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2021 Vol. 40 No. 1
Published: 2021-02-18
Continuous Casting Technology
Strand Quality
Continuous Casting Equipment
Technology Exchange
Continuous Casting Technology
1
YANG Jie, YAO Hai-ming, LÜ Hao, MA De-gang, LI Jing-zhe
Research of slab segregation of dual phase steel for automobiles
The research of slab internal segregation of DP780 was carried out for finding the influence of process conditions of continuous casting and the cause of banded structure. Test equipments and test methods of original pisition analysis, drilling cutting composition testing, optical microscope and scanning electron microscopy (SEM) were used, the influence of tundish superheat, casting speed on slab macrosegregation was analyzed, the influence of secondary cooling ratio and tundish superheat on primary and secondary dendrite spacing was analyzed, and the influence of slab dendrite segregation on banded structure of hot rolled plate was studied, mechanism and countermeasures has been clear about banded structure happening of dual phase steel. The results showed that the degree of superheat was less than 30 ℃, the level of slab center segregation of dual phase steel could be controlled under C1.0, center equiaxial grain ratio could reach 12.25%. Casting speed had little influence on the center equiaxial grain ratio of slab. Primary and secondary dendrite spacing of dual phase steel slab were reduced by reducing superheat and improving secondary cooling ratio.
2021 Vol. 40 (1): 1-8 [
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9
LI Kang-kang, ZHANG Cai-jun, XIAO Peng-cheng, YUAN Zhi-peng, HOU Ming-shan, ZHENG Ying-hui
Analysis on interface fluctuation of steel slag in mold of high casting speed thin slab continuous casting
In order to deal with the instability behavior of molten steel in the thin slab mold with increasing casting speed, taking the 1 520 mm×90 mm thin slab mold as the research object, the liquid level tracking technology VOF method was used to model and calculate the steel slag interface in the thin slab continuous casting mold. The fluid flow and the behavior of steel/slag interface in thin slab continuous casting mould were simulated. Combined with the actual production process, the effects of casting speed, immersion depth and mold flux viscosity on mold flow field and slag interface were analyzed by 1∶1 physical model and numerical simulation. The results show that when the liquid steel flow rate is 0.20-0.25 m/s and the interface is stable, the mold flux viscosity higher than 0.237 Pa·s can be applied. When the liquid steel flow rate is 0.25-0.30 m/s and the viscosity of mold flux is 0.382 Pa·s, the slag entrapment rate of low carbon steel is less than 0.5%, showing good slag entrapment ability.
2021 Vol. 40 (1): 9-14 [
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15
HE Hao, WANG Qiang, XIAO Hong, PENG Peng, MA Zhi-min, LIAO Yun
Numerical simulation and design optimization of on-line induction heating process for billet steel rolling
Aiming at the popular uneven edge temperature during induction heating and rolling for billet castings, a coupled magnetic-thermal model has been presented, together with a following finite element analysis. Based on the industrial data from actual application, the validated model has been adopted for the optimization of the induction coils. It is shown that the magnetic flux density of the coils at the edge area has been improved with the new design, which is beneficial to reduce the temperature difference of rolling products. Accordingly, the possible edge crack due to uneven temperature during hot rolling process can be well controlled specially for alloyed steels.
2021 Vol. 40 (1): 15-20 [
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21
JIN Lei, SI Yu, LI Ke-jian
Production practice and furnace condition maintenance of 80 t converter to increase scrap ratio
Main raw materials for converter steelmaking are scrap steel and molten iron. Due to the continuous consumption of domestic and foreign iron ore resources and high-quality coking coal resources, as well as the increasingly stringent requirements for energy conservation and emission reduction, the production cost of molten iron in blast furnaces has increased, while the price of scrap has gradually decreased. Increase the scrap ratio and reduce the consumption of molten iron to reduce the cost of converter steelmaking. After the scrap steel is increased, the new oxygen lance position control, the flexible addition of light-burned dolomite and lime two auxiliary materials, and the use of anthracite as the heat source to increase the temperature of the converter in the early stage, the steel mill eats up to 250 kg/t of scrap, and the average tapping volume is 83.5 t, and the furnace age is controlled between 14 000 and 17 000 furnaces.
