In order to effectively reduce and control the non-metallic inclusions in a GCr15 bearing steel produced by BOF→LF→VD→CC process and improve its product quality， the characteristics and evolution mechanism of inclusions in bearing steel produced by the whole process were analyzed firstly by methods of systematic sampling， automatic analysis and scanning of inclusions and thermodynamic calculation in the present study. The results show that the inclusions in molten steel are mainly MgO-Al ₂O ₃ and Al ₂O ₃ after the slag melting during LF stage， and they are transformed into CaO-MgO-Al ₂O ₃ and CaO-Al ₂O ₃ with the size of 1-5 μm in the end of the LF stage. The type of inclusions remains unchanged after VD soft blowing. However， the inclusion density decreases from 16.53 pcs/mm ² in the end of the LF stage to 14.02 pcs/mm ²， resulting in an inclusion removal rate of approximately 15.2%. The number density of inclusions in the tundish increases to 16.39 pcs/mm ². The types of inclusions are still mainly CaO-MgO-Al ₂O ₃ and CaO-Al ₂O ₃， of which 1-2 μm and ＞ 2-5 μm size accounted for 62.8% and 35.6%， respectively. The number of CaS-containing compound inclusions in the billet increases significantly. Thermodynamic calculation explains the evolution causes of the above inclusions. It is found that when the w［Al］ _s is at 0.02%， the stable existence of MgO-Al ₂O ₃ is associated with a significant variation in Mg content， ranging from 0.000 3% to 0.01%， which facilitates the formation of MgO-Al ₂O ₃ or CaO-MgO-Al ₂O ₃ type inclusions during the production of GCr15 bearing steel. The T.Ca/T.O ratios of the molten steel in LF ending， VD soft blowing process， and tundish were observed to be 0.39， 1.0， and 0.62， respectively； these values align with the theoretical （T.Ca）/（T.O） ratio range （0.13 to 1.25） conducive to the formation of five distinct types of calcium aluminate. As a result， a substantial quantity of calcium aluminate inclusions was detected. During the cooling process of the molten steel， a transformation of inclusions occurs. The liquid calcium aluminate inclusions diminishes， while the quantities of MgO·Al2O3 and CaS inclusions markedly increases.

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.

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.

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.

This article presents the smelting practice of 9Ni steel for ultra-low-temperature pressure vessel in a certain steel plant by the "BOF → LF → scraping slag/fetching slag → LF → VD → CC" process. The decarburization and desulfurization in the BOF + LF process require that the steel produced by the converter has a low phosphorus （w［P］） ≤ 0.009%） and carbon content （w［C］） ≤ 0.05%）， with an average desulfurization rate of 74.3% and an average decarburization rate of 51.2%. The control of phosphorus content is more difficult than carbon content in the production process. In the scraping slag process， the average phosphorus reversion rate in the molten steel is 16.89%， while in the fetching slag process， it is 22.61%. Although the scraping slag process results in a lower phosphorus reversion rate in the molten steel， the processing time is increased by 15 to 20 minutes， and the average molten steel loss is increased by 3.1 t per heat. After adjusting the addition of nickel plates from the converter to the ladle furnace， the average nickel recovery rate increases by 3.74%. Through optimizing the production process， the molten steel in the tundish meets internal control requirements for phosphorus（ P）， sulfur （S）， nitrogen N， total oxygen （T.O）， and carbon （C）， ensuring high purity of the molten steel， the macrostructure center segregation of the cast slab reaches 1.0～1.5 grade in class C， the internal and surface quality of the cast slab are good. The rolled steel plate exhibits excellent performance at -196 ℃.

Effect of different alloying processes on inclusions of 18Cr ultra-pure ferrite stainless steel during refining process were investigated by using industrial experiments and thermodynamic calculations. The results showed that the inclusion type of 18Cr ultra-pure ferrite stainless steel before titanium alloying is CaO-Al ₂O ₃-MgO， and the inclusion type changes to CaO-Al ₂O ₃-MgO-TiO _X after titanium alloying. After titanium alloying， the number density of inclusions and the weight percentage of TiO _X in Nb-Ti double stable heats number （Ti： 0.181%， Nb： 0.147%） are lower than those in single Ti stable heats number （Ti： 0.324%）.

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.

