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.

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.

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%.

Based on analysis of factors on cutting quality of free-cutting steel AISI 1215, with using the process measures including decreasing carbon content in steel from 0. 094% to 0. 072%, during LF refining using silicon-manganese deoxidizing addition and controlling LF refining end active oxygen content 60 x 10 ^-6 - 80 X 10 ^-6, decreasing 140 mm x 140 mm billet mold water rate from 1 900 ~ 2 050 L/min to 1 700 〜1 850 L/min, decreasing secondary cooling water ratio from 1.15 L/kg to 0. 90 L/kg and optimizing rolling process to increase the average diameter of sulphide in steel from original 2.09 μm to 3. 11 μm, the cutting quality of coil of low-carbon high-sulphur (0. 072% C, 0. 365% S) free-cutting steel increases markedly and the surface roughness of parts is about 2 μm to meet the requirement of user.

Low-alloy high-strength fastener stee which is widely used in automobiles， high-speed rail， aviation， aerospace， defense， and other fields due to its excellent mechanical properties and in line with the trend of lightweight development. In recent years， with the continuous progress of industrial technology and the increasing requirements for material performance， the development of low-alloy high-strength fastener steel has shown a new trend. It is expected that the actual practical application strength level of fasteners will exceed grade 16.8. In this paper， through the typical application of fasteners products， firstly it points out that fasteners require good mechanical properties， processing performance， and heat treatment performance. Specific performance and application environment-based evaluation is carried out to ensure safety and reliability. Secondly， this paper analyzes the history and trends of high-strength fastener steel， including high-strength fastener steel， ultra-high-strength fastener steel， and non-quenching high-strength fastener steel， and discusses the role of composition in enhancing steel properties. Then， the paper introduces the research and application of key technologies for high-strength fastener steel， focusing on the design of steel composition， control of non-metallic inclusions， resistance to delay fracture and steel manufacturing technology. The paper also discusses the impact of related content on product performance， in order to enhance the comprehensive performance of fasteners， reduce their hydrogen embrittlement sensitivity， and meet the requirements of intelligent manufacturing， it is necessary to keep the ［H］ content in steel below 1×10-6， further reduce the size of inclusions， and control the fluctuation range of main elements in steel more precisely： w［C］±0.01%， w［Si］±0.02%， w［Mn］±0.02%， w［Mo］±0.01%， the development of low hydrogen embrittlement sensitive bainitic steel is rapidly advancing.At the same time， while environmental regulations become increasingly strict， the concept of green manufacturing and recyclability is gradually incorporated into the production of low-alloy high-strength fastener steel，and the proportion of electric furnace steel smelting and hydrogen metallurgy varieties has significantly increased..Finally， the paper looks ahead to the future of low-alloy high-strength fastener steel， which will move towards high performance， low cost， environmental protection， and intelligentization. With the progress of science and technology and changes in market demand， low-alloy high-strength fastener steel will play an important role in a wider range of fields and provide a solid material basis for the development of modern industry.

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.

Developmental 110SS steel Φ325 mm × 55 mm thick-wall seamless pipe ( /% ：0. 28 ~0.33C,0. 20 ~ 0.30Si, 0.60~1.00Mn, ≤0.015P, ≤0. 005S, 1. 20 ~ 1.45Cr,0. 65 ~0.85Mo,0.01 ~ 0.05Al, 0.01 ~0.05Ti, 0. 01 ~ 0. 05Nb,0. 01 ~0. 10V ) is produced by process of BOF-LF-RH-CC-ASSE1 rolling. By controlling BOF end point [C] ≥ 0. 03% , LF refining slag basicity 3. 0 ~4. 0, HR vacuum treating for ≥30 min, CC steel overheating ≤15 ℃ , continuous casting speed 0, 30 ~ 0. 50 m/min, steel pipe quenching temperature at 880 ℃ and tempering at 650 ℃ , the product inclusion size is less than 20 μm，yield strength is 760 ~820 MPa, at that time, the thick wall seamless steel pipe meets the requirements of hydrogen sulfide-proof.

Haynes 230 is an important candidate material for high temperature components in ultra-high temperature gas-cooled reactors， concentrating solar power and advanced ultra-supercritical coal-fired generating plants.In order to establish the alloy microstructure control criterion， it adopts the hot-rolled forming plate and adjusts the solid solution temperature，the law of microstructure evolution of the behavior of precipitation phase dissolution and the change of grain size during solution treatment were studied，The results showed that the hot-rolled plates were composed of equiaxed austenitic grains with the average grain size of 32 μm. the main precipitation phase was detected to be M6C carbide and the metal cluster M was composed of W and Mo. The carbide content and particle size of M6C varied little and the austenitic grains coarsened little during solution treatments in the temperature range of 950-1 150 ℃. With the increasing of solid solution temperature to 1 180-1 200 ℃， the carbide content of M6C decreased， the particle size decreased， and the grain was coarening；At 1 230 ℃ and 1 250 ℃， the dissolution of M6C and the coarsening of grains became obviously with the average grain size to be 142 μm and 201 μm， respectively. Tensile strength at room temperature and 750  ℃ decreased slightly with the increasing solution temperature ， while tensile strength at 900  ℃ increased. The grain size and the related solution temperature was recommended to be controlled in rang of 76-142 μm and 1 200-1 230  ℃ based on the present experimental investigation， respectively.

