The collaborative utilization of organic solid waste in the steel process has natural advantages. High temperature conditions and a complete pollutant treatment system in the process are conducive to the harmless disposal of organic solid waste. Futhermore, there is no possibility of them casusing secondary pollution to the environment. Organic solid waste is used as fuel to replace fossil energy, which not only cuts steel production costs but also reduces CO₂ emissions, turning waste into treasure. The collaborative utilization of organic solid waste in the steel process achieves multiple benefits such as green sustainable development and ecological environment protection, and meets the actual development needs of steel companies. The research progress of organic solid waste disposal in steel processes, and outlines the current utilization status and technical bottlenecks of organic solid waste in iron ore sintering, blast furnace ironmaking, rotary hearth furnace, electric arc furnace steelmaking and other steel production processes were summarized. Combining the advantages and characteristics of the rotary hearth furnace technology in the field of solid waste, the author proposes a new multi-kiln integrated organic solid waste treatment technology centered on the rotary hearth furnace, specifically including the organic solid waste heat transfer system, the rotary hearth furnace system, and the conversion pyrolysis furnace system and flue gas control system. The system uses a pyrolysis gasification furnace to pyrolyze organic solid waste to produce combustible gas and pyrolysis carbon. Combustible gas is used to replace natural gas to provide energy for the rotary hearth furnace. Pyrolytic carbon can replace coke powder, coal powder and iron and zinc dust sludge to prepare carbon-containing pellets, and obtain valuable metal dust and metallized pellets under rotary hearth furnace smelting conditions. After the valuable metal dust is enriched, high value-added metals such as zinc ingots, lead ingots, and indium ingots are obtained through a combined fire-wet process. Metalized pellets are produced through a hydrogen plasma melting pyrolysis furnace to produce molten iron. The flue gas of the entire process is concentrated in the rotary hearth furnace flue gas treatment system to achieve ultra-low pollutant emissions, which provides a new idea for the coordinated treatment of urban organic solid waste in the steel process.

Taking Panxi vanadium titanium magnetite as the research object, the current status of the comprehensive utilization process plan for Panxi vanadium titanium magnetite was analyzed. Considering the traditional process of using carbon reducing agents or adding additives to reduce the excess carbon and additive residues in the product, it will cause pollution to the produced product, especially sodium salt additives, which are an environmental pollution factor and have the disadvantage of high industrial processing costs, the use of hydrogen reduction grinding process to treat vanadium titanium magnetite to achieve the separation of iron and titanium elements was proposed. The research process first involves reducing vanadium titanium magnetite with hydrogen gas, reducing the majority of iron oxides in the ore to metallic iron, and then separating titanium and iron elements through fine grinding and magnetic separation. Research has shown that the metallization rate of vanadium titanium magnetite can reach 86.21% after 4 h of reduction at 1 200 ℃; Reduced vanadium titanium magnetite was finely ground for 60 min to obtain a particle size of D50 about 10.5 μm Under the condition of a magnetic field strength of 80 mT, wet magnetic separation can be carried out on m particles to obtain metal iron powder with TFe mass percent of 89.34%, TiO₂ mass percent of 0.83%, V₂O₅ mass percent of 0.33%, and non-magnetic materials with TFe mass percent of 6.22%, TiO₂ mass percent of 36.82%, and V₂O₅ mass percent of 2.35%, thereby achieving the separation of iron and titanium elements. The application of reduction grinding process in the separation of iron and titanium elements in vanadium titanium magnetite has a good effect. The obtained metal iron powder has a high iron content and iron yield, and the effective enrichment of vanadium and titanium elements in the slag is conducive to the subsequent extraction of vanadium and titanium elements; Hydrogen gas as a reducing agent will not cause secondary pollution. The reduction grinding process is expected to achieve comprehensive utilization of vanadium titanium magnetite, with good application prospects, and can further carry out larger scale experimental research.

China's municipal solid waste is generated in large quantities, and the energy it contains is also very considerable. Other wastes in the municipal solid waste are mainly composed of hydrocarbons, which have a high calorific value and can be used in some of the processes in the iron and steel industry. It can achieve the resource utilization of the hydrocarbon component of municipal solid waste,while reducing its own fossil fuel consumption and corresponding carbon emissions. Based on the calculation of material balance and heat balance, the influence of blast furnace injection of municipal solid waste on coal ratio, raceway adiabatic flame temperature, gas properties and blast furnace carbon emission were analyzed and discussed. The results show that the decomposition heat of municipal solid waste is 1 731.69 kJ/kg, which is higher than that of pulverized coal. At a fixed raceway adiabatic flame temperature of 2 121 ℃, the maximum volume of municipal solid waste instead of pulverized coal injection is 73 kg, and at a fixed oxygen volume percent of 22% in the blast, the maximum volume of municipal solid waste instead of pulverized coal injection is 83 kg. The amount of bosh gas decrease with the increase of the amount of municipal solid waste injection. The proportion of H₂ in the bosh gas increases with the increase of the amount of municipal solid waste injection. The production of 1 t pig iron can reduce carbon emissions by up to 169 kg when 40% of MSW pulverized products are inject 1：1 instead of pulverized coal. Based on the calculation of material balance and heat balance, the maximum volume of blast furnace injection of municipal solid waste instead of pulverized coal is 83 kg, which is close to the waste plastics injection rate of foreign blast furnaces. After the injection of municipal solid waste, the raceway adiabatic flame temperature of blast furnace remains within the range of empirical values in China, and the proportion of reducing gas in the bosh gas increases, the bosh gas index decreases, the utilization coefficient of the blast furnace increases, and the carbon emission decreases. The research results of can provide a theoretical basis for the development of pollution and carbon reduction technology by co-disposal of municipal solid waste in blast furnace ironmaking process.

