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2021 Vol. 40 No. 4
Published: 2021-08-18
Continuous Casting Technology
Strand Quality
Continuous Casting Equipment
Technology Exchange
Continuous Casting Technology
1
2021 Vol. 40 (4): 1-1 [
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74
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2
HU Wen-guang, JI Cheng, ZHU Miao-yong
Numerical simulation of continuous casting bloom solidification end reduction process for heavy-haul railway rails
Northeastern University, Shenyang 110819, Liaoning, China)Abstract: Three-dimensional models is established using finite element simulation technology aiming to study the thermal/mechanical behavior of continuous casting bloom under different reduction amounts for heavy-haul railway rails steel. The bloom′s internal shrinkage deformation behavior, strain distribution phenomenon, deformation behavior of the bloom and the reduction force required by the tension leveler in the casting and reduction process is analyzed in this study. The result shows that increasing the reduction amount can make the deformation transferred to the center more and the center void close better, but at the same time the larger pressing capacity of the machine is required. The production requirements and production capacity should be considered comprehensively so the most suitable reduction process can be selected, which provides theoretical and data support for the designation of the bloom′s reduction process.
2021 Vol. 40 (4): 2-6 [
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173
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7
LIU Yu, XU Zhi-qiang, ZHANG Dong-dong, WANG Xin-hua
Space-time characteristics and evolution rules of breakout during continuous casting
Breakout is a serious accident during continuous casting. It is very important for the steady and smooth continuous casting if the space-time characteristics and its evolution rules of breakout in mould are accurately recognized. Based on the visual characteristics, the characteristics of typical sticker breakout were analyzed from the aspect of time evolution. The spatial characteristics of hot and cold regions, such as the area, temperature velocity and location, were studied and analyzed in order to obtain the difference and critical condition of true and false sticker breakouts. The results show that the hot region area of sticker breakout is mainly concentrated in 1 973 to 7 795 pixels. The temperature velocity greater than 1.02 ℃/s is the necessary condition for sticker breakout. The temperature velocity of the cold region is in the range -0.57 to -4.22 ℃/s. When the temperature velocity is less than -2.52 ℃/s, there is no false sticker breakout, but there are 12 cases of true sticker breakout. The gathering location of hot and cold region of true sticker breakouts is concentrated in the range 46
th
-64
th
and 5
th
-47
th
, respectively. The research provides an easy way to distinguish true and false sticker breakouts and is helpful to recognize the instantaneous morphology of slab surface in mould more fully and accurately.
2021 Vol. 40 (4): 7-10 [
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173
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11
WANG Lin-jie, KONG Ling-zhong, FENG Liang-hua, YANG Jie, CHEN Deng-fu
Interfacial behavior of steel and slag in billet mold during high casting speed
For continuous casting of high speed, the control of flow behavior of molten steel and mold slag under high steel quantity in mold is an important link to ensure reasonable solidification and cooling control in mold area. A mathematical model of multiphase flow, heat transfer and solidification coupling in a three-dimensional billet continuous casting mold was established to study the transient flow phenomenon of HSS in the mold and its effect on the liquid level fluctuation and the flow of protective slag.The results show that the impact of HSS on the steel slag interface in the crystallizer causes obvious bulge on the meniscus surface, and causes severe fluctuation of the interface near the nozzle.The flow behavior of the liquid flux is greatly affected by the fluctuation of the liquid level. The discontinuous flux causes the formation of the solid flux film with uneven thickness, and the irregular solid flux film in turn hinders the inflow of the liquid flux.
2021 Vol. 40 (4): 11-16 [
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154
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17
LI Jian-quan, WU Guo-rong, SUN Yan-hui, LEI Yang-wei, ZHOU Ming-jia
Precipitation behavior of carbonitride in P590L steel in CC process
To investigate the precipitation behavior of carbonitride in microalloyed steel, the P590L microalloyed steel slab was taken as the research steel grade. The precipitates were extracted from the tensile samples by carbon film extraction reconstruction method.The second phase precipitates were observed by JEM2100 transmission electron microscope. The precipitation behavior of micro-alloying elements Ti and Nb was systematically examined and analyzed. The influence of temperature on the quantity and size of precipitates and the influence trend of precipitates on thermoplastility were also analyzed. The results show that a small amount of square TiN and Ti-Nb compound precipitates above 70 nm appear at 1 100 ℃, and Nb(C, N) precipitates occur at 1 100~1 000 ℃. With the decrease of temperature, the number of precipitates increases, the size decreases and becomes more dispersed, and the thermoplasticity decreases with the increase of the number of precipitates.
