Deoxidation of liquid steel and alloy during electroslag remelting (ESR) is always an ongoing concern for producing advanced clean steel and alloy. The increasing demands for more excellent performance of steel urge metallurgists to further improve the steel cleanliness. Lowering the oxygen content and non-metallic inclusions amount during the ESR process is of great importance as ESR is the last processing procedure for refining liquid steel in the steel product manufacturing process. Deoxidation of ESR is dependent on one or more aspects including the initial oxygen content and oxide inclusions in the electrode, remelting atmosphere, deoxidation schemes, slag compositions, reoxidation degree, melting rate and filling ratio. This paper reviews the state of the art in the deoxidation of ESR and deoxidation-related oxide inclusions. The oxygen transfer behavior during ESR process is described first. Deoxidation of liquid steel during ESR is discussed based on the thermodynamic and kinetic considerations. The dependence of the oxygen on the processing parameters of ESR is reviewed and discussed. The influence of these parameters on the oxide inclusions associated with the deoxidation of ESR is also assessed. The suggestions for the future work are proposed in this article.
The converter furnace and the continuous casting are the most important stages in steel production. Modern integrated processes directly connect the converter furnaces and the continuous casting machines with a flow of molten metal, and the steel is manufactured synchronously between the various machines. Starting from the traditional handmade programs for the management of these processes, during the last two decades there has been a notable increase in studies and publications in this field, trying to formulate scheduling in a rational and automatic way. The process has been approached for years through the development of both physical and operational research models, many of them theoretically. The main purpose of this study is to present a critical and in-depth evaluation of the previous studies, so that the state of the art of scheduling in steelworks can be evaluated. An approach based on a Systematic Literature Review (SLR) has been used, trying to search, evaluate, synthesize and analyze all the relevant studies for this specific field. As a result, the conclusions of the various analyses are presented and a study route is proposed for the design of the optimal planning methodology in the steelworks.
Our strategy is to enhance the fracture property of ultra-high-strength low-alloy steels with a yield strength of 1.4 GPa or over by arresting the propagation of brittle cracks in hierarchical, anisotropic, and ultrafine-grained structures. This provides a fail-safe design in addition to suppressing crack initiation. The present article reviews the strength, ductility, toughness, and delayed fracture resistance of ultra-high-strength low-alloy steels with ultrafine elongated grain structures processed by the deformation of tempered martensitic structures at elevated temperatures (referred to as warm tempforming). The evolution of heterogeneous microstructures during warm tempforming using multi-pass caliber rolling is discussed, as are the microstructural factors controlling the strength and fracture properties of warm tempformed steels. Furthermore, we apply warm tempformed steels with ultrafine elongated grain structures to the fabrication of ultra-high-strength bolts.
Relationship between yield strength, σys, and V-notch Charpy absorbed energy, vE, at room temperature for various steels; ultrafine grain ferritic steel,30) JIS-low-alloy,31) AISI/SAE-low-alloy,32) 0.34%C-2%Si-1%Cr-3%Ni,33) ausformed 0.2%C-3%Ni-3%Mo,34) HY130,35) HY180,25) AF1410,26) high-purity 18%Ni,27) 18%Ni (250),28) and 18%Ni (350)29) maraging steels. Data for 0.4%C-2%Si1%Cr-1%Mo steels that were quenched and tempered at a temperature of 500°C (QT) and tempformed at a temperature of 500°C with an equivalent strain, εeq, of 1.75 (TF),5) are also shown. (Online version in color.)
