The formation mechanism of surface defects, including the independent linear defect, independent tarpaulin defect, the mixture of linear and tarpaulin defect, and the shallow pit defect on the hot rolled SPA- H coil in Shougang Company was studied. The morphologies of defects and microstructures were examined using metallographic microscope, scanning electron microscope and energy dispersive spectrometer. It was concluded that the formation of both linear and tarpaulin defects and their mixture should be closely related to the two factors: Oxide scale that contains both silicon oxide and chromium oxide; The copper enrichment in the oxide scale near the steel matrix. The shallow pit results from the debris of broken tarpaulin which was rolled into the steel during the finish rolling.

MA island is an important part of some steel structure, whose content has a certain effect on the mechanical property such as ductility and strength. In this experiment, the quantitative method of MA island was analyzed. In the quantitative analysis, the samples were polished and eroded at first, and the MA islands were invaded into white. Then the confocal microscope was used to collect images, and the MA island had obvious contrast with the matrix organization. By using Sisc- Ias8 metallographic analysis software of Zhongkeyi and according to the two value segmentation to quantitate, the quantitative results of MA island were obtained. And finally the application of quantitative methods in the dual phase steel was described. The experiment showed that the quantitative technique of MA island could make up the deficiency of the previous quantitative analysis method, and rapidly and accurately analyze the percentage content of MA island in the steel structure.

Titanium-bearing blast furnace slag can be directly used to make raw materials such as concrete, slag wool and concrete blocks, but its valuable vanadium and titanium resources cannot be effectively utilized. China's titanium-bearing blast furnace slag reserves are large and still growing at a rapid rate every year. Therefore, the extraction of titanium resources from titanium-bearing blast furnace slag has become a research hotspot. Based on the review of the relevant research on the extraction technology of titanium from blast furnace slag, the process, advantages and disadvantages of the extraction technology of titanium from blast furnace slag from different enrichment forms such as ferrotitanium alloy, titanium dioxide and titanium tetrachloride are summarized, and the feasibility of each process is analyzed and discussed, hoping to promote the sustainable and healthy development of titanium resources and achieve the purpose of comprehensive utilization of resources.

By means of numerical simulation, taking a 300 t converter in a steel mill in the north as the prototype, a three-dimensional model of the bottom blowing converter was established. The effect of argon blowing at the converter bottom on the mixing effects of converter under the non-uniform gas supply system was studied, and the design scheme was optimized. The results showed that with the increase of bottom blowing argon flow rate, the average velocity and the average turbulent kinetic energy in the molten pool increased, and the proportion of the weak flow zone decreased, but the proportion of dead zone decreases less. When the argon flow rate of a single plug brick was 440 m³/h, the average velocity of the flow distribution ratio of 1∶1, 2∶1, 3∶1 and 4∶1 was 0.189, 0.204, 0.167 and 0.168 m/s, respectively. And the dead zone ratio was 17.5%, 11.60%, 23.53% and 20.23%, respectively. The mixing effect of converter was the best when the flow distribution ratio was 2∶1, followed by 1∶1 and 4∶1, and the worst was when the distribution ratio was 3∶1.

In order to obtain the appropriate Nb content in the Nb microalloyed H13 steel, the primary carbide in H13 steel was taken as the research object, and the H13 steels melted in the laboratory with different Nb mass fraction addition were analyzed to study the precipitation mechanism of the primary carbide. The results showed that when the Nb mass fraction in H13 steel is lower than 0.03%, the primary carbide in the H13 steel was mainly the V-rich phase. When the Nb mass fraction in H13 steel reached 0.05%, the primary carbides were mainly the V-rich phase and the Nb-rich phase. Therefore, the Nb mass fraction in the Nb microalloyed H13 steel should be lower than 0.03%. The Nb mass fraction had a significant effect on the precipitation sequence of the primary carbide in the FCC phase. As the Nb mass fraction increased, the precipitation sequence of carbide in FCC phase changes from V-rich phase to Nb-rich phase, and the thermal stability of the Nb-rich phase was much higher than that of the V-rich phase. The theoretical calculation results were basically consistent with the experimental observations, and the industrial test results also demonstrated the results of this study.

