Analysis of cracking phenomena in continuous casting of 1Cr13 stainless steel billets with final electromagnetic stirring

Solidification cracking that occurs during continuous casting of 1Cr13 stainless steel was investigated with and without final elec- tromagnetic stirring （F-EMS）. The results show that cracks initiates and propagates along the grain boundaries where the elements of carbon and sulfur are enriched. The final stirrer should be appropriately placed at a location that is 7.5 m away from the meniscus, and the appropri- ate thickness of the liquid core in the stirring zone is 50 ram. As a stirring current of 250 A is imposed, it can promote colurnnar-equiaxed transition, decrease the secondary dendrite arm spacing, and reduce the segregation of both carbon and sulfur. F-EMS can effectively de- crease the amount of cracks in 1Cr13 stainless steel.

Interactions of Sn and S and their effects on the magnetic properties of non-oriented silicon steel sheets

The interactions of Sn and S and their effects on the magnetic properties of non-oriented silicon steel sheets were discussed in reference to industrial production. Results show that minor amounts of Sn can improve magnetic induction sharply but have little effect on core loss when the S content is below 10 × 10 ^-4%. The precipitation of AlN can be restrained effectively by Sn. Sn, as the nucleus, can remove some of the inclusions with a size of 0.5μm or larger, but has little effect on inclusions smaller than 0.5 μm,which is the key factor affecting core loss. Sn improves the magnetic induction of finished steel sheets mainly through the change of the steel texture. The relationship between the magnetic induction and Sn and S content can be regressed as B50 = 1.69 -4.37 ws ＋0.30 Ws,. From the regression formulation,the magnetic induction can be improved by 0.03 T when 0.01% Sn is added under relatively low S content conditions.

Effects of calcium treatment on non-metallic inclusions and magnetic properties of non-oriented silicon steel sheets

Based on the industrial production of non-oriented silicon steel,calcium treatment by CaSi wire feeding during the RH refining process was studied. The thermodynamics of CaS inclusion formation was analyzed, and the morphology and the size distribution were observed. Furthermore, the change in inclusion characteristics after calcium treatment and the effect of calcium treatment on magnetic properties were discussed. The results show that the formation of MnS and A1N inclusions were restrained, and the aggregating, floating and removing of microinclusions after calcium treatment were effectively promoted. The cleanliness of liquid steel was obviously increased. The main type of inclusions was single phase of CaO, with some complex inclusions composed of CaO, SiO2 and MgO. No CaS inclusion was observed after an appropriate calcium treatment. The size of all inclusions was distributed in the range of 2 - 20 μm, and the number was about 1.8 × 10^5/mm3. In addition, as an increasing amount of calcium was added,the core loss gradually decreased to a stable level, and the magnetic induction decreased quickly after a slow increase. The optimal calcium treatment mode depends on the chemical composition of steel.

Industry experiment & effect of oxidation resistance coating for steel slab

Spraying test were conducted twice before steel slabs were put into the furnace and the effects of the oxidation resistance coating were investigated and verified. By comparing the change of slab weight, rolling force of the roughing mill ＆ finishing mill, thickness of oxide film on the surface slabs by an XL-30 SEM and acid pickling speed of slabs with and without coating,it was found that the oxidization waste in the furnace decreased by 40 percent with the use of the coating and the corresponding yield capacity could increase by 0.2 percent at least. Besides, the thickness of oxide scale film on hot roiled products was reduced by 1.44 micrometers and the acid pickling time was shortened by 6s with the coating technology, while the total rolling force of RM ＆ FM did not changed. Furthermore, the application prospect of this technology was also discussed in this paper.

Molten steel level stability in continuous casting slab mold under electromagnetic stirring

Fluctuation of molten steel level in continuous casting process is a critical issue. The analytic function for the liquid steel surface stability index( F) of the continuous casting slab mold under the action of electromagnetic stirring was derived. The effects on the F value of the electromagnetic field,casting mold,submerged entry nozzle,and casting speed were observed,and the stability of the process parameters of a practical continuous casting system was evaluated. The main results generated are as follows:①Based on the free flow jet theory,a formula is established for the level stability index of continuous casting slab mold under electromagnetic stirring.②According to the results of calculation,the various parameters in decreasing order of the magnitude of their influence are magnetic flux density,nozzle submersion depth,casting speed,slab width,stirring current frequency,and nozzle side-hole inclination angle.③For practical continuous casting with a slab thickness of 230 mm,the calculated F values are between 3 and 5 for different matches between slab width and casting speed,but the parameter optimization space is much larger for wider slab widths and lower casting speeds.