In dephosphorization process in steelmaking, phosphorus in molten iron is distributed into molten slag after oxidized, and it forms 3CaO·P2O5. It has been known that dicalcium silicate (2CaO·SiO2) formed in molten slag and 3CaO·P2O5 make a solid solution, which could promote dephosphorization efficiency from molten iron. It has been reported that 2CaO·SiO2–3CaO·P2O5 solid solution (α phase) is formed for entire composition range at higher temperatures than 1673 K, and many previous studies on dephosphorization behavior assumed that the α phase would be precipitated from molten slag. However, we found that the α phase cannot be obtained at low phosphorus concentrations when the pellet of 2CaO·SiO2 and 3CaO·P2O5 powders mixture is annealed and quenched to room temperature. In this study, we conduct high temperature in-situ X-ray diffraction analysis to the aerodynamically levitated sphere of the 2CaO·SiO2–3CaO·P2O5 liquid to identify primary crystallized phase. It has been verified that the α phase is precipitated from the liquid for wide phosphorus concentrations. In addition, a rapid phase transition of the 2CaO·SiO2–3CaO·P2O5 solid solution has been detected by the time-division X-ray diffraction with high resolutions when the levitated sample containing the α phase is quenched from the precipitated temperature.
Electromotive force measurement (EMF method) has developed for many decades. It provides a universal approach to measure quantities such as oxygen partial pressure and activity coefficient of metals. Here we present a new design of oxygen sensor, aiming to avoid complications and inaccuracies which are caused by the effect of extra metallic lead wires. Hereafter, we focus on the development of a cleaner electrochemical deoxidation technology by using the newly developed apparatus. The EMF experiments demonstrate a favorable agreement with previous literature, and the electrochemical deoxidation experiments show remarkable results of oxygen contents reducing. All of these results pinpoint the feasibility of the newly developed apparatus. Based on these positive results, we discuss a possible application of this study in the steelmaking process, illustrating a high potential of a further and ultimate deoxidation by a cheaper and cleaner approach.
Idea of oxygen pump application in the steelmaking process.
The slag of rare earth Bayan Obo complex iron ore (REBOCIO) after direct reduction and melting contains a lot of rare earth elements (REEs). In this work, the isothermal reduction and melting separation experiments of REEs-bearing iron carbon composite pellets and the detailed characterization of rare earth (RE) slag were conducted, with the aim at developing knowledge of the reduction mechanism and the behavior of REEs during the direct reduction and melting process. The results indicate that the pellets can be optimally reduced at 1200°C for 15 min with a C/O ratio of 1.2. The RE-containing phases differ depending on the reaction conditions. When the temperature is relatively low at 1100°C, the major RE phase in the slag is Ce4.67 (Si O4)3 O; while (Ca, Ce, La)5(SiO4)6F becomes the dominant RE phase in the slag at 1400°C. The main crystalline phase in the air-cooling slag are cuspidine (Ca4Si2O7F2), (Ca, Ce, La)5(SiO4)6F and fluorite (CaF2). The particle size of the RE phase increases as the cooling rate decreases. In the case of furnace cooling, the RE phase in the slag has a more complete structure, namely hexagonal prismatic. And the RE phase is hexagonal system with space group P 63/m and unitcell parameters a = 9.5908(3) Å, b = 9.5908(3) Å, c = 7.0268(2) Å, β = 90 (3)°, and V = 559.75(4) Å3.
Granulation and packing of iron ores are highly essential for having a strong function with packed bed porosity distribution, and further affecting the subsequent sintering process. In this study, high-resolution X-ray computed tomography technique was applied to investigate the influence of moisture, hydrated lime and concentrate levels on granule properties and porosity distribution of packed bed based on the Taguchi orthogonal array tests, and the optimum granulation factors combination was determined by the defined porosity segregation degree for improving packed bed homogeneity. Moisture was found to be the dominant factor affecting granule size with a major percent contribution of 94.42%. Bulk bed porosity was significantly affected by all three selected factors of moisture, hydrated lime and concentrate levels. The percent contribution order was shown as hydrated lime (55.10%)> moisture (29.12%)> concentrate (14.36%). The whole packed bed was found to exhibit significant inhomogeneity. Axial porosity increases from the bottom upwards along the packed bed height, and radial porosity appears a symmetric parabolic distribution where porosity achieves the minimum of 0.3 at bed center and increases sharply near the wall. To achieve the homogeneous packed bed of iron ore granules, the optimum granulation factors combination for decreasing axial and radial porosity segregation are determined as 6.8% moisture, 4% hydrated lime, 0% concentrate and 5.8% moisture, 4% hydrated lime, 0% concentrate, respectively. The results provide the theoretical guidance for granulation and packing in iron ore sintering to improve sintering yield and quality.
