The effect of TiN crystallization on the solidification structure of Ti-added ferritic stainless steel were studied in Ti/Mg, Ti/Ca, Ti/Mg/Al, Ti/Ca/Al, Al/Ti/Ca and Ti/Mg(Ca)/Ca(Mg) deoxidations carried out at 1600°C using an Fe–17.5(11)%Cr–0.25%Mn–0.20%Si–0.2 to 0.3%Ti–0.01%C–0.003 to 0.04% N alloy on a mass percent basis. Compositional analysis of the oxide particles and TiN layers generated during the deoxidation using scanning electron microscopy in conjunction with an electron probe microanalyzer, coupled with observation of the morphology and homogeneity of complex TiN+oxide particles, revealed that the TiN layers were formed through the postulated mechanism of the co-crystallization of TiN and oxide. Ti/Mg and Ti/Mg/Al deoxidations performed in an Al2O3 crucible yielded a very fine solidification structure at high N contents (>200 ppm) because of the presence of complex particles consisting of the TiN layer with a small amount of oxide phases. In the Ti/Ca, Ti/Ca/Al and Al/Ti/Ca deoxidations using an Al2O3 crucible, a relatively fine solidification structure was observed when a low oxide content was present in the TiN layer. Ti/Ca/A and Al/Ti/Ca deoxidations carried out using an MgO crucible in the presence or absence of MgO–CaO–Al2O3 slag gave rise to solidification structures that were relatively finer in comparison with those obtained using an Al2O3 crucible. Very fine structures were observed at low N contents (36 to 80 ppm) in the Ti/Mg/Ca and Ti/Ca/Mg deoxidations using an Al2O3 crucible because of the effective surface composition of the oxide particles for δ-phase solidification.
Key phase diagram experiments for the CaO–CaF2 system were conducted using an equilibration and quenching technique and thermal analysis. Equilibration and quenching experiments using sealed Pt capsules followed by FE-SEM EDS compositional analysis and XRD phase analysis were performed to determine the CaO and CaF2 liquidii and the solubility of CaO in solid CaF2. Thermal analyses with DSC and TGA were used to determine the temperatures of the eutectic and the α- to β-CaF2 polymorphic transition. For the first time, noticeable solubility of CaO in α- and β-CaF2 solids is observed above 1000°C. The maximum solubility of CaO in solid CaF2 is about 5 mol% at the eutectic temperature (about 1361°C) while no solubility of CaF2 in solid CaO is detected. Based on the thermodynamic optimization using the present CaO and CaF2 liquidii and the eutectic temperature measurements, it is concluded that the CaO–CaF2 binary is a simple eutectic system with the eutectic reaction L(CaO = 15 mol%) → CaO(pure solid) + CaF2(solid solution with CaO = 5 mol%) at 1361°C. The α- to β-CaF2 polymorphic transition is located at about 1146°C and the melting point of CaF2 at 1420°C.
The mechanism of SR (Slag-Ring) formation in the actual rotary kiln that proposed in the previous paper has been examined by the firing experiment of the anthracite and limestone composite Ni-ore briquettes using the batch type experimental kiln. The rapid increases in the degree of reduction and CO gas content and the sticking begin to take place at about the same time. The temperature of raw materials apparently begin to decrease from around 1200°C owing to the sticking of raw materials to the tips of alumina (SSA-S) protecting tube with an inserted thermocouple, entering the depression region. Therefore, from above mentioned the mechanism of SR formation is confirmed. A large amount of charge of powdery materials and the increase in the gas velocity at the top of SR causes SR to shrink and fall into the vicious circle, which allows the serious difficulty in the operation of the kiln. The sintering of briquettes provides the suppression of powder generation coming from the fracture of that, which allows no occurrence of sticking. The mechanism of MR (Metal-Ring) formation is extremely involved in the behavior of fine particles as well as SR. A large amount of fine reduced metal with high C content without the growth transports toward the discharge end, allowing that to melt and be precipitated on the wall by Ostwald ripening.