Effect of quenching temperature on the microstructure of Si-containing steel during quenching and partitioning

This study aims to investigate the effect of the 1-step quenching and partitioning （Q＆P） process on the microstructure and the resulting Vicker＇ s hardness of 0.3C-1.5Si-1.5Mn steel by using in-situ dilatometry ,optical microscopy （ OM ）, scanning electron microscopy （ SEM ）, X-ray diffractometry （ XRD ）, and Vicker ＇ s hardness measurement. Systematic analyses indicate that the microstructure of the specimens quenched and partitioned at 150℃ ,200 ℃ ,250℃ ,and 300℃ mainly comprises lath martensite and retained austenite. The dilatometry curve of the specimen partitioned at 150℃ is presumably ascribed to the formation of isothermal martensite. In the early stages of partitioning at 200℃,the nearly unchanged dilatation curve is closely related to the synergistic effect of isothermal martensite formation and transitional epsilon carbide precipitation. In the later stages of partitioning at 200 ℃ ,the slight increase in the dilatation curve is due to the continuous isothermal martensite formation. With further increase in partitioning temperature to 250℃, the dilatation increases gradually up to 3600 s, which is related to carbon partitioning and lower bainite formation. Partitioning at a higher temperature of 300 ℃ causes a rapid increase in the dilatation curve during the initial stages, which subsequently levels off upon prolonging the partitioning time. This is mainly attributed to the rapid diffusion of carbon from athermal martensite to retained austenite and continuous formation of lower bainite.

Advanced green refractory technologies for coke ovens at Baosteel

To construct world-class iron and steel enterprises, Baosteel has adopted a strategy of environmental management that emphasizes environmental protection in the low-carbon and ecological manufacturing of steel products. In recent years, Baosteel has developed a series of advanced green refractory technologies （including composite refractory precast blocks with a unique ceramic glaze, and high-thermal-conductivity/high-density silica brick） for use in Baosteel coke ovens. The results of these applications not only reduce production costs and increase production efficiency, but also facilitate clean production by coke ovens. Baosteel＇ s coke oven has become China＇ s leading example of the application of green refractories.

Effects of quenching and over-aging temperatures on mechanical properties of ultra-high strength cold-rolled martensite steels

As cold-formed steel has the highest strength-to-weight ratio of any material,ultra-high strength martensitic steel is attracting great interest from global car manufacturers. This paper explores the effects of the quenching and over-aging temperatures on the strength and cold bendability of C-Mn-Si martensitic steel. Due to its high carbon content,water-quenched C-Mn-Si martensitic steel has high hardenability and can obtain ultra-high tensile strength and uniform martensitic morphology when the water-quenching temperature is higher than 710 ℃.Increasing the over-aging temperature of this experimental steel decreases its tensile strength,increases the total elongation,and first increases then decreases the yield point until reaching a peak at 180 ℃. Besides,when increasing the over-aging temperature,the bendability of this experimental steel initially improves and then decreases,and reaches its optimal bendability at an over-aging temperature of 180 ℃. Based on SEM characterization and a microhardness distribution analysis,the over-aging temperatures were found to affect the size of the carbides and differences in the microhardness of the experimental steel. Therefore,they have significant influence on bendability.

Effect of surface roughness on the surface lubrication performance of galvanized steel sheets with a self-lubricated coating

Four kinds of galvanized steel sheets having different surface roughness values were used to prepare the steel sheets with a self-lubricated coating. The effects of surface roughness on the surface lubrication performance of the steel sheets were examined using a friction coefficient tester. Results revealed large dynamic friction coefficients for the galvanized steel sheets, which increased remarkably with surface roughness. Once the self-lubricated coating was applied, significant drops in the dynamic friction coefficients were measured. After the first stage of the friction test,the coefficients were almost unchanged, which reflected a weak dependence on the surface roughness of the self-lubricated steel sheets. However, the dynamic friction coefficients gradually increased as the test progressed, where these increase clearly correlated with the surface roughness of the self-lubricated steel sheets.