This paper presents mass accounting models that trace the flow of major individual elements from iron ore through to iron lumps, pellets or sinter, the transformation of these intermediate products into pig iron (PI) or direct reduced iron (DRI), and the transformation of PI and DRI into crude steel in a basic oxygen furnace (BOF) or electric arc furnace (EAF) with the addition of scrap iron or steel or varying purity. Account is taken of non-iron oxides (gangue), addition of fluxes, the production of slag, and iron losses in slag. Simple relationships are developed giving the flux requirements for and slag production from a BF for various iron inputs, and relationships are developed giving flux requirements, the production of slag, and iron yield as a function of the proportions of PI, DRI and scrap inputs to a BOF or EAF. The mass and flow analysis presented here, and the energy flow analysis presented in a companion paper, provides a foundation for tracking the impact on energy use and iron losses of alternative pathways that might be used in the future as part of a broad-based effort to reduce energy use and associated greenhouse gas emissions.
In this work, the multiphase mathematical simulation (steel-argon-slag-air) was used to improve the mixing time in a secondary refining ladle, which is validated with a physical scale model using dye tracer dispertion and measurement of mixing time. An experimental 3k-p design was performed to optimize the number of cases and analyze the effect of injection gas flow arrangement. A mathematical methodology was described to determine the mixing time in a ladle with a multi-sensor system. By means of an analysis of variance, it was found that the angle of separation between plugs is the most relevant variable to reduce mixing time. It was determined that, by using a good asymmetric configuration in both gas flow and location of the porous plugs, it is possible to reduce the mixing time in a secondary steel refining ladle.
A new mold flux based on non-Newtonian fluid for the peritectic steels casting was prepared. The heat transfer behavior and lubrication property of this non-Newtonian mold flux were examined by heat flux simulator, ultraviolet-visible-near-infrared spectrometer (UV-Vis/NIR), Raman spectroscopy, SEM, and confocal laser scanning microscopy (CLSM), and the results were compared with the conventional mold flux used in peritectic steels casting. The results showed that the heat transfer property of liquid layer of N1 slag was reduced through the destruction of silicate network structure by shear stress. Compared with the data obtained under static and stirring conditions, the qmax and degree of polymerization (DOP) of N1 slag were reduced from 0.921 MW/m2, 0.728 to 0.716 MW/m2, 0.583, respectively. However, the shear stress has no effect on the heat transfer property of liquid layer of N0 slag. Second, the heat transfer properties of solid slag layer of N0 and N1 slag were all inhibited through increasing the crystallization rate, crystallization fraction, and slag film thickness by shear stress. While, under stirring condition, the slag film thickness and t2 of N1 slag was lower than that of N0 slag. Third, the heat transfer behavior of air gap layer of N0 and N1 slag were all controlled by shear stress. The surface roughness (Ra) and shedding time of N0 and N1 slag with agitation were increased to 54.49 um, 61 s and 52.87 um, 59 s, respectively. Finally, the break temperature of N1 slag was 9 K lower than that of N0 slag.