Chromium (Cr) was concentrated as chromium spinel in the vanadium slag produced by pre-oxidizing vanadium-containing hot metal in Pan-steel in China. Due to the chromium-rich Hongge ores used, chromium concentration in this slag was much higher than that in common vanadium slags. To propose a process for effective Cr extraction from the slag, mechanisms of Cr oxidation in Pan-steel vanadium slag under sodium roasting conditions were studied experimentally and with thermodynamic simulations. Chromium slags without vanadium were synthesized in the laboratory to mimick mineralogical characteristics of Pan-steel vanadium slag and characterized by XRD, SEM/EDS and TG-DSC techniques. Conditions for Cr extraction from the chromium slag after sodium roasting by leaching with water were studied and optimized. Results showed that Cr spinel was encapsulated in the silicate phase. During sodium roasting, Cr spinel was oxidized and decomposed after oxidation and decomposition of the olivine phase. Sodium carbonate began to react with chromium oxide, which was produced by decomposition of Cr spinel, at 537°C and large amount of sodium chromate appeared after 800°C. However, multi-component liquid phase (mixture of Na2Cr2O4, Na2CrO4 and Na2CO3) was produced after 1000°C, which suppressed the conversion of Cr(III) to Cr(VI) by inhibiting oxygen supply. A conversion about 90% was obtained when the chromium slag was roasted at 1000°C for 2 h with Na2CO3 addition in stoichiometric ratio to total amount of Cr2O3 and SiO2. 96% of Cr in the leaching liquid was recovered as chromium sesquioxide in fine powder form and high purity by reducing and precipitating.
A finite element model of coke was generated using micro X-ray CT, and coke strength was numerically evaluated using its microstructure. First, three-dimensional (3-D) and two-dimensional (2-D) stress analyses of coke were compared. Next, 3-D stress analyses of cokes produced from caking coal and slightly caking coal were conducted in order to investigate the effect of the 3-D microstructure on coke strength. Furthermore, the strength anisotropy of coke was evaluated by stress analyses assuming a uniaxial tensile test in three directions. We found that the maximum principal stress magnitude and stress concentration area are smaller in the 3-D stress analysis than in the 2-D stress analysis. Moreover, the stress concentration area and strength anisotropy of coke produced from slightly caking coal are larger than those of coke produced from caking coal. The results indicate that stress analysis based on micro X-ray CT images is very useful for investigating the relationship between coke microstructure and strength.
Large amounts of injectants are used in the blast furnace (BF) process to reduce coke consumption, but this changes the gas composition in the BF shaft where iron ore reduction takes place. H2 and H2O gases change markedly in the gas atmosphere at high injection levels, which makes it important to investigate their effects on the reduction of iron oxides in a CO–CO2 atmosphere. The gaseous H2 and H2O content in the BF shaft atmosphere is approximately 8%. In the present work olivine pellets were reduced in H2–H2O–CO–CO2 and CO–CO2 atmospheres with equal reducing potentials of H2 and CO by fixing the H2/H2O and CO/CO2 ratios. No significant differences in the reduction rates of iron oxides were found between the H2–H2O–CO–CO2 and CO–CO2 atmospheres at high temperatures but at lower temperatures H2–H2O–CO–CO2 had higher reduction rate. Activation energies determined for hematite to magnetite reduction for both gas mixtures indicated better initial stage and later stage reduction in the H2–H2O–CO–CO2 atmosphere. Field Emission Scanning Electron Microscope (FESEM) analysis was carried out on samples, and wüstite relics were found in the inner parts of pellets reduced to iron in the CO–CO2 gas but not in the samples reduced in the H2–H2O–CO–CO2 gas.
Low RAR (reducing agent rate) operation of the blast furnace is one of effective techniques for reducing CO2 emissions. Coke mixed charging is a well-known and available measure to achieve low RAR operation by improving permeability and reducibility. Utilization of hydrogenous reducing agents is also an efficient measure. A reduction test under load was performed to investigate the effect of coke mixing with hydrogen addition on reduction behavior of the ore. Simultaneous use of coke mixing and hydrogen addition accelerated the reduction rate through the carbon gasification rate, and it was also decreased pressure drop. The effect of coke mixing and hydrogen addition on blast furnace operation was examined using a two-dimensional mathematical simulation model. In case of the ore layer mixed with coke, hydrogen addition in the reduction gas increased the hydrogen reduction ratio and decreased the direct reduction ratio. As a result, RAR decreased and permeability improved.
