In order to reduce the harm of B-type and D-type inclusions in Al deoxidized GCr15 bearing steel， a comparative industrial experimental study was conducted on refining VD low alkalinity slag and normal alkalinity slag. The results showed that when refining slag alkalinity was reduced from 9.34 to 1.96， the proportion of plastic inclusions in the steel increased from 14.81 % to 40.65 %. As the same time， the content of total oxygen （T. O） decreased from 7.7 × 10 ^-6 to 4.9 × 10 ^-6； the content of total aluminum （T. Al） and acid-soluble aluminum （Al _S） decreased from 279 × 10 ^-6 and 210 × 10 ^-6 respectively to 80 × 10 ^-6 and 75 × 10 ^-6. Thermodynamic calculation shows that the increase of ［Si］ activity in the liquid steel causes the decrease of Al ₂O ₃（inc） content in the composite inclusion， and the acid soluble aluminum （Al _S） content in the steel falls within the range of equal aluminum concetration lines corresponding to plastic inclusions， the theoretical calculations are consistent with experimental results. The VD refining with low basicity slag is beneficial for achieving control over the plasticization of inclusions in bearing steel.

The high-end equipment industries in the fields of aerospace， energy， petrochemical， shipbuilding， rail transportation， new energy vehicles， energy conservation and environmental protection， and electronic information have developed strongly， putting forward higher requirements for the quality and performance of special steel and special alloy materials， and the demand has surged. Therefore， in recent ten years， China's special metallurgy industry has been rapidly development. This paper first analyzes and summarizes the new requirements of ultra-high strength steel， supper alloy， corrosion resistant alloy， heat resistant steel， special stainless steel， high performance bearing steel， tool and die steel and precision alloy for the above-mentioned high-end equipment manufacturing. Secondly， the development status and trend of traditional special metallurgical processes and several new special metallurgical processes are analyzed. It is emphasized that the combination with basic oxygen furnace/electric arc furnace steelmaking process can provide high clean consumable electrode for electroslag remelting and vacuum arc remelting， and can also provide pure raw material for vacuum induction furnace. The short process of the electroslag remelting with continuous casting billet as the consumable electrode can significantly improve the production efficiency and reduce the production cost. At the same time， the duplex process of high nitrogen stainless steel smelting and the process flow of powder metallurgy and spray forming of tool and die steel are also briefly introduced. Third， China's special metallurgical industry development status， as well as the progress of new technology and new equipment have been summarized. Finally， suggestions and prospects for the technical development of special metallurgy in China in the next ten years are put forward.

The technical characteristics of electric arc furnace steelmaking with direct reduced iron as a substitute for scrap steel are analyzed， and the main factors affecting the smelting power consumption are expounded . The results indicate that a large amount of steel left in melting pool （≥ 40%） and intensive mixing such as enhanced oxygen supply， bottom blowing， and electromagnetic stirring are important ways to promote melting and shorten the tap-to-tap cycle （which can be shortened by 8%-10%）. The proportion of direct reducing iron exceeds 30%， continuous feeding should be used. The feeding speed in the early and middle stages of smelting is generally equal to the melting speed of 28-33 kg/min （power supply power is 1 MW）. It is necessary to match lime and dolomite to prevent the erosion of slag line， and the whole smelting process should be sprayed with carbon foam slag to ensure the power supply efficiency. To reduce power consumption of smelting， direct reduction iron with high C content， high metallization rate， low SiO ₂ content， low P content， low S content， and higher temperature should be used as much as possible within a certain suitable range （that is， w［C］ 1%-4.5%， metallization rate ≥ 90%， w［SiO ₂］ ≤ 6%， w［P］ ≤ 0.1%， w［S］ ≤ 0.04%）. The compact short process combining direct reduction iron vertical furnace and electric arc furnace is an important direction for low-carbon， energy-saving， and clean production.

