For improving the level of GCr15 bearing steel CC billet chemical homogenization and defects such as inner crack and shrinkage cavity， the soft reduction process was optimized by the physical calculation of shell thickness growth ratio， steel grade thermal property test， desin casting process under large pressure and combined soft reduction test， monitor the surface temperature of the casting process and the working condition of the tension leveler. The results show that the reasonable starting position R of continuous casting SR is 42%～45%， in order to obtain better macrostructure quality， the starting position of three CC billet sizes 200 mm×200 mm， 240 mm×240 mm， 300 mm×340 mm is 1～3 m behind the original process； Taking 200 mm×200 mm GCr15 billet as an example， increasing the amount of casting reduction from 1.25 mm/m to 2.5 mm / m， which can reduce the cracks of billet， significantly improve the Y-Z longitudinal of casting billet macrostructure composition and homogenization， and the central carbon segregation index of the rolling material generally reaches 0.97～1.03， realizing the goal of not producing obvious cracks under soft reduction， and modifying the central segregation and V-segregation defects.

In response to the surface defects such as concavities， deep vibration marks， cracks， and slag pits on the surface of continuous casting billets during the smelting of N2M2T high-strength welding wire steel in a certain steel plant，combined with theoretical analysis and actual production conditions on site， an analysis was proposed to analyze the surface defects of N2M2T high-strength welding wire steel continuous casting billets from four aspects： the physical and chemical properties of protective slag， mold vibration parameter mode， primary cooling water distribution， and N content in the steel. The analysis results indicate that the surface defects generated by continuous casting billets are mainly related to the physicochemical indicators of the protective slag， mold vibration parameters， and N content in the steel， but not to the primary cooling water distribution. Production practice shows that by increasing the alkalinity of the protective slag from 0. 6 to 1. 19， the C content is reduced from 13. 51% to 8. 21%， and the viscosity is reduced from 0.666 Pa. s to 0.156 Pa. s； The deviation rate of mold vibration parameters has been increased from 0.15 to 0.20， and the vibration frequency formula has been adjusted from 60+50 V to 90+60 V； Control the N content in steel to ＜50 × 10 ^-6， continuous casting process △ N ＜ 7 × 10 ^-6； The surface defects of N2M2T high-strength welding wire steel continuous casting billet have been significantly improved， and the qualification rate of the billet has increased from 85% to over 95%， providing assurance for stable rolling of subsequent steel rolling

This article analyzes the causes of flocculent flow in the continuous casting process of low-carbon， low sulfur， and low oxygen aluminum killed steel X65， and finds that the cause of flocculent flow in the stopper rod is the adhesion of high Ca calcium aluminate to the head of the stopper rod. In the early stage of pouring， the head of the stopper absorbs heat， causing a sharp decrease in the temperature of the surrounding steel liquid， and the precipitation of high melting point calcium aluminate is adhered to the head of the stopper， causing the stopper curve to rise. In addition， by thermodynamic calculations， the Ca content required to form 12CaO·7Al ₂O ₃ in low-carbon， low sulfur， and low oxygen aluminum killed steel X65 at 1 540 ℃ is 16×10 ^-6， excess Ca further reacts to form high melting point calcium aluminate. Under the condition that magnesium refractory materials are used in all areas in contact with the molten steel， such as the working layer of the intermediate ladle， stopper rods， nozzles， and bowl mouths， and in the production of low-carbon， low sulfur， and low oxygen aluminum killed steel， the more Ca content is fed into the molten steel， the more severe the upward movement of the stopper rods. Using high alkalinity slag system and Al to reduce O and S in steel， and then controlling the Ca feeding amount between 0.065 0～0.071 5 kg/t， and controlling the calcium content in the tundish between （10～15）×10 ^-6 can effectively control flocculent flow.

 In order to solve the problem of high sealing rate of inclusions and bubble defects in IF steel with high drawing speed， the effects of immersion depth and drawing speed on the flow field of mold were studied by numerical simulation. The results show that under condition of the electromagnetic stirring current intensity 600 A and frequency 3.5 Hz， with the casting speed increases， the active index of free liquid level shows a trend of first increasing， then decreasing and then increasing. At the casting speed about 1.05 m/min， max value is up to 0.67， at the casting speed about 1.6 m/min， the minimum value is 0.35， the flow-field uniformity index is slightly reduced， the best free liquid level active index is 0.5 ± 0.05； When the casting speed is below 1.0 m/min， with the SEN immersion depth increases， the free liquid surface active index gradually increases to 0.40； When the casting speed is greater than 1.0 m/min， with the SEN immersion depth increases， The free liquid surface active index index gradually decreases； When the casting speed is greater than 1.4 m/min， with the SEN immersion depth increases， the free liquid level active index drops sharply to 0.37； After the optimization of mold electromagnetic stirring process of IF steel ， the average sealing rate of inclusions and bubble defects in the casting billet decrease by 4%， and remarkable results are obtained.