Segregation of solute elements is an inherent characteristic of alloy solidification. Macro/semi-macro segregation seriously affects the mechanical properties of the final products. High-carbon steel billets is an important base material for producing high-end rod wire, while macro/semi-macro segregation is more serious due to its high carbon element content and low distribution coefficient. In order to control the segregation defects of high-carbon steel delicately, the morphology characteristics of segregation in 82B cord steel billet (the carbon content is 0.82 wt%) produced by continuous casting were studied based on fractal theory. It is shown that segregation morphology has fractal characteristics. Different calculation methods of fractal dimension describe segregation characteristics from different angles; fractal dimension calculated by perimeter-area method (DPA) can quantitatively characterize the complexity of segregation profile, while fractal dimension calculated by the box-counting method (DBC) reflects the spatial distribution characteristics of segregation in billets. Secondary dendrite arm spacing (SDAS) mainly affects the complexity of segregation profile. In additional, negative-correlation is shown between DPA and cube root of local solidification time (the fitting coefficient is 0.79). This result demonstrated the potential of DPA as a parameter for estimating local solidification time of the billet in which the measurement of SDAS is difficult.
The casting quality of crossing in a railway turnout is required to be higher because of the significant impact load on the rail. The simulation results of using different fever risers, the temperature field, solidification process and casting defects, were obtained by the implicit finite element method based on the ProCAST software. To improve the authenticity of the visualization of the casting process, a numerical simulation assumption of the mass flow rate attenuation was proposed for the overflow of molten metal from the risers during tilt pouring. The result shows that the temperature field is more uniform when the risers with exothermic energy of 1200 kJ/kg were chosen and the defects converge to the risers in accordance with the principle of sequential solidification. Compared with insulation riser, shrinkage porosity proportion decreased from 23.10% to 17.01%, and the shrinkage cavity proportion decreased from 1.002% to 0.530%. However, changing the burned time has no obvious effect on the casting. At the same time, the process optimization scheme of risers was put forward in this study and the casting defects such as shrinkage cavity and porosity are predicted according to the ‘V type’ feeding area of the fever risers. This improvement has greatly improved the performance of the casting, and the passing gross tonnage could reach 300 million tons.
Electromagnetic stirring (EMS) has been used to improve the steel quality in continuous casting process and EMS position is a key factor in optimizing the stirring performance. In order to clarify the issue that where to install the electromagnetic stirrer, a mathematical model, coupling electromagnetic field and fluid flow field, was developed in this paper. Three cases differing in EMS position have been investigated: the stirrer was installed above the submerged entry nozzle (SEN) port; the stirrer was installed near it; and the stirrer was installed below it. The model was validated by the comparison of electromagnetic flux density. The influence of EMS position on electromagnetic force, flow field and inclusion removal was analyzed. Index Rc was introduced to quantify the possibility of slag entrapment. The results shows that as the stirrer moves downwards, the maximum electromagnetic force increases, index Rc increases first and then turns to decrease, and the electromagnetic force causes the jet to bend more horizontally, resulting in an inactive zone when the stirrer is installed near the SEN port. Furthermore, under our computed condition, to improve the inclusion removal, the stirrer is suggested to be installed below the SEN port.
Considering the “furnace-caster matching” modes, this paper focuses on the scheduling problems from practical steelmaking-continuous casting production lacking refining span. Aiming at the improvement on quality and output of steel products, a mathematical model is established with multi-objective optimization including the minimum earliness/tardiness of starting cast times, the shortest waiting times of heats among different processes and the shortest idle times of converters. A heuristic algorithm based on the optimization of “furnace-caster matching” mode is developed to solve this model, which involves two procedures of device assignment and conflict elimination. Through the detailed analysis on workshop layout and production rhythm, four classes of matching modes of “refining furnace-caster” are proposed to perform the assignments of refining furnaces. The assignments of converters rely on three categories of greedy strategies in terms of minimizing conflictions among heats. A rough scheduling solution with some possible conflicts among heats is obtained through combining “furnace-caster matching” modes and greedy strategies. Then applying the linear programming method to eliminate the conflicts and generate the final solution. Based on the proposed algorithm and the improved genetic algorithms, simulation experiments are carried out by introducing actual production plans as instances. The results indicate that heuristic algorithm based on the optimization of “furnace-caster matching” mode is the right candidate owing to its acceptable scheduling solutions with the better process matching relations and the highlighted performances under crane constraint. Currently, the proposed model and algorithm have been successfully used in a large converter steel plant in China.
