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2022 Vol. 57 No. 1
Published: 2022-01-15
Technical Reviews
Raw Material and Ironmaking
Steelmaking
Metal Forming
Materials
Equipment Technology
Technical Reviews
1
DENG Zhi-yin, PENG Peng, ZHU Miao-yong
State of art in study on sintering of ladle filler sands and improvement of ladle free-opening rate
In order to avoid oxygen lancing when teeming, the studies on the sintering of ladle filler sands and the practices on ladle free-opening are summarized. The sintering properties of filler sands, and the influential factors of ladle free-opening as well as its improvement methods are introduced, while the sintering mechanism of different types of filler sands and the effect of liquid steel on sintering are discussed in detail. As reported, the sintering structures of different types of filler sands are very similar, and generally divided into sintered layer (including partial sintered layer) and non-sintered layer. The thickness of the sintered layer is quite thin, while most of the sand grains are non-sintered. The formation of the liquid phase is the key to the sintering of ladle filler sands, and more liquid generation would result in serious sintering. Proper control of the formation of the liquid phase in ladle filler sands and the thickness of the sintered layer is crucial for the teeming of alloyed steels. The composition and the size of filler sands, steel composition, temperature as well as holding time are the main influential factors to improve ladle free-opening rate. Liquid steel is involved in the sintering process and enhances the formation of the liquid phase, accelerating the sintering. The development of a new kind of filler sands should take the steel composition into account. In general, conventional chromite-based filler sands can obtain a high free-opening rate during the teeming of conventional steel grades. In case of the steel grades containing high contents of alloys (especially Mn and Al), the application result of the chromite-based and zircon-based filler sands is unsatisfied, and new types of ladle filler sands are required to restrain the acceleration of liquid steel on the sintering and improve the ladle free-opening rate.
2022 Vol. 57 (1): 1-12 [
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13
REN Ying, LI Xin-zhe, YUAN Tian-xiang, CHEN Wei, ZHOU Hai-chen, ZHANG Li-feng
Source analysis and control status of slag defects on surface of hot-rolled coil
The slag entrainment defects on the surface of hot-rolled coils have an extremely bad effect on the quality and product performance of hot-rolled coils, resulting in the degradation of product grades and even scrapping, and deteriorate the service deadline and performance of the products to a certain extent. With the continuous improvement of the cleanliness of the molten steel in the smelting process, the quality problems caused by slag entrainment defects appear to be particularly serious. The sources of surface slag entrainment defects under different production processes are slightly different. The main sources of defects are ladle slag entrapment during refining, ladle roughing slag during unsteady pouring, tundish covering agent involvement during steady pouring, mold slag entrapment, and so on. The control and optimization of slag entrainment defects on the surface of hot-rolled coils are of great significance to improve its surface quality. The sources of slag entrainment defects were summarized and analyzed, including the ladle refining slag, tundish covering agent, mold flux, refractory lining, and so on. The effect of the fluid flow of the molten steel inside the mold, mold flux properties, and meniscus behavior on the mechanism of the slag entrainment were summarized and analyzed. The methods to control slag entrainment defects on the surface of hot-rolled coils at home and abroad were summarized and analyzed. Some guiding suggestions were putting forward, adding electromagnetic coils around the submerged entry nozzle to reduce the vortex through the direct action of the DC magnetic field, adding a baffle at the tundish shroud to improve the eccentricity of the ladle outlet, changing the nozzle parameters to reduce the shear force induced by the upper recirculation steel fluid flow, changing properties of the mold flux or adding the electromagnetic force to balance the surface tension of the slag-steel interface, and optimizing casting parameters such as the argon flow rate.