In order to explore the influence of dephosphorization slag structure evolution on dephosphorization effect and phosphorus migration and enrichment behavior at different molten iron temperatures, laboratory experiments were carried out at molten iron temperatures of 1 340 ℃ to 1 420 ℃. The effect of different conditions on the dephosphorization efficiency, and the structural characterization of the dephosphorization final slag after the experiment was carried out by using XRD, SEM-EDS, FTIR and Raman spectroscopy. Thermodynamic theoretical analysis shows that with the increase of temperature, the phosphorus distribution ration decreases gradually. The experiment of hot metal dephosphorization shows that when the temperature of hot metal is 1 380 ℃, the dephosphorization efficiency of hot metal is the highest, too high or too low temperature is not conducive to dephosphorization, and the silicon content of hot metal decreases gradually with the increase of temperature. And with the increase of temperature, the silicon content of molten iron gradually decreases. The results of XRD and SEM-EDS analysis show that phosphorus is mainly enriched in the 2CaO·SiO₂ crystallization region, and the phosphorus-rich phase is composed of 2CaO·SiO₂-3CaO·P₂O₅ solid solution. The increase in temperature will reduce the proportion of phosphorus-rich phase. Raman and infrared analysis results show that the Si—O—Si bond is less affected by the temperature increase. When the temperature is low, the contents of Q¹（Si）, Q²（Si） and Q³（Si） in slag increase. When the temperature rises to 1 380 ℃, the Si—O—Si bond is broken and Q⁰（Si） increases. The silicate structure with low polymerization degree promotes the migration and aggregation of phosphorus, and the phosphorus in the form of Q¹（P） gradually increases. When the temperature is between 1 380 ℃ and 1 420 ℃, the higher molten iron temperature inhibits the migration of phosphorus, and the silicon entering the slag tends to exist in the form of high polymerization degree, and the polymerization degree of slag gradually increases with the desilication reaction. In addition, due to the remarkable increase of FeO₆ octahedron and the improvement of silicate polymerization degree, the migration of phosphorus into the silicon-oxygen network structure was inhibited, and the phosphorus in the form of Q⁰（P） gradually increased and the diffusion degree of phosphorus in slag increased. It can provide theoretical guidance and reference for iron and steel enterprises to solve the problem of excessive phosphorus content in molten iron and control a reasonable pre-dephosphorization temperature.

Complex multivariate and multiphase coupling reactions occur inside the converter. Since the static control model can only consider the beginning and end states of the converter smelting process, it is impossible to know the continuous molten steel composition and temperature changes in the entire smelting process, making it difficult to accurately control the end point of the converter steelmaking. Therefore, the mechanism model of the converter smelting process is of great guiding significance to actual production. Based on the static model, the converter smelting process model is established based on the coupling reaction mechanism, and software that can be used for model calculation is written in C# language. The model can calculate the slag-making agent, coolant, and oxygen consumption required in the smelting process, and can calculate the temperature of the bath, the composition of the bath, and the composition of the slag with the blowing time, and make a more accurate prediction of the temperature, composition, and slag composition of the molten steel end point. By changing the operating parameters of the model, the influence of different oxygen supply intensities on the decarbonization rate and the influence of bottom blown argon air flow on the dephosphorization rate were studied. The results show that the change in oxygen supply intensity has a more obvious impact on the early and mid-stage of the decarbonization process, and it has a smaller impact on the late stage of the decarbonization process. The increase of the bottom blown argon air flow has a greater impact on the early stage of the dephosphorization process, which can increase the rate of the dephosphorization reaction, but with the increase of the argon air flow, the FeO content in the slag decreases, resulting in a decrease in the dephosphorization rate. By comparing the actual data of 100 furnaces of a steel mill converter with the calculation results of the model, it was found that the hit rate of the carbon content of the end point of molten steel in the range of deviation -0.02%-0.02% is 89%, and the hit rate of the end point of molten steel temperature in the range of deviation （t±10）℃ is 83.0%. The deviation between the actual measurement data and the theoretical calculated value within a certain range is small, which has the significance of guiding practical production.

