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 melting method of nickel-based superalloy is the decisive factor related to the alloy quality. Vacuum induction melting can effectively control the content of O， N， H and other gases and harmful impurities in alloy ingots， and accurately control the alloy composition. On this basis， the remelting of alloy （electroslag remelting and vacuum arc remelting） can further reduce the content of S， P and other harmful impurities， eliminate the defects such as component segregation and shrinkage cavity， and optimize the control of the solidification structure， so as to achieve the melting of large size and high-quality alloy ingots. This paper reviews the progress of the melting process of nickel-based superalloy， and focuses on the principles and characteristics of common melting technologies including vacuum induction melting， electroslag remelting， and vacuum arc remelting. The research progress of "vacuum induction melting + protective atmosphere electroslag remelting"， "vacuum induction melting + vacuum arc remelting" duplex melting process and "vacuum induction melting + protective atmosphere electroslag remelting + vacuum arc remelting" triple melting process in nickel-based superalloy melting are discussed. Finally， some suggestions on the selection and development direction of nickel-based superalloy smelting process are propounded.

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.

Cr12MoV flat steel mainly adopts the long process of die casting ingot， multi-fire forging and rolling， which has low production efficiency， low yield， high cost and high energy consumption. In order to solve the problems of poor thermal conductivity and ductility of cold working die steel， a short process of 90 t EBT-LF-VD-150 mm×630 mm continuous casting rectangular billet and one-fire heating +15-pass rolling was designed. The rectangular continuous casting billet and rolled 19 mm thick flat steel products of Cr12MoV steel were successfully developed， continuous casting center porosity 1.5 grade， center segregation ≤1.0， the finished flat steel eutectic carbide unevenness level ≤3， the defects inspection quality grade reaches grade A， and the performance indexes meet the standard requirements. Cr12MoV cold working die steel products have achieved mass production and achieved good economic benefits.

Serious white spots defect occurs on the surface of (4.4～4.6) mm×2050 mm wide-thick cold rolled strip of 316L stainless steel (/%:0.02C,17. 12Cr,10. 15Ni,2.06Mo) for tank container in production process. The causes of the white spots are researched by means of feature analysis, steels grades comparison and on-site defect tracking, the results show that there is much emulsion on the surface of cold rolled strip, on which the formed oxide scale is unevenly distributed in case of incompletely degreasing and annealing at 980 ℃,the color of the oxide scale on the surface with much emulsion is white, these white oxide scales are changed into white spots after pickling. Besides, the influencing factors of the residu al emulsion on the surface of rolled strip and the removal effect of residual emulsion are systematically studied. By applying oil scraping system for nonwoven-fabric roller, adding air knife purging system, controlling emulsion concentration 1.5%~ 3% and temperature(55±3)℃,repairing two sets of magnetic filtration system in rolling process, through controlling de- greasing electrical conductivity7.5 μs/cm and loop filling speed 50 m/min,adjusting9～12 area Furnace temperature to 1030 ℃,the unqualified rate of white spots is reduced from 10% to 0.5% or less.

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）.

Φ1200 mmS355NL/Q355NE steel (Ceq0.38-0.41) continuous casting round bloom is manufactured by 100 t KR-BOF-LF-RH-R18M continuous casting process. Full protective casting, precise cooling process, three-stage electro- magnetic stirring, slow cooling process and other technical measures are adopted. The superheat is controlled at 1545 ℃, the drawing speed is 0.14-0.20 m/min, the electromagnetic stirring is 300 A/2 Hz, the secondary cooling water ratio is 0.20 L/kg, the slow cooling time into the pit is ≥72 h, and the pit exit temperature is ≤300 ℃. The results show that [0]≤0.0018%,[H]≤0.00008%; the central porosity of cast bloom≤1.5  rating, the central crack≤1.5 rating, the shrinkage cavity ≤0.5 rating, and the carbon content range of the whole section≤0.07%. Chemical composition, macrostruce, surface quality all meets the standard requirements. After the round bloom is forged into wind turbine flanges with wall thickness of 450-550 mm by customer, the test results of inclusions, mechanical properties, internal flaw detection and other quality indexes are satisfactory, which fully meet the technical specifications and user requirements.