2021 Vol. 40 (4): 17-20 [
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122
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21
DU Feng-ming, LI Da-wei, SA Xiao-xia, HUANG Ruo-xuan, SHEN Yan, HAN Xiao-guang
Non-uniform friction behavior of slab during continuous casting mold
Friction and non-uniform lubrication are the key factors affecting the quality of continuous casting billet. In view of the complex friction behavior of the billet in the mold, a full-scale heat transfer model and a friction calculation model were established, and the actual heat flow was obtained by using the inverse algorithm. The friction behavior of the billet was described in detail, and the factors affecting the friction were further studied.The results show that, starting from the meniscus, the surface of the slab transitions from liquid friction zone to mixed friction zone and then to solid friction zone. The friction state of billet is asymmetric, which reflects the necessity of establishing a full-scale model. The model provides a useful tool for understanding the complex process in the mold and optimizing the technological parameters of continuous casting.
2021 Vol. 40 (4): 21-25 [
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197
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Strand Quality
26
GUO Liang-liang, WANG Ying-chun, XU Guo-dong
Analysis of surface cracking mechanism of high nitrogen and molybdenum alloy continuous casting
S31254 is a super austenitic stainless steel(SASS), which contains a large amount of alloying elements such as Cr, Ni, Mo, N and Cu, and has excellent corrosion resistance and comprehensive mechanical properties. At present, the main problem of S31254 alloy continuous casting is surface crack. By studying the material properties, thermal simulation fracture mechanism and
in-situ
observation of solidification of S31254 alloy, the cause of crack defect of S31254 was analyzed by metallographic microscope and scanning electron microscope. The results show that there are a large number of precipitates in the as-cast grain boundary of S31254 alloy. The precipitates include Sigma phase (σ), Chi phase (
χ
), Laves-phase and nitrides etc. The precipitates are characterized by rich Cr and Mo and poor Ni. When the temperature rises to about 1 240 ℃, all precipitates melt into austenite phase, and the final molten precipitates are
σ
phase. As the precipitated phase of S31254 alloy precipitates along the grain boundary, the as-cast grain boundary becomes brittle, and the fracture mechanism of the cast billet specimen changes into the brittle fracture along the grain boundary, which reduces the high temperature plasticity of the alloy and increases the tendency to crack.
2021 Vol. 40 (4): 26-30 [
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31
JIANG Dong-bin, ZHANG Li-feng, CHEN Tian-ming, LI Hong-guang, LI Jian-quan
Characterization of macrosegregation and semi-macrosegregation in continuous casting bloom
In order to obtain the distribution of macroscopic segregation and semi-macroscopic segregation in continuous casting bloom, the carbon-sulfur detection, chemical analysis, direct reading spectroscopy, and metal in-situ analysis were used to analyze the macrosegregation behavior of C and Mn elements in thickness direction of the bloom. The semi-macroscopic segregation distribution characteristics of continuous casting billet were investigated by low-power microstructure corrosion and image scanning processing. The result shows that the carbon-sulfur detection and direct reading spectroscopy detection are suitable for the macroscopic segregation detection of C. For the Mn segregation, the direct reading spectroscopy and metal in-situ analysis characterization methods are more appropriate. It also found the semi-macroscopic segregation degree can be quantitatively characterized by the semi-macroscopic segregation area ratio and the semi-macroscopic segregation degree. In the direction of the thickness of continuous casting bloom, the segregation of C and Mn elements fluctuates with the increase of the distance from the surface of the bloom, and the segregation is larger at the center of the bloom. The semi-macroscopic segregation mainly exists in the inner part of bloom, and the degree of semi-macroscopic segregation reaches the maximum in the dendrite transition zone and the center zone.
2021 Vol. 40 (4): 31-37 [
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38
YUAN Peng-fei, JIANG Zhao-hui, ZHAO Hai-ming
Cause analysis and control of intermediate crack in Q345B continuous casting slab
Aiming at the problem of forging crack caused by the intermediate crack of Q345B continuous casting slab with 280 mm×2 000 mm size in TISCO, the forming mechanism of intermediate crack was analyzed by means of macro inspection and model calculation. On this basis, the solution measures of Q345B crack defect were proposed, which provided technical support for reducing the crack defect rate of forging material. The results show that the main influencing factor for the middle crack of Q345B slab is the precision of roll gap, and the continuous casting process parameters are also important conditions for the formation and propagation of slab cracks. In view of the above reasons, the process of improving roll gap accuracy, reducing superheat and increasing secondary cooling intensity can improve the equiaxed grain quality and basically eliminate the intermediate crack defects. The development of F-EMS process can fundamentally improve the internal quality and thoroughly solve the problems of intermediate cracks.