The multi-mode thin plate continuous casting and rolling （MCCR） production line is not only different from traditional continuous casting-hot rolling processes, but also from traditional thin plate continuous casting and rolling processes. Currently, there is only one MCCR production line in China and abroad. The MCCR process adopts high casting speed casting, which has a large steel throughput. The casting speed has a significant impact on the cleanliness of the rolled plates produced by this process, especially the characteristics of non-metallic inclusions in the steel. Based on this, in the current work, the effect of casting speed in the range of 4.7-5.2 m/min on the characteristics of non-metallic inclusions in rolled plates of a low carbon aluminum killed steel produced by MCCR process was investigated employing the automatic scanning electron microscopy. The results showed that the inclusions in the rolled plate were mainly Al₂O₃-CaO type, with the mass percent of Al₂O₃ of 69%-72% and the mass percent of CaO of 16%-22%. The composition of inclusions was almost unchanged with the increase of casting speed. The characteristic evolution of >5 μm inclusions in the plate with casting speed showed an opposite trend with that of >2 μm inclusions. As the casting speed increased, the number density and area percent of >2 μm inclusions in the rolled plate overall showed a slight upward trend, but the average size of inclusions changed little. However, as the casting speed increased from 4.7 m/min to 5.0 m/min, the number density, area percent, and detected maximum size of >5 μm inclusions all showed a decreasing trend, and their fluctuation in the width direction of the rolled plate also decreased. While the characteristics of >5 μm inclusions almost kept unchanged when the casting speed increased to over 5.0 m/min. The phenomenon that the number of large-sized inclusions in steel decreased with increasing casting speed was explained from the perspective of the forces on inclusions at the solidification front. Based on the results, it was recommended to use a continuous casting speed of 5.0 m/min or above when producing low-carbon aluminum killed steels under the MCCR process.

Taking the eight-strand tundish as the research object, through the combination and verification of numerical simulation and physical simulation, explores the influence of blocking flow operation on the temperature field, flow field, liquid level fluctuation, dead zone distribution and inclusion removal rate at the end of casting. And the optimal blocking flow scheme was comprehensively determined to provide theoretical guidance for on-site production. The results show that the dead zone volume fraction can reach 2.0-2.5 times of the original, and the liquid surface wave height is enhanced. When Outlet1 is blocked, the fluctuation of position4 is the strongest. The dead zone volume percent of numerical, physical simulation and dead zone visualization results are 24.9%, 31.7% and 26.2%, respectively. When Outlet3 and Outlet4 are blocked, the fluctuation of position 5 is the strongest. The dead zone volume percent is about 23.5%, 29.6% and 24.3% in numerical, physical simulation and dead zone visualization results, respectively. Compared with the distribution of dead zone and the removal rate of inclusions during normal casting, when Outlet1 was blocked, the dead zone in the remote strand region expanded and the inclusion removal rate increased by 4.87% on average; when Outlet3 was blocked, the dead zone in the middle region expanded and the inclusion removal rate increased by 5.29% on average; when Outlet4 was blocked, the dead zone in the near strand region expanded and the inclusion removal rate increased by 7.61% on average. In addition, when outlet1 is blocked, the maximum outlet response time difference and the maximum average residence time difference under numerical and physical simulation are 14 s and 9 s respectively, and the maximum average residence time difference are 27 s and 18 s respectively. The residence time distribution curve （RTD） has a high coincidence, and the temperature field is more uniform. Therefore, based on the multi-angle characterization results, if the blocking flow operation is necessary in the actual production process, in order to maintain the original flow characteristics of the liquid steel in the tundish and reduce the disorder and blindness of the blocking flow operation, blocking outlet1 strand is the best scheme. In addition, the fluid dead zone critical rate of 0.008 8 m/s can be used for fluid dead zone rate calibration, and its accuracy is mutually verified by numerical and physical simulations.