The high-temperature tensile thermal deformation processes of continuously cast and mold cast S30432 steel tube billets in same heat were investigated using the Gleeble thermal simulation machine， different thermal simulation conditions were set for temperature series of 1 000， 1 050， 1 100， and 1 150 ℃， and strain rates of 0.1， 1， and 5 s-1.The high-temperature stress-strain curves of continuously cast and mold cast S30432 steel billets from in same heat were obtained for both types of billets under various high-temperature tensile conditions， and these curves were corrected and fitted to align as closely as possible with actual experimental situations. The constitutive equations for the hot deformation of the continuously cast and mold cast S30432 steel billets from the same heat were derived through fitting， and a comparative analysis of the high-temperature hot plasticity differences between the two processing methods was conducted. The results indicated that the hot plasticity of both types of billets exhibited certain regularities at different tensile temperatures and rates， the continuously cast tube billets showed more significant fluctuations in hot plasticity and were slightly inferior to the mold cast tube billets in overall performance， providing insights for improving and optimizing the piercing process of the tube billets. Scanning electron microscopy was employed to characterize the microstructural features of the high-temperature tensile fracture surfaces， it was observed that the predominant fracture mode at high temperatures was ductile rupture， with most fracture surfaces exhibiting dimple features. However， under specific conditions， some samples of continuously cast tube billets exhibited poor hot plasticity and its fracture form was transformed into brittle fracture patterns. For the high-temperature plastic processing of S30432 steel continuously cast tube billets， it is recommended to employ higher strain rates and temperatures to achieve enhanced processing performance.

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

Compares the effects of two different tundish argon replacement methods, scheme I uses the argon rod to replace the air in the inner cavity of the tundish, and scheme 0 uses the joint action of argon gas pipe and argon rod on the tundish cover to replace the air in the tundish. Select the same steel grade, specification, replacement time and pipeline pressure to carry out the process test. Through comparison: (1) scheme U can more effectively replace the air in the inner cavity of the tundish and reduce the probability of secondary oxidation； (2) The oxygen content, nitrogen content, Als/Alt, inclusions in steel and other indicators of scheme H is better than those of scheme I , indicating that the protective casting effect of scheme II is better； (3) Scheme U can effectively prevent the formation of inclusions below 10 μm, especially small particle inclusions in the range of 2 μm ≤ X ＜5 μm.

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

The distribution of C,Si,Mn and Cr elements in cross sections of Φ450 mm continuous casting round billet and Φ130 mm round steel of high hardenability bearing steel GCr15SiMn was analyzed by original position statistic distribution analysis(OPA)and borehole chemical analysis.The contact fatigue life of the material was tested by the thrust plate con-  tact fatigue testing machine.The results show that the segregation tendency of C element in bearing steel GCr15SiMn continuous casting round billet is large,and it is easy to produce center positive segregation,while the segregation tendency of Cr,Si and Mn element is small.The central carbon segregation in casting bloom was improved by adopting stable low superheat casting and three-stage strong electromagnetic stirring.After(1240±20)℃×5 h high temperature diffusion and large deformation rolling with primary pass deformation ≥90 mm,the carbon segregation of φ130 mm round steel can be further improved. The rated contact fatigue life L ₁₀ of the test steel under 5.3GPa high stress load reaches 3.58×10 ⁶  times,which is close to the level of ESR steel.

This paper summarizes the reports of latest developments on industrial application of continuous casting technology in high speed steel production abroad. In addition, and summarizes some Chinese enterprises and research institutions have done some research and industrial trial production in this field. It is suggested to increase investment on the research and development of continuous casting technology of high carbon and high alloy steel grades. Compared with the traditional casting, the research shows that continuous casting can reduce the thickness of coarse carbide by 40% and the grain size by 50%,and the carbide pattern is also changed from flat and lamellar to fibrous, which will facilitate the carbide refinement in the subsequent forging and rolling process.Finally,it is proposed that the continuous caster straightening machine,water cooling process,billet cross-section size and finished forging ratio can be optimized. If a breakthrough can be male in current technology of mature arc continous casting machine,it will be condueive to improve the quality of casting billet,and achieue industrial application of high carbon and high alloy die steel casting.