According to the production practice of multi-section billet caster, from the point of view of process and equipment design and production practice, the following ideas are put forward. The total length of the secondary cooling zone is 7 685 mm and divided into four zones, and the fourth zone is refined into the fourth zone + the extension zone of the fourth zone to adapt to the production of multi-section and multi-steel with higher casting speed. The distribution ratio of the secondary cooling zone is 0.33-0.39-0.19-0.09 (the extension zone of the fourth zone is closed) and 0.35-0.39-0.12-0.14 (the extension zone of the fourth zone is opened) and the water ratio ranges from 0.3 to 1.2 L/kg. The unique quick change assembly of complete wanter and mist nozzle for secondary cooling can save section change time up to 2.5 h. The best installation position of final electromagnetic stirring of each sectional production is 9.2 m from the meniscus. The full leaf spring hydraulic vibration and continuous straightening technology are adopted. The multi-section billet caster designed according to the above ideas can achieve high casting speed, good quality billet, high operation rate of continuous caster, and provide practical experience for the transformation or design of the same type of continuous caster.

In order to investigate the effect of uneven heating during annealing on the sheet microstructure and forming property, cold rolling and continuous annealing were applied on the hot-rolled SAE1010 low carbon steel plate. The microstructure of the edge and center of hot-rolled, cold-rolled and annealed steel plate was investigated. The tensile and bending tests were carried out on the edge and central samples of the annealed plate. The results showed that a small amount of island-shaped pearlite in the hot-rolled specimens was distributed at the ferrite grain boundary and the grain size of the edge area was smaller than that of the central area. And partial lamellar cementite in the pearlite was degraded to be spherical. The microstructure of the cold-rolled sheet was characterized by the grain breakage along the rolling direction. There were many larger grains and granular cementite clusters in the edge area of the annealed steel, and the microstructure of the central area was relatively tiny and uniform. The elongation of the core material of the annealed sheet was higher than that of the edge, while the strength was smaller than that of the edge. After 180° bending, the core steel plate did not crack and the edges appeared cracks. The annealing temperature uniformity had an important influence on the microstructure and property of SAE1010 low carbon steel sheet.

The high voltage electron microscope was employed to perform electron beam irradiations on SUS316L austenitic stainless steel with a dose of 3.6 dpa at 350, 400, 450 and 500 ℃. The effect of the electron beam radiation on the swelling rate of material at different temperatures was discussed by observing and analyzing the number density of void, the dislocation loop and the swelling rate in the sample after irradiation. The result showed that the second defects such as dislocation loops and voids, occur in the samples at different temperatures. The radiation swelling was caused by voids. And the swelling increased with the increase of temperature in the region of 350-450 ℃, and reached the maximum at 450 ℃. Above 450 ℃, the swelling rate decreased. Under different temperatures, the two kinds of secondary defects had different sink strength to the point defects, and the swelling rate was related to the proportion of dislocation loops and voids in the microstructure. The experimental study on the relationship between the irradiation swelling rate and secondary defects provided the basis for further understanding the mechanism of radiation swelling and seeking the method of restraining irradiation swelling.

There is a strong possibility that edge cracks may occur in cold rolling process of 980 MPa level dual- phase steel. And the main reason was the formation of bainite phase and the heterogeneous precipitation of carbides, which mainly occurred in the tail of the hot rolled coil. The main reason for the formation of bainite was that the temperature of hot rolled coiling was higher than that of bainite, and the temperature of the edge of the steel coiling was lower. As a result, the edge entered the temperature region of bainite. The reason for the heterogeneous precipitation of carbides was that after the coil rolled off the hot line, the temperature dropped through the ferrite area, ferrite was formed and the carbide was precipitated. At the same time, the cooling speed of the edge was faster, and the carbide can not achieve the homogenization distribution and spheroidization. Cracks may easily occur in the bainite, the ferrite and bainite binding zone, and the carbide segregation zone during cold rolling. In the subsequent production, under the strip tension and shear force by roll surface, cracks extended along the original direction, and the severe case can result in the strip- break. Increasing the hot tail coiling temperature, lining into the slow cooling pit or reducing the coiling temperature can inhibit the three kinds of crack sources, and reduce the formation of edge cracks and the risk of strip- break.

Activated carbon for granular desulfurization and denitrification was prepared from raw coal, coal tar, asphalt and activated carbon powder. The effects of different activated carbon powder additions on the reconstituted strength and desulfurization performance were investigated. The research showed that with the increase of the amount of activated carbon powder, the wear resistance and compressive strength of the reconstituted desulfurization and denitration activated carbon showed a downward trend. The desulfurization value increased gradually with the increase of the activated carbon powder amount. The desulfurization and denitration activated carbon with excellent product performance and high resource recovery rate can be prepared under the condition that the carbon powder in the mixed coal powder was 15%-23%. The corresponding wear resistance, compressive strength and desulfurization value range were 97.01%-97.40%, 56.63-63.57 daN and 28.92-29.54 mg/g, respectively.