Aiming to solve the problem of the instability of the flow field and steel slag surface in the thin slab continuous casting mold under high casting speed, the FTSC（flexible thin slab caster） mold and MM-EMBr（multi-module electromagnetic braking） system of a steel company were used as research objects, the LES and VOF model were used as numerical simulation to perform multi physics field coupling calculation on the flow field of mold under different electromagnetic induction intensity, the key is to study the effect of different magnetic induction intensities on the flow field inside the mold and the steel slag interface under the conditions of immersion depth of 190 mm and casting speed of 6 m/min. The results show that without electromagnetic braking, the flow field inside the mold gradually changes from the initial double circulation mode to a single circulation mode as the impact depth increases, the steel slag interface is unstable and fluctuates greatly, the maximum velocity of the steel slag interface exceeds 0.65 m/s, and the maximum wave height exceeds 40 mm, slag entrapment and slag holes appear at the steel slag interface, part of the turbulent kinetic energy of the upflow molten steel is converted into potential energy, which makes the position of the steel slag interface rise gradually and makes the liquid slag layer thinner; after the MM-EMBr system is turned on, when the magnetic induction intensity at position C directly below the SEN is not less than 0.09 T, the speed and angle of the main jet can be effectively controlled to make the impact point of the narrow wall fluctuate up and down within a certain range, so as to control the flow field in the mold; with the increase of magnetic induction intensity, the total turbulent kinetic energy in the mold gradually decreases, when the magnetic induction intensity of AB, C, DE increases to 0.17, 0.15, 0.12 T, the maximum velocity of steel slag interface can be controlled within 0.30 m/s, the maximum wave height can be controlled within 10 mm, the average height of steel slag interface position is controlled within -2-2 mm, and the turbulent kinetic energy of steel slag interface can be controlled within 0.045 J/kg, this electromagnetic braking intensity is the most effective, and the flow field in the mold and the steel slag interface are relatively stable; when the magnetic induction intensity continues to increase, the turbulent kinetic energy in the mold and at the steel slag interface increases instead, it shows that the stronger the magnetic induction intensity is, the more ineffective it is, the best braking effect can be achieved only by the cooperation of all modules.

CVC technology is an advanced flatness control technique that emerged in the 1980s. This technique achieves the desired strip shape control by laterally shifting the working rolls' axes in the rolling mill. The lateral movement helps in obtaining the required convexity of the roll gap, thereby controlling the shape of the outgoing steel strip. During the hot rolling process, changes in the thermal roll profile of CVC working rolls significantly impact the convexity of the roll gap. Accurately predicting the thermal roll profile of the working rolls is crucial for enhancing the precision of strip shape control and reducing roll wear. Taking the 1 780 mm hot continuous rolling production line of a factory as the research object, large-scale finite element analysis software ANSYS/LS-DYNA is used to establish the three-dimensional thermal crown finite element simulation model and the three-dimensional finite element rolling simulation model of the work roll at the fourth stand. The influence of different rolling parameters such as rolling time, rolling speed, and rolling gap time on the thermal crown of the work roll is analyzed. The thermal crown obtained under different rolling parameters is substituted into the rolling simulation model to analyze the influence of different rolling parameters on the strip shape.At the early stage of rolling, the thermal crown of the work roll changes significantly, and the thermal crown of the work roll increases, while the crown of the strip decreases. After 4 000 s, the thermal crown of the work roll reaches a stable state, and the crown of the strip no longer changes. The rolling speed has a smaller impact on the thermal crown, and its impact on the strip shape is also smaller after the thermal crown becomes stable. As the rolling intermittent time increases, the cooling time increases and the thermal expansion decreases, leading to an increase in the crown of the strip. With the increase in strip width, the heat absorption at the edges of the work roll increases, and the thermal crown at the edges of the work roll changes significantly, leading to an increase in the crown of the strip. The simulation results show that rolling time, rolling interval time, and strip width have a greater impact on strip shape, while rolling speed has a smaller impact. The research results can provide references for on-site roll original crown curve design and strip shape control.

Longitudinal variable thickness rolling is an effective technical means to achieve light weight and low loss of rolled products. Different from conventional rolling, the rolling gap changes continuously during longitudinal variable thickness rolling, resulting in the change of rolling force, friction force, length of deformation zone and other important rolling parameters, forming an unstable rolling state, which makes it difficult to accurately predict the plane shape of rolled parts. In order to solve the problem of plane shape prediction in the rolling process of variable thickness, a multi-stage steady-state processing method is proposed. The variable thickness rolling area is divided into several rolling stages along the longitudinal, and each stage is approximately stable rolling state, so that the plane shape prediction problem of variable thickness rolling is transformed into the plane shape prediction problem of multi-stage constant thickness rolling. Each stable rolling stage is divided into several strip elements along the transverse. According to the bar variation method, the transverse displacement of each strip element line is listed as the undetermined parameter in the deformation power function in the deformation zone. According to the principle of energy minimization and variational method, the transverse displacement function of rolling outlet of each element can be calculated. Then, the transverse displacement of the strip elements line after rolling can be obtained by the whole variational calculation of each steady rolling stage. It is proposed that the midpoint of the edge element is the feature point of the plane shape, and the feature points of the edge element are arranged according to the division order of the steady rolling stage, which can form the feature series of the plane shape of the rolled piece. Achieve the prediction of the edge shape of the rolled piece. Based on the principle of metal volume invariance, the longitudinal extension of each element after rolling can be calculated according to the width and thickness of each element. The longitudinal extension of each stage elements are arranged in order and summed to obtain the longitudinal length of each equivalent element. According to the metal flow characteristics in the forward area and backward area of the deformation zone, the longitudinal length distribution of the rolled strip element after variable thickness rolling is transformed into the feature series of the end plane shape, which can predict the end plane shape of the rolled piece. The correctness and feasibility of this method are verified by experiments.