Influence of annealing conditions on selective oxidation of boron in BH steel sheets

Annealing experiments were conducted on BH steel to which 10 × 10^-6 boron was added. The annealing temperature,holding time, H2 content, and dew point were varied in the experiments in order to investigate their influences on the selective oxidation of boron. A higher annealing temperature and longer holding time is found to lead to a higher concentration of boron at the extreme surface, which reaches saturation after the steel sheet is held for a critical period of time that depends on the annealing temperature. The effect of H2 content on the selective oxidation of boron depends on the annealing temperature and dew point. It has almost no influence on the external oxidation of boron when the sheet is annealed at 820 ~Cin an atmosphere with a dew point of -40℃. At a dew point of - 10℃, a lower H2 content results in a lower peak value of boron in the subsurface area but deeper internal oxidation of boron. An increase in the dew point from -40℃ to - 10℃ can significantly promote internal oxidation of boron at depths of 50 - 200 nm from the surface. With the suppression of external oxidation of boron as well as manganese and silicon, a relatively clean surface with reduced and refined oxides can be achieved by increasing the dew point.

Development of top high-grade non-grain-oriented silicon steels at Baosteel

The development, production and application of top high-grade non-grain-oriented （NGO） silicon steels at Baosteel were introduced in this paper. Top high grades refer to the highest grades in the intemational silicon steel product standard and above. B35A230 and B50A250 were developed at Baosteel in 2009 and have been used in inverter compressors for air-conditioners, small transformers and big hydropower generators in the Three Gorges project. Small- batch production of B35A210 and B50A230, which exceed the highest grades listed in the intemational silicon steel product standard,began in 2010. That was a breakthrough in the silicon steel making history in China. Presently,Baosteel＇ s high- grade NGO products have passed the strict qualifications of the three major electric power equipment manufacturers in China and the leading international power equipment suppliers like ALSTOM, GE, SIEMENS, VESTAS, etc. These products are characterized by low iron loss, low anisotropy, good punchability and a high lamination factor. They have been used in the 770 MW hydropower generator at Xiluodu Power Station in the three gorges area, 1 000 MW thermal power generators and 2.5 MW wind power generators.

The effect of cooling rate and coiling temperature on the microstructure and mechanical properties of a plain carbon steel

The effects of cooling rate and coiling temperature on microstructure and mechanical properties of a plain carbon steel were investigated by combining metallography and tensile experiments. The results indicate that ferrite grain size is refined and bainite transformation occurs to ensure high strength and elongation, as the cooling rate is quick enough. Yield strength and tensite strength improve with the decreased finish cooling temperature, but the elongation decreases too significantly to meet the requirements. Thus, the cooling rate must be quick enough, and the appropriate coiling temperature should be carefully selected to obtain refined ferrite and a small amount of bainite to improve the strength while the plasticity is also ensured. Under this condition, the Mn element concentration can be reduced to save cost or produce higher strength steel with same chemical composition.

某X80钢级CO_(2)输送管道断裂事故调查分析情况介绍

2020年发生在美国密西西比州的一起CO_(2)管道断裂事故,引发对CO_(2)管道安全的广泛关注。该管道于2009年投产,输送超临界态CO_(2),最高设计压力14.9 MPa,管径610 mm,采用API 5L PSL2 X80 HFW钢管,是目前钢级最高的超临界态CO_(2)长距离输送管道。该事故是大雨造成事故地点上游土壤移动引起管段轴向应变过大导致环焊缝失效,调查未发现钢管母材和环焊缝缺陷,母材和环焊缝性能均满足当时标准要求,但调查结果也显示环焊缝强度低于母材。编译并汇总了美国管道和危险品安全管理局(PHMSA)发布的事故调查报告及有关重要信息,介绍了事故调查采用的根本原因分析步骤及主要内容、分析结论、管道重新启用情况及CO_(2)管道安全的工作措施等,供国内管道行业从业人员参考。

Effect of cold-rolled annealing processes on microstructure and properties of ultra-pure ferritic stainless steel

In this study, the influence of annealing processes for cold-rolled sheets on the microstructure and mechanical performance of ultra-pure 430 ferritic stainless steel was investigated. Thermo-Calc calculation, organization observation, SEM detection,and tensile tests were used to discern the optimal annealing process. It is found that the microstructure is made up by the fine and uniform recrystallized ferritic grains after annealing. The optimum annealing process for ultra-pure 430 stainless steel is 950 ℃ for 90 s. After annealing, the stainless steel can obtain the optimum microstructure,recrystallization texture, and mechanical properties.

Comprehensive longevity technology of Baosteel No.3 BF

Baosteel No. 3 BF has been running smoothly and stably for more than 18 years and has become China＇ s longest-life blast furnace, producing many advanced economical and technical indexes. Comprehensive longevity technology has been developed in terms of the design, operation, and maintenance of the No. 3 BF during the prolonged period of research and practice. To obtain stable and smooth operation and to prolong the campaign life, the following measures have been taken： appropriate designing of the furnace profile and cooling system; improving raw material quality and optimizing the operating system; improving the cooling intensity and water quality;and adopting various longevity maintenance measures to ensure the safety of the body and the hearth temperature.