The microstructure and mechanical properties of the 340 MPa-grade cold-rolled high strength low alloy (HSLA) steels with and without orange peel defects were analyzed. The results show that the yield point elongation of the stress-strain curve of the defective steel plate reaches 3.73%. The yield extension is too large, which leads to the orange peel defect on the surface of the stamped front windshield beam connecting plate. In the laboratory, the technique of the pre-stretching of the steel sheets is used to simulate the skin pass and stretching straight process for the industrial production of the steel sheets. With the increasing the pre-deformation amount, the length of the yield platform of the sample decreases, and when the pre-tension amount exceeds 1.8%, the yielding platform of the sample disappears. Further analysis of the microstructure reveals that the high annealing temperature leads to the coarse grain size and the abnormal grain orientation, which is the root cause of the "orange peel" defect of the stamped steel plate. In the annealing process, the reasonable control of leveling and tension straightening can eliminate or shorten the length of the yield platform of the test steel and avoid the occurrence of orange peel defects on the stamping parts.

The effects of different coiling temperatures on the microstructure and properties of C-Si-Mn-Al hot-rolled high strength steel used for mixing tank were studied in the laboratory. And the structure and mechanical properties of the tested steels at different coiling temperatures were analyzed and studied by several techniques such as laser scanning confocal microscope (LSCM), scanning electron microscope (SEM), and electron backscatter diffraction (EBSD). The experimental results showed that ferrite and pearlite were obtained by coiling at 580 and 550 ℃. Ferrite and bainite were obtained at 400 ℃. Ferrite, bainite and martensite were obtained at 300 ℃. And Ferrite and martensite were obtained at 150 ℃. As the coiling temperature decreased, the tensile strength and hardness of the tested steel gradually increased, and the elongation gradually decreased. The tensile strength of the tested steel coiled at 300 ℃ was 1 029 MPa and the Vickers hardness was 342.6. The tensile strength coiled at the 150 ℃ was as high as 1 265 MPa, the Vickers hardness reached 360.7, and the yield ratio reached the lowest, only 0.58.

The precipitation behavior of the second phase particles in P- bearing high strength IF steel was studied by using stress relaxation method on Gleeble- 3500 thermal- mechanical simulator. The results showed that the stress relaxation curve could be divided into three stages because of the pinning effect of precipitates of alloy elements on the dislocations and grain boundaries, and therefore the precipitation- time- temperature （PTT） curve showed a typical "C" shape. The precipitation temperature at the nose point was about 850 ℃, with the precipitation- start time of 14 s and the precipitation- end time of 246 s, respectively. With the extension of the isothermal relaxation time, the amount of the second phase particles increased gradually, and the appearance grew coarsening during this process. The spherical shape Ti4C2S2 and TiC precipitates were observed. The FeTiP precipitate, which presented as the bar or rectangular shape, was found in the second phase particles because the focused steel was alloyed with P element. Caused by the segregation of P at the grain boundary, the FeTiP precipitate was mainly located along the grain boundary.

Shendong bituminous coal has the characteristics of high moisture content, which has different effects on its production, transportation, storage or application in blast furnace injection. In view of this characteristic of Shendong bituminous coal, five representative high-water Shendong bituminous coal from different mining areas were selected to explore the effects of moisture on its grindability under the condition of different drying time, and the blast furnace coal injection simulation test device was used to study the variation trend of the combustion rate with the moisture content. The water loss mass fraction under different conditions to the analytical moisture content was defined as the water loss rate to explore the relationship between grindability and burning rate relates and the water loss rate. It could be concluded that when the water loss rate increased, the coal grindability and combustion rate both showed an upward trend. With the increase of drying time, the grindability increased slowly. With the increase of water loss, the combustion rate and combustion rate showed an approximately linear growth.

To study the vacuum arc remelting process by means of computer simulation technology has gradually grown into a new trend. This method not only helps to ascertain the influences and mechanism of various technological parameters on the vacuum arc remelting process, but also can effectively predict the stability of the remelting process as well as the metallurgical quality of the ingot. Hence, the development history and the scientific research findings of the numerical simulation of the vacuum arc remelting process in the past 30 years were briefly introduced. Meanwhile, the research progress and the application status of the vacuum arc remelting model, the metal molten pool model and the microstructure model were reviewed in detail by taking the smelting process simulation, the macroscale simulation and the micro-scale simulation as the breakthrough point. Finally, a new development direction was proposed for the further development and application of numerical simulation of the vacuum arc remelting process in China.