2021 Vol. 40 (1): 21-25 [
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26
ZHANG Kai-fa, WANG Ming-lin, ZHANG Hui, YANG Bao, WANG Xue-bing, LIU Bin
Numerical simulation of heat transfer and heat charging process
In order to study the temperature change and heat gain and loss in the process of heat transfer and heat charging, and optimize the on-site production system, based on the heat transfer and heat charging process of a steel plant, a two-dimensional heat transfer model of Chamfering slab cooling and solidification, roller transportation and in furnace heating is established by using finite element method, and the correctness of the model is verified by field temperature measurement.The results show that the quasi ellipse temperature distribution with the lowest corner temperature, the second narrow surface temperature and the highest core temperature will be formed during the hot transfer process; during the furnace heating process, the low temperature region will gradually move from the corner to the center, and gradually form the quasi ellipse with the highest corner temperature and the lowest core temperature Shape distribution. During furnace heating, the maximum heat absorption of slab in the first heating stage accounts for about 52.01% of the total heat absorption, followed by the second heating section accounting for 35.26%. The heat absorption capacity of preheating section and soaking section is small. Through the numerical simulation of hot delivery and hot charging process, it is found that there is a problem of too long casting time in the furnace. Under the existing process, the billet can be discharged from the furnace after entering the soaking section for 368 s. By adjusting the production rhythm or reducing the furnace temperature, the output can be increased or the energy consumption can be reduced.
2021 Vol. 40 (1): 26-35 [
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36
GUO Luo-fang, HUI Rong, WANG Guang-shun, GAO Yong-bin, CHEN Dian-qing, LI Yong-kang
Study and application on soft reduction operation models of convex roller for high carbon steel
A mathematical model of solidification heat transfer which is close to the actual conditions is established based on a continuous casting machine with soft reduction in a domestic iron and steel company and by combining the solidification heat transfer principle of continuous casting and nail-shooting experiments verification. The downforce interval predicted by this mathematical model has been applied to the pre-stressed steel wire strand of YL82B, and a good application results have been obtained. The results show that after the nail-shooting experiments verification, the calculation results of the mathematical model are basically consistent with the thickness of the solidified shell and the temperature of the wide surface. It has been verified by industrial tests that the central carbon segregation, press crack and loose center of the billet of YL82B steel can achieve the desired effect, when the the solid phase ratio
f
of YL82B steel under soft reduction with convex roll is 0.38-0.90.
2021 Vol. 40 (1): 36-40 [
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41
WANG Zhi-guo, WANG Ming-lin, WEI Jun-you, ZHANG Hui, CHEN Li, WU Xuan
Physical simulation on surface velocity of molten steel in slab molds with different shapes
Flow behavior of molten steel on the surface of mold with different corner shapes was studied by 1∶1 hydraulics model. The effects of casting speed, nozzle insertion depth and cross-sectional width on the surface velocity of molten steel in the corner of slab mold with different corner shapes were investigated. The results show that, compared with the right-angle mold, the presence of chamfered mold chamfered surface has a significant effect on the liquid velocity at the corner, and increases with the increase of the chamfered surface length. In addition, in the right-angle mold, the corner flow field changes little with various process parameters,and the fluid flow at corner belongs to the dead zone. The existence of chamfering changes the flow state of the corners, increases the flow velocity of the molten steel in the corners and benefit for improving the surface quality of the slab.
2021 Vol. 40 (1): 41-46 [
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DU Yi-zhe, LI Li, WANG Qin-zheng, CHEN Deng-fu
Analysis of slab temperature and stress under single roll heavy pressing for extra thick slab
In order to obtain the influence of different reduction on slab temperature, stress and strain during heavy reduction, and to evaluate the tendency of corner and internal crack, the solidification heat transfer model of ultra heavy plate was established by using secondary cooling software of slab continuous casting, and the stress-strain model of single roll heavy reduction was established by Abaqus finite element software. The temperature distribution and stress-strain behavior of medium and extra thick plate were studied by numerical simulation. The results show that the surface temperature of the slab will be reduced by heavy pressing, and the decrease of the central temperature is about 1.4 times of that at the corner. The results show that the stress distribution of the slab along the thickness direction presents symmetry along the center, the stress decreases from the inner and outer arc to the center, and the temperature in the corner is the lowest and the stress is the largest. When the reduction increases from 5 to 30 mm, the maximum stress in the corner increases from 84 to 170 MPa, and the tendency of corner cracks increases. In the range of 5~30 mm reduction, the maximum equivalent plastic strain at the solidification front of the slab is less than the critical strain, so there is no internal crack in the slab.