The reduction kinetics of FeTiO3 powder by hydrogen has been studied. According to the isothermal reduction experiments at the temperatures of 1023 K, 1073 K, 1123 K and 1173 K, it was found that the reduction products were mainly Fe and TiO2. During the reduction process, chemical reaction was found to be the rate controlling step. Meanwhile, the particle size distribution of FeTiO3 powder has a significant influence on the reduction kinetics.
Low reducing agent operation of the blast furnace has an important role in mitigating carbon dioxide emissions in the steel works. Low reducing agent operation results in a low coke rate in the blast furnace. In low coke rate operation, the permeability in the blast furnace is considered to change remarkably due to the increase in the ore-to-coke (O/C) ratio. Charging methods based on conventional layered charging should be improved to a new method such as coke mixed charging. In this study, a DEM-CFD model considering the softening behavior of ore particles in the cohesive zone was applied to evaluate the gas flow in low coke rate operation. First, the softening melting test was simulated by the overlapping of particles in DEM. The layer structure and void fraction distribution in the blast furnace were calculated for normal coke rate and low coke rate operation by DEM. Second, gas flow behavior was analyzed by the DEM-CFD model, focusing on the cohesive zone. From the results, it was estimated that the gas flow was influenced by the coke slit structure in the cohesive zone and the permeability of ore layers mixed with coke particles. Under the normal coke rate of 350 kg/t, coke mixed charging has little effect on permeability through the thin coke slit. However, in low coke rate operation, coke mixing can improve the permeability of the cohesive zone.
Increasing coke gasification rate can lowers the temperature of the thermal reserve zone, resulting in a decrease of carbon consumption and a reduction of the reducing agent rate of blast furnaces. To achieve this increase, the enhancement of coke reactivity itself or the close arrangement of iron ore and carbonaceous materials has been investigated in Japan. Against this, RCA, "Reactive Coke Agglomerate," having a high carbon content, has been developed, and it was found that the agglomerate mixed-in sinter layer had two functions: one having high reducibility itself and the other enhancing the reduction of the surrounding sinter. As a result of the two functions, a significant decrease of the temperature of the thermal reserve zone and an increase of gas utilization by using the agglomerate mixed-in sinter layer in a BIS test was achieved. As for the strength after reaction, disintegration was fairly small in comparison with that of the sinter both in the laboratory scale test and in a basket test using a plant's vertical probe. Long-term plant trials have been conducted at the Oita Works No. 2 Blast Furnace with a maximum use of 54 kg/tHM. It was found that RCA could lower the temperature of the thermal reserve zone and carbon consumption in a commercial blast furnace. Carbon consumption was decreased along the relationship of 0.36 kgC/tHM per 1 kgC/tHM of input carbon from RCA.
Thermodynamic information on the equilibrium between dissolved Cr and O in steel melt is the basic knowledge to control Cr content in the stainless steel. The case of using alumina refractories is considered in the present work. Molten Fe–Cr alloy equilibrated with Cr2O3–Al2O3 solid solution when Cr content of the alloy was high and equilibrated with FetO·(Cr, Al)2O3 solid solution when Cr content of the alloy was low. The equilibrium oxygen contents in Fe–Cr alloy at given Cr contents using Al2O3 crucible in the present work were lower than those using Cr2O3 crucible reported previously. It was found that oxide in equilibrium with Fe–Cr alloy will control and affect the O content when Al content is low.