The proper amount of silica in the raw material of the sinter production contributes to the formation of the sintered binding phase, but the high silica content increases the liquid phase viscosity and adversely affects the mineral composition of the sintered binding phase. The influence of high-silica iron ore from Brazil on the sintered binding phase is still unclear. Therefore, the micro-sintering method was used to investigate the liquid phase fluidity of the mixed ore in different proportions of the high-silica ore powder. Based on the principle of "K-value method", the semi-quantitative analysis of its minerals was carried out to obtain the content of minerals such as fayalite, calcium fayalite and calcium silicate. The results showed that with the increase of the ratio of the high-silica iron ore powder in the mixed ore, the liquid phase fluidity of the binding phase decreased, and the mineral contents such as fayalite and calcium silicate also increased significantly. Based on this, the method of improving the reactivity of the mixed ore was used to improve the liquid phase fluidity of the sintered binding phase and reduce the content of fayalite and calcium silicate.

Bearings are amongst the most vital steel components in the modern industry, and the main failure mode of bearings is the rolling contact fatigue (RCF) in the subsurface. In order to better understand the RCF failure process of bearing steel, the rolling contact fatigue process of bearing steel from two aspects of mechanics and materials science was first described, proposing that the essence of RCF process was a subsurface microstructural alternation process caused by the interaction between dislocation and carbon atoms. Then it introduced the engineering model and theoretical model for predicting the RCF life of bearings, pointing out that the combination of engineering models and theoretical models along with the combination of microstructural alternations under cyclic loading and RCF life were two important directions for future work. Finally, the problem of whole-process and multi-scale design for bearing steel was prospected, and the important work ideas of coupling physical metallurgy algorithms with artificial intelligence algorithms as well as multidisciplinary intersection were put forward.

The continuous development of China′s industrial manufacturing field in recent years has posed new challenges to the research, development and manufacturing of domestic bearing steel. The development and production of high-quality bearing steel has become one of the urgent problems to be solved in the domestic bearing industry. The research progress of bearing steel at home and abroad is comprehensively discussed in terms of the classification of bearing steel, the main influencing factors of bearing steel performance and the development of heat treatment technology and so on. In order to realize the quantitative production and application of domestic high quality bearing steel, the methods of process optimization, control of inclusions and carbides, lack of testing equipment and technical evaluation indexes for the development of high quality bearing steel in China are put forward.

For high-quality weathering bridge steel, it is not only required to have excellent low-temperature impact toughness, but also to have higher requirements for its corrosion resistance. The effects of different calcium treatment processes on low-temperature impact and corrosion resistance of weathering bridge steel were studied. The test results showed that compared with the traditional calcium treatment process, the improved calcium treatment process improved the yield of [Ca] in molten steel. In this way, the calcium treatment process was sufficient and the test steel plate with better low-temperature impact performance was obtained. Compared with the original calcium treatment process, the impact energy of the test steel increased by 5.3% at －20 ℃and 7.5% at －40 ℃. Compared with ordinary Q420qE steel, calcium treatment II increased the relative corrosion rate from 43.5% to 32.40%. Moreover, the rust layer of accelerated corrosion specimen had clear texture and relatively high density. XRD analysis result showed that the content of the α-FeOOH crystalline phase in the rust layer reached 91.8%, and the corrosion resistance was improved.

The effects of the superheat of the steel in tundish, electromagnetic stirring current, secondary cooling intensity, casting speed and sectional dimension on the central equiaxed crystal ratio were investigated through the macro examination of oriented silicon steel slab. The results showed that under the test conditions, when the superheat of the steel in tundish was controlled within the range of 14-18 ℃, the change of the central equiaxed crystal ratio caused by the difference of the superheat was small, and the variation range was only 0%-3%. The influence of the electromagnetic stirring current and the sectional dimension of the slab on the central equiaxed crystal ratio was obvious. With the increase of the stirring current, the central equiaxed crystal ratio increased, and it decreased when the sectional dimension of the slab increased. The influence of the secondary cooling intensity and casting speed on the central equiaxed crystal ratio was relatively small. With the increase of the secondary cooling intensity, the central equiaxed crystal ratio decreased, and it increased when the casting speed increased.