In this paper， one 180 t double-hole bottom argon blowing ladle is taken as the research object. Based on the specific production conditions， six modes of argon bottom blowing in ladle are numerically simulated， and combined with the field test， it is compared with the argon blowing mode currently adopted. The results show that： （1） The mixing time of molten steel decreases with the increase of argon blowing amount. When argon blowing amount is constant， the argon blowing mode with differential flow rate is stronger than that with constant flow rate. （2） Different modes of argon blowing at the bottom of ladle have different locations and areas of slag holes. When the total flow rate is constant， the maximum velocity of molten steel surface in the differential flow argon blowing mode is greater than that in the constant flow argon blowing mode， which is easy to cause slag entrapment. （3） The fluctuation of slag layer thickness at the slag line in differential flow argon blowing mode is greater than that in constant flow argon blowing mode， and the greater the flow difference， the more severe the fluctuation. （4） The differential flow argon blowing mode further strengthens the refining effect of molten steel by argon blowing at the bottom of ladle through the cooperation of "strong-weak" streams. And the industrial test shows that the number of larger inclusions in steel is obviously more than that in argon blowing mode （400 L/min-600 L/min） with constant flow rate （500 L/min-500 L/min）.

Using CO ₂ in steelmaking process can realize the utilization of CO ₂ resources， which is a green， low cost， high efficiency and easy to achieve smelting technology. This article was based on the application of steelmaking CO ₂ technology， the development and application of CO ₂ in the converter and electric arc furnace in recent years were introduced. According to the domestic steel enterprises actual production situation， the practical effects of resource application of CO ₂ in energy-saving， consumption reducing， and improving the quality of molten steel in steelmaking process were summarized. It also analyzed the current application status of CO ₂ gas as reaction gas， stirring gas， etc. in steelmaking process. Application of CO ₂ in steelmaking process had the advantages of lower cost， better thermodynamic conditions， stronger stirring ability， and higher gas calorific value， the application prospects can be very broad. The research results indicate that application of CO ₂ in steelmaking process can increase the dephosphorization rate of molten iron by 5% to 7%， and save production costs of over 9 yuan per ton of steel. Resource application of CO ₂ in steelmaking process will be one of the key research directions for achieving higher efficiency and lower cost emission reduction in China’s iron and steel industry. Based on an estimated annual output of crude steel of 1 billion tons in China， application of CO ₂ in steelmaking process can reduce the total CO ₂ emissions of the iron and steel industry about 5%.

The continuous cooling expansion curve of 18CrNiMo7-6 wind power steel was tested by using a Gleeble-3800 thermal simulator at a cooling rate of 0. 1-30 ℃/s. The static continuous cooling transformation curve （CCT curve） of 18CrNiMo7-6 wind power steel was plotted by using metallographic hardness method. The microstructure transformation law of 18CrNiMo7-6 wind power steel under different cooling rate conditions was analyzed. The experimental results show that the Ac ₁ phase transition temperature of 18CrNiMo7-6 wind power steel is 765 ℃， and the Ac ₃ phase transition tempera ture is 843 ℃. When the cooling rate is less than 0. 5 ℃/s， the microstructure of the experimental steel is ferrite and pearlite， and high-temperature phase transformation occurs； At a cooling rate of 0. 5-1 ℃/s， ferrite disappears and plate-like martensite is initially formed； Starting from 2 ℃/s， the microstructure is mainly bainite and martensite， with both medium temperature and low temperature phase transformations occurring simultaneously； After 10 ℃/s， the bainite content de creases and the martensite content increases with the increase of cooling rate； When the cooling rate is greater than 20 ℃/s， the microstructure is entirely martensitic with only low-temperature phase transformation occurring； During the process of increasing the cooling rate from 0. 1 ℃/s to 30 ℃/s， the hardness of the wind power steel shows an upward trend.