To examine the reaction mechanism of the variation of calcium content in inclusions and the molten steel and the effect of flux composition on the reaction, the variations of molten steel content and inclusion content during CaO, 60%CaO–40%CaF2 or 50%CaO–50%CaSi powder blowing onto the molten steel under reduced pressure were investigated with 15 kg scale experiments. From the experimental results, it was found that the inclusion composition was changed from Al2O3 to Al2O3–CaO by CaO flux that did not contain CaSi alloy, and that the reaction path of the inclusion composition was changed remarkably by CaSi alloy in CaO flux. From the experimental results and the chemical thermodynamic calculation, the effects of the flux and CaSi alloy on the change in composition of inclusion and melts were examined.
In this paper, 1500 kg scale experiments of CaSi mixed CaO powder top blowing onto the Al killed steel were carried out under reduced pressure. And the effects of CaSi alloy ratio in the mixture on reactions of desulfurization and nitrogen removal were examined. Aluminum decreasing rate decreased and rate constant of desulfurization and nitrogen removal increased with increasing CaSi mixing ratio to flux. It is supposed from the above that deoxidation and desulfurization reaction can simultaneously occur by blowing the mixture of CaSi and CaO powder and the effect of calcium mixing powder on desulfurization can be explained by promotion of CaO desulfurization and CaS formation. It is suggested that lower oxygen and sulfur activity due to reaction between molten steel and powder with CaSi increased rate constant of nitrogen removal.
A mathematical model was developed using ANSYS 12.0 in order to simulate non-isothermal melt flows in a delta shaped four strand billet caster tundish. The fluid inside the tundish considered was water, so that the CFD model could later be validated against water model experiments. The buoyancy term was included in the momentum equation using Boussinesq's approximation. Experiments were performed for both the bare tundish, and the tundish fitted with an impact pad. For the bare tundish, step inputs of 5–15°C hotter fluid resulted in significantly stronger natural convection currents towards the extremities of the tundish. On the other hand, for cases of a tundish fitted with an impact pad, the effect of buoyancy driven flows due to step inputs of hot water, was much less pronounced since the pad itself had a big effect on regulating the fluid flow patterns. Step-down conditions were also simulated, where 10–15 degrees cooler fluid was introduced into a hotter liquid within the tundish. Detailed calculations were performed using the DPM, in order to evaluate the number of inclusions passing through the SENs under such transient conditions. While the step-up conditions facilitated the flotation of inclusions because of upward buoyancy driven flows, the step-down condition generated catastrophic results in terms of liquid metal quality. One third and full scale water model experiments were done to validate the numerical model and it was found that the mathematical predictions were in good agreement with the experimental results.
Describing the conditions for reaustenitization of spheroidal graphite cast irons is of interest for their heat-treatment after casting, e.g. for manufacturing austempered ductile irons. Differential thermal analysis has been used to characterize the direct eutectoid transformation and the reverse transformation, i.e. the reaustenitization. This has been applied to a standard and a Ni-bearing alloy, with a ferritic matrix for the former, both a ferritic and a pearlitic matrix for the latter. The results are discussed in relation with the stable and metastable three phase fields. While earlier description of the direct eutectoid transformation is confirmed, the one for reverse eutectoid has been found more complex and is amended.
Chatter vibration is detrimental to the quality of the metal strip in the rolling process. A numerical model was proposed to investigate the vibration characteristics. A rolling mill that includes the driving system was modeled by multibody dynamics to investigate the cause and characteristics of the chatter vibration. The proposed numerical model was validated by theoretical analysis and an experiment that was carried out during manufacturing. The frequency of chatter with high amplitude was in the range computed theoretically by the equation for chatter frequency. The range of chatter frequency was very similar to that predicted by the multibody dynamic analysis, if the speed range of the work roll was in steady state. Because the derivative of the chatter frequency was different from that of the gear mesh frequency (GMF), it could be claimed that the frequencies of the chatter and the gear mesh were not related. It was observed in the analysis that the GMF generated by the helical gear was transmitted to the work roll. The amplitudes of the gear mesh and chatter frequencies became high when the rolling force was high, but the chatter frequency did not occur when there was no rolling force. The effects of the speed of the work roll and the ratio between the dynamic and static components of the rolling force to the chatter vibration were also investigated. We found the chatter frequency that affects vibration of the rolling mill strongly, and analyzed the effect of the rolling parameters on chatter frequency.
