion of the dead zone between the tundish with and without plasma heating. The temperature near the heating position increased sharply, and the temperature difference of molten metal between the inside and outside of the weir was large. Moreover, the overall temperature distribution in the tundish was not uniform. When the heating position was located inside the weir, the proportion of the dead zone significantly decreased, reaching 29.2%. Further, the average residence time increased by about 57 s. The temperature of the outlet of the tundish increased significantly (about 7 ℃), and the temperature distribution in the tundish was uniform.
Abstract: Coherent lances have been playing an extremely important role in the process of supplying oxygen to an electrical arc furnace, which has been widely used in metallurgy, and its metallurgical and operational benefits have been well reported. When compared with the conventional supersonic oxygen lance, the coherent lance could increase the oxygen utilization rate, strengthen penetration ability, and achieve a good stirring effect. However, there was limited research about the flow field characteristics of a coherent jet using different restriction structures for a coherent lance tip. This paper analyzed velocity and temperature profiles at various parameters and conditions. Both numerical simulation and combustion experiment have been carried out to investigate the velocity and temperature profiles using three kinds of restriction structures at room and high ambient temperature conditions. Further, the impact diameter and depth of the molten bath have also been analyzed at a certain lance height. The result shows that the restriction structure could delay energy transmission in a radial direction, which enlarges a high-temperature zone in an axial direction, resulting in the increase of the velocity potential core length and the improvement of the mixing ability of the main oxygen jet.
Abstract: With the gradual depletion of high-grade iron ore resources, the usage amount of low-grade iron ore is increasing year by year. Moreover, given the environmental protection requirements and the objective to reduce industrial cost, the usage of scrap is significantly increasing. The above occurrences have led to a large increase in the percentage of residual elemental arsenic in steel. Also, the requirement for lower arsenic content in finished steel is increasingly stricter. Presently, the iron and steel enterprises have not yet developed a mature technology for dearsenication in molten steel; moreover, the theoretical studies on the dearsenication in molten steel are relatively few, which lead to a lack of relevant theoretical data. Therefore, how to realize an effective method for dearsenication in molten steel is a technical problem in the iron and steel industry. Considering the problems of poor dearsenication in the steelmaking process and the previous experimental results of dearsenication in laboratory. The dearsenication in the process of steelmaking was investigated through an industrial trial of dearsenication in the molten steel in the ladle furnace (LF) refining furnace. The Al–Mg–Ca alloy was chosen as dearseicating agent, The industrial test about dearsenication in the molten steel show: the dearsenication in the molten steel can be realized in the LF furnace, the sulfur and calcium content in the molten steel is restrictive factor for dearsenication under industrial condition; the control level of sulfur and calcium in molten steel is put forward to ensure the effect of dearsenication. The sulfur content in molten steel must be reduced to less than 0.01% before dearsenicating in LF furnace, the calcium should be higher than 0.0055% after adding Al–Mg–Ca alloy.
Abstract: Duplex stainless steel 2101 has low production cost, excellent performance, and good resistance to NaCl corrosion. Duplex stainless steel 2101 can be used as marine stainless steel. In recent years, duplex stainless steel 2101 has been considered a valuable material. The “electric furnace + argon oxygen decarburization (AOD) + die casting” process was used to produce duplex stainless steel 2101. During the AOD refining process, the changes of temperature and Cr, C, and Si contents were investigated. Results show that the AOD furnace has a good decarburization effect. The C content (mass fraction) decreases from 2.5% to <0.03%. During the reduction period, Si has a good reduction effect on Cr. During the refining process, the most important step is decarburization. However, after decarbonizing to 0.1%, the required conditions become harsh. The factors affecting the decarburization and chromium retention of duplex stainless steel 2101 were analyzed using thermodynamic calculation formulas. The results show that the carbon–chromium balance is mainly affected by CO partial pressure and temperature. The lower the CO partial pressure, the higher the temperature, which is favorable for decarburization. When the CO partial pressure is constant and w[C] < 0.1%, the slope of the carbon–chromium equilibrium curve is increasing rapidly with the w[C] value decreasing. It means that the increased temperature range becomes larger making decarbonization more difficult, and the lower CO partial pressure is required for further decarburization. Further decarburization under the conditions of PCO/P0 = 0.4 and w[Cr] = 21.5% is conducted. To reduce w[C] to <0.03%, the temperature in the furnace needs to be increased over 1746.1 ℃.
