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2020 Vol.  55 No.  11
Published: 2020-11-15

0 Yao-Bin HOU Lukuo Hong
Study of gas-solid reaction decarburization of Fe-C alloy strip in CO/CO2
In order to study the decarburization effect of Fe-C alloy strips in Ar-CO-CO2 atmosphere, the decarburization atmosphere was determined by a combination of thermodynamic analysis and experiments. The Fe-C alloy strips were decarburized in mixed 66.25%Ar-25%CO-8.75CO2 gas. Taking the Fe-C alloy strip with an initial carbon content of 4.2% as the research object, the effects of different decarburization temperature, strip thickness and decarburization time on the decarburization effect were studied. The results show that for 2mm thFe-C alloy strips which were decarburized for 60 minutes at 1293K, 1353K, and 1413K, the average carbon content were 2.748%, 1.870%, and 1.134%, respectively. The Fe-C alloy strips with thicknesses of 1mm, 1.5mm and 2mm were decarburizated at 1413K for 60min,the average carbon contents were 0.32%, 0.92% and 1.05% respectively. It has been proved that increasing the decarburization temperature, prolonging the decarburization time and reducing the thickness of the strip all help to improve the decarburization effect .
2020 Vol. 55 (11): 0-0 [Abstract] ( 154 ) [HTML 1KB] [PDF 0KB] ( 211 )
0
Microstructure inheritance of continuous casting steel deformed by hot-core heavy reduction rolling technology during reheating process
The Hot-core heavy reduction rolling (HHR2) technology can break the coarse casting microstructure and affect the microstructure and properties of the final product by affecting the morphology of austenite after reheating, as well as improving the internal shrinkage and porosity of the continuous casting steel. Two typical steels, such as microalloyed steel and medium carbon steel were selected as the research objects. The effects of HHR2 technology on the microstructure of continuous casting steel and the austenitic morphology after reheating were studied by the integrated pilot experiment of steelmaking, continuous casting and rolling in this paper. The results show that the casting microstructure can be improved and fine microstructure can be obtained at room temperature by HHR2 technology. For medium carbon steel, the fine microstructure obtained by HHR2 technology cannot keep fine after reheating, and the austenite grain size after reheating is larger than that of the non-deformed casting steel. However, for microalloyed steel, the fine microstructure obtained by HHR2 technology can be maintained after reheating due to the nailing effect of the second phase particles.
2020 Vol. 55 (11): 0-0 [Abstract] ( 166 ) [HTML 1KB] [PDF 0KB] ( 206 )
0 Wan-Li DENG
Prospect of Energy Management and Control System in Iron & Steel Industry under Intelligent Manufacturing
There are some problems in energy management and control system, such as multi-level production organization, discrete system architecture, experiential management and control, which make it difficult to face the goal of intelligent manufacturing in iron and steel industry. In terms of methodology, the energy management and control system should build its own HCPS according to the paradigm of intelligent manufacturing in the process industry, learn the technical thinking of intelligent optimization of production processes and overall intelligent optimization of the entire production process, and learn from the concept of supply and demand interaction of Energy Internet, deployment of IT architecture that is synergistic with the enterprise as a whole. On this basis, the prospect of energy management and control system is described from production management model change, digital system establishment, optimized control functions, and refined energy management.
2020 Vol. 55 (11): 0-0 [Abstract] ( 135 ) [HTML 1KB] [PDF 0KB] ( 231 )
0
Influence of Ca Treatment on the Effect of Rare Earth in C-Mn Steel
To clarify the influence of Ca treatment on the effect of Rare Earth (RE) in C-Mn steel, scanning electron microscope, optical microscope and ultra-depth three-dimensional microscope were used to observe inclusion and microstructure for test steels. Combining with thermodynamic calculation and impact fracture analysis, the influence of RE and Ca-RE complex treatment on mechanical behavior of C-Mn steel was studied comparatively. The conclusions were as follows: after RE added into steel, the inclusion was changed into nearly spherical complex inclusions containing RE oxide, the size and aspect ratio of the inclusion decreased. For the steel treated by Ca-RE,almost all the inclusions became spherical complex inclusions of RE-Ca, and the cleanliness of steel increased. Ca in steel can increase the yield of RE from 7.6% to 42.4% improving the utilization rate of RE effectively. After the complex treatment of Ca-RE, the content of pearlite increased and so did in the strength of steel. All findings indicated that it is feasible to use Ca to improve the effect of RE in C-Mn steel.