The precipitation behavior of microalloyed carbonitrides in steel is directly related to its strength. For the purpose of revealing the precipitation rule of MX（M=Nb,V and Mo; X=C and N） composite carbonitrides in Nb-V-Mo-N quaternary microalloyed steels with different Mo contents,the precipitation thermodynamic phase diagram,driving force and interfacial energy of MX second phase in austenite and ferrite matrix,as well as the solid solution rule of alloying elements in austenite under the equilibrium condition were calculated using Thermo-Calc software. Besides,the precipitation characteristics of MX carbonitrides under non-equilibrium condition were also studied by field emission scanning electron microscope,transmission electron microscope and electron probe microscope analyzer. The results showed that the MX phases in the 0Mo steel were Nb-rich high-temperature precipitates （FCC_A1#1） and V-rich intermediate-temperature precipitates （FCC_A1#2）. The （V,Mo）C low-temperature precipitates （MC_ETA） were also formed in 0.26Mo and 0.50Mo steels. With increasing Mo content from 0 to 0.50%,the precipitation temperature and the maximum precipitation amount of FCC_A1#1 and FCC_A1#2 did not change significantly,whereas the precipitation of MC_ETA phase was promoted. Moreover,the submicron Nb-rich MX particles precipitated in the high-temperature austenite region could pin the grain boundaries and induce the heterogeneous nucleation of acicular ferrite. The nanosized V-rich MX particles interphase precipitated in the intermediate-temperature two-phase region and randomly precipitated in the low-temperature ferrite region interacted with dislocations and effectively hindered their movement. In addition,the microstructure of 0Mo experimental steel at room temperature was composed of polygonal ferrite and pearlite. With increasing Mo content from 0 to 0.26%,the proportions of polygonal ferrite and pearlite were decreases,promoting the formation of acicular ferrite and a small amount of bainite. When the Mo content further increased to 0.50%,the proportion of ferrite was obviously decreased while that of bainite was increased. The ferrite grain size decreased from （10.2±0.42）µm to （6.7±0.42） µm. The microhardness increased from （223±13.8）HV_0.1 to （318±19.9）HV_0.1,and the yield strength and tensile strength enhanced from （496±5.3） MPa and （618±9.7） MPa to （554±6.7） MPa and （823±13.3） MPa,respectively. By exerting the synergistic effect of various alloying elements in Nb-V-Mo-N quaternary microalloyed system,the precipitation of MX carbonitride was optimized,consequently improving the strength of structural steel.

High strength weathering steel plays an important role in structural steel with its advantages of high strength,weather resistance and light weight. At present,high strength weathering steel usually adopted composition design of high Ti content can inevitably produce Ti inclusion,which deteriorates the properties. Therefore,the high strength steel with high Ti content needs to make up for the lack of performance by appropriately reducing Ti and increasing Nb,and optimizing cooling control meanwhile. Aiming at the Nb containing high strength weathering steel under different finish cooling temperatures,the microstructure was characterized by means of metallographic microscopy,scanning electron microscopy and electron backscattered diffraction. The tensile and impact properties were determined. The effect of finish cooling temperature on the microstructure and mechanical properties of Nb containing high strength weathering steel was analyzed. The results show that a mixed microstructure of ferrite and granular bainite formed in each sample with the finish cooling temperature range from 575 to 650 ℃. With the decrease of the finish cooling temperature,the morphology of ferrite changed from massive to acicular,the content of M/A components gradually decreased,and the average grain size was refined. Moreover,the yield strength,tensile strength,yield to strength ratio and impact energy increased,and the elongation decreased gradually with the decrease of the finish cooling temperature. With the decrease of finish cooling temperature,the grain refinement effect was obvious,the proportion of grain boundary strengthening increased gradually,resulting in the increased yield strength. The fraction of high angle grain boundaries increased,the energy required for impact crack propagation increased,and the impact energy was improved. On the one hand,the decrease of finish cooling temperature reduces the fraction of M/A constituents,weakens the strain hardening ability,and leads to the increase of yield ratio. On the other hand,with the increase of supercooling,dislocation density increases and grain size decreases,and the resistance during dislocation slip increases,resulting in the decrease of elongation after fracture. For this experimental steel,the optimal temperature range is 600-625 ℃.