There are many dynamic disturbances during the continuous annealing production line (CAPL) in iron and steel enterprise. Traditional robust operation optimization considers only the maximum disturbance range in previous production and overrides the dynamic changes of these disturbances, which often results in high production cost and low product quality. Therefore, this paper proposes a novel multiobjective dynamic robust optimization (MODRO) modeling method by further taking into account the dynamic changes of these disturbances and adopting a time series prediction model based on a least square support vector regression (LSSVR) to predict the range of disturbances in next time slot. The main feature of the model is that the robustness can be dynamically adjusted according to the disturbance range predicted by the LSSVR. To solve this model, an improved NSGA-II algorithm is developed based on a new crowding metric. Numerical results based on actual production process data illustrate that the proposed MODRO modeling method is obviously superior to traditional static robust operation optimization, and that it can significantly improve the strip quality and the capacity utilization of the CAPL, and reduce the total energy consumption.
A roller-plate system is taken as the research object in this paper. The influence of rolled products of metal plates (thick or middle thick plate) as an excitation parameter on the vibration characteristics of the system during warm rolling process is mainly studied. In view of the hysteresis characteristics between rolling force and deformation of rolled products of metal plates in actual process, Duffing equation is innovatively introduced into the dynamic model and used to generate nonlinear force. The analytical solution of the dynamic model of the roller-plate system is obtained by asymptotic methods, and the correctness of the analytical solution is verified by Runge-Kutta method. Finally, the influence of nonlinear stiffness and nonlinear damping on vibration characteristics of rollers is analyzed, which provides an important theoretical basis for the study of nonlinear vibration characteristics and vibration suppression of roller-plate system during warm rolling.
Laser-induced breakdown spectroscopy (LIBS) is a promising method for the rapid determination of compositions of stainless steels in steel scrap. LIBS is widely known as a method for very rapid elemental analysis in open-air without any pretreatment. We applied a laboratory-build LIBS system for mutual identification of 5 types of austenitic stainless steels, SUS304, SUS310, SUS316, SUS321, and SUS347. The certified reference materials of JSM M 200 were employed for establishing supervised models, conducting partial-least-square regression (PLSR) for the determination of Cr, Ni, Mo, Ti, and Nb. Since it needed more than 10 minutes of calculation time when all the wavelength range were utilized for PLS2 regression, suitable emission lines in the determination were picked up for the reduction of calculation amount and time. When we select single emission lines having higher excitation levels to avoid an affection by self-absorption, the good determination results for Cr, Ni, Mo, and Nb could be obtained with reasonable accuracy and precision by the calculation with PLS1 regression.
With the goal of real-space mapping of dislocation information using a wavelength-resolved (spectroscopic) neutron transmission imaging method, broadenings of multiple Bragg-edges in neutron transmission spectrum were investigated in detail for the first time. Data of time-of-flight (TOF) neutron transmission imaging and diffraction experiments on a polycrystalline low-carbon ferritic steel sample while undergoing tensile testing were analysed. The Bragg-edge neutron transmission spectroscopy was combined with the classical Williamson-Hall method corrected by the crystal elastic anisotropy using the ratio of diffraction Young’s modulus, namely, the corrected classical Williamson-Hall (ccWH) method. As a result, the broadening values evaluated from the ccWH analysis of Bragg-edge data were consistent with results of both our TOF neutron diffraction experiments and previous reports. In addition, it was deduced that the line-broadenings appearing in the plastic deformation condition during tensile testing in our experiment were mainly caused by micro-strain (dislocation density) effect and not by crystallite size effect. Finally, a Bragg-edge broadening mapping method, using a simultaneous multiple Bragg-edges profile analysis based on the ccWH method, could identify plastically deformed zones in the sample more clearly than a traditional single Bragg-edge broadening analysis method.