2020 Vol. 55 (11): 0-0 [Abstract] ( 145 ) [HTML 1KB] [PDF 0KB] ( 198 )
0
Aggregation Behavior of MgAl2O4 Inclusions in Magnesium-treated Low Carbon Steel
In order to study the aggregation behavior of MgAl2O4 inclusions, single MgAl2O4 inclusions and multi-particle MgAl2O4 inclusions in magnesium-treated aluminum deoxidized mild steel were observed by metallographic sample method and organic solution electrolytic separation method combined with field emission scanning electron microscope. Thermodynamic calculation results indicate that MgAl2O4 inclusions are precipitated in the liquid phase. FactSage calculated the phase transformation law of inclusions in steel, and the predicted types of inclusions were consistent with the experimental observations. The analysis of the multi-particle MgAl2O4 inclusions shows that the cavity bridge force is much greater than the capillary force, van der Waals force, and viscous force. Therefore, the cavity bridge force is the main force that causes the aggregation of MgAl2O4 inclusions. The molten steel condition is that temperature increase and the low aO and low [pct S], cavity bridge force value is small, which causes the weakest aggregation ability of MgAl2O4 inclusions.
2020 Vol. 55 (11): 0-0 [Abstract] ( 149 ) [HTML 1KB] [PDF 0KB] ( 222 )
0
Analysis of evolution and formation mechanism of calcium-containing non-inclusions of Q345D steel
The formation mechanism of calcium-containing inclusions during the production of Q345D steel was investigated through industrial trials. Thermodynamic calculations are used to study the transformation mechanism of inclusions during solidification. The results showed that calcium in steel mainly comes from VD vacuum and calcium treatment. The CaO content of inclusions before vacuum is very low. However, after vacuum break, CaO content of inclusions increased due to entrainment. After calcium treatment, CaO content of inclusions further increased. The composition of the inclusions changed significantly during solidification. The content of CaO in inclusions of slab decreased significantly, and the content of CaS increased significantly, which is consistent with the thermodynamic calculation results. The large-sized calcium-containing inclusions in slab are mainly divided into calcium aluminate, calcium aluminate surrounded by CaS, calcium aluminate with spinel surrounded by CaS, CaS and Al2O3 bonding type, and CaS and spinel bonding type. The larger the inclusion size is, the higher the content of CaO is. The content of CaS in large-size inclusions is extremely low.
2020 Vol. 55 (11): 0-0 [Abstract] ( 198 ) [HTML 1KB] [PDF 0KB] ( 240 )
0 Hai-Yan TANG
Structure optimization of a five-strand channel induction heating tundish and application
Channel induction heating has been pay widely attentions by metallurgical workers in recent years because it can effectively compensate the temperature drop of the molten steel in a tundish and its high heating efficiency along with simple equipment. However, the tundish structure with the induction heater is quite different from the conventional tundish, and the flow field cannot be optimized simply by adding retaining walls, dams or stabilizers. Aiming at the problems of a high pouring superheat degree and a large temperature difference between the edge flow and the middle flow for a five-strand channel induction heating tundish in a domestic steel plant, several schemes were designed and their effects on the flow field of the tundish were compared through water simulation in the present work. The optimized split channel scheme A6 can reduce the dead zone fraction of the tundish from 29.50% to 20.33%; the average residence time is prolonged by 40s compared with the straight-through prototype scheme, and the consistency of each strand is significantly improved. Industrial tests show that the temperature difference between the edge strand and the middle strand of the optimized split channel is 3.5°C lower than that of the prototype channel, and good application results have been achieved.