Structure control of iron oxide scale is an important index to evaluate the adhesion of scale,which directly affects the amount of powder loss and surface quality during product stamping. Currently,Mn element is commonly added to high-strength series steel to improve product strength level. In order to study the influence mechanism of Mn addition on the structure and eutectoid transformation of iron oxide scale,Girder steel with Mn mass percent of 1.8%-1.9% and low carbon steel with Mn mass percent of 0.15%-0.25% were used as the analysis objects. Firstly,the FeO transformation characteristics of Mn-containing steel at different temperatures were observed by thermograys and electron microscopy. It was found that with the increase of holding time at high temperature,the oxygen content in the FeO layer near the interface of Fe₃O₄ easily reached susaturated state and decomposed,forming the characteristics of pre-eutectoid Fe₃O₄ layer transformation. At low temperature,Fe ion migration and diffusion rate decrease in short distance and FeO decomposition change to petal-like Fe₃O₄ in the middle.At the same time,it is confirmed that the nose tip temperature of FeO eutectoid transformation of Mn-containing steel is around 450 ℃. It is found that the eutectoid reaction always starts at the interface of FeO and Fe₃O₄,because there are phase fluctuations and energy fluctuations at the interface of the two phase regions,which creates favorable conditions for the nucleation and growth of the new phase. The eutectoid decomposition of FeO is different between Mn containing steel （1.8%） and low Mn steel （0.18%） at 450 ℃ for 60 min. The eutectoid decomposition ratio of Mn containing steel is only 18%,while that of Mn containing steel can reach 60%. The average interval between the eutectoid sheets of Mn-containing steel was 350 nm by SEM. The layer spacing of low Mn steel is 250 nm. It is found that FeO proportion of Mn steel in hot coil sheet increases under the same process conditions. At last,SEM and electron probe analysis showed that the eutectoid structure （Fe₃O₄ and α-Fe） of Mn-containing steel had obvious Mn emission characteristics during the eutectoid transformation process,which led to the increase of Mn elements in the adjacent undecomposed FeO regions. According to the binary phase diagram analysis,it is found that the dissolution of MnO in FeO can stabilize the FeO phase,reduce the driving force of phase transformation,and inhibit the eutectoid transformation of FeO containing Mn in general.Therefore,it can be seen that the effect of MnO-FeO on the structural transformation of scale needs to be considered for Mn-containing high-strength steel （hot-cold system ）. From the perspective of easy descaling and pickling of cold-rolled high-strength steel,from the perspective of eutectoid scale ratio control of hot-rolled black-scale steel,combined with the characteristics of hot-rolled continuous cooling,the difference matching coiling temperature and cooling mode is the direction of further research.

The capacity of shipbuilding steel for large heat input welding could be significantly improved by Mg treatment. On the one hand,the addition of Mg in steel could refine the inclusions and improve the probability of IAF inducing. On the other hand,Mg could enhance the high-temperature stability of pinning particles,and effectively restrain the coarsening of original austenite grains in HAZ. The high-temperature stability of second phase particles in steel is the key to the effect of Mg oxidation metallurgical,but further in-depth research is still insufficient,especially the influence mechanism of Mg on pinning particles. Therefore,this study starts from the welding simulation experiments of different welding heat input,systematically analyzes the influence of heat input on the constitution of pinning particles in steel,and analyzes and discusses based on the thermodynamics of particle precipitation,thermodynamics of MgO generation,crystallography relationship between particles,and diffusion behavior of elements in steel. The purpose is to ascertain the influence mechanism of Mg on pinning particles in steel. The results show that,for the industrial shipbuilding steel with Mg treatment,when the welding heat input exceeds 200 kJ/cm,some pinning particles will lose their effectiveness. With the increase of welding heat input,the size of pinning particles in HAZ first decreases and then increases,and the more large-sized TiN particles with higher welding heat input. At this time,most pinning particles are composite particles,with TiN-MgO-Al₂O₃ as the matrix,coated with NbC particles on the surface. The results of particle precipitation thermodynamics analysis,MgO generation thermodynamics analysis,particle precipitation mismatch relationship and diffusion coefficient analysis of elements in steel show that,due to the close temperature range of MgO generation and TiN precipitation,and their co-precipitation behavior,MgO-TiN composite precipitates will generate with long-term high temperature,and greatly enhance the high-temperature stability of second phase particles in steel. The results of welding simulation experiment and theoretical analysis show that,with Mg treatment,composite particles with high temperature stability such as MgO-TiN-Al₂O₃ may be generated in steel during continuous casting and large heat input welding processes. However,for the Mg treated steel,the amount of MgO in steel is far lower than the precipitation amount of TiN,which would affect the pinning effect of second phase particles in steel. Therefore,improving the Mg content in steel is the key to improving the capacity of Mg treated shipbuilding steel for large heat input welding.