In order to solve the problem of the uniformity of coke charging in large-scale coke dry quenching furnace, the coke charging process of 260 t/h large-scale coke dry quenching furnace in Shougang was analyzed by using three-dimensional discrete element method. It was concluded that with the increase of the bell angle, the tip of the coke stack gradually moved toward the center. When the bell angle was 50°, the difference between the coke quality and coke particle size in the x-axis and y-axis directions was the smallest, and the distribution was more uniform. The increase of the stockline level caused the summit of the coke stack to gradually move towards the wall of the reserve chamber. When the stockline level reached 11 m, the double peak shape of the coke stack disappeared, which was not helpful to control the uniform decline of coke in coke dry quenching furnace. Therefore, the best stockline should be less than 11 m.

A three-dimensional steady-state mathematical model was established for the 160 mm×160 mm billet mold with Fluent software. The surface velocity of the mold and the flow field state of the molten steel in the mold were taken as the main reference targets. The corresponding immersion depth of the nozzle in the under different casting rate conditions was simulated, and the numerical simulation results were verified by water simulation. The results showed that when the casting rate of the billet mold was 1.7-1.9 m/min and the immersion depth was within the range of 80-100 mm, the flow field in the mold was suitable, and there was no slag entrapment caused by the violent fluctuations of the liquid level. The research results can provide theoretical guidance for the development of a reasonable casting process for the billet continuous casting mold.

Central soundness and carbide defects of bearing steel bars are closely related to the internal quality control of bloom castings. Taking GCr15 bearing steel as the research object, a two-dimensional longitudinal solidification and heat transfer model was established for the casting process of the bloom semi-products. The accuracy of solidification model is verified by field temperature measurement. Based on the theory of compensating the local solidification shrinkage and controlling the central shrinkage cavity under the soft reduction at the end of solidification, the reasonable soft reduction interval in the pasty region can be revealed through the accurate prediction of the solidification process. Among them, under the conditions of casting tests, the effective soft reduction interval corresponding to the solid phase ratio of the center of the casting is from 0.30 to 0.75, which refers to 16.4-22.5 m from the meniscus. The test results showed that the solidification structure and morphology of the bloom castings are little affected by soft reduction. However, after soft reduction, the central porosity index drops from greater than or equal to 1.5 to 0.5-1.5, which can meet the rolling requirements, and the central shrinkage cavity is basically disappeared, indicating that reasonable soft reduction position and moderate soft reduction amount can obviously improve the degree of central porosity and central shrinkage cavity of the bearing steel bloom castings, so as to improve the qualified rate of the following rolled material. However, the unreasonable or unstable distribution of the position and amount of press-down may lead to the occurrence of mid-way cracks, thus reducing the stability and consistency of the rolled material quality. For the present production, it is recommended to keep the constant casting speed and press down at No.3 to No.6 pressure roller to assure the internal quality of the steel.

The ironmaking technology supports the development of the whole process flow of HBIS Group. Based on the basic idea of "Taking the blast furnaces as the center to ensure the long-term stable and smooth operation of blast furnaces", HBIS Group was committed to improving the utilization coefficient of blast furnace, increasing the coal ratio and reducing the fuel ratio of blast furnace. The gas utilization was improved by optimizing the burden distribution system. The reasonable adjustment of burden structure was taken to deal with the environmental protection production limit. The air supply parameters were explored to adapt to the change in raw fuel conditions. At the same time, the blast furnace longevity control technology had been explored, the new environmental protection technology had been developed, and the intelligent control level had been improved. Important breakthroughs had also been made in the smelting of vanadium-titanium ore, high-volume pellet smelting, flux pellets, and alkaline pellet production. Through the series of measures, the economic and technical indexes of various types of blast furnaces in HBIS Group had been continuously improved with remarkable results.

The high-end bearings, such as the main bearings of high-speed machine tools and aero-engine bearings, are often in service under extremely severe working conditions and have a very high demand for high service life and reliability, which require a very good mechanical performance guarantee in the bearing area of bearing rings. As an advanced technology of bearing rings, the near-net cold ring rolling (CRR) method not only has remarkable technical and economic effects such as energy saving, material saving and high efficiency, but also can greatly improve the performance of bearing ring through cold plastic deformation strengthening, which has become the international mainstream forming technology of bearing rings. The research progress of the microstructure evolution during the CRR process, the influence of CRR on the subsequent heat treatment and the coordinated control of the CRR process and heat treatment transformation are briefly described, and the technical difficulties of the near-net CRR process for bearing rings are summarized and prospected.