2020 Vol. 55 (11): 0-0 [Abstract] ( 124 ) [HTML 1KB] [PDF 0KB] ( 222 )
0
Research and optimization of mold flux for high speed continuous casting of low carbon steel thin slab
In view of the problems such as too thin slag layer, frequent bond alarm and too many longitudinal cracks on the surface of slab during high speed continuous casting of low carbon steel thin slab, the optimization direction of the lubrication and heat transfer performance of the mold flux is determined based on the fully consideration of the solidification shrinkage characteristics of low carbon steel, and industrial experiments are carried out. The basicity of the mold flux is increased from 1.10 to 1.30, the mass fraction of Li2O is increased from 0.57% to 1.06%, the mass fraction of Na2O is increased from 5.48% to 8.16%, and the mass fraction of Carbon is reduced from 7.71% to 6.72%. The rheological properties of two kinds of mold flux and the three-layer structure of slag film are further studied. It is found that after optimization, the proportion of liquid slag layer in the slag film increases, and the lubrication coefficient(α) of the slag film increases; at the same time, the proportion of crystal layer in the slag film also increases to a certain extent, and the heat transfer coefficient(β) of the slag film increases, so that the lubrication performance and the control heat transfer capacity of the mold flux are improved. From the results of mineral phase analysis, it can be seen that the increase of basicity of the mold flux will promote the precipitation of wollastonite to a certain extent, leading to the increase of crystallization rate and thermal resistance of slag film, thus controlling the heat transfer. The production practice shows that after the increase of casting speed, the use of the new type of mold flux can basically avoid the generation of bond and crack, and the production efficiency and slab quality are significantly improved. It has a certain guiding significance for the production and application of the low carbon steel thin slab high speed mold flux in the enterprise in the future.
2020 Vol. 55 (11): 0-0 [Abstract] ( 171 ) [HTML 1KB] [PDF 0KB] ( 224 )
0
Research on Hot Rolling of 2205 Stainless Steel-Carbon Steel Composite Rebar
This paper applied metal cladding method to manufacture 2205 duplex stainless steel with carbon steel core HRB400. Thermal simulation experiments were conducted by geleeble-3800, the high temperature rheological curve and thermal processing diagram of 2205 stainless steel were studied. Finally, the rolling temperature of the composite steel rebar was determined to be ≥1150℃.Through numerical simulation of composite rolling, it is found that during rough rolling deformation, the strain is concentrated on the surface layer and 1/4 position of the rolled part. With the continuous infiltration of the deformation to the core, the stainless steel cladding layer where the plastic strain is larger is thinner. In the process of finishing rolling pass of K1, it is found that the thickness of the stainless steel cladding is the thinnest at the root of the transverse rib and the thickest at the crest of the transverse rib. Near the interface of composite rebar, the diffusion distance of Cr, Ni and Mo is 18-20μm, and the microstructure from carbon steel to stainless steel is ferrite and pearlite microstructure, decarburization microstructure, composite interface, austenitic stainless steel microstructure, ferrite and austenitic stainless steel microstructure.
2020 Vol. 55 (11): 0-0 [Abstract] ( 156 ) [HTML 1KB] [PDF 0KB] ( 206 )
0 Dong-cheng Yang-huan XU Hong-Min LIU
Data-driven Intelligent Prediction Model of Edge Seam Defects for Hot rolling strip
Edge seam defects are easy to occur in hot rolling strip, which not only seriously affect the yield, but also may affect the downstream process of hot rolling. It is very difficult to establish an accurate mechanism prediction model because of the complex and changeable factors affecting the edge seam defects. Therefore, this paper first analyzes the main influencing factors of edge linear defects; then, based on modern intelligent methods, the intelligent prediction models of edge seam defects based on logical regression and neural network are established respectively, and the accuracy and generalization ability of the two models are analyzed; finally, based on the neural network intelligent prediction model, the heating process parameters are optimized, which makes the defect rate and defect closure rate are significantly reduced. The research results in this paper have practical significance for improving the surface quality of hot rolling strip, and can be applied to similar rolling lines.