Abstract: The water model with a similarity ratio of 1∶2 was established for a three-strand beam blank tundish. The molten steel flowing character was researched in different flow control devices by using the F-curve, and the flow field of the tundish was optimized. The volume fractions of dead region, plug flow and well-mixed flow are calculated. The standard deviation of the stagnation time of 1, 2 and 3 flow and the maximum value of standard deviation function of F-curve were used to evaluate the dispersion of each flow. Three cases were considered during the experiments, i.e, prototype flow control device, turbulence inhibitor without dams combination, turbulence inhibitor and dams combination. The results show that short circuit flow exists in the middle nozzle of the prototype tundish, and poor consistency between nozzles, which may lead to the uneven temperature and cleanness of the three-strand beam blanks, leading to different quality of different beam blanks in one heat. Using the turbulence inhibitor without dams combination, the short circuit flow appears in the middle of tundish with the angle of diversion holes being 60°. When the angle is 86°, there is no short circuit flow, and the consistency between strands becomes better. When the angle is 110°, the short circuit flow appears in the two sides of the tundish nozzle with the best consistency between strands. There is no correlation between the consistency of the tundish strands and the dead volume fraction. When the consistency of the tundish strands is good, the dead volume fraction may not be small. After optimization, the angle of the diversion hole of the tundish turbulence inhibitor is 110°, the dam is 2400 mm away from the tundish center. There is no short-circuit flow, the consistency of 1# and 2# nozzles is the best, the dead volume fraction is reduced to 9.67% from 17.89%, and the reduction rate is 11.25%. The maximum standard deviation of the F-curve is reduced to 0.016 from 0.3.
Abstract: Optimization of the continuous-casting production technology for high-carbon steel is one of the most important areas of research related to the steelmaking process. This article aims to address the problems of carbon segregation and reticulated cementite defects in the production process of SWRH82B high-carbon steel in a Chinese steel plant. In this study, Fluent software was used to perform a numerical simulation combined with experimentation to establish a heat-transfer model for the solidification of an eight-strand continuous caster. We numerically calculated the heat-transfer characteristics of the solidification and studied the effect of different parameters on the carbon segregation and inclusions of SWRH82B high-carbon steel, including casting speed, degree of superheating, and final-electromagnetic stirring of the eight-strand continuous caster. We also analyzed the relationship between the main elements during the continuous-casting process of the SWRH82B high-carbon steel and its microstructure and properties. The results indicate that carbon segregation in the center of the billet was the main cause of reticulated cementite. The degree of superheating and casting speed were then optimized, which promoted the homogenization of the components of liquid steel and reduced the inclusion content. When the degree of superheating was reduced to 25 ℃ and the casting speed was increased to 2 m·min?1, the carbon segregation index of the billet was reduced from 1.17 to 1.11, the sorbite rate was 89%, the cementite network grade decreased from 4 to 1, and the C inclusions were substantially eliminated. When the end electromagnetic stirring current was set to 370 A and the frequency to 7 Hz, the carbon segregation index decreased to its lowest value of 1.04. The defects occurring in the production process of SWRH82B high-carbon steel were addressed by optimizing the continuous-casting process parameters, which provides theoretical and practical support for the high-quality production of high-carbon steel.