The effect of refined cementite on the microstructure, conventional mechanical properties, wear resistance and contact fatigue properties of GCr15Si1Mo bearing steel was studied. Through controlling the heat treatment process, the size of cementite and bainite ferrite lath in the microstructure was refined from 0.49 to 0.20 μm, and 66 to 41 nm, respectively, and the distribution density of cementite also increased. Then through SEM, TEM, XRD, hardness, impact, wear and rolling contact fatigue tests, the macroscopic properties and microstructure of the material were obtained. The results showed that after refining cementite, the wear resistance and rolling contact fatigue property of the specimen were better than that produced by the conventional process, while the toughness was worse. The research proved that the finer cementite can have a certain influence on the microstructure, conventional mechanical properties, wear resistance and rolling contact fatigue property of the bearing steel, which provided support for the later research on the control of cementite in bearing steel.

Continues cooling phase transformation behavior and strengthening mechanisms of the Ti-containing steel were systematically studied by thermal simulation testing machine, high-resolution transmission electron microscope and metallographic microscope. The result showed that the microstructure was mainly composed of ferrite and pearlite at the low cooling rate (0.5-1 ℃/s). When the cooling rate was gradually increased (1-5 ℃/s), the bainite structure appeared and the ratio of bainite increased. And the microstructure mainly consisted of bainite at the high cooling rate (5-10 ℃/s). The strengthening mechanisms of the Ti-containing steel were precipitation strengthening and fine-grain strengthening. TiN mainly precipitated as fine particles dispersing and its size was 10-20 nm. The optimized cooling rate was (1.5±0.5) ℃/s for the 20 mm HRB400E steel industry trial production, the yield strength was above 430 MPa, the elongation after fracture was above 20%, the maximum gross elongation was above 15%, and the ratio of tensile strength and yield strength was above 1.4.

The process of chemical heat treatment has an important influence on the service performance of bearing steel. Microstructure and mechanical properties of carburized layer of a novel Cr-Co-Mo-Ni bearing steel after preliminary nitriding treatment were investigated. The results show that after preliminary nitriding treatment, the carburized layer can be differentiated as mixed region of precipitates and acicular martensite, mixed region of acicular martensite, lath martensite and precipitates, as well as mixed region of precipitates and lath martensite. A large number of tiny pores were found at the position which was original white light layer formed by nitriding. Less Cr carbides precipitated at the surface layer of the sample during the whole process of preliminary nitriding treatment. With the increase of the depth of the carburized layer, more Cr carbides with largr size precipitated at the subsurface layer. Compared with samples carburizing only, the size of precipitates after tempering was smaller in the preliminary nitriding treatment samples at the same surface position. The preliminary nitriding treatment can improve carburizing efficiency and increase the hardness of carburized layer. The hardness of the preliminary nitriding treatment sample is higher than that with carburizing only from 0.12 to 0.82 mm at carburized layer. The improvement of hardness of heat treatment after carburizing is also significantly higher than that with carburizing only.

The importance of spheroidization annealing process in bearing production is summarized. The rule of microstructure transformation of bearing steel from lamellar pearlite to granular pearlite is analyzed, the thermodynamic mechanism of the broken-up of lamellar cementite, and the transformation from short rod to granular of pearlite, and the process of granular ostwald grow were discussed. At the same time, the defects of bearing spheroidizing process are pointed out. Firstly, there are problems such as unfiorm distribution of carbides and differences in size. Secondly, the spheroidizing annealing process is not suitable for the development of new bearing steel due to the problems of immobilization and formatting. Thirdly, the microstructure inspection after spheroidizing annealing is rough and not meticulous enough. The development trend of the spheroidizing annealing process of bearing steel is pointed out. Firstly, the original lamellae should be more uniform and refined by introducing plastic deformation or increasing cooling supercooling in the rolling or forging stage, and avoid network cementite during production. Secondly, new spheroidizing annealing process should be developed, such as introducing electric field, magnetic field or high temperature and high pressure stress field in possible conditions to improve the traditional spheroidizing annealing process. Thirdly, the standardized quantitative inspection of spheroidizing microstructure should be carried out.

To clarify the modification behavior of rare earth to inclusions in highly clean bearing steel for the purpose of providing references for rare earth (RE) treated bearing steel, highly pure RE alloy was added to highly clean bearing steel, and inclusions and their precipitation behaviors in bearing steel with different RE contents were characterized and analyzed with scanning electron microscopy and energy disperse spectroscopy. The results show that RE addition can modify Al₂O₃ and MnS inclusions into RE inclusions in highly clean bearing steel. The RE-S-As-P inclusion can act as the nucleus of RE-O-S-As-P-C inclusion to promote its precipitation. With the increase of RE content, the reaction sequence of RE elements with inclusion forming elements should be O, S, As, P and C successively, and the evolution sequence of RE inclusion type is expected to be mainly RE₂O₃、RE₂O₂S、RES、RE-O-S-As、RE-S-As、RE-S-As-P、RE-O-S-As-P-C、RE-O-As-P-C、RE-O-P-C和RE-O-C.