2020 Vol. 55 (11): 0-0 [Abstract] ( 188 ) [HTML 1KB] [PDF 0KB] ( 220 )
0
Research and development of low Mo alloyed Q345 fire-resistant steel
Through the design of composite microalloyed components of low carbon, low Mo (~0.2%) and Nb, V, Ti, the continuous cooling transition (CCT) curve of the experimental steel was measured by Formastor-Digital automatic phase change tester, using Gleeble-1500 thermal simulation test machine studied the influence of different cooling processes on the microstructure and hardness of the test steel after deformation, and successfully developed Q345 fire-resistant steel, and used SEM, EBSD, TEM and physical phase analysis for hot rolling and The high temperature tensile specimens were microscopically characterized. The results show that the bainite structure begins to appear when the cooling rate of the test steel is above than 1.9oC/S. When the cooling rate is 9.6oC/S, the bainite content and matrix hardness are moderate, which is the best cooling rate after rolling. The content of MC phase and the percentage of particles below 18nm in the experimental steel were increased by 16.4 and 9.8% respectively compared to the hot-rolled samples. These precipitated nano-scale particles played a good role of precipitation strengthening at high temperature, making up for the high temperature. The loss of high-temperature yield strength due to the decrease in shear modulus and the failure of fine-grain strengthening strengthens the experimental steel with excellent high-temperature strength.According to the analysis of the room temperature and high temperature strengthening mechanism of the experimental steel, solid solution and precipitation strengthening are the main strengthening methods of Q345 fire-resistant steel.
2020 Vol. 55 (11): 0-0 [Abstract] ( 210 ) [HTML 1KB] [PDF 0KB] ( 220 )
0 Feng Hu
Effect of refinement of bulk structure on fracture behavior of bainitic steel
The medium carbon bainitic steel consists of sub-micro structured bainitic-ferrite and retained austenite. The retained austenite plays a leading role for the toughness, it can significantly increase the toughness of bainitic steel by refining the size of blocky structure. In order to explore the effect of block structure refinement on mechanical properties and fracture behavior, the two-step bainite isothermal process was used to study the refinement of the bulk structure, mechanical properties, tensile and impact crack behavior of medium carbon (0.3wt%) bainitic steel. Optical, scanning electron (SEM), transmission electron (TEM) microscope, X-ray diffraction (XRD), etc. were used to characterize and analyze the type and size of microstructure, tensile and impact properties, and fracture morphology of the test steel. The results show that compared with the one-step bainite process, the newly formed bainite ferrite in the two-step bainite process divides and refines the bulk martensite + retained austenite, and the work hardens with the increase of true strain The effect of the rate is better; the fracture form is ductile fracture, and the number and depth of the dimples are better than one-step bainite transformation, and the plastic toughness is better.
2020 Vol. 55 (11): 0-0 [Abstract] ( 99 ) [HTML 1KB] [PDF 0KB] ( 241 )
0 Xiao-Fei HE
Application Study of Extreme Value Method in Inclusion Evaluation of High Quality Gear Steel
In this paper, high quality Mn-Cr system gear steels is selected as the research object. Through large-area analysis of automatic scanning electron microscope, it’s found that the equivalent size of the largest inclusion in the test steel is 34.17 μm. The Gumbel statistical extremum method is further used to predict the maximum inclusion in the Mn-Cr system gear steel. Under the condition of 99.9% probability, the detection area is about 100 000 square millimeters and the maximum inclusion size in the test steel is predicted to be 62.1μm, which satisfy industrial and routine scientific research detection and analysis.
2020 Vol. 55 (11): 0-0 [Abstract] ( 96 ) [HTML 1KB] [PDF 0KB] ( 186 )
0
Study on In-situ Tensile Fracture Mechanism of New Type Austenitic Heat-resistant Steel C-HRA-5
Fracture mechanism is one of the main research directions of mechanical properties of materials. In order to clarify the uniaxial tensile fracture mechanism of C-HRA-5 steel, the entire tensile process was observed by in-situ SEM, and the initiation-propagation-fracture of microcracks in this heat-resistant steel was analyzed in depth. The results show that C-HRA-5 steel exhibits typical ductile fracture characteristics at room temperature and 700 °C. The fracture of the material is mainly affected by the M23C6 phase and the MX phase, and microcracks originate from the trigeminal grain boundaries where the M23C6 phase aggregates. At room temperature, microcracks are connected to the cracks in the MX phase of the crystal, forming transgranular cracks; At high temperatures, micro-cracks form local transgranular cracks under the action of shear stress τ, resulting in the ultimate failure of the material.
