Journal of Iron and Steel Research(International)最新文献

A new continuous bending and straightening casting curve with the aim of full using of high-temperature creep deformation was proposed. The curvature of bending and straightening segment varies as sine law with arc length. The basic arc segment is shortened significantly so that the length of bending and straightening area can be extended and the time of creep behavior can be increased. The distance from solidifying front in the slab was calculated at 1200 °C by finite element method. The maximum strain rate of new casting curve at different locations inside the slab is 6.39 × 10⁻⁵ s⁻¹ during the bending segment and it tends to be 3.70 × 10⁻⁵ s⁻¹ in the straightening segment. The minimum creep strain rate is 7.45 × 10⁻⁵ s⁻¹ when the stress is 14 MPa at 1200 °C. The strain rate of new casting machine can be less than the minimum creep strain rate. Thus, there is only creep deformation and no plastic deformation in the bending and straightening process of steel continuous casting. Deformation of slabs depending on creep behavior only comes true. It is helpful for the design of the new casting machine and improvement of old casting machine depending on high temperature creep property.

Ladle slag affects steel cleanliness at the end of the Ruhrstahl-Hereaeus (RH) and holding process. The relationship between composition of ladle slag, total oxygen (TO) and inclusions was investigated using X-ray fluorescence (XRF), infrared absorption, and SEM + EDS methods. The results indicate that TO in steel at the end of RH increases linearly with increasing FeO content in slag. TO is lower when${\omega }_{\text{CaO}}/{\omega }_{{\text{Al}}_{\text{2}}{\text{O}}_3}\left(\text{C}/\text{A}\right)=1.5-2.0$ than that of C/A = 1.0–1.4 under an approximate content of FeO. During the holding process, irregular Al₂O₃ inclusions are newly generated due to slag reoxidation. Additionally, Al₂O₃-Ti_x O inclusions are newly generated in the steel when the content of FeO is higher. By combining experimental and thermodynamic calculation results, it is determined that the slag has a good melting property within the zone of C/A=1.2–1.8 and adsorption capacity of Al₂O₃ when the content of SiO₂ in slag is controlled at 4%–6%. The increase in the C/A ratio and the decrease of FeO content in slag can slow down the reoxidation rate.

In order to determine the critical forging penetration efficiency (FPE) of 06Cr19Ni9NbN steel, a new model was presented to describe critical FPE, which is significant to optimize the steel forging process. The plane strain compression tests were conducted to obtain the model and confirm its validity. The results indicated that the dynamic recrystallization (DRX) volume fraction increases and the grain size decreases with the rise of reduction ratio. Meanwhile, the compression process was simulated by DEFORM software. The tensile tests were conducted and the results demonstrated that the mechanical properties gradually become stable when the reduction ratio increases to 30%, 34% and 40% at 1200, 1100 and 1000°C, respectively. The calculated results based on this new model are consistent with experimental results, indicating that the model is suitable to predict the critical FPE for the steel.

Studies show that manganese sulfide (MnS) inclusions in pipeline steel affect the lateral performance of steel in its rolling deformation, as well as the hydrogen-induced cracking and sulfide stress corrosion cracking resistance performance. To inhibit the precipitation of MnS and its effect on pipeline steel, a quenching experiment and a diffusion couple experiment, which investigated the evolution of MnS inclusions in Ti-bearing X80 pipeline steel, were conducted. The experimental results show that the transformation of the MnS inclusions during solidification is as follows: MnS→ titanium sulfide (TiS) → Ti₄C₂S₂. The transition temperatures of MnS to TiS and TiS to Ti₄C₂S₂ are 1673 and 1273 K, respectively, and the overall size of the sulfide decreased as well. Thermodynamic calculation results confirm that the transition temperatures of MnS to TiS and TiS to Ti₄C₂S₂ are 1623 and 1203 K, respectively. When the sulfur content in the X80 pipeline steel is 0.0015%, all the sulfur in the steel can be converted into Ti₄C₂S₂ with a titanium content of more than 0.02%.

The models and influencing factors of steel ladles exchange during the steelmaking and continuous casting process of H steel plant were investigated. Based on analysis of the operation process and turnover time of steel ladles, relationship models for the turnover number, turnover rate, continuous casting number, number of ladles with additional turnover, and number of ladles without additional turnover were built. The turnover rules of steel ladles for one basic oxygen furnace (BOF) matching one continuous caster (CC) and two BOFs matching two CCs modes were simulated by using a Gantt chart. The models of steel ladle exchange were proposed for casting of a single CC and overlapping casting of two CCs. By analyzing the influencing factors, the following conclusions were drawn. The exchange ladle should not have the task of transporting liquid steel in the CC that stops casting earlier. The end time of the empty ladle in the CC that stops casting earlier should be earlier than the start time of the full ladle in the CC that stops casting later. After evaluating the factors influencing the start casting time, turnover cycle, casting time, continuous casting number, and overlapping time, a prioritization scheme of steel ladle exchange was proposed based on the steel grade. First, the turnover cycle and single heat casting time were determined; based on these, a reasonable ladle turnover number was calculated. Second, the turnover number and continuous casting number were optimized for maximizing the number of ladles without additional turnover. Lastly, to reduce the casting number during the overlapping time to be lower than the turnover number, the overlapping time was shortened.