2021 Vol. 40 (4): 38-42 [
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Continuous Casting Equipment
43
XU Yan-yi, ZHANG Yun-hu, LI Qing-ping, ZHENG Tian-qing, ZHAI Qi-jie
Distribution and evolution of temperature in constant temperature billet of continuous casting process by induction heating
Constant temperature billet of continuous casting is an effective means to realize direct rolling process. In order to achieve the purpose of constant temperature casting of round billet, a method of constant temperature casting by variable power induction heating in the cutting section of continuous casting billet was put forward according to the principle of induction heating. Feasibility study on the method was performed by numerical simulations. The numerical results showed that magnetic flux density and induced electric current are induced inside the billet by applying alternating current into coils. Magnetic flux density and induced electric current are assembled in the vicinity of the billet surface. In addition, Joule heating induced by induced electric current is beneficial to a uniform distribution of temperature in round billet. The effect of induction heating on constant temperature round billet first increases and then decreases with the increase of frequency or the velocity of billet. It indicated that a constant temperature round billet can be obtained by induction heating with a variable power. In order to optimize induction heating power, a theoretical model on induction heating power was established. According to the theoretical model, induction heating power achieving constant temperature billet is related to geometric dimensions, material properties, initial temperature and velocity of billet and the length of coils.
2021 Vol. 40 (4): 43-58 [
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59
LIU Zhi-yuan, DING Ning, WANG Chong-jun, GUO Wen-bin, LUO Cheng, LÜ Si-run
Application and practice of intelligent electromagnetic stirring control system in continuous casting process
Electromagnetic stirring is an effective way to improve the internal quality of slab and expand the production variety. In order to solve the quality problems that the ratio of C-grade products was only 45.48% and the proportion of central porosity was 14.72% before electromagnetic stirring in the secondary cooling zone of No.3 slab caster, the intelligent control system of electromagnetic stirring was implemented. When the technological conditions such as drawing speed, tundish temperature and steel grade changed, the oscillating magnetic field was formed by the current fluctuation in real time. At the same time, the process is optimized comprehensively by means of molten steel purity, roll gap precision, narrow temperature and narrow composition control.The results show that the ratio of C-grade increases from 45.48% to 100%, the proportion of center porosity decreases from 14.72% to 0, and the pass rate of steel plate flaw detection increases from 95% to more than 99.80%, reaching the quality control level of billet equipped with soft reduction casting machine.
2021 Vol. 40 (4): 59-65 [
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Technology Exchange
66
DUAN Hai-yang, WANG Xu-dong, YAO Man
Predicting longitudinal crack of slab based on dynamic time warping and k-Nearest Neighbor
Longitudinal cracks are typical surface defects of slabs, which seriously affect the quality of casting slabs and process progression. The identification and prediction of longitudinal cracks is of great significance to improve the quality of the cast slabs. According to the dynamic evolution and one-dimensional propagation characteristics of the mould thermocouple temperature in time series during the formation and propagation of longitudinal cracks, the typical variation trends of the thermocouple temperature in time series under longitudinal cracks and normal conditions were captured and extracted. Dynamic Time Warping (DTW) method is used to measure the similarity and difference of time series temperature under different working conditions, and k-Nearest Neighbor (kNN) classification algorithm is used to establish online identification and classification model for longitudinal crack of continuous casting billet.The results show that the model has a high accuracy rate for the identification of longitudinal crack and normal condition samples, which provides a reliable way for real-time detection and accurate prediction of slab longitudinal cracks.
2021 Vol. 40 (4): 66-71 [
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72
LIU Zhi-yuan, YANG Quan-hai, WANG Chong-jun, GUO Wen-bin, LUO Cheng, DING Ning
Research and practice on high casting speed of continuous casting slab
High casting speed production of continuous casting machine is one of the most effective measures to greatly improve the production efficiency of continuous casting.In order to solve the problem of mismatch between furnace and continuous casting caster caused by lower service life of tundish and slower casting speed, the production process is adjusted by optimizing the equipment structure and improving the production efficiency starting from the improvement of tundish service life and the regulation of casting speed. The results show that the overall process optimization can greatly improve the matching capacity between furnace and the caster, accelerate the consumption of molten steel, and increase the production efficiency of the continuous casting caster, which laying a solid foundation for high-efficiency continuous casting.
2021 Vol. 40 (4): 72-78 [
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