Based on the BOF-ARS(argon stirring)-LF-RH-CC process of bearing steel production in Shaoguan Steel Plant, the characteristics and sources of large size inclusions were explored through the method of water immersion ultrasonic test combined with metalloscope, scanning electron microscope and the systematic sampling during the metallurgical-continuous casting process, and the improved process was proposed. Results showed that there were mainly two kinds of large inclusions, one was low-melting CaO-MgO-Al₂O₃-SiO₂ inclusion from 6% to 7% SiO₂(mass percent), whose size was from 50 to 500 μm, and the other was CaO-MgO-Al₂O₃ without SiO₂, whose size was larger than 500 μm. The source of the former was the slag entrapment caused by the uneven slagging, which was the result of the combined charge of low basicity slag with high viscosity and high melting point lime during steel tapping. The latter was induced by the charge of large bulk of calcium-aluminate slag during the refining process, which was difficult to be melted rapidly and was entrapped into steel. Therefore, the design of refining slag and the optimization of the slagging process were the key points to decrease the large size inclusions. The improved slagging technology was applied by feeding the large bulk of calcium-aluminate slag during tapping in advance, instead of the low-basicity slag, and the addition amount of other slag was reduced during LF refining process. The basicity of refining slag (w(CaO)/w(SiO₂)) was controlled in the range from 5 to 9, and the mass percent of Al₂O₃ was from 23% to 28%. After the improvement, the fluidity of slag was good, and nozzle clogging was reduced. The main inclusions in the products were micro MgO-Al₂O₃ spinel and composite sulfides. The qualified rate of bearing steel products evaluated by ultrasonic test was significantly improved.

It is difficult to evaluate the quality of bearing steels with long fatigue life through conventional technology analyzing the purity and the homogenization of bearing steels. And a more scientific and intuitive method was proposed to evaluate the quality of bearing steels. The multidimensional and quantitative distribution of inclusions can be characterized by a scanning electron microscope. The type and size of inclusions can be analyzed in detail and accurately. In addition, the segregation of each element and density distribution of materials can be accurately analyzed through the quantitative analysis of homogenization by in-situ analysis. The application of those technologies can provide a technological basis for the quality evaluation of bearing steels with ultra-long fatigue life. The rotational bending fatigue property of bearing steels produced by Xingcheng Special Steel was larger than 1 000 MPa. And the rolling contact fatigue property was more than 2×10⁷times.

Some solidification defects such as macrosegregation will occur during the solidification of GCr15SiMn steel ingots. The effect of superheat on the macrosegregation of GCr15SiMn ingot was analyzed. GCr15SiMn ingots of 1 kg were smelted by vacuum induction furnace. The solidification structure and macrosegregation of the steel ingot were obtained by acid erosion and OPA, respectively. The flow rule of molten steel was studied by ProCAST software. The results showed that at high superheat (70 ℃), a certain degree of negative segregation appeared in the lower part of the center, and serious positive segregation formed in the upper part of the center with porosity. The porosity range was smaller and the carbon distribution was more uniform at moderate superheat (50 ℃). In the case of low superheat (20 ℃) and extra-low superheat (-20 ℃), the porosity range was enlarged. Moreover, severe negative segregation was formed at the initial stage of solidification and severe positive segregation was formed at the end of solidification. The mechanism of superheat affecting segregation was that the heat convection was strong during solidification and solute floated upward at high superheat, causing serious positive segregation in the upper part of steel ingot. When the superheat was extra-low, a large number of crystals nucleated and remained at the bottom of the steel ingot in the early stage of solidification, and serious negative segregation formed at the bottom.

The high cycle and ultra-high cycle fatigue properties of 100Cr6 bear steel, as well as the failure probability distribution at the traditional fatigue limit, were investigated by means of rotating bending fatigue, SEM+EDS and SEM. And the inclusion composition and size were also summarized. The results showed that the traditional fatigue limit of 100Cr6 bearing steel was 967 MPa, and some samples had fatigue fracture failure after having passed 10⁷ cycles at the stress amplitude of 960 MPa, not having the infinite life. At the stress amplitude of limit fatigue nearby, compared with normal distribution, the fatigue life data was more consistent with two-parameter Weibull distribution. Comparing to the method of metallographic examination and SEM, it was easier to find the larger and rigid inclusions classified as D-type and Ds-type by using the fatigue+EDS method.