In the steel industry is facing the new normal situation of transformation and upgrading， with the help of intelligent equipment to drive the steel industry to green and high-end development is expected to achieve the optimization of the steel production organization. Continuous casting tundish with constant temperature and low superheat can effectively improve the quality of steel， so it is necessary to develop the heating technology of tundish. Therefore， tundish heating temperature control technology has been paid more and more attention. Regarding to the hot issues of tundish plasma heating technology， which has attracted increasing attention in recent years， systematically describes the heating principle and equipment characteristics， introduces the research and development of equipment and metallurgical functions of plasma heating technology at home and abroad， and mainly analyzes the influence of plasma heating technology on the flow field， temperature field， inclusion removal and chemical composition of steel liquefication in tundish， and the metallurgical effect of practical application. Based on the deep understanding of the research and application of plasma heating technology， the new problems found in the heating process of a new type of hollow graphite electrode plasma equipment independently developed in China are discussed， and the ways to further improve its metallurgical effect are discussed. Analysis indicates that the domestically developed hollow graphite electrode plasma heating equipment is better suited to meet the transformation needs of China's steel industry. This equipment provides an effective solution to issues such as the instability of superheat in casting steel， lower cleanliness levels in molten steel， and uneven composition of molten steel. It addresses the shortcomings in the intelligent positioning of the "one-key heating" intermediate package， thus enhancing its precision.

Microstructure and properties of Φ457 mm×70 mm 12Cr1MoVG steel pipe （/% ： 0.13C， 0.21Si， 0.56Mn， 1.07Cr， 0.31Mo， 0.20V， 0.008P， 0.004S， 0.02Ni， 0.004Cu， 0.012 4Al） after 1 000 ℃ normalizing plus using water mist accelerated cooling and 740 ℃ tempering were studied by means of microstructure observation， tensile test ， impact test at room temperature， hardness test and high temperature durability test. The results showed that the microstructure consisted of ferrite and bainite， with the volume of bainite accounting for 65%， and the grain size of 7-5 grade. Yield strength was 416 MPa， tensile strength was 575 MPa， impact energy at room temperature was 206-244 J， brinell hardness was 187HBW. The endurance strength under 575 ℃×10 ⁵ h was 86 MPa. It lasted 51 480 hours at 575 ℃/100 MPa unbroken. After 27 198 hours， it cracked under 575 ℃/120 MPa， and the crack originated from grain boundary creep pores， no serious spheroidization was found in the bainite matrix surrounding. The structure stability was excellent.

According to the analysis and assumption of the low-carbon development of the iron and steel industry， the future iron and steel production and manufacturing processes will gradually evolve into three categories： blast furnace-converter long process， all-scrap electric arc furnace short process and hydrogen metallurgy-electric furnace process.The key factors affecting the carbon emission level of the three types of processes include process structure， raw material structure， energy structure， product structure， equipment level， management level， technical level， etc. This paper uses the "carbon peak and carbon neutrality" analysis model （CISRI-CPCN） constructed by China Iron and Steel Research Institute to draw a carbon reduction roadmap for the three types of processes.The research results show that the carbon emission of the three types of processes decreases annually. From 2020 to 2060， the CO2 emission of the long process will be reduced from 2.0 t/t （steel） to 0.87 t/t （steel）， and carbon neutrality can be achieved through carbon sinks， carbon trading and other means. In 2050， the short process will be reduced from 0.45 t/t （steel） to close to 0， which is expected to achieve "near-zero carbon" smelting. In 2060， the hydrogen metallurgical electric arc furnace process （50% scrap steel + 50% hydrogen direct reduced iron raw material structure） will be reduced from 1.31 t/t （steel） to close to 0， basically achieving carbon neutrality. Comprehensively considering the development needs of the national economy， it is recommended that the steel industry gradually adjust the product structure of the three types of processes in the development of steel industry  reduction in the future. The product structure of the long process should gradually transform into the production of flat products， especially high-end flat products， which are mainly distributed in coastal deep-water port areas. The short process should take the long products for construction as the entry point， gradually replace the small and medium-sized blast furnace-converter process， and partially produce single varieties such as combined steel and other high-quality special steel or stainless steel， mainly in the layout around cities with rich scrap steel resources. At present， the hydrogen metallurgy-electric furnace process is still in the stage of exploration and development， and many difficulties in green hydrogen， economy， technical reliability and engineering needed to be overcome.