With the continuous development and utilization of Marine resources,the demand for high-strength steel continues to increase. The cantilever beam,pile leg and lifting electric gear of the offshore platform need the strength of high-strength steel to reach 690 MPa or more,and the corrosion resistance should be better. E690 steel is currently a high strength steel with high comprehensive performance for offshore platforms. With the continuous improvement of the depth of Marine resources development,the environment of high-strength steel used for offshore platform is more and more severe,and it is subjected to seawater erosion and biological fouling in the seawater immersion area for a long time,but also to withstand the damage of waves,low temperature and ocean currents and other harsh sea conditions,the corrosion problem is becoming more and more prominent. Based on the array electrode technology,the corrosion exposure experiment of E690 steel was carried out in the full immersion area of Zhanjiang solid sea environment. The corrosion rate,corrosion morphology and polarization curve of E690 steel were tested and analyzed under the electric connection state. The results show that at the beginning of the exposure experiment,the corrosion current density increases and the corrosion rate increases with the increase of the depth. Due to the influence of temperature and dissolved oxygen,E690 steel formed a macroscopic corrosion battery under electric connection,and galvanic corrosion occurred. The lower sample had a higher corrosion rate as the anode metal,while the upper sample was protected as the cathode,and the corrosion was light. With the extension of exposure time,the corrosion current density and corrosion rate of E690 steel decreased significantly at the later stage of the experiment. The protective effect of corrosion products and attached organisms on the substrate inhibits the anodic dissolution reaction of E690 steel,which is the main factor affecting metal corrosion,while the galvanic corrosion had little effect.

Aiming at the problems of unstable compression process and insufficient mechanical properties of truss structure, a kind of honeycomb truss structure was designed based on board honeycomb structure. Three different parameters of aspect ratio of 1.5, 1.0 and 0.5 were designed by adjusting the height of the structure, and 316L stainless steel was used to prepare the structure by selective laser melting （SLM）. The internal structure of the sample was analyzed by optical microscope and electron microscope. It was found that the sample had small grain size and few internal defects, no macroscopic defects were found, and the overall molding quality was good. The mechanical properties of the structure were also studied by theoretical, experimental and simulated means. The results show that the yield strength of the upgraded structural samples with different aspect ratios is 256, 142, 106 MPa, respectively, which is 524%, 306% and 279% higher than that of the original structure, and the performance of the sample with aspect ratio of 0.5 is the best. The yield strength of the upgraded sample with the same relative density is increased by 159% compared with the original structure. With the decrease of the aspect ratio, the compression process of the sample becomes more stable, and the stress-strain curve tends to be flat in the yield stage. ABAQUS software was used to simulate the quasi-static compression of the designed structure. The simulation results show that the simulated quasi-static compression process of the structure with aspect ratio of 1.5 is unstable, and some members appear to be disturbed. With the decrease of the aspect ratio, the whole process is gradually stabilized and the yield strength of samples is increased. The finite element analysis results agree with the experimental results, and it proves that aspect ratio adjustment of the structure can improve the compression stability of the member. The design method of this truss structure can be applied to the design of other lattice structures, at the same time, the structure can be used as the basic unit of lattice structures and the supporting unit of additive manufacturing, which can provide ideas for improving the mechanical properties of 316L stainless steel samples of lattice structures.

24CrNiMo alloy steel has excellent toughness, hardenability and wear resistance, and is widely used in high-speed train brake discs. There are some problems such as casting defects, low yield and limited forming structure of brake discs prepared by casting and forging. electron beam selective melting（EBSM） is a metal additive manufacturing technology using electron beam as energy source, scanning and stacking point by point, line by line and surface by surface to form three-dimensional entity, which has natural advantages for the integrated preparation of parts with complex forming structure, difficult processing and high precision. Metal materials with fine grain size, uniform composition and excellent mechanical properties can be prepared. 24CrNiMo alloy steel was prepared by electron beam selective melting. The influence of different process parameters on the density, microstructure, hardness and friction wear of the sample was investigated. The results show that the density increases first and then decreases with the increase of energy density. Under the process parameters of current beam 13 mA and scanning speed 5 m/s, the density and hardness of the formed samples are the highest, reaching 98.96% and 355HV_0.3, respectively. The microstructure of 24CrNiMo alloy steel formed by EBSM is mainly composed of granular bainite（GB） and interbainite（Bm）, and the matrix is bainitic ferrite（BF）. With the increase of energy density, the heat input increases, the grain orientation changes from random distribution to （101） and （001） direction, the grain size increases gradually, and the residual austenite content increases. The friction and wear test shows that the shaped sample with energy density of 39 J/mm³ has the highest wear resistance. The main wear mechanisms are adhesive wear and abrasive wear. Residual austenite content and defects are the main reasons for the difference in friction and wear properties. This experiment provides some basic research and theoretical guidance for the subsequent development of EBSM brake disc preparation.