In hot sheet rolling, the sheet rear end often snakes, contacts the inlet side guide, buckles, and goes into the roll gap, whereas the overlapped rear end of the sheet is squeezed. Although a number of researches on the simulation of the sheet snaking are reported, no researches have been performed to simulate both the sheet snaking and the sheet buckling. In this study, a combined method to simulate the sheet snaking by the rigid-plastic FEM and to analyze the sheet buckling by the elementary theory of buckling was proposed. First, the method in which the in-plane lateral load and the in-plane bending moment were assumed at the surface of the simulation region by the rigid-plastic FEM was proposed. Next, the amount of snaking at the sheet rear end simulated by the rigid-plastic FEM agreed with that analyzed by the elementary theory of rolling. Finally, the effects of rolling conditions on the occurrence of squeezing, such as the difference in the sheet thickness in the direction of the roll axis, the difference in the roll gap in the direction of the roll axis, and the amount of the sheet off-center, were clarified.
Tension leveling is applied in metal strip production lines to improve the flatness of metal strips by a combination of tension and bending. To develop tension leveling technology, finite element (FE) analysis is increasingly used in tension leveling process design to reduce the number of trial productions and provide a deeper insight into the process. For the FE analysis of tension leveling, since the material properties affect the leveling results, a material constitutive model that can accurately describe the material behaviors during tension leveling should be applied. In our previous investigation, an advanced constitutive model was constructed for the FE analysis of tension leveling with high accuracy. Here, we report the results of an analysis on tension leveling to clarify the effect of constitutive relations on FE analysis results. Leveling mechanisms for high-strength steel strips were also clarified on the basis of FE analysis results.
The application of high strength steel sheets in automobile manufacturing has increased dramatically. To improve the joint performance of high strength steel sheet, an optimized RSW process was proposed. Double-pulse welding schedule was employed in the process. Under the second pulse current, the central temperature in the weld was higher than Ac3, and the second nugget was formed. The weld including two nuggets with different size and same center was obtained under the optimized process. By Vickers hardness analysis, the soft-hard alternating structure in the weld was formed. Under the same nugget size, the cross-tension strength of joints increase 30% by the optimized process. By comparison, the maximum tensile shear strength of RSW joints under dual-nugget process was higher than that under traditional heat treatment process. Furthermore, the temperature field under dual-nugget process was simulated and the weld thermal cycle of typical nodes in different weld regions were obtained. The simulation results explained the formation mechanism of the soft-hard alternating structure in the welds. The two ellipsoidal softening zones were formed respectively under different pulse welding currents.
Distribution of micro-Vickers hardness at welded zone under dual-nugget RSW process (Process 6 in Table 1). (Online version in color.)
In this work, T23 steel was treated by two thermal cycles, to simulate the second heating process in coarse grained heated affected zone (CGHAZ) of weld. Meantime, the effect of microstructure evolution on reheat cracking sensitivity was investigated by using strain-to-fracture (STF) tests. It was found that the second thermal cycle procedure could alter the grain boundary network of prior austenite grain boundaries (PAGBs) of CGHAZ. The extent of boundary evolution was dependent on the peak temperatures of the applied thermal cycles. Kernel average misorientation (KAM) and fracture surface observation was applied to analyze plastic deformation and fracture mode after STF tests. The relevancy between the grain boundary character and reheat cracking sensitivity were analyzed quantitatively using fractal analysis. The results showed that the zigzag configuration of the PAGBs with larger fractal dimension could prevent the reheat crack from propagating and reduce reheat cracking susceptibility. The increase of the peak temperature of the second thermal cycle would lead to grains coarsening and straight grain boundaries, which improve the reheat cracking sensitivity for the reheated CGHAZ in T23 steel.