A sort of lightweight porous ceramic foam ball that can float on the water was recently made from the natural zeolite. The diameters of porous ball and its macroscopic pores are around 5 and 1 mm, respectively. Such ball surface could be modified to activate in different ways, i. e. loading the active alumina or desilicating the ball. Both of modified products have been investigated to adsorb the toxic ion of arsenic (As) in water effectively. This kind of porous ceramic ball was prepared by powder sintering, using natural clinoptilolite powder as the primary raw material. An active-alumina-loaded porous ceramic product was generated by sol-gel method with pseudoboehmite (AlOOH) as the main composition. The active Al atom on the porous ball surface could also be achieved by desilicating the ceramic ball in the NaOH solution. Such a desilicated product exhibited a good activity to adsorb the arsenic ion although carrying no active alumina. With this effective porous structure, the present products can be expected to become practically advantageous.

Currently, the market demands for large-scale and high-quality slab ingots are increasing significantly. A novel electroslag remelting withdrawal (ESRW) process with two series-connected electrodes and a T-shaped mould was developed to produce large-scale and high-quality slab ingots. It is very difficult to obtain large slab ingots with good surface quality and high width-to-thickness ratio. And it is not efficient for improving the quality of slab ingots by using trial-and-error-based approaches because the ESRW mechanisms are very complex. Thus, a three-dimensional mathematical model was developed to determine the relationship between process parameters and physical phenomena during the ESRW process. The relationship between the temperature field of the ESRW process and the surface quality of slab ingots was established. A good agreement between the simulated and measured temperature fields of slab ingots was obtained. The results indicate that the maximum values of current density, electromagnetic force and Joule heat all occur at the electrode-slag interface between the two electrodes. It can be found that the flow is turbulent and the temperature distribution is uniform in the slag pool with the influences of buoyancy and electromagnetic force. The wrinkles in the narrow faces of slab ingots are caused by the relatively lower input power. Increasing the electrode width and reducing the curvature can significantly improve the surface quality of slab ingots.

A concept of production scenario for the steelmaking-continuous casting production process and the mathematical description of such concept were proposed. The production scenario was described with the variation of the equipment status and the production material properties based on the executing production schedule. Then, the dynamic characteristics of the production process could be described with the evolution process of production scenario. Through analyzing the influence of the dynamic production scenario on production scheduling, three key points about the scheduling problems were identified: the problem for integrating the schedules of different batches that is non-neglected when making a schedule, the problem for matching the material flow with the schedule that should be solved when implementing a schedule, and the problem for eliminating the deviations between the initial schedule and implemented schedule that should be solved when rescheduling in a disturbed environment. Finally, a set of experiments were conducted, and the results demonstrated that making the production schedule and solving the rescheduling problem for steelmaking-continuous casting process with addressing the above three problems improve the adaptability of the schedule in dynamic environment.

Hot stamping has been widely used in car industry to produce safety components. Most existing researches focused on the stamping and quenching process, but less on the mechanical properties of stamped parts. The fracture behaviors of hot stamped boron steel B1500HS have been studied, and other four commonly used sheet metals with different strengths, including Q235, TRIP780, QP980 and MS1300, were also introduced for comparison. Both uniaxial tests and mechanical trimming tests were performed, and the fracture surfaces under different stress states were observed and discussed. The SEM observations showed that the fracture models are closely related to the stress states, i. e., the tensile surfaces have ductile rupture characters while the trimming surfaces have brittle rupture characters. Compared with other steels, the quenched boron steel has smaller dimple size accompanied by shear planes in the tensile surface, and has smaller burnish zone in the trimming surface, and its cutting surface with ‘S’ like shape is also very different with others. Furthermore, two fitted empirical models were derived to describe the quantitative correlations between the average dimple diameter and the steel strength and between the percentage of burnish zone and the steel strength.

The grain refinement and macrosegregation control of GCr15 bearing steel were investigated under a type of rarely-used electromagnetic stirring, vertical electromagnetic stirring (V-EMS), in continuous casting. V-EMS can create an upward electromagnetic force and generate longitudinal loop convection, which enables the better mixing of the upper part with the lower part of the liquid steel. The results showed that applying V-EMS can enlarge the region of the equiaxed grain, decrease the secondary dendrite arm spacing (SDAS) and reduce the segregation of both carbon and sulfur. After applying V-EMS, liquid steel with a high solute concentration is brought to the dendrite tips, making the dendrite arms partially melt. The length of the dendrite fragment is approximately 1.8 mm, 10 to 12 times the SDAS. Upon increasing the amount of cooling water from 2.0 to 3.5 m³/h, the dendrite fragments exhibit an obvious aggregation following V-EMS. Finally, a criterion for dendrite fragmentation under V-EMS was derived based on the dendrite fragmentation theory of Campanella et al.