2020 Vol. 55 (11): 0-0 [Abstract] ( 161 ) [HTML 1KB] [PDF 0KB] ( 203 )
0
Mixed Crystal of Inherent Grain Size in Track Pins 1E1158M Steel
1E1158M steel developed by Caterpillar is used for track pin and the final heat treatment is quenching and tempering. However, the inherent grain size appears mixed crystal after final heat treatment, which affects the performance. In this paper, the thermal simulation test and the quantitative analysis of microstructure were carried out to investigate the mixed crystal phenomenon of inherent grain size of 1E1158M steel under different finishing temperatures. The results show that the abnormal grain growth temperature of hot-rolled and normal-fired microstructures is both 850°C, and the finishing rolling temperature has an effect on mixed crystal degree. When the finish rolling temperature is 850°C, the austenite grains are partially recrystallized at the end of rolling, and the degree of mixed crystals is serious. As the finishing temperature increases, the inhomogeneity of the intrinsic grain size decreases and the recommended finishing temperature is 1000°C.
2020 Vol. 55 (11): 0-0 [Abstract] ( 184 ) [HTML 1KB] [PDF 0KB] ( 198 )
0
Experimental study on carbothermal reduction of tall pellets bed in laterite nickel ore
Abstract: Laterite nickel ore is one of the main raw materials for the production of ferronickel alloy. The size of ferronickel particles after carbothermal reduction is very important for the later magnetic separation. Based on this, the experimental study of carbothermal reduction of laterite nickel ore under the condition of tall pellets bed was carried out. Also, the influence and mechanism of reducing temperature, reducing time and amount of additive CaO on the size of metallized ferronickel particles were investigated. The experimental results show that, under the condition of C/O=1.0, the optimum reducing parameters are 1400℃ and 45min. Under these conditions, 70% of ferronickel particles are +40μm, and the biggest particles are about 100μm. The reduced pellets obtained under these conditions can be magnetic separated to obtain metallized ferronickel particles, and most of the element Ni can be recovered. The research results of the present work can give some guidelines for choosing reasonable reducing parameters for carbothermal reduction of laterite nickel ore in tall pellets bed.
2020 Vol. 55 (11): 0-0 [Abstract] ( 153 ) [HTML 1KB] [PDF 0KB] ( 211 )
0
Prediction of Component Activity of Titanium Bearing Slag System by Modified Molecular Interaction Volume Model
A large number of titanium bearing slag is produced in the process of steel smelting with the application of titanium protecting material and titanium bearing iron ore, while the depth development of titanium resource comprehensive utilization technology is limited due to the lack of thermodynamic data of multi-component titanium bearing slag system. Using the modified molecular interaction volume model (M-MIVM (FII)), the activity of each component in Al2O3-CaO-SiO2, FeO-MnO-SiO2, FeO-MnO-TiO2, FeO-SiO2-TiO2, MnO-SiO2-TiO2 and Al2O3-CaO-FeO-TiO2 was predicted and compared with the experimental values. The results show that the predicted values of M-MIVM (FII) are in good agreement with the experimental data. The average relative error in activity prediction of the six systems is 11%, which is within the experimental error range of 30% proposed by Turkdogan. M-MIVM (FII) is better than MIVM both in parameter fitting and activity prediction, which has better prediction effect on the component activity of multi-element titanium bearing slag system. On this basis, M-MIVM (FII) was used to predict the activities of TiO2 in Al2O3-CaO-SiO2-TiO2 melt, and the influencing factors were analyzed. The results show that the predicted activities of TiO2 are in good agreement with the experimental data, and decrease with the increase of slag basicity and Al2O3 content, which is consistent with the experimental law. A significant advantage of the M-MIVM(FⅡ) lies in its ability to predict thermodynamic properties of multicomponent melt by only using the component activities or infinite activity coefficients in their sub-binary systems.
2020 Vol. 55 (11): 0-0 [Abstract] ( 161 ) [HTML 1KB] [PDF 0KB] ( 229 )
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