As one of the indispensable core components of advanced aero-engine， nickel-based single crystal turbine blades （hereinafter referred to as single-crystal blades） have extremely demanding requirements in terms of dimensional accuracy of the hollow structure， uniformity of alloying element distribution， and metallurgical quality of the surface and inner cavity. It is found that the control of temperature gradient during directional solidification directly affects the performance and quality of single crystal blades， and whether the continuous acquisition of stable heat flow becomes the key of directional solidification .With the continuous progress of computer technology， numerical simulation has become one of the important methods of single crystal blade directional solidification research. Firstly， introduce the single crystal blade technology is introduced and the heat transfer method in the directional solidification process is then analyzed.Secondly， the optimization methods of boundary conditions of interfacial heat transfer coefficient for numerical simulation are summarized， focusing on the application of Beck's inverse method and finite difference method in the solution of interfacial heat transfer coefficient. The results proves that the two methods can be used to solve the interfacial heat transfer coefficient between castings/shells， where the accuracy of the simulation of the temperature field can be effectively improved.Finally， the research progress of numerical simulation of the temperature field during directional solidification is also traced， and the influence of process parameters on the temperature field is summarized. Based on the analysis of the research progress of numerical simulation of temperature field during directional solidification of nickel-based single crystal turbine blades， the optimization direction of the directional solidification process and the subsequent development trend of the related technology are proposed to promote the research and development process of single crystal turbine blades.

Melt flow-VAR simulation method was used to study the effect of melting rate on the molten pool shape and macro segregation of low-cost corrosion-resistant high-strength stainless steel ingot during vacuum arc remelting， the morphology of molten pool changed form "shallow flat" to "U-shap"， and finally to "deep V-shap"， with the increasing of melting rate from 3.2 kg /min to 6.2 kg /min and the metal pool volume was gradually increased. The depth of molten pool increased from 120 mm to 175 mm with increasing the melting rate from 3.2 kg /min to 5.2 kg/min. When the melting rate exceeded 5.2 kg/min， the time to reach steady state was extended， the proportion of ingot cylindrical crystals increased， and the segregation degree of alloying elements was intensified. 4.2 kg /min was determined as the actual melting rate， the mushy zone width was narrow， and the molten pool depth was 140 mm in the stable melting stage. The metallurgical quality of the ingot remelted at 4.2 kg/min was evaluated， the alloy compositions at different positions of the ingot at the said melting speed had good uniformity， the result of macrostructure inspection showed that there was no obvious macrostructure defects in the ingot. After homogenization at 1 220 ℃ for 4 h， the micro segregation of C， Cr， Ni and Mo elements in the steel was significantly improved .

The disc cutter is the key component of the shield machine， and it is also the most easily worn and failed component in the tunneling construction process. The wear of the disc cutter ring is mainly composed of three types of abrasive wear， adhesive wear and fatigue wear， among which abrasive wear and adhesive wear are the main wear mechanisms. In the process of rock breaking， strong extrusion and high impact make the cutter ring often wear， eccentric wear， blade， fracture， blade collapse， shedding and other failures. The cost of cutter ring loss accounts for 5%-10% of the total project， and the maintenance and replacement of cutters caused by the cutter ring failure greatly reduce the engineering construction efficiency. At present， the commonly available materials for cutter rings are DC53 and H13 steels， and their wear resistance and impact toughness depend on the type， morphology， size， quantity， distribution and matrix structure characteristics of carbides in those steels. In order to inprove the performance of the disc cutter ring， domestic and foreign scholars have carried out a series of studies on the optimization of alloy design for the cutter ring， the one-time forming preparation of the cutter ring， the induction heat treatment preparation of the gradient performance cutter ring， and the development of the bimetallic composite cutter ring， which provides a strong support for the performance enhancement of the cutter ring.

With the gradual improvement of the system science system， the iron and steel production mode has undergone a transformation from the empirical mode to the scientific production mode due to scientific innovation and development， the iron and steel industry with the characteristics of the process system can apply the system engineering approach to think and analyze as a whole， with the technical means of systems science to abstract the complex electric arc furnace steelmaking process description， the complex involving multiple states of matter and energy states of the electric arc furnace The abstraction of the steelmaking process into a unit system with material and energy transformation as constraints， a comprehensive understanding of the energy and material transformation process in the electric arc furnace steelmaking production， the constraints additional process timing factors， you can establish a process model for the simulation of the production process， for the actual working conditions of the electric arc furnace smelting process system analysis and abstraction， to be able to establish a process control model with process operation as the control factor， for the actual production of furnace charge It can analyze the key process factors affecting the technical and economic indexes， solve the problem of "synchronization" of target temperature and carbon content， and achieve the production effect of shortening the smelting cycle of single furnace by 2 minutes.