2022 Vol. 57 (1): 13-27 [
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28
WANG Yu, PENG Xiang-fei, LI Jun, YANG Yang, LI Guo-ping, LIU Yan-lin
Research progress on strengthening mechanism and ballistic performance of high nitrogen austenitic stainless steels
High-nitrogen austenitic stainless steel (HNASS) is a novel material which is developing rapidly and used in transportation, marine engineering, building materials, medical equipment, military industry and other fields. Compared with traditional austenitic stainless steels, HNASS has excellent mechanical properties,such as good strength, toughness, high creep resistance and corrosion resistance. Nitrogen in HNASS has good effect on refining grain size, deformation, solution and precipitation strengthening, which reflects the multidirectional effects of nitrogen in steel, and has a significant effect on the strength improvement of austenitic stainless steel. Among the various strengthening effects, the solution strengthening of nitrogen produces a similar effect with the grain refining, that is, the plasticity of the material is not reduced when the nitrogen element is used to enhance the strength of the material. At the same time, in the aspect of dynamic mechanical properties, with the increasing of HNASS compression strain rate, the compressive strength increases first and then decrease, while the strain hardening index will increase. HNASS also has excellent impact energy absorption effect and hardening properties, especially the dynamic impact hardening properties, which obtained more plastic deformation through the plastic area. Therefore, HNASS has a broad application prospect in the field of anti-missile Armor protection. In order to systematically and comprehensively analyse the research status of nitrogen element on strengthening mechanism and dynamic protection performance of HNASS, the effect of nitrogen element in HNASS along with its dynamic mechanical properties and penetration plate target action were systematically reviewed in combination with the research status at home and abroad. The research prospects of HNASS in high efficiency nitrogen fixation process, effects of nitrogen content gradient and multi-component composite system were also proposed.
2022 Vol. 57 (1): 28-38 [
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39
LIU Zheng-jian, LI Si-da, ZHANG Jian-liang, WANG Yao-zu, WANG Gui-lin, NIU Le-le
Production practice and development trend of iron ore sinter with ultra-high basicity
In order to meet the national call for carbon peak carbon neutralization, iron and steel enterprises have higher and higher requirements for energy saving and emission reduction in production. Due to the huge solid waste emissions in the production process, sintering process is often faced with problems such as insufficient sintering capacity caused by production limit. The world production practice shows that high proportion pellet smelting in blast furnace has the advantages of low fuel ratio and less slag amount. At the same time, it has brought development prospects due to the excellent pellet performance and more environmental-friendly production process. In order to cooperate with the application of a high proportion of pellet charge structure and avoid problems such as insufficient sinter production capacity due to limited production because of environmental protection, many domestic steel companieshave launched ultra-high basicity sinter production explores. Firstly, this article studies the relationship between mineralization mechanism and quality of ultra-high basicity sinter from two aspects of sintering process and mineral composition change, and finds that the basicity of sinter is in the range of 2.10-2.80. With the increase of basicity, the main mineral bonding phase gradually changes to calcium ferrite bonding phase, and the mineral composition gradually becomes stable.When the basicity exceeds 2.80, the vitreous and cracks in the bond phase gradually increase, which seriously affects the quality of sinter. Then this article summarizes the production profile and technical and economic indicators of ultra-high basicity sinter in typical domestic steel enterprises. The sintering process and mineralization mechanism of ultra-high basicity sintered ore were clarified based on the practice and the principles of mineralogy. Finally, the problems in the production of ultra-high basicity sinter in iron and steel enterprises are summarized. Based on sintering process, mineralization mechanism and previous practical experience, the causes of the problems are discussed, and corresponding solutions are proposed.
2022 Vol. 57 (1): 39-47 [
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Raw Material and Ironmaking
48
WANG Liang, CHENG Shu-sen, LIU Peng-bo, CHEN Yan-bo
Effect of K
2
O and Na
2
O on activity of components and MgO content of high Al
2
O
3
slag
With the acceleration of consumption of high-grade iron ore and the gradual dilution of resources, the available iron ore raw materials for iron and steel enterprises are gradually transformed into medium and low grade raw materials. Especially high alumina iron ore, the use of such raw materials will undoubtedly increase the Al
2
O
3
mass percent of blast furnace slag and affect the existing operation system of blast furnace.In order to ensure the metallurgical properties of slag, about 8% MgO must be added to the blast furnace slag, which contains 15%-17% high Al
2
O
3
. Because of high Al
2
O
3
content, the metallurgical properties of blast furnace slag become worse. However, the MgO content of POSCO′s blast furnace slag with similar mass percent of Al
2
O
3
is only about 4%, but the blast furnace has achieved high efficiency, stability and smooth running. Therefore, the effects of K
2
O and Na
2
O on the activity of each component in the quaternary slag system CaO-SiO
2
-Al
2
O
3
-MgO of blast furnace slag were studied based on the physical chemistry mechanism of the blast furnace CaO-SiO
2
-Al
2
O
3
-MgO quaternary slag system. The relationship between alkali metal oxides in slag and gas under the condition of slag-gas equilibrium was studied. The effects of K
2
O, Na
2
O and MgO on viscosity were calculated. The results show that considering the component activity of blast furnace slag CaO-SiO
2
-Al
2
O
3
-MgO, the distribution of alkali metals between slag and gas and the slag viscosity, the content of MgO can be reduced appropriately when the alkali metal oxides K
2
O and Na
2
O exist, and the component activity of blast furnace slag CaO-SiO
2
-Al
2
O
3
-MgO and slag viscosity can be kept basically unchanged.It is not only helpful to reduce the addition of magnesium-containing flux in blast furnace raw materials, improve the grade of raw materials, discharge alkali efficiently, reduce alkali harm, reduce carbon emissions, prolong the life of blast furnace and reduce costs, but also promote the iron and steel enterprises to achieve the goal of energy saving and emission reduction.