Finite element simulations are widely conducted to evaluate the heat transfer and deformation during welding. Basically these welding simulations require input variables such as shape parameters and heat source parameters, which are not directly measured by the experimental method. In this study, two methods were proposed to obtain these input parameters more efficiently: a method of automatically identifying toe radius and reinforcement angle from height profile, and a method of estimating a heat source model in welding simulation. In the first method, the toe radius and reinforcement angle were extracted from the height profile by Akaike’s information criterion. The extracted results were consistent with the manual fitting results. In the second method, the optimal combination of the heat input parameters was automatically searched by Bayesian optimization. Comparing the accumulated regrets, it was found that the probability of improvement and upper confidence bound provide more efficient optimization than the other acquisition functions in the calibration of the heat input parameters. Both temperature history and shape of fusion zone and heat-affected zone calculated at the optimized condition were in good agreement with the experimental results. These results demonstrated that the two proposed methods are effective to create a numerical model for welding simulation.
This study presents the effects of silicon (Si) and manganese (Mn) concentration and of heating rate on the ferrite recrystallization kinetics in seven model alloys with different Si and Mn concentrations, which are of relevance for the development of Advanced High Strength Steels (AHSS). The recrystallization kinetics were studied with in-situ 2D X-ray Diffraction (2D-XRD) and ex-situ microstructure observations using Scanning Electron Microscopy (SEM). The experimentally observed differences in the recrystallization start temperature (Ts), dependent on the Si and Mn concentrations and the heating rate, can be described by combining the non-isothermal JMAK-model with a modified version of Cahn’s solute drag model. The modified Cahn model takes into account – in an approximate manner – that the interaction energy of the solute atoms with the grain boundary depends on the Si and Mn concentrations in the boundary and the Wagner interaction parameters. The collective contribution of the Si and Mn atoms to the increase in the Ts with respect to the reference alloy (without Si and with very little Mn) is higher than would be expected from the simple addition of the effects of the Si and Mn concentrations alone. This means that the interaction between Si and Mn atoms leads to an additional increase in Ts, i.e. a coupled solute drag effect. For the later stages of recrystallization, we have studied the change in the number density and the growth rates of the recrystallizing grains using SEM. The observations show non-random nucleation, early impingement of the grains in the normal-direction and non-constant growth rates of recrystallizing grains.
In this paper, the microstructure, precipitates and mechanical properties of a 0.3%V-alloying high Mn austenitic TWIP steel after hot rolling and aging treatment were investigated, aimed to improve the yield strength of high Mn austenitic steel. Experimental results showed that an elongated and unrecrystallized grain structure could be obtained at a finish rolling temperature of 850°C or below in 0.3V steel. The amount of VC precipitates was very small and most vanadium remained in solution after hot rolling. Therefore, the solute drag effect of dissolved vanadium rather than the Zener pinning effect of VC precipitates was mainly responsible for the inhibition of recrystallization. The yield strength increase of 0.3V steel with deceasing finish rolling temperature was much more remarkable than that of V-free steel. Quantifying possible strengthening mechanisms revealed that most of the YS increase was due to the dislocation strengthening in 0.3V steel. The aging treatment for 30 min promoted the precipitation of VC, but the precipitation amount was still much less than the equilibrium precipitation amount. The comparative analysis on precipitation kinetics of VC in high Mn and low Mn steels indicated that the former had a more sluggish precipitation rate than the latter. This result was further analyzed in terms of the effect of Mn on the solubility product of VC in austenite.
A finite element model was developed to predict deformation, temperature, phase fraction and hardness during heat treatment of an automotive drive shaft. The heat generation due to induction was treated as one of the boundary conditions for heat flux on the specimen together with the conduction heat loss during quenching. As for diffusional transformation, the transformation kinetics were modeled by Johnson–Mehl–Avrami–Kolmogorov equation, whereas the Marburger equation was used for displacive martensitic transformation. The transformation plasticity was considered through the constitutive equations corresponding to each transformation mechanism and these equations were incorporated into the finite element model. Besides the transformation plasticity, an implicit procedure to calculate the thermo-elasto-plastic deformation was implemented in the model. The prediction accuracy for phase evolution, residual stress, hardness and dimensional change of the specimen was verified from the measured data. The effect of transformation plasticity on whole deformation behavior was described by the developed model.