The effect of different cooling and tempering conditions on the strength and toughness of SA533B steel

The microstmcture and mechanical properties of SA533B low-alloy steel were investigated under different cooling and tempering conditions. Steel plates cooled at 40℃/s and 25℃/min,exibited microstructures of auto-tempered martensite and bainite, respectively. During tempering, the strength of steels quenched at the two different cooling rates decreased continuously with an increase in the tempering parameter, which is defined by T （20 ＋ log t）, where T is the temperature and t is the holding time. However, the rate of change of the strength scales with the degree to which the virgin microstructure deviates from equilibrium. The strength of the martensitic steel decreased faster and finally obtained a value close to that of the bainitic steel. The ductility and toughness gradually improved during tempering, passed through a maximum value, and finally diminished. The level of maximum toughness was also found to depend on the cooling rates of SA533B steel. The high cooling rate with a microstructure of auto-tempered martensite exhibited a larger toughness and a lower ductile-brittle transition temperature than the low cooling rate with a microstructure of bainite, because the former had finer precipitated cementite particles at quenching and a slower coarsing rate during tempering.

Transverse thickness difference control technology for non-oriented silicon steel

Transverse thickness difference is an important quality index of non-oriented silicon steel strips. In order to fulfill users＇ accuracy requirements on the transverse thickness of silicon steel and improve the production yield, the factors influencing transverse thickness difference were analyzed. Then the work roll shape, control strategy and incoming hot-rolled strips were optimized. Since the optimization measures were implemented in the actual production, the thickness difference of non-oriented silicon steel has been reduced greatly and fulfilled the requirements placed by users. These measures have achieved remarkable effects.

High-speed steel rolls used for cold rolling

During cold rolled production of steel, each change of rolls causes a halt in production and affects the roll＇ s grinding maintenance and consumption. Consequently,rolls are very critical to the costs of steel production. Besides the rolling accidents, surface quality problems, including inhomogeneous wear and a decrease of the surface roughness of the rolls are other main reasons for outage and a change of the rolls. Therefore, safe rolls, with superior wear resistance and roughness retentivity will be a future trend in the cold rolling steel industry. In this study, the property characteristics and in-service performance of high-speed steel （HSS） cold rolling work rolls at Baosteel are discussed. The results of this study indicate that in-service performance of HSS cold work rolls has an improvement over conventional rolls. Implementation of HSS work rolls will prolong the rolling campaign and improve the rolling stability, thus, the cost of cold rolling production can be better controlled.

Effect of nut coke on the reduction behavior in iron-making blast furnace

Ore-coke mixed charging is a potential technique for optimizing the charging pattern. Recently, the charging of small-sized coke（ nut coke） with the ferrous burden layer has been applied to reduce raw material usage and decrease costs. Various studies indicate that mixing nut coke with ferrous burden can enhance the reduction kinetics,improve the softening and melting properties, and have a positive effect on the permeability. Although mixed charging, especially the addition of nut coke to the burden layer, has been used in the industry for various reasons ,the mechanisms and side effects for using nut coke are not well understood, and the mixing ratio remains limited in actual blast furnace operation. High-temperature experimental studies were conducted to increase the understanding of the complex process of reduction, softening and melting properties, and permeability in a blast furnace when mixing nut coke with an ore layer. The effect of the nut coke mixing ratio and nut coke size was investigated under various reducing conditions. To describe the reduction processes of burden materials, numerous experiments were interrupted at different stages of the reduction, and the collected materials were examined by using image analysis. The reduction degree of mixed charging（iron ore mixing with nut coke） was improved when using nut coke at the temperatures of 800 ℃ and above. The reaction rate of ore-nut coke mixed charging was higher than that of standard charging without the use of nut coke.

Comparative study on the corrosion behavior of low alloy steels in sulfuric acid solution

The corrosion behavior of a weathering steel SPA-C and two acid resistance steels（ S-TEN1 and ND）in sulfuric acid solution was investigated by using potentiodynamic polarization and weight loss measurement techniques. Both potentiodynamic polarization and weight loss measurement tests indicated that corrosion resistance of these three alloy steels was as follows： ND ~ S-TEN1 〉 SPA-C. Surface analysis of the corroded samples conducted after the immersion test indicated that two layers were formed on the substrates, with the outer layer comprising FeSO4. H20 and the inner layer mainly comprising iron oxides. The addition of Cu, Cr, and Sb refined the corrosion products and improved the adhesion ability between the rust layer and the substrate.