2022 Vol. 57 (1): 48-56 [
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57
HOU Piao, YU Wen-zhou, BAI Chen-guang, PAN Cheng, YUAN Wan-neng, LI Tao
Viscous flow properties and influencing factors of vanadium-titanium magnetite smelting iron
Vanadium-titanium magnetite is one of the important iron ore resources in China, which has extremely high comprehensive utilization value. The efficient smelting of vanadium-titanium magnetite will bring huge economic benefits, the viscous flow properties of molten iron is the key factor affecting the anterograde of the blast furnace. The molten iron bearing vanadium (V) and titanium (Ti) can be smelted from the vanadium-titanium magnetite ore by blast furnace. The fluidity of V-Ti bearing molten iron is poorer than that smelted from the ordinary iron ore, which may result in difficulties in iron discharge and retaining of molten metal in tapping channel and iron ladle. In this case, the smelting process can be seriously affected. The effects of V and Ti contents on viscosity of molten iron were obtained through the self-developed viscosity tester in the research of V-Ti bearing molten iron.Meanwhile, the growth mechanism of high melting point phase in molten iron was explored by means of microscopic in-situ analysis and characterization, and the influence mechanism of composition on viscosity was deeply revealed.The results indicate that the viscosity of molten iron gradually increased with the increasing of Ti content when the mass percent of Ti varied from 0.10% to 0.50%. The V content had no significant effect on viscosity of molten iron when the mass percent of V was lower than 0.30%, while the viscosity of molten iron increased sharply with the increasing of the mass percent of V when it was higher than 0.30%. In addition, the main reason for this phenomenon is the precipitation of high melting point carbonitrides (TiC, TiN, VC, VN) which can distribute in molten iron, and then increases the viscosity and deteriorates the fluidity of molten iron. It is demonstrated that there are two mechanisms for the growth of high melting point phases in molten iron. One is the nucleation growth of high melting point phase, and the other is the growth of high melting point phase by collisional polymerization after nucleation.
2022 Vol. 57 (1): 57-65 [
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Steelmaking
66
ZHU Hang-yu, WANG Wei-sheng, ZHAO Ji-xuan, LI Jian-li, SONG Ming-ming, XUE Zheng-liang
Effect of manganese raw materials on non-metallic inclusions in low alloy TRIP steel
To clarify the effects of manganese materials on the cleanness of TRIP steel and the hereditary character from manganese alloys to steels, the type, morphology, and size of non-metallic inclusions (NMI) were detected using SEM-EDS. Then, the NMI characteristics in TRIP steel were systematically discussed based on high-temperature experiments and thermodynamic calculations. The results show that, the main inclusions in electrolytic manganese were MnC, MnC-MnO, MnO-MnS and trace MnO, the main inclusions in manganese metal were single MnO, single MnS and complex MnO-MnS, and the medium carbon ferromanganese mostly contained complex MnO-SiO
2
and MnO-SiO
2
-MnS inclusions, the trace MnC particles and enrichment phases of residual elements were also detected. During alloying process, the dominant NMI was Al
2
O
3
after the addition of Al and Si, and then the NMIs were changed to Al
2
O
3
, MnS, AlN, Al
2
O
3
-MnS and Al
2
O
3
-AlN after manganese addition after Mn alloying. For TRIP steel, after alloying with electrolytic manganese, manganese metal and medium carbon ferromanganese, there was little difference in the types of NMIs in the steel. Due to the high-Al characteristic in molten steel, the MnC and MnS inclusions from manganese materials were dissolved to molten steel, and then the MnO and SiO
2
inclusions were reduced to Al
2
O
3
. The evolution route of manganese and silicon oxides during the smelting process was MnO/MnO-SiO
2
→Al
2
O
3
→MnS/Al
2
O
3
-MnS. During the solidification, pure AlN and MnS inclusions precipitated or Al
2
O
3
-MnS and Al
2
O
3
-AlN complex inclusions were formed, due to the enrichment and segregation of Al, N, Mn and S elements. Moreover, the addition of manganese materials may promote the formation of AlN inclusion, the possible explanation was that manganese materials contained N element or Mn increased the solubility of N element.