The cause of the formation of the wave shape defects on the edge of SFB700 hot rolling strip with the thickness of 3.0- 6.0 mm was analyzed, which was mainly controlled by the trend of wave shape on the edge finish rolling outlet and concerned with the inhomogeneous edge cooling of the strip after rolling. And the emergence of wave shape defects on the edge was decreased by optimizing the rolling strip shape control strategy, adjusting the water quantity difference on both sides and side spray angle in the cooling area. At the same time, a new temper process was used to eliminate the wave shape defects on the edge. Therefore, the occurrence rate of the wave shape defects on the edge of SFB700 was reduced significantly.

Reducing the disadvantageous factors such as network and banded carbides in high carbon chromium bearing steel is beneficial to improve the comprehensive properties of bearing steel. G8cr15 bearing steel is a type of bearing steel newly-included in the national standard, and the performances of GCr15 and G8Cr15 are compared through a series of experiments. The results show that as compared with GCr15 bearing steel, G8Cr15 bearing steel shows very low ability of forming network carbide and ribbon carbide, and it also exhibits higher hardenability, good impact properties and wear resistance. Finally, it is verified by industrial production that G8Cr15 can replace GCr15 to produce bearing parts, and it is unlikely to produce network carbide.

According to the lateral roll mark defect after roll changing on 6- H CVC temper mill, the sample plate of lateral roll mark was tested and analyzed by the 3D surface profiler. The differences in the representation parameters of the defect area and the normal area were obtained. The distribution of the contact pressure between the rolls was studied, and then the generation mechanism of lateral roll mark was found out. On this basis, the control measures for the optimization of CVC roll profile and roll gap closing speed were put forward. The measures were used in the industrial production, and the lateral roll printing defect was eliminated.

Multi-direction forging (MDF) experiments with cumulative strains 1.2 and 5.4 were carried out on M50 steel at 1 000 ℃ and 1 100 ℃. The effect of cumulative strain and temperature on carbide fragment mechanism of M50 steel was analyzed. The results show that rod M₂C carbides in original M50 steel were obviously broken after MDF and granular M₂₃C₆ carbides were obviously dissolved in 1 100 ℃. Low-temperature MDF made carbides show finer size and more dispersed morphology. The forgings had different deformations at different positions, resulting in different fragment effects of carbides. Carbide fragmentation was more obvious at the place where the deformation was large. Low temperature and high strain increased the level of stress concentration and increased the degree of primary carbide fragmentation. Stress concentration was the most important driving force for the fragmentation and dispersion of carbides.

Lithium-ion power batteries are the heart of new energy vehicles. The key performance and safety of lithium batteries are directly determined by the consistency of rolling thickness, compaction density and peel strength of electrodes, which are the core components of lithium-ion power batteries. For the rolling technology and equipment of lithium battery electrodes, the research status and achievements of domestic and foreign scholars in recent years on new rolling technology, rolling effects on porosity and electrochemical properties, theoretical models of rolling process and rolling equipment were reviewed and summarized. The outlook of electrodes rolling process theoretical research and intelligentization of rolling equipment and process were forecasted based on the future demand of lithium battery industry and the development status of electrode preparation industry.

Based on the production of slag samples, the high-titanium-type blast furnace slag with different Ti (C,N) content was prepared by using coke as a reducing agent. The effect of Ti (C,N) on the distribution coefficient of sulfur between slag and iron L_S was investigated at different temperatures. Under the experimental conditions, the effect of temperature on the desulfurization capacity of high-titanium-type blast furnace was far more significant than that of Ti(C,N). Ti(C,N) had excellent wettability with slag, so ions in slag can be absorbed around Ti(C,N) particles, which can reduce the activity of free migration of ions in slag and hence reduce the desulfurization ability of slag to some extent. However, since Ti(C,N) was not uniformly distributed in the slag in the form of aggregation, its influence scope was limited and the free oxygen ions in most areas of the slag were not significantly affected. Hence the effect on Ti(C,N) on the thermodynamic and kinetic conditions of the desulfurization reaction was little. At the same temperature, as the mass fractions of Ti(C,N) increasing, although the apparent viscosity of slag increased significantly, the distribution coefficient of sulfur between slag and iron i.e. L_S did not decrease significantly. However, at the same mass fraction of Ti(C,N), the thermodynamic and kinetic conditions of the desulfurization reaction were significantly improved with the increase of temperature, so the distribution coefficient of sulfur between slag and iron L_S increased significantly.