 Steel for ultra-low-temperature pressure vessel is steel specifically applied to liquid nitrogen （-196 ℃） and below， and requiring sufficient mechanical strength and toughness under extreme low-temperature conditions. In general， the strength and hardness of steels increase as the temperature decreases， but at the same time this is accompanied by a significant increase in the risk of brittle fracture and a decrease in plastic deformability， creating significant difficulties and challenges in their design and application. Based on the demand for high strength and toughness of ultra-low-temperature pressure vessels at temperature of -196 ℃ and below， and in response to the bottleneck problem that it is difficult to combine high toughness and high strength of steel at ultra-low temperatures， the performance characteristics of steel in ultra-low-temperature environments are introduced from the classification of steel and the current status of the research， respectively. In addition， new methods， processes and research and development progress of steel toughening in ultra-low-temperature environments are summarized， focusing on the analysis of low-temperature toughness mechanisms and strengthening strategies of several typical ultra-low-temperature steels， as well as their tough-brittle transition mechanisms， which mainly include martensitic phase transformation， dislocation motion and twin crystal formation and other micro-mechanisms. The effects of factors such as chemical composition， crystal structure and grain size on the low-temperature toughness of steel are summarized. Finally， based on the existing research results， the preparation and strengthening of steels for ultra-low-temperature pressure vessels are prospected.

The basic alloying elements in super-bainitic steels are C-Mn-Si and the structure of ultra-fine bainite, martensite and residual austenite is obtained by low temperature phase transformation at 300 〜500 ℃. In order to decrease critical cooling velocity, promote bainite transformation, partial super-bainitic steels are added Cr,Ni,Mo etc. alloy elements with decreasing C, Mn content to improve weldability of steel products. The super-bainitic steel has ultra-high strength and better plasticity, and its yield and tensile strength are respectively 〜1 200 MPa and 1 600 ~ 1 700 MPa with elongation ~ 15%. The yield strength of new generation super-bainitic steel is more than 1 300 MPa, and its tensile strength is more than 1 700 MPa.

High-nitrogen austenitic stainless steels exhibit high strength and toughness， strong wear and corrosion resistance， and also possess non-magnetic property along with excellent biocompatibility. These attributes have garnered them extensive attention across a variety of fields， including ocean engineering， energy and chemical industries， national defense and aviation， and biomedical applications. However， in the preparation process， it still faces a series of problems and technical challenges such as inaccurate control of nitrogen enrichment levels， easy precipitation of nitrogen during solidification of high-nitrogen steels to form pores， and precipitation of coarse nitrides during hot working， which limits its large-scale development and application to a certain extent. The development status， preparation process， and strengthening mechanisms of high-nitrogen austenitic stainless steel have been systematically elaborated. Firstly， a review of the domestic and international development history and current research status of high-nitrogen austenitic stainless steel are reviewed. Secondly， the production and preparation processes for high-nitrogen austenitic stainless steel have been summarized， encapsulating various techniques for the melting-casting method. This includes a comparison and analysis of their advantages and disadvantages， such as the Larger Pool Method， Pressurized Induction Melting， Pressurized Ladle Blowing， Pressurized Electroslag Remelting， and Pressurized Plasma Arc Melting. Additionally， an overview of the powder metallurgy process for fabricating high nitrogen steel is presented， which includes methods such as Mechanical Alloying， Gas Atomization， Plasma Rotating Electrode Process， and Solid-state Powder Nitriding. Furthermore， a summary is provided around various forming processes including Hot Isostatic Pressing， Spark Plasma Sintering， Metal Injection Molding， Hot Pressing Sintering， Cold Pressing Forming， and Additive Manufacturing. Ultimately， the discourse delves into the mechanisms underlying nitrogen's fortification role in austenitic stainless steel， encompassing Solution Strengthening， Grain Refinement Strengthening， Strain Hardening， and Precipitation Hardening. Moreover， the dialogue addresses the predominant challenges encountered in the evolution of high nitrogen austenitic stainless steel， proffering a prospective outlook on the field's advancement.

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.

Analysis of phase composition, particle size and hardness of metallographic structure and sulfide inclusions in 1215MS free cutting steel Φ12 mm coil are carried out by means of optical microscope, scanning electron microscope with energy dispersive spectrometer, microhardness tester and thermdynamic software Thermo-Calc. The results show that, the proportion of ferrite in 1215MS steel is 93% -96% ,and the proportion of pearlite is 4% ~5% ; the average equivalent diameter of ferrite is 22.30 μm,the average diameter of pearlite is 16. 83 p.m, sulfide is evenly distributed in the edge of grain boundary and the ferrite,the equivalent diameter of sulfide is 5.077μm, the average Vickers hardness of MnS, ferrite, and pearlite is 80 HV10,100 HV10,175 HV10,respectively.