2022 Vol. 57 (1): 66-73 [
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74
CHEN Lu, LI Chang-rong, XIONG Xing-qiang
Crystallographic analysis of modification of Al
2
O
3
inclusions in high carbon hard wire steel by lanthanum
In order to control and improve the number, shape and distribution of alumina inclusions in high carbon hard wire steel, improve the purity of steel, refine the structure of steel, and even the chemical composition of steel, rare earth lanthanum is added to high carbon hard wire steel. The element studies its modification of alumina inclusions. The rare earth oxygen (sulfide) compound formed by adding rare earth lanthanum to high carbon hard wire steel was characterized by scanning electron microscopy and energy spectrum analysis, and the modification of it on alumina was studied. It is found that the addition of lanthanum can change the shape of inclusions. The inclusion changes from an irregular shape to a more regular ellipse, and as the distance between inclusion surface increases, it gradually disperses. Thermodynamics and edge-edge matching model were used to calculate the interatomic mismatch along the dense row crystal direction between γ-Fe and Al
2
O
3
and the interplanar mismatch of the dense row crystal plane. The possibility and effectiveness of lanthanum inclusions as the nucleation core of primary phase during solidification of molten steel were explored. The results show that after adding lanthanum, according to the Gibbs free energy of inclusions in the temperature range of 1 000-2 000 K, the order of possible inclusions produced in steel is, La
2
O
3
>La
2
O
2
S>LaAlO
3
>LaS>La
3
S
4
. The edge-edge matching model was used to calculate the atomic matching between rare earth oxygen (sulfide) compounds and γ-Fe and Al
2
O
3
. It is found that La
2
O
3
, LaS, La
2
O
2
S and La
3
S
4
may all be the cores of Al
2
O
3
and γ-Fe heterogeneous nucleation. Moreover, La
2
O
2
S may preferentially become the nucleation core of γ-Fe heterogeneous, while LaS may preferentially become the core of Al
2
O
3
heterogeneous nucleation,the modification mechanism of alumina inclusions in steel is revealed, which provides a theoretical basis for the treatment of non-metallic inclusions in high-carbon hard wire steel.
2022 Vol. 57 (1): 74-82 [
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83
LIU Wen-xiang, REN Lei
Influence of outlet angle for submerged entry nozzle on fluid flow in a wide slab casting mold
The outlet angle of submerged entry nozzle affects the kinetic energy loss of jet,then affects the flow behavior in the mold. A 1∶4 scale water model of slab mold was built. The influence of 0° and +5° nozzles on the flow behavior in wide slab casting mold was studied using particle image velocimetry under the condition that pulling rate was 0.425 m/min and nozzle immersion depth was 40 mm. The results show that there is a big difference in jet morphology between 0° and +5° nozzle. When the angle is 0°,the jet flow is relatively concentrated and spread slowly,it will spread to the wide surface in the direction of thickness when it reaches the narrow surface. However,at +5°,the jet has a process of upward impact and back again,and the expansion range of jet is larger than that of the 0° nozzle. This will make more jets impact the wide surface before reach the narrow front(which can reach the wide surface within 0.3 s). It means that the molten steel scours dendrite at the front of solidification for wide surface more greatly in actual production,which is not conducive to the growth of slab shell. When the liquid steel flows through +5° nozzle,it first impacts the bottom of nozzle in the direction of gravity,and then returns +5° to shoot from the nozzle. In this process, the kinetic energy loss of liquid steel is greater than 0° nozzle. In addition, the liquid steel flows through a longer distance in the wide-width mold than in the ordinary mold,so the kinetic energy is lost more. This is disadvantageous to the melting of slag and affecting the continuous casting. Comparing the flow fields of the center section,1/4 section and section close to the wide surface under 0° and +5°,the closer to the wide face the velocity of the whole flow field is smaller. At the angle of 0°,the velocity decreases from 0.103 m/s in the central plane to 0.042 m/s in the wide face,and it decreases from 0.097 m/s to 0.066 m/s in the angle of +5°. The symmetrical and asymmetric flow patterns in the mold under 0° and +5° conditions were analyzed. At 0°,86% of the flow states are symmetrical and 14% are asymmetric,while 69% of the flow states are symmetric and 31% are asymmetric at +5°.