The Peroxidation of molten steel at the end of the converter will not only lead to the decrease of alloy yield and the increase of smelting cost， but also lead to the increase of deoxidation products and the poor cleanliness of molten steel. Therefore， it is always the key point of process control to avoid the peroxide of molten steel at the end of converter. Aiming at the problem of terminal peroxide of 100 t converter in a domestic factory， this study finds that the average scrap ratio of this factory is up to 26%， the average terminal C content is only 0.055%， and the average terminal temperature is 1 605 ℃. Without considering the heat balance in the furnace， the adoption of high scrap steel batching resulted in insufficient heat in the furnace， which forced the supplementary blowing to raise the temperature， resulting in a low hit rate of the terminal carbon and temperature， and then lead to the problem of molten steel peroxidation. Therefore， from the perspective of optimizing the burden design， this study establishes the calculation model of the maximum scrap ratio based on the raw material conditions of the plant. In the actual production， the raw material conditions are comprehensively considered to add scrap， which reduces the number of heats requiring supplementary blowing for temperature rise. After the application of the model， the end point temperature of converter increases by 10 ℃， the end point carbon content increases by 0.036%， and the oxygen content of molten steel decreases by 206.3×10 ^-6. The data shows that the effect of cost reduction and quality improvement is significant.

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.

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 surface depressions and longitudinal cracks of 2Cr13， 3Cr13， and 4Cr13 casting billets produced through 4-machine and 4-strand continuous casting machines in a special steel plant were analyzed and studied， the surface depression and longitudinal cracks of Cr13 stainless steel billet were solved by processing measures. Pre-melting mold flux consisting of 28%-31% SiO ₂ ， 28%-31% CaO ， 6%-9% Al ₂O ₃ ， 7%-10% Na ₂O and 3%-6% F ^- were used， and comprehensive carbon preparation， especially the addition of carbon black was increased； the total carbon content was 15%-18%. The basicity of mold flux was controlled at about 1.0， the melting temperature was 1130-1150 ℃， and the viscosity at 1300 ℃ was 0.40-0.55 Pa·s. The turning temperature of the mold flux was 1140-1180 ℃， and the crystallization rate was about 48.8%. The superheat of 2Cr13 liquid steel in the tundish should be less than 30 ℃， and the superheat of 3Cr13 and 4Cr13 liquid steel should be less than 35 ℃. Automatic slagging is adopted in continuous casting process to control appropriate slag layer thickness and keep liquid level stable.

The practical application of particle dephosphorization with compound injection agent on 130 t electric arc furnace is carried out. The composition of dephosphorization slag system in the oxidation period of electric furnace is designed, basicity of slag is controlled between 2.2-2. 8, and the content of iron oxide is controlled between 15% -20%. The composite powder of carbon powder (15% -20%), CaO powder (40% -60%), MgO powder (25% -30%) and CaC powder (5% - 10%) prepared in a certain proportion is injected with nitrogen as the carrier. After adopting the smelting process of injection compound injection agent on EAF steelmaking of 40Cr, 0.45C steel, 20CrMnTi and 60Si ₂Mn etc alloy steels, the reaction area of flux is accelerated, the slag forming speed is improved, and various production indexes are improved. Among them, the power consumption per ton steel is reduced by 90 kWh/t, the steel material consumption per ton steel is reduced by 9. 3 kg/t, the flux consumption per ton steel is reduced by 4. 8 kg/t, the productivity is increased by 5% -6%, and the comprehensive production cost per ton of steel is reduced by 25 yuan/t.

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.

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.

By using combination teachnology of 20 t EAF-LF-VD, 20 t argon protection ESR unit remelting, 1 250 ~1 280 ℃ high temperature homogenization treatment, 60 MN oil pressure quick forging machine multiple forging and 1 000 〜1 050 ℃ high temperature solution treatment process, the inclusion(≤0.5 rating) , structure and lateral impact energy (KV2 25 〜31 J) of produced 640 mm x 1 100 mm 4Cr5Mo2V heavy die steel are higher than the requirement in standard NADCA#207-2018 for advanced steel leave,and the isotropy of steel reaches 0.95.

The technological measures to control oxygen content of gear steel in 100 t EAF⁃LF⁃VD⁃CC⁃CR whole process are put forward. The rotary bending fatigue properties， fracture and inclusion size of gear steel 20MnCr5 with oxygen content 0．000 53％ ~ 0．001 45％ are investigated. The results show that the higher the oxygen content， the larger the size of maximum inclusion and the lower fatigue strength of steel， while [O] ≤0．001 0％ ，with [O] decreasing， the fatigue strength of steel decreasing within a narrow range； the critical inclusion size of the test steel without fatigue crack under the surface is 21 μm and the shallow zone 30 ~ 430 μm away from the surface is relatively safe zone， where inclusions are difficult to cause fatigue cracking．

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.

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 .