The annual output of steel melted by converter was nearly up to 190 million tons in China in 2003, which was 85.2% of annual output of steel in China and was 25% of world converter steel output in that year. The number of 50 ~ 300 t converters increased to 134 sets in 2003 from 75 sets in 2001, and the process and technology of converter steelmaking further optimized. the new grade steel and quality steel melted by converter increased very fast including lo w alloy steel, atmospheric corrosion resistant steel, TRIP(transformation induced plasticity steel, and special steel such as alloy structure steel, gear steel, bearing steel and steel for boiler. In the future the converter steel production mainly depended on potential- tapping and revamping of excellent iron and steel producers to further improve technology and equipment, expend ·steel grade range, increase quality of steel, reduce consumption and improve environment.

In view of the high silicon and phosphorus content of hot metal in a steel works, a converter slag-retaining double-slag smelting process is used to obtain a stable dephosphorization rate of hot metal. The specific process is to add slag-forming materials such as lime and sludge balls after the start of the blowing process for 3 min. The oxygen supply intensity is 2. 5 m ³ (t ·min) at 0 ~ 3 min, and 3. 2 m ³/( t ·min) at 3 ~ 4. 5 min. The temperature is controlled at about 1320 °C. After the converter has first deslagging, it starts to blow and adds the late slag forming material. When the carbon monoxide in the furnace rises to a stable level, the oxygen lance position is raised appropriately to improve slagging and control the end-point carbon. The test results show that the average dephosphorization rate of hot metal in the dephosphorization period is 58.09% ,and the average dephosphorization rate of molten steel in the decarburization period is 85. 56% ； When the temperature of the semi-steel is 1320 °C ,the basicity of the slag is 2.0,and the TFe content in the slag is 18% ,a better dephosphorization effect can be obtained in the dephosphorization period. When the molten steel temperature of the converter liquid after first deslagging is 1580 °C ,the basicity of the final slag is 3. 5,and the TFe content in the final slag is 20%, a better dephosphorization effect can be obtained in the decarburization period. [P] _e/[P] _r ratio at the end of the converter is 0. 90. The petrographic composition of the slag during dephosphorization and decarburization poriod from the experiment is suitable for dephosphorization of hot metal.

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.

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.

Based on the requirements of 400 km/h high-speed railway for high fatigue properties of axles， the mechanism of ultra-high fatigue performance of axle was analyze， the key to high fatigue performance was the size of fine carbide and martensite lath. The microstructure parameters such as the width of martensitic lath sheaf ， the distribution of precipitated phases were determined as key control units affecting the yield strength of high-speed railway axle steel. The target microstructure of high-speed railway axle steel was designed， and the optimal alloy composition of 400 km/h high-speed railway axle steel was determined by high-throughput calculation. The developed high-speed rail axle with a speed of 400 km/h had good strength and toughness matching after quenching at 850-950 ℃ and high-temperature tempering at 620 ℃， with a tensile strength greater than 880 MPa and an impact energy of 180 J at -40 ℃. At the same time， the grain size and carbide size of the axle treated by this process are fine， and the grain size is refined to 9.0 level. Both high cycle and ultra-high cycle fatigue performance met the standards. After the overall heat treatment of the axle， the ultra-high cycle fatigue test of the small-sized sample was stable to level 3， and the fatigue limit was 517 MPa at 108 cycles， indicating a high fatigue limit. The overall fatigue performance of the axle was predicted through the sample reduction of the axle， and the predicted values were in good agreement with the actual values. The axle as a whole passed 107 cycles of fatigue assessment under a test force of 320 MPa.

Analysis results show that the center segregation of continuous casting billet is serious, easy to cause cup and cone fracture when the rod is drawn； the non-metallic inclusions in the wire rod cause the wire fracture due to the stress when the wire rod is pulled out and twisted; if the content of O and N in steel is too high, the strength and hardness of steel will increase, and the toughness will decrease； reasonable coiling temperature and cooling rate can ensure the ideal micro structure o£ the wire rod. By controlling [O]≤20 X 10 ^-6, N]≤40 X 10 ^-6,costing liquid superheating ≤25℃,, rolling billet heating at 1100~1170 ℃ and coiling at 910~93O℃ etc process measures the drawing fracture is avoided.

The application status and processing technology of cold extrusion forming steel for steering tie rod at home and abroad are described. The main technical indicators and the performance of the corresponding parts of ordinary quenched and tempered steel, pre-quenched and tempered steel and non-quenched and tempered cold heading steel for steering tie rod are introduced. Production practice shows that compared with ordinary quenched and tempered steel ML40Cr and pre-quenched and tempered steel ESW90, the strength and plasticity of automobile steering tie rods produced by non-quenched and tempered cold heading steel 30MnVS6 can reach the same level, but the impact toughness is significantly lower. The research progress of improving the strength and toughness of non-quenched and tempered cold heading steel is discussed from the four aspects of chemical composition, microstructure, non-metallic inclusion and segregation. By normalizing treatment, the impact energy KV2 of steel 30MnVS6 increases from hot-rolled status 62 ~67 J to 108 ~ 115 J.