Additive manufacturing （AM） of high-strength steels has become one of the main technological directions in the field of metal additive manufacturing. Firstly the research progress and frontier dynamics of AM metallic materials and technologies are traced， the relevant studies on the key grades of three types high-strength steels has been analyzed respectively， including low alloy ultrahigh-strength steels， high alloy ultrahigh-strength steels and stainless high-strength steels， the relative works on powder metallurgy， printing process， heat treatment， microstructure and mechanical properties of various typical high strength steel have been summarized in detail.Secondly it focuses on the typical applications and main achievements of AM high-strength steels at home and abroad. Furthermore， in view of current shortcomings in the development of the system establishment of AM high-strength steels， relevant suggestions are put forward in three aspects including the forward design and research of special alloys， the development of large-scale high-precision and intelligent facilities， and the system construction of standards. Based on the analysis of research and application progress of AM high-strength steels， the focus of key areas direction and the further development trend of relevent technologies are proposed， in order to further promote the industrial application of AM high-strength steel.

According to the research and production status of 300M steel for commercial aircraft landing gear in China， the production process and fatigue properties of 300M steel by single vacuum melting process in China are introduced. The relation of fatigue strength， tensile strength and fracture toughness， and fatigue crack source inclusion species of 300M steel for domestic commercial aircraft landing gear are analyzed， and the market potential， future green development direction of 300M steel for commercial aircraft landing gear in China is prospected. Through research and tackle key problems， China has formed 300M steel technology by single vacuum smelting for commercial aircraft landing gear. Fushun Special steel and Bao Wu Special Metallurgy have established process production system with mass production capacity on 300M steel by single vacuum smelting.With the development of production technology， it is necessary to focus on the performance stability， purity and fatigue performance of the material， strengthen control during production， continue to optimize the melting and forging process， reduce energy consumption and costs， accumulate data and improve the material standard system. At the same time， the single vacuum 300M steel of ϕ1 080 mm and more larger ingot type is developed， which is fully in line with international standards in quality， standards， costs and certification

In order to improve the problems of low oxygen supply intensity and long smelting cycle of 210 t large converter in a domestic steel plant， the parameters of the currently used six-hole oxygen lance nozzle were optimized and the jet dynamics characteristics were defined by numerical simulation. The results showed that： When the lance position was less than 1.5 m， the change of axial velocity did not change significantly with the Angle. When the lance position was more than 1.5 m， the decrease of axial velocity increased with the increase of the nozzle Angle. The coalescence behavior of jet was obviously improved with the increase of dip Angle. The effective kinetic energy of the jet decreased rapidly with the flow of the jet， when the lance position was 1.5 m， it only accounted for about 20% of the initial kinetic energy， and then the kinetic energy attenuation slowed down， and the kinetic energy loss was only about 5% when it reached 2.7 m. The optimized design parameters of the six-hole oxygen lance of 210 t converter are as follows： inclination Angle 15.5°， Mach number 2.06， throat diameter 45.89 mm， outlet diameter 61.14 mm. The industrial test results show that the optimized oxygen lance can reduce the oxygen blowing time by 43 s and increase the dephosphorization rate by 11.4%.