Abstract: The inclusions in the consumable steel electrode and electroslag remelted steel were characterized using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). The evolution mechanism of oxide–sulfide complex inclusions during electroslag remelting (ESR) was elucidated based on inclusion experimental identification and thermodynamic calculation. The results show that the combination of protective atmosphere and deoxidation operation during ESR lowers the total oxygen content from 0.0017% in the electrode to 0.0008% in the ingot. The number proportion of the inclusions smaller than 3 μm in the steel greatly increases after ESR. The inclusions in the steel electrode are two oxide–sulfide complex types of CaS+CaO–Al2O3–SiO2–MgO containing about 3% MgO and CaS+CaO–Al2O3–SiO2–MgO containing about 11% MgO. SiO2 in the original oxide inclusions that had not been removed in ESRR process was reduced by soluble aluminum in liquid steel, and the products remain in the ESR process until in remelted ingot. The CaO–Al2O3–SiO2–MgO inclusions with uniform elements distribution, which contain about 1%MgO and about 2%SiO2, in the ingot are newly formed oxide inclusions in the ESR. CaS inclusions in the steel electrode were removed during the ESR through dissociating into soluble calcium and sulfur in liquid steel, and in the way of reacting with Al2O3 in liquid oxide inclusions. The shell-type CaS around low-melting-temperature oxide inclusion generated as a result of the reaction between CaO in the oxide inclusion and dissolved aluminum and sulfur in liquid steel during solidification of liquid steel in the ESR process. The shell-type CaS around high-melting-temperature oxide inclusion is the reaction products of enriched soluble Ca and S during solidification of liquid steel. Patch-type CaS in the oxide–sulfide complex inclusion precipitated from the complex inclusion melt during the cooling of liquid steel in the ESR process.
Abstract: Incoloy825 alloy is extensively used in the aerospace and petrochemical industries owing to its excellent corrosion resistance and mechanical properties. It is a solid solution-strengthened Fe?Cr?Ni-based corrosion-resistant alloy. The changes in the Al and Ti contents of the alloy determine the precipitation temperature of the strengthening phases γ '(Ni3AlTi) and Ti (C, N) in the alloy. At present, the main production methods of Incoloy825 alloy are vacuum melting and electroslag remelting. However, owing to the reaction of the components in the slag with the Al and Ti elements in the alloy during the electroslag remelting process, the axial component distribution of the Al and Ti elements in the electroslag ingot is not homogeneous, which seriously affects the quality of the electroslag ingot. It is necessary to control the Al and Ti contents in Incoloy825 alloy and reduce the volatilization of fluoride during the electroslag remelting process. The thermodynamic model of slag metal reaction was established using FactSage thermodynamic software. A low-fluorine slag system suitable for controlling Al and Ti contents was designed, and the relationship between the components in the slag and the activity ratios of Al2O3 and TiO2 was studied, the result was verified by a high-temperature slag metal equilibrium experiment. The results show that the CaO and Al2O3 contents in slag increases with increase in the $\lg \left( {{{a_{{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}}^2} / {a_{{\rm{Ti}}{{\rm{O}}_{\rm{2}}}}^3}}} \right)$ value, while the Ti content in the alloy decreases with increasing Al content. Moreover, as the TiO2 content in the slag increases, the $\lg \left( {{{a_{{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}}^2} / {a_{{\rm{Ti}}{{\rm{O}}_{\rm{2}}}}^3}}} \right)$ value decreases, Ti content increases and Al content decreases. The CaF2 and MgO contents in the slag increase have a little effect with the $\lg \left( {{{a_{{\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}}^2} / {a_{{\rm{Ti}}{{\rm{O}}_{\rm{2}}}}^3}}} \right)$value. When the difference between the Al and Ti contents in the alloy is large, the elemental Ti in the alloy is easy to be oxidized; when difference between the Al and Ti contents is small, the elemental Al is easy to be oxidized. When the mass percent of CaO and Al2O3 in the slag are 30%?33% respectively, the mass percent of TiO2 is 6%?12%, the mass percent of CaF2 is 20%?30%, the mass percent of MgO is 1%?5%, the Al and Ti contents in the alloy can be controlled.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