In the light of problems of smelting ultra-low phosphorus steel (%/： <0. 03C、<0. 01 OP、<0. 015S、< 0.06Mn、vO. 02Cr、<0.02Ni), the lower liquid temperature at 90 t BOF tapping and serious overoxidation of liquid, led to heating refining by LF, are tested and studied by process optimization. The results show that during BOF (0. 018% - 0. 025% P) tapping process by adding lime and refining slag to produce slag with binary alkalinity 7 and P2O5 <0.5%, the dephosphorization rate of liquid in ladle reaches up to 75%, the phosphorus content of finished products is less than 0.010%, the smelting time is shortened by 3 ~ 4 min. At the same time, the dephosphorization rate of ladle decreases with the increase of liquid steel temperature at the end of converter blowing, the BOF optimum end-point temperature is between 1 630 °C and 1 655 °C. By adopting ladle dephosphorization technology, the smelting process of ultra-low phosphorus steel is shortened to converter blowing—►RH treatment—►continuous casting, and the LF refining process is omitted.

In accordance with the current in electroslag remelting(ESR)GCr15 bearing steel D inclusions exceeding the standard problem,the different slag systems are designed,and respectively with the help of Factsage software and empirical formulae to calculate the melting characteristics of the slag system,viscosity,electrical conductivity and other physical parameters,using laboratory slag metal balance experiments and field 2.5 t electroslag remelting experiments,the results show that, the optimal ESR slag system is 55CaF ₂-25Al ₂O ₃- 15CaO-5MgO.With use of the optimal slag system the average total oxygen content in steel is 41.98% lower than that with the traditional slag system,and can reduce the change in the total oxygen content of steel in different locations of electroslag ingot; as compared to the original slag system the number of 1-5  μm inclusions  decreases by 31.25%.Through the slag system on inclusions control,it can improve class D inclusion in GCr15 bearing steel,rating level reaches 0.5,and can better“clean”electric slag ingot.

The research and application achievements of die casting steel materials in China are introduced.By studying the influence of alloying elements on material properties of die material, a new die casting die steel with low Si, V and Ni, CO and W has been developed. By reducing the content of S in steel, using RE to change the shape of inclusion and optimizing forging process, the isotropic properties of the die-steel can reach more than 90%；To make a comparison between conventional electric slag, gas shielded electric slag and vacuum consumable  process remelted three die-casting material,  nitrogen in steel is respectively  150×10 ^-6,90 ×10^-6 and 40×10 ^-6, oxygen content in steel is respectively 24×10 ^-6, 15×10 ^-6 and 6×10 ^-6; By ASPEX Explorer metal quality analyzer inclusions index statistics and analysis of three kinds of technology, using vacuum consumable smelting exponential decline in non-metallic inclusions, non-metallic inclusions and no larger than 5 um, material impact performance boost, 7 mm × 10 mm gap impact energy can reach 450 J；To develop high-end die-casting mould material microstructure, the non-notched impact evaluation index standard and specification are established with the development of integrated die casting technology, the future mold material shall develop toward large-scale, super pure, high precision and long life direction.

The process of ultra - pure 316H steel for nuclear power produced by 20 t EAF-AOD-LF-VD-Φ430 mm elecrode-Φ590 mm ESR ingot-homogenizing treating-Φ310 mm forged bar flowsheet is studied by means of composition calculation ,smelting process and electroslag slag analysis, homogenization annealing process test and other methods. When the composition satisfies 0. 042% ~ 0. 047% C, ≤ 0. 55% Si, 1. 60% ~ 1. 80% Mn, 17. 00% ~ 17. 30% Cr, 12. 20% ~ 12. 40%Ni,2. 50% ~2. 60% Mo, ≤ 5 x10 ^-6H, ≤ 30x 10 ^-6 O,0. 055% ~0.070%N, the Φ430 mm electrode is remelted with CaF ₂： Al ₂O ₃: CaO =60%: 30%: 10% slag system electroslag into Φ590 mm ESR ingot, then homogenization treated at 1 200 ~ 1 250 °C for 30 h, it can produce products to meet the standards, that is inclusion rating units- A and C being 0, B _thin 0.5,B _thick being 0,D _thin 1. 0,D _thick 0 -0. 5 and Ds being (0 ~0.5) ；ferrite content ≤ 0. 5% .

Based on the development and current situation of domestic special steel smelting technology of high strength steel, the special smelting technology of the high strength steel, ultra-high strength steel and ultra-high strength stainless steel produced at Fushun Special Steel are summarized and analyzed. The typical new material special melting technology and preparation process in the field of ultra-high strength steel at Fushun Special Steel are briefly introduced, and the technology bottleneck and current situation of high quality special steel in industrial production are analyzed and discussed.