By establishing three-dimensional physical and mathematical model of gas-liquid flow in 180 t RH including vacuum chamber， immersion tube and ladle ， using VOF two-phase flow model and FLUENT software numerical simulation ， the influence of side-blown argon nozzle arrangement and gas flow rate on gas-liquid two-phase circulation flow in RH is studied. The effects of jet flow rate and upper and lower spacing on the void fraction of the outlet section of the riser， the outlet velocity of the riser and the downcomer and the circulating flow rate are analyzed as the jet holes arranging in a single layer and in a double-layer staggered arrangement. The results show that argon rises along the wall in the upward tube and carries the molten steel upward. The gas content in the cross section of the tube increases gradually along the direction of movement， and the gas content reaches the maximum at the outlet section. The smaller the void fraction of the outlet section of the riser is， the larger the central velocity of the outlet section of the riser and the outlet section of the downcomer is， the larger the circulating flow is， and the shorter the mixing time is. The double-layer arrangement of the jet pipe， reducing the spacing and increasing the blowing volume are beneficial to the improvement of the circulating flow rate and the shortening of the mixing time.

With the continuous improvement of material requirements for high-performance aviation engines， the degree of alloying and the mass fraction of the γ' phase in new nickel-based superalloys for high-temperature applications continue to increase. This leads to progressively more challenging melting processes for these alloys. High-alloyed wrought nickel-based deformation superalloys are generally produced through a triple combination process of Vacuum Induction Melting （VIM） + Protective Atmosphere Electro-Slag Remelting （PESR） + Vacuum Arc Remelting （VAR）. Due to the influence of alloying degree， alloys are prone to solute segregation and elemental partitioning between liquid and solid phases during the melting process， making electrodes and ingots susceptible to cracking under the combined effects of thermal stress and phase transformation stress. This not only causes arc fluctuations during the subsequent remelting process but also adversely affects the quality of the ingots. Electrode crack formation is a complex metallurgical defect that occurs in the solidification process of superalloys and has been a common technical challenge that has long plagued the expansion of ingot sizes for high-alloy， difficult-to-deform superalloys in China. Therefore， this paper reviews the recent research progress of the author’s team and research groups at home and abroad in the crack formation mechanism， influencing factors of crack and crack control of wrought nickel-based superalloys， and looks forward to the future development direction of wrought superalloy precipitation strengthened nickel-based superalloys.

Super austenitic stainless steel （SASS） has been developed widely for industries like marine， environmental protection， chemical industry and other harsh conditions. Due to the higher degree of alloying， the solidification segregation is more serious during solidication process ， and the precipitation phases is many and complex. In this paper， the microstructure composition and evolution law of precipitated phase of super austenitic stainless steel S31254 during solidification were analyzed with thermodynamic calculation software Thermo-Calc， as well as the function of major alloying elements Mo、Cr、Ni、N during solidification and their influence on microstructure evolution， the effect of Mo-Cr element interaction on the evolution of coagulation phase organization. The results indicate that the liquidus and solidus phase line temperatures of this steel grade is 1 394.4 ℃ and 1 358.6 ℃ respectively. The equilibrium solidification path is L → γ ， and non-equilibrium solidification path is L → L ₁+γ→L ₂+γ+δ→γ+δ+σ. Mo segregation is the main cause of the σ precipitation， and the content of Mo in the liquid phase of δ and σ phases precipitation is 8.5 % and 11.3 % respectively.

In this paper， the main research object is the deformed superalloys that have passed the national acceptance， identification or batch production， which are included in the China Superalloy Manual （2012 edition），through a large number of literature research， the role of Nb in deformed superalloys is summarized. The results show that Nb is not only the main solution strengthening element， but also the main precipitation strengthening element in superalloys. In the solution strengthened superalloy， NbC and Z-（Ni _0.04Cr _0.83Fe _0.13）1.9（W _0.15Mo _0.09Nb _0.76） _3.3 N are mainly Nb formed， which can significantly improve the creep strength of the alloy， reduce the creep rate， and ensure the good welding process performance of the alloy； In precipitation strengthened superalloys γ′- Ni ₃（Al，Ti）、γ″-Ni ₃ Nb、δ-Ni ₃ Nb、ε- Ni ₃（Nb，Ti） and Laves-（FeCoNi） _1.84（NbTiSi） etc are mainly Nb formed， and good comprehensive properties can be obtained by controlling the changes of the size， morphology and distribution of the precipitated phase. At present， nearly 30% of deformed superalloys are strengthened by Nb， and the development of modern superalloy materials has been inseparable from the participation of Nb.