2021 Vol. 40 (1): 47-54 [
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Strand Quality
55
LI Quan-hui, TAO Biao, XU Zhi-xiang, ZHOU Jian, WANG Qiang-qiang, HE Sheng-ping
Effect of mold slag on slag-scratch on continuous casting billet of GCr15 bearing steel
To solve the problem of slag-scratch defect on the surface of GCr15 steel strand continuous casting billet, the physical and chemical properties of the mold flux were systematically analyzed, and two solutions were proposed to improve the melting and lubrication of mold flux, and industrial trials were conducted to test the effect of mold slag.The viscosity of the mold flux at 1 300 ℃ was reduced from 0.35-0.55 to 0.15-0.25 Pa·s, the melting point was lowered from 1 180-1 220 to 1 060-1 110 ℃, the slag consumption of steel was increased from 0.27 to 0.35 kg/t(steal), and the slag-scratch defect was eliminated.
2021 Vol. 40 (1): 55-58 [
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Continuous Casting Equipment
59
YANG Chang-lin
Optimization method of design of roller arrangement for vertical-curved slab caster
For the conventional vertical-curved slab caster, the design of roller arrangement and the relationship among the radius of curved zone, the length of bending zone, the length of straitening zone and the height of caster are introduced. The optimization method of designing roller arrangement parameters is proposed, and the stress of the caster before and after optimization is briefly analyzed. Results indicate that, for the vertical-curved slab caster, when the length of caster and the height of vertical zone are given, the radius of curved zone and the length of bending zone could be determined by the height of caster. The straightening length of the casting machine can be calculated according to the height of the casting machine, the radius of curved zone, and the length of bending zone. The optimized results obtained by computer program indicate that bulging force and the withdrawal resistance for moving strand could be decreased by decreasing the radius of curved zone and increasing the length of straitening zone.
2021 Vol. 40 (1): 59-65 [
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Technology Exchange
66
GONG Jiang-rong, LIU Peng-tao, HAN Li-min
Discussion on dedusting method in casting area of continuous caster
With the implementation of ultra-low emission requirements in the iron and steel industry, dedusting in the casting area is gradually becoming a necessary configuration of continuous casting machine. When adding dedusting facilities in the casting area, it is the key to the successful implementation dust removal in casting area to minimize the influence of new equipment on existing process operation and minimize modification of casting equipment and platform structure. Combined with the design practice, this paper introduces three typical methods of dust removal in casting area of domestic continuous casting production at present, and analyzes and compares the structure characteristics of dust collecting hood, the influence on process operation and equipment,and the amount of platform modification. It provides a reference for the choice of dust removal method in casting area of continuous casting production.
2021 Vol. 40 (1): 66-69 [
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YANG Xue-yu, ZHENG Li-yun
Effective control of slag removal on breakout in thin slab continuous casting
Based on the characteristics of CSP thin slab process and mold in Handan Iron and Steel Co., Ltd. the influence mechanism of slag strip on the breakout such as adhesive breakout, slag leakage, longitudinal breakout is analyzed. Combining many process and production factors such as mold liquid steel level, heat flow, mold powder type, mold top mouth flame, breakout prediction alarm to analyze the formation of slag strips, it achieves fine control of the slag removal operation of the mold, optimizes the lubrication and heat transfer conditions of the shell in the mold, and has a significant effect on reducing the breakout rate. The annual breakout rate of CSP is reduced from 0.07% to 0.03%.
2021 Vol. 40 (1): 70-73 [
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HUANG Yu-zhu
Design optimization of mold width adjusting mechanism for continuous casting machine
Continuous casting machine mold width adjustment has some problems during use in a steel mill, including severe corrosion of parts, falling off of connecting bolts, motor overload, and insufficient accuracy. The reasons for the above problems are poor sealing of the protective sleeve, unreasonable design of the connection bolt, low rated power of the motor, complicated connection structure. Original design has been optimized. The width adjustment mechanism after the design optimization has been used for a period of time, which not only improves the accuracy, but also greatly reduces maintenance costs and spare parts material costs.
2021 Vol. 40 (1): 74-76 [
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HU Zhi-wei, YU Yan-wen, FAN Zhi-hui, ZHAO Wei, LU Xing-hua
High-temperature resistant ceramic gasket with good plasticity and application in steel plant
In order to improve the high temperature resistance and poor tightness of the traditional gasket, a new high temperature resistant plastic ceramic gasket was developed independently. With a new thermoplastic ceramic gasket, the aluminum loss of 1450CCM steel decreased by 15%, the Titanium loss decreased by 20%, and the abnormal proportion of “aluminum loss not less than 0.004%, nitrogen increase not less than 0.000 85%” of oriented silicon steel was reduced. The cleaning is not necessary when nozzles in tundish were continuously used for less than three times. The amount of argon sealing at the long nozzle was reduced from 580 to 380 NL/min. The liquid level of tundish casting flow area is calm and the casting ability is good.
2021 Vol. 40 (1): 77-80 [
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