2022 Vol. 57 (1): 83-92 [
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93
PAN Wei-jie, LI Min, ZHU Li-long, HE Sheng-ping
Effect of Na
2
O on properties of ultra-high basicity continuous casting mold fluxes
During the continuous casting of peritectic steel, defects of longitudinal cracks of casting strands frequently appear. Production practice shows that mold fluxes with strong crystallinity can effectively reduce the occurrence of longitudinal cracks, but it will deteriorate the lubrication function of mold fluxes. In recent years, the ultra-high basicity continuous casting mold fluxes have the characteristics of low initial crystallization temperature and fast crystallization rate, which can successfully balance the contradiction between lubrication and heat transfer in the continuous casting of peritectic steel. However, there are few studies on the effects of related components on the crystallization properties of the ultrahigh basicity mold slag, and the corresponding structural characteristics are also rarely reported. Na
2
O is a common component element in mold fluxes and plays an important role in adjusting the properties of mold fluxes. The effect and mechanism of Na
2
O content on the melting flow characteristics and solidification and crystallization properties of continuous casting mold fluxes at ultra-high basicity(
R
=1.75) was analyzed by hemispherical point melting temperature tester, rotational viscometer and high temperature in-situ crystallization performance tester. The results showed that the viscosity (1 300 ℃) of mold fluxes,melting temperature,break temperature and crystallization temperature all decreased with the increase of Na
2
O content,while the crystallization rate first decreased and then increased,and the crystallization rate was the lowest when mass percent of Na
2
O was 6%. In addition,it is found that the main precipitates in the ultra-high basicity mold flux were gun spar(Ca
4
Si
2
F
2
O
7
). With the further increase of Na
2
O content,the new crystalline phases CaF
2
and Na
2
CaSiO
4
F appeared in the mold flux.
2022 Vol. 57 (1): 93-101 [
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Metal Forming
102
GONG Dian-yao, GAO Zhi-yu, XU Jian-zhong, ZHAO Xian-ming
Finite element simulation of "out-of-square" during ultra-fast cooling of small-size H-beam steel
Ultra-fast cooling is of great significance for the microstructure optimization and performance improvement of H-beam steel. The "out of square" after cooling is an important factor affecting product quality and production stability and also limits the popularization and application of the ultra-fast cooling process. In the cooling process of H-beam steel, the heat transfer coefficient is the key parameter. In order to study the effect of heat transfer coefficient on the "out of square" of small-size H-beam steel during ultra-fast cooling,a 2-D thermal mechanical coupling simulative model is established using Abaqus to simulate the cooling process of the small size H-beam steel. Considering the different cooling characters of the flange and web positions,the section of H-Beam steel is divided into 16 particular cooling areas with particular heat transfer coefficients. As well as three cooling solutions are proposed,under different cooling conditions,the cooling processes are simulated respectively and the temperature field,stress field,and the width difference between upper and lower are obtained. The character of uneven temperature field distribution accompanied by irregular stress field is analyzed. The experiment is conducted to simulate the cooling process of small size H-beam steel. The temperature field after cooling is obtained using the thermal image instrument. The simulation results meet experimental data well. Based on the experiment and simulative calculation,the relevant regularities are summarized,including the uneven Mises stress and equivalent strain distribution along paths specified on the simulative model, which are at the lateral direction of upper and lower flanges and the vertical at
R
corner. The linear relationship between the changing heat transfer coefficients of
R
corner and width differences are analyzed, and a mathematic model is built to describe it. The research results have theoretical significance and reference value for optimizing the cooling process and improving the uniformity of ultra-fast cooling of small H-beam steel.