In response to the problem of coarse slag-bonding rim in 430 stainless steel production process t the chemical composition and physicochemical properties of the mold powder and slag-bonding rim are compared and analyzed using ICP- OES, hemispherical point melting point meter, viscometer and other equipment, and the microstructure of the slag-bonding rim is observed through the electronic probe to explore the mechanism of slag rim formation and growth. It is found that except C content of slag-bonding rim being 0.53% and C content original mold powder being 2.87% , the composition of the slag-bonding rim and the original mold powder is not much different, but viscosity and melting point are reduced, about 70% of the area of the slag rim consists of the sintered phase, the remaining 30% is the crystalline phase, mainly composed of cuspidine and melilite. The sintered phase of a large number of bonding become a main reason for the formation and growth of the slag rim. Increasing the proportion of pre-melt material to 70%-80% and the content of carbon black in the mold flux ^2% , and further stabilizing the melting process of the mold powder in production, can effectively inhibit the growth of the slag rim.

The traditional mold flux is mainly composed of CaO and  SiO ₂ as the base material,supplemented by an appropriate amount of fluxing agent such as CaF ₂;and the fluorine-free mold flux is to choose B ₂O ₃ 、TiO ₂ and other suitable flux to replace CaF ₂ to achieve the role of green metallurgy.In this paper,the influence laws of heat transfer of the traditional fluorine mold flux CaO-SiO ₂-CaF ₂ and new fluorine-free mold flux CaO-SiO ₂-B ₂O ₃ and CaO-SiO ₂-TiO ₂ flux films are re- viewed from three aspects of basicity, chemical composition and crystallization properties of the mold flux. Summarizes the metallurgical workers in nearly a decade of fluoride and fluorine-free mold fluxs film heat transfer of research results,it is concluded that the fluorine-free mold flux silicon calcium borate and perovskite crystal mineral phases and traditional mold flux  cuspidine  have  similar  crystallization behavior,the  content  of B ₂O ₃  and  TiO ₂  range  from  4%  to8%  and  3%  to 11%  can  effectively  control the heat transfer,thereby reducing the  occurrence  of slab longitudinal  cracks.

The effects of soft reduction (0 ~ 8 mm) and casting speed (0.42 ~ 0.49 m/min) of cast bloom on macrostructure and segregation of 42CrMo steel Φ195 mm rolled product are tested. The results show at present process condition that when the superheat degree of 42CrMo steel is controlled at 20 ~ 30℃ with secondary cooling specific water content 0.3 L/kg, mold and end electromagnetic stirring 100 A/l.5 Hz and 400 A/8 Hz, the casting speed 0. 49 m/min and the total soft reduction 6 ~ 8 mm, the internal quality of 42CrMo steel rolled product can be efiectively improved.

The capping technology of low alloy steel SG610E 250 mm x2 000 mm continuous casting tail slab is studied. The results show that with traditional water-cooling capping process, there are severe shrinkage cavities at distance 2 000 mm from the slab end；while with the low-speed casting anhydrous capping,the distance of slab shrinkage cavities decreases to 900 mm,but the slab surface temperature drops into the third brittle zone due to the long duration of ≤0. 2 m/ min casting speed, which lead to transverse cracks on Nb-V-Ti microalloying low alloy steel casting tail slab. Therefore, a non-stopped-pouring speed casting 0.4 m/min anhydrous capping technology for wide and thick slab is developed which improves the internal quality and reduces the surface crack incidence of the steel tail slab.

Two kinds of A and B mould powder, A(/% ) ：28 -32SiO2,38 ~40CaO,4. 8-6. 0TC,2. 3 ~4. 3A12O3,  6.7~9. 7F； B(/% ) ：25. 2 ~26. 4SiO2,41 ~ 43CaO,4. 8 ~ 6. 0TC ,2. 3 ~ 4.3A12O3 10. 5 ~11. 8F for high strength peritectic steel S690 jumbo-wide slab are designed. After mould powders are used in situ, theirs heat transfer properties and films are analyzed. The results show that the properties of powder A with basicity 1. 25 ~ 1. 35, viscosity at 1 300 ℃ 0. 11 ~ 0. 16 Pa • s, solidification temperature 1 170 - 1 200 °C are optimum. As compared with powder B (basicity 1.58 ~ 1.64, 1 300 °C vicosity 0. 07 ~0. 10 Pa • s, solidification temperature 1 220 ~ 1 250 ℃ ), the cast slab crack rate decrease from 0. 69% to 0. 30%.