Focusing on the characteristics of rolling bearings, the types of bearing steels, and the gap between bearing steels at home and abroad, this paper summarizes the art of the status of the requirement of the bearing steel of the high-end equipment, the types of the bearing steels, the processing equipment and metallurgical quality of the bearing steels, the heat treatment technologies, and the evaluation technologies for both metallurgical quality and performance. It is put forward that the important role to improve the rolling contact life of the bearing steel by ultra-purification technologies among different melting routes, the new heat treatment technologies and the new bearing steel developments. This paper pointed out that it needs to be done in the future through the refinement, the homogenization and the stabilization of the inclusions, carbides and the matrix of the bearing steel to improve the quality and performance of existing bearing steels, to develop the high performance heat treatment technologies, to innovate the high performance bearing steel and to strengthen the basic research on the mechanism of the fatigue-resistance of the bearing steels, which would finally enhances the rolling contact fatigue life of the bearing steel significantly.

The mechanical properties of 40CrNi2Si2MoV martensitic steel are affected by the large size carbides，the strength and toughness of martensitic steel can be effectively improved by optimizing the composition design and reasonable heat treatment process. The effects of M ₆C carbide on mechanical properties and microstructure of ultrahigh strength steel were studied at different quenching temperatures （860 ℃-1150 ℃）， and the evolution of M ₆C particle size， quantity and composition was studied by means of SEM and TEM. The results show that large M6C particles reduce the toughness of ultrahigh strength steel， and the M ₆C particles in the 880 ℃ quenching sample are large （~400 nm）， which is easy to cause stress concentration around the large M ₆C carbide ， weaken the binding force between the matrix and M ₆C carbide， and easy to crack around M ₆C carbide， resulting in material fracture.With the increase of quenching temperature， the size and quantity of M ₆C particles in the test steel decrease， and the concentration of Si in M ₆C particles is increased， and the atoms in M（Fe， Mo， Ni， Co） ₆C are replaced by Si， which improves the stability of M ₆C carbide. The size of M ₆C particle in the 1050 ℃ quenching temperature test steel is 25 nm， and the growth of the original austenite grain （8.5 μm） is inhibited. The strength of the test steel is 2227 MPa and the elongation is 7.0%， achieving a good strength and toughness matching.

The 125ksi grade 15Cr super martensite stainless steel exhibits excellent high strength and high toughness matching， and corrosion resistance to CO2， which making it a promising material for oil well pipes exceeding a depth of 7 000 m. This paper comprehensively discusses the control technology for achieving high strength and high toughness in 15Cr super martensite stainless steel tubing through composition design， production process optimization， and microstructure regulation. In terms of composition control， a δ ferrite-free composition design is employed with a chromium content （ w[Cr]） of 15%， nickel content （ w[Ni]） ranging from 6.5% to 7%， carbon content （ w[C]） between 0.01% and 0.03%， and copper content （ w[Cu]） varying from 1.25% to 1.5%. The appropriate combination of chromium and nickel elements plays a crucial role in reducing the δ ferrite content， while the optimal balance between carbon and copper contents is key to obtaining superior mechanical properties characterized by high strength and high toughness. Regarding the smelting process， this study investigates the influence of impurity elements on electric furnace steel. The results show that vanadium （V）， nitrogen （N）， and aluminum （Al） impurities increase the hardness of the 15Cr steel alloy.and raise the tempering temperature to 550 ℃-575 ℃， which can reduce the hardness and ensure the toughness. Concerning hot processing and molding techniques， the dynamic recrystallization behavior are obtained through hot deformation tests conducted on the15Cr steel alloy. The optimum hot perforation deformation temperature for seamless pipe manufacturing falls within 1100°C to 1150°C as it facilitates grain refinement via fine recrystallized grains formation. Microstructure regulation involves determining an appropriate normalizing temperature during heat treatment processes. The research results suggest that normalizing at temperatures ranging from 950°C to 980°C helps maintain grain size without significantly grown， while the match of high strength and high toughness can be obtained.

The flexible bearing steel with long fatigue life using for robot harmonic speed reducer has been successfully de⁃ veloped by applying EAF process technology. The ratio of scrap to hot metal was controlled more than 80%. This paper compared the metallurgical quality of flexible bearings and traditional rolling bearings in terms of non-metallic inclusions， austenite grain size and carbide banding structure， the fatigue strength of steel used for flexible bearing and traditional roll⁃ ing bearing under 107  cycles was tested by the method of rotary bending fatigue test. The O content of steel used for flexible bearings of robot harmonic reducer was less than 0. 000 4%， the Ti content was much less than 0. 001%， non-metal inclu⁃ sions of class A sulfide≤1. 0 grade， non-metal inclusions of class B and D oxide ≤0. 5 grade. The size of the maximum spherical inclusion was less than 30 μm. The test results show that the flexible bearings have ultra-high purity. By increas⁃ ing Al and N chemical composition in the smelting process， the austenite grain size was 10 grade in the flexible bearing steel， much higher than 8. 5 grade in the traditional rolling bearing steel. The proportion of carbide banding structure of 7. 1 and 7. 2 grade was higher than that of traditional bearing steel in the means of extending the high temperature diffusion time. The ultra-high austenite grain size and the decrease of the width of carbide banding structure showed that the flexible bearing steel had an ultra-high structure uniformity. In addition， the rotary bending fatigue strength of the flexible bearing steels was 1 016 MPa， its fatigue life was slightly higher than that of the traditional rolling bearing steels.