2022 Vol. 57 (1): 102-109 [
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110
LI Xue-tong, SUN Ye-xuan, LIU Ya-xing, REN Ming-hua, TAN Chao-chao, JIA Wen-qiang
Optimal setting technology of process lubrication system for 3+1 emulsion system
In order to study the quality difference between the upper surface and the lower surface of the cold-rolled strip due to insufficient lubrication,over-lubrication and insufficient cooling in the rolling deformation zone to produce stainless steel products with a 3+1 emulsion system,a certain steel the newly-built six-stand tandem cold rolling mill is the research object. From the perspective of emulsion process lubrication,the layout of the 3+1 type emulsion process lubrication system of the mill is introduced,and the influence of process lubrication system parameters on rolling stability is analyzed. factor. By revealing the intrinsic relationship between the concentration,temperature and flow rate of the emulsion and the dynamic viscosity of the lubricating oil film,a model of the relationship between the emulsion process lubrication system and the thickness of the lubricating oil film was established;further,starting from the friction heat and deformation heat,combined with the convective heat transfer mechanism of heat transfer,established the relationship model of emulsion process lubrication system and cooling effect; and based on this,established the relationship model of process lubrication system,slip and thermal slip. With the goal of maximizing the comprehensive control of the rolling stability of the upper surface of the strip,the stability of the lower surface of the rolling,the difference in lubrication of the upper and lower surfaces of the strip,and the cooling effect of the emulsion,the process of the 3+1 emulsion system has been developed. The comprehensive optimization setting technology of the lubrication system realizes the quantitative optimization of the emulsion concentration,temperature and flow rate of the 3+1 type emulsion system. This technology has been promoted and applied to a six-stand tandem cold rolling mill in a steel plant. The application results show that the optimization method fully exploits the overall lubrication and cooling capacity of the 3+1 emulsion system and ensures that the six-stand tandem cold rolling mill The rolling stability of each stand greatly reduces the difference in the quality of the upper and lower surfaces of stainless steel products,creates greater economic benefits for the site,and has the value of further popularization and application.
2022 Vol. 57 (1): 110-118 [
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Materials
119
WANG Li-guang, WANG Shu-huan, DUAN Yang-hui, LI Jie, FENG Yun-li
Effect of Nb on primary recrystallization behavior of low temperature grain-oriented silicon steel
In order to obtain the primary recrystallization structure conducive to the development of secondary recrystallization,the effect of Nb on the primary recrystallization behavior of low temperature grain-oriented silicon steel was studied,the effects of 0.055% Nb and Nb-free samples on the primary recrystallization structure,texture and grain boundary characteristics of intermediate annealed plate of low temperature grain-oriented silicon steel were studied by OM and EBSD techniques. The results show that the addition of Nb forms fine dispersed Nb (C,N) in the silicon steel matrix,enhances the inhibition of the inhibitor on the growth of primary recrystallized grains,makes the primary recrystallized microstructure of Nb-containing samples more fine and uniform,the average grain size in the surface direction is 11.53 μm,while the Nb-free sample is 12.95 μm. The average grain size in the thickness direction of the Nb-containing sample is 12.46 μm,while the Nb-free sample is 13.78 μm. After intermediate annealing,the surface texture of the Nb-containing sample and the Nb-free sample is relatively weak,but Nb-containing sample have more sharp γ-fiber texture. Two samples of subsurface layer γ-fiber texture and Goss texture are strengthened,and the Nb-containing sample γ-fiber texture is relatively stronger. The beneficial texture content of {111}<112>,{411}<148> is relatively high in the Nb-containing sample.The main grain boundaries in the primary recrystallized samples after intermediate annealing are high-energy grain boundaries and large angle grain boundaries. The high energy grain boundaries in the Nb-containing sample are more than Nb-free sample. The grain boundaries of Nb-containing and Nb-free samples are mainly distributed in Σ3-Σ11 Between grain boundaries,the addition of Nb can increase Σ9 grain boundary content. After the high temperature annealing,the secondary recrystallized microstructure of the Nb-containing sample is more complete than the Nb-free sample,and the final product has better magnetic properties,with
B
800 reaching 1.89 T and
P
1.7/50being 1.37 W/kg.