Harsh environment in Blast Furnace (BF) poses a big challenge for metallurgical industrial radar measurement of burden surface for ore and coke. The improved signal processing algorithm enhances the real-time performance. Antenna is specially designed for continuous stable signal acquirement, high temperature resistance and anti-dust ability. The experiment results illustrate that the single radar meets the accuracy requirement of solid bulk material. A new BF Burden Surface Measuring System is developed for real-time BF 3-D imaging. Distributed 6-radars array mounted on the top of 2500 m3 BF. A virtual 3-D imaging is achieved with a reconstruction algorithm of 6-radars array according to the actual shape of BF. 3-D imaging system with 6-radars array provides an improved technique for intelligent control of burden distribution during BF iron making process.
A new original position statistic distribution analysis method to reflect the different composition distribution and segregation in nickel-base super alloy was developed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The distribution of more than 20 trace elements at intragranular solid solution phase and crystal boundary in wrought super alloy GH698 was investigated using the micro-area analysis of LA-ICP-MS technique. For most of the trace elements, no significant difference was found between the content in the crystalline grain and that at the crystal boundary. Only a few elements such as Mg, Zr, B and P showed slight segregation at crystal boundary. However, according to the compositional two-dimensional isohypsic chart and statistic degree of segregation, which was obtained by original position statistic distribution method combined with LA-ICP-MS, the segregation of As, Mg and Te was more serious in the cross section scope (10 mm × 10 mm) of the wrought super alloy sample. The results showed that the original position statistic distribution analysis results were in good agreement with the crystal boundary segregation and eutectic structure enrichment obtained by metallographic analysis.
Hot Press Forming (HPF) of Tailor Welded Blank (TWB) was investigated with particular focus on the formability and phase transformation of the constituent base materials. Dilatometric analyses were conducted to study strength differentials for various cooling rates after heat treatment. U-draw bending tests were performed to evaluate the influence of a number of process parameters, namely, blank and tool temperatures, and cooling time, on the mechanical properties of the product. Formability at elevated temperature was assessed using forming limit diagrams for each monolithic material under realistic hot press forming conditions. Lab-scaled forming tests of a newly designed B-pillar were carried out to evaluate the formability of TWB under an actual hot press forming process. Finally, coupled thermo-mechanical finite element simulations, which utilize flow stresses and forming limit diagrams determined under realistic HPF conditions, were carried out. In particular, finite element simulation results for the weld-line displacement and thinning of the TWB were compared to experimental data for validation purpose.
Duplex hardening is a process in which conventional heat-treatments such as secondary or case hardening are followed up by surface nitriding to achieve exceptional properties, particularly in the context of aeroengine bearings. Hardness values in excess of 1000 HV can in principle be achieved, and although the hardness decreases as a function of depth below the surface, some level of enhancement can occur to a depth of up to 0.2 mm. The process can be applied to both through hardened and case hardened bearing steels such as M50 and M50NiL respectively, with concomitant increases in rolling contact fatigue resistance and tribological properties. The process has not yet been universally adopted and is ripe for a critical assessment.
Double-ellipsoidal volumetric heat with Gaussian distribution of heat intensity is one of the most popular heat source model used in fusion welding process simulations. However, the major difficulty of this kind of heat source model is to define the parameters before start of simulation. It is common practice to define the heat source parameters from experimental measurement of weld dimensions for a particular welding condition that meet the demand of two parameters i.e. weld width and penetration. Till date, the definition of front and rear length of double ellipsoidal is to-some-extent arbitrary in linear welding. A sensitivity analysis shows that this ratio has significant effect on weld dimensions as well as thermal distortion and residual stress of final weld joint. This problem has been addressed in present work where the optimum value of the ratio of front and rear length of double ellipsoidal heat source model is designed within the kernel of an integrated optimization algorithm. The ratio is assumed as function of weld velocity and a suitable functional form is designed over a range of welding current and velocity. The proposed trend of ratio along with optimum values demonstrate fair agreement of experimentally measured weld dimensions for linear gas tungsten arc (GTA) welding process. 3D finite element model of thermal and mechanical analysis is developed and assuming elasto-plastic response of material. Temperature dependent material properties along with latent heat of melting and solidification are incorporated in numerical simulation.