Boron-added 9Cr-3W-3Cr-VNb ferritic/martensitic heat resistant (MARBN12) steel is the candidate material for components used at intermediate temperatures, i.e., 923 K or less, in advanced ultra-supercritical (A-USC) power generation systems because they can suppress Type IV fracture under creep conditions. For evaluation of the creep strength of the heat affected zone (HAZ), simulated HAZ samples with peak temperatures of about 1173 K, 1223 K, 1273 K, and 1323 K with a heating rate of 100 K/s and a cooling rate of 40 K/s were crept at 923 K. Compared with the conventional Gr. 92 steel, the B-added steel showed about 10 times longer creep lifetime. Furthermore, minimum creep lifetime was observed around the AC3 point of about 1223 K. Electron back-scattered diffraction analyses revealed that clear fine-grained HAZ was not formed and that martensite remained in the simulated HAZ samples of the MARBN12 steel. Microstructural change occurred only around the prior austenite grain boundary (PAGB), i.e., fine grains were formed there. It generated grain boundary sliding in the vicinity around PAGB, leading to shorter creep lifetime than the base metal. Results show that the creep lifetime around HAZ in the MARBN12 steel was affected by the microstructure near PAGB. Also, that in the Gr. 92 steel was influenced by the grain size, i.e., Type IV fracture.
The better uniform elongation of the 1 GPa-grade TRIP-aided multi-phase steel with retained austenite (γR) shape of needle-like was discussed by in situ neutron diffraction experiments during tensile test. The better uniform elongation can be ascribed by not only the deformation-induced martensitic transformation of γR but also the deformation behavior of γR and ferrite phase. Especially, the tensile deformation behavior of γR is found to be closely associated with both of the stress-strain curve and the deformation-induced martensitic transformation of γR. The tensile deformation behavior of γR should be considered as one of the conditions to obtain better TRIP effect.
The effect of lattice defects on the tribological behavior under tricresyl phosphate (TCP) added poly-α-olefin (PAO) lubrication was investigated in the nanostructured steels produced by heavy plastic deformation processes. In surface-nanostructured SUJ2-bearing steel, tribological behavior with high friction coefficient was observed in ball-on-disk tests when compared to non-deformed steel. In addition, a similar phenomenon was observed in ultra-low carbon (ULC) steel with a high density of lattice defects (grain boundary, dislocation and so on). By increasing the density of lattice defects, a higher friction coefficient was observed. The reason for the tribological behavior with high friction coefficient seems to be that the compound film of Fe–O–P system formed in the ball-on-disk test was worn down.
Experimental and numerical investigations were carried out on turbulent flow in a staggered tube bundle. In the experiment, a hot-wire anemometer was employed to investigate the developments of the flow at the Reynolds number of 9160. In microscopic numerical study, the standard k-ε model was used with a boundary fitted coordinate system to calculate velocity, pressure drop and kinetic energy of turbulence. The new macroscopic turbulence model with volume averaging and additional source terms was proposed for turbulent flows in tube bundles or packed beds. The turbulence constants were determined by the microscopic numerical experiments. The microscopic and macroscopic numerical results were in good agreement with the experimental results, or the empirical equation in the axial velocity and kinetic energy of turbulence.
As the basis of injection metallurgy, an impinging gas jet on a liquid bath surface was simulated and experimentally verified. The SPH simulation of the gas-liquid two phase flow was developed by using the XSPH method, and the calculation speed was considerably increased with the use of general-purpose computing on graphics processing units. For N2 gas – water bath system, the simulated shapes and penetration length of the cavity were in good agreement with the experimental results, and the three modes of cavity were reproduced by the calculation. N2 gas–molten iron bath system was also simulated. The cavity mode was “dimpling mode” for all calculations.