In order to investigate the stress corrosion cracking behavior of ultra-high strength stainless steel， the influence of Nb microalloying on the corrosion fatigue properties of Cr-Co-Ni-Mo series ultra-high strength stainless steel was studied by OM， XRD， TEM and other testing methods in combination with corrosion fatigue test. The results show that the steel has stress corrosion sensitivity in 3.5% NaCl solution， and the stress corrosion cracking mechanism of the steel was a mixed mechanism involving hydrogen embrittlement and anodic dissolution. Niobium alloying improved the corrosion fatigue performance of the steel， that is， the corrosion fatigue strength of steel increases from 440 MPa to 495 MPa after adding 0.11% Nb. The main reason is that niobium alloying refined the grain size of steel， promoted the precipitation of irreversible hydrogen trap of NbC in steel， and increased the amount of prior austenite grain boundaries， the proportion of low-angle grain boundaries， the number of Σ3 grain boundaries， and the volume fraction of austenite in steel.

 Investigated the effects of three different methods of cold treatment （air cooling to room temperature， 0 ℃ ice water treatment ， -73 ℃ cryogenic treatment） on the microstructure and properties of S46500 ultra high strength stainless steel after solid solution holding at 982 ℃ and aging treatment at 510 ℃/4 h . The results showed that： After -73 ℃ cryogenic cooling treatment， the tensile strength and yield strength were increased respectively by 292 MPa and 295 MPa， compared to the sample cooled to room temperature. Plasticity and toughness decreased slightly， elongation reduced from 13% （room temperature） to 10.5% （cryogenic temperature）. The impact was reduced from 64 J （room temperature） to 48 J （cryogenic temperature） .With the decrease of cold treatment temperature， the reverse austenite content gradually decreased， and the austenite content decreased from 8.2% to 6.6% compared with that of cryogenic temperature at room temperature .

The chemical composition of C97D2-E wire rod for MT grade steel cord was designed by increasing carbon content and Cr alloying to improve the strength of cord steel. A new solidification heat transfer model was established by using Scheil-Gulliver solidification micro-segregation theory to guide C97D2-E continuous casting process， and the defects of central segregation， porosity and internal crack of continuous casting slab were solved. After optimization， the carbon segregation index of semi-finished product can be controlled within 1.05. The air-cooling process was optimized by using specially designed tuyere nozzle and“optiflex” device of Stelmor ， after air-cooling process optimization， the spacing between the layers of wire rod sorbite was obviously reduced， and the sorbite plate was more straight， the lamellar space of the rod was controlled at 89 nm， the particle size of the pearlite was more uniform and smaller， and the size of the pearlite was controlled at 20 μm； the tensile strength of finished steel wire reached 4 089 MPa， there was no delamination during torsion and no broken wire during laying to 5 000 m， which can meet the requirements of 2×0.30 MT steel cord.

Through the standard detection and rating the metallurgical quality of the high clean bearing steel prepared by vacuum degassing process， such as chemical composition， macrostructure， carbide inhomogeneity and non-metallic inclusions， and quantitative analysis of the quantity， type， size and cleanliness index of non-metallic inclusions in the steel is carried out by Aspex scanning analyzer. Based on the rolling contact fatigue life test results， the relationship between non-metallic inclusions and bearing steel contact fatigue life was established. The results show that the oxygen content of high clean bearing steel is not more than 0.000 5%， the titanium content is not more than 0.000 8% and the large particle inclusions DS is not more than 0.5， however it is still a contact fatigue failure mechanism dominated by inclusions， among which the size of oxide inclusions are large and there are holes around the inclusions， which is easy to cause stress concentration and fatigue cracks. The maximum size of oxide inclusions in high clean bearing steel is controlled below 10 μm， and the rated life L10 under 4.5 GPa high contact stress is more than 1×107 times， which is expected to replace electroslag remelting bearing steel for high-speed rail， high-speed machine tool spindle， wind power spindle and other high-end equipment fields.