In this study, the full potential of C60 fullerene for use in the low-temperature solid-carburizing of SUS316L stainless steel is demonstrated. The carburizing of this austenitic stainless steel with C60 was conducted in a vacuum atmosphere without any surface activation treatment of the specimen surfaces. The uncarburized SUS316L had the lattice parameter of approx. 3.5963 ± 0.0001 Å and the Vickers hardness of 172 MPa measured by the Nanoindentation method. After carburizing at 475°C for 200 h, the lattice parameter of the specimen surface was approx. 3.6545 ± 0.0001 Å and the Vickers hardness was approx. 742 MPa. After carburizing at 500°C for 100 h, the lattice parameter of the specimen surface was approx. 3.6592 ± 0.0002 Å and the Vickers hardness was approx. 837 MPa. These results are comparable to those obtained by low-temperature gas- and plasma-carburizing reported in previous works.
Solubility of Fe in the liquid of Al–Mg–Si alloys was determined at 973 K. The liquid of Al–Mg–Si alloy with Fe concentration of up to 15 wt% was heated at 973 K. After equilibration a part of liquid was sampled and solidified to analyze the chemical compositions by X-ray fluorescence. The solubility of Fe was determined as functions of Mg and Si concentrations in weight percent as follows, CFe = –(0.14 ± 0.00)CMg + (0.02 ± 0.01)CSi + (2.74 ± 0.03) The solid phase coexisting with the Fe saturated liquid was FeAl3 in which Si was dissolved up to 2.4 at%.
The work hardening mechanism and deformation behaviour of Hadfield steel crossing during explosion deformation were investigated by means of its ability to memorize the history of deformation and stress. The results show that the explosive stress causes little macroscopic distortion of the surface of the Hadfield steel crossing but higher work hardening degree, revealing an additional work hardening ability to compare with static deformation. Under the explosive deformation, the high strain rate results in much less strain threshold for inducing twin formation in Hadfield steel than that under static compression. During the explosive deformation, slipping and twinning are simultaneously operated in a competitive way. It is therefore concluded that the deformation twins are responsible for the additional work hardening of the Hadfield steel crossing subjected to the explosive treatment.
This work analyses the wear behavior of a modified white cast iron (MWCI) with moderate chemical composition using 1.77Ni, 1.42Cr, 0.26Mo and 1.59Cu in comparison to a conventional white cast iron (CWCI). The wear test has been carried out for alloys in the as cast condition using a pin-on-disc test in the loads of 80, 100, 120 and 140 N. Microstructural characterization, hardness, frictional coefficient and the total weight loss have been assessed in each alloy. For a low load of 80 N, the total weight loss of MWCI (0.5 mg) is much less than that of CWCI (1.3 mg). The total weight loss has been increased to 2.8 mg for MWCI, while it is still less than that of CWCI (~3.7 mg) with increasing the load to 140 N. Investigation shows that the wear resistance of the specimens is strongly depended on the hardness derived from their microstructures. More plastic deformation and detachment of the tribolayers are observed on the surfaces with a lower hardness. The wear rate of specimens has been increased with increasing the load especially in the specimens with lower hardness. It has been found that the specimen with a higher hardness shows a lower frictional coefficient under the range of applied loading.
High permeability commercial CRGO, cold rolled grain oriented steel was subjected to uni-axial tensile strain in three principal orientations: (110) <001>, (110) <110> and (110)<111>. The samples exhibited remarkably different stress-strain behavior. The numerical values of the strain hardening exponent, n, largely determined the degradation in magnetic properties: namely increase in Hysteresis loss (H) and drop in Permeability (μ). Changes in magnetic properties were also correlated with microstructural observations: misorientation and dislocation density developments, relative recovery, residual strain and deviation from ideal <001>. The study established constitutive relationships between degradation in magnetic properties and various parameters of the deformed microstructures.