In order to reveal the evolution mechanism of microstructure and mechanical properties of Fe-24Mn-6Si-9Cr-6Ni iron-based shape memory alloy with solution temperature,the alloys were firstly solution treated at 950,1 050,and 1 100 ℃ respectively. Subsequently,the microstructure was characterized by using metallurgical microscope,X-ray diffractometer,scanning electron microscope and transmission electron microscope. The mechanical properties were investigated using tensile tests at room temperature. The experimental results show a significant increase in austenite grain size with increasing solution temperature,along with an increase in lamella length of thermally induced ε martensite and twin size. The solution treated alloy is mainly composed of γ austenite and thermally induced ε martensite. When the solution temperature was increased to 1 100 ℃,α′ martensite appeared in the alloy,which is a novel phenomenon. TEM analyses confirmed that α′ martensite can form at the intersection of thermally induced ε martensite. Tensile tests showed that the alloys solution treated at 950 ℃ had the highest yield and tensile strengths of 350 MPa and 805 MPa,respectively,with an elongation of about 50%. When the solution temperature was increased to 1 050 ℃,the strength decreased due to the increase in grain size,but the elongation can reach more than 70%. With a further increase in solution temperature,the strength and elongation of the alloy decreased,but the elongation was still higher than 60%. The work hardening rate of the alloy decreased significantly at the beginning of plastic deformation and gradually reached a stable value as the strain continued to increase. The work hardening rate decreased with increasing solution temperature at the same plastic strain. The Hollomon equation was used to fit the stress-strain relationship,and it was found that the work hardening exponent increased with the solution temperature when the plastic strain was higher than 0.1.

Front-end fine desulphurization technology of blast furnace gas has become the focus of current research, and the key point is to develop low-temperature, high-activity and long-life catalyst for the hydrolysis of organic sulfur （mainly carbonyl sulfur COS）. Activated carbon （AC） -based catalyst was prepared by co-impregnation method with AC as the carrier and metal oxide as the active component. Furthermore, the effects of the type and the loading amount of metal oxide on the desulfurization ratio and COS hydrolysis ratio of the catalyst were experimentally investigated. Simultaneously, the transformation mechanism of sulfide during the desulfurization process was revealed by utilizing modern analysis and testing technology. The results showed that the removal effect of COS by pure AC catalyst is poor, and the desulfurization ratio and the COS hydrolysis ratio were lower than 30%. The desulfurization property of catalyst can be improved by loading metal oxides. As the loading amount of iron oxide is about 3%, the high-active desulfurization （desulfurization ratio >99%） time is approximately 48 min, and the breakthrough sulfur capacity is 63.72 mg/g. With increasing the loading amount of iron oxide, the specific surface area, total pore volume, and micropore volume of the catalyst are decreased, and the catalyst still has abundant pore structure. Meanwhile, the desulfurization ratio, COS hydrolysis ratio, and breakthrough sulfur capacity are all increased firstly and then decreased with increasing the iron oxide loading amount. When the loading amount of iron oxide is 16%, the desulfurization performance of the catalyst is better, and the high active desulfurization time and the high active hydrolysis （COS hydrolysis ratio >99%） time are about 78 min, and the breakthrough sulfur capacity reaches 104.21 mg/g. By means of BET, XRD, XPS, and SEM, it was found that under the action of the catalyst, COS is firstly hydrolyzed into H₂S, and then H₂S is converted into sulfate and elemental sulfur under the action of oxidation functional groups and metal ions, which are attached to the pores of the catalyst, thus the removal of sulfide is realized.

The Ca content in steel slag is relatively high. Utilizing steel slag as a substitute for natural ore as a Ca source for carbonation reactions to sequester CO₂ is a promising method for both solid waste utilization and carbon reduction. The use of indirect wet carbonation not only significantly improves carbon fixation efficiency but also enables the production of high-purity, high-value-added calcium carbonate products. In this study, AOD stainless steel slag （AOD slag） was chosen as the material. Firstly, chemical analysis and mineralogical analysis were conducted to confirm its high carbon fixation potential. Subsequently, based on the indirect wet method to accelerate the carbonation process, the efficient leaching behavior of Ca from AOD slag was investigated. Orthogonal experiments and single-factor experiments were employed to explore the effects of leaching temperature, hydrochloric acid concentration, liquid-to-solid ratio, and stirring speed on Ca leaching efficiency. Finally, the carbonation reaction was carried out, and the transformation ratio of calcium ions, purity of calcium carbonate, and microstructure were studied using XRD, SEM-EDS, and TG-DTG. The results indicated that hydrochloric acid concentration and liquid-to-solid ratio were the main factors influencing Ca leaching from AOD slag. As the leaching reaction proceeded, the silicate colloids formed by the dissolution of Si-based groups hindered the further leaching of elements within AOD slag. Increasing temperature and acid concentration effectively eliminated the impact of silicate colloids, promoting Ca leaching. Under the conditions of leaching with 1.5 mol/L HCl at 85 ℃, a liquid-to-solid ratio of 50 mL/g, and a stirring speed of 600 r/min, the leaching ratio of Ca from AOD slag could reach 90.51%. Through thermogravimetric analysis, the purity of the CaCO₃ product prepared after indirect carbonation was 96.04%, and the conversion ratio of Ca reached 83.96%. The results provide experimental and theoretical foundations for the efficient resource utilization of metallurgical solid waste by carbon sequestration using steel slag Ca and simultaneous preparation of high-value-added CaCO₃ products.