2022 Vol. 57 (1): 119-125 [
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126
ZENG Chun, CHENG Zhao-yang, WANG Xiang-long, WU Zhang-han
Trial production of Fe-6.5%Si steel ultra-thin strip
In order to study preparation process of Fe-6.5%Si steel ultra-thin strip,and gain good magnetic properties,using 6.5%Si steel cast strip manufactured by strip casting machine as raw material,then be rolled through single warm rolling,double warm rolling and room temperature cold rolling based on the theory of deformation induced disordering(DID) to prepare 0.1 mm thickness Fe-6.5%Si steel. The analysis results show that texture of annealed sheet produced by single warm rolling is mainly composed of γ type with high strength,warm reduction achieved 90%,thus result in high deformation energy,so the annealed sheet has the biggest recrystallization grain size,the lowest iron loss and the lowest magnetic flux density among three processes. Texture of the annealed sheet produced by double warm rolling composed of γ type and η type with high strength,which result in higher magnetic flux density than that of single warm rolling. The 6.5%Si steel thin strip produced by double warm rolling has the best comprehensive magnetic properties,this process,on the other hand,with high production costs and low efficiency; On the base of theory of DID,6.5%Si steel hot-rolled sheet′s warm rolling is carried out at 300-450 ℃ and 45%-65% reduction,thus 6.5%Si steel be softened and then be cold rolled at room temperature to 0.1 mm thickness,ordered phase disappeared in warm-rolled sheet and cold-rolled sheet,the matrix is changed into disordered phase. The annealed sheet produced by room temperature cold rolling has smaller recrystallization grain size and little higher iron loss. Since cold rolling promotes {111}<112> deformed grain nucleation at cold-rolled shear band to come into being favorable texture,so magnetic flux density been greater enhanced. On the base of theory of DID,cold rolling at room temperature has high production efficiency,further lower iron loss shall be gained after annealing process optimization,this process provides technical reference for strip casting mass-produce 6.5%Si steel ultra-thin strip with good magnetic properties.
2022 Vol. 57 (1): 126-132 [
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133
ZHAO Li-jie, ZHANG Fang, PENG Jun, CHANG Hong-tao, MING Shou-lu, ZHU Rui-zong
Chemical composition and pore control of porous stainless steel prepared by rolling steel skin
In order to give full play to the advantages and characteristics of high iron grade,low content of impurity elements and large amount of iron oxide scale,and to develop high value-added metal products,this paper adopts vacuum reduction sintering method to prepare 316 porous stainless steel,and determines the appropriate factors affecting the preparation process and porosity. In the research process,a high-temperature vacuum tube furnace was used to reduce and sinter the samples;direct-reading spectroscopy,combined oxygen,hydrogen and nitrogen detectors,X-ray diffraction analyzers,scanning electron microscopes and other equipment were used to determine the chemical composition,phase composition and microstructure of the samples. The morphology was analyzed. The research results show that using rolled steel skin as the main raw material,with reducing agent and other alloy powders,qualified 316 porous stainless steel can be obtained through high-temperature vacuum reduction. The best preparation process is determined to be 10
-3
Pa vacuum and heat preservation at 1 200 ℃ for 3 h. During the reduction and sintering process,the yield of Mn alloy is only 61%. The prepared sample is a single austenite structure,and at the same time,Cr
7
C
3
is precipitated in the grain,and there is a σ phase precipitation near the grain boundary. The porosity of the sample was increased from 37.26% to 40.27% within 0-3 h of holding time,and the holding time was extended to 4 h,the sintering between the metal particles was more complete,and the porosity was reduced to 35.16%.The billet pressure was increased from 76.43 to 152.87 MPa,the porosity of porous stainless steel decreased from 42.07% to 34.44%,showing a gradual decrease trend. When the sample preparation pressure was greater than 152.87 MPa,segregation of the pore former occurred,causing the porosity to slightly increase to 35.76%. The porosity of porous stainless steel increases by 9.3% for every 10% increase in pore-forming agent ammonium bicarbonate. Through orthogonal test analysis,it is found that the amount of pore former has the most significant effect on the porosity of porous stainless steel,followed by sample preparation pressure,and holding time has the least effect on porosity.
2022 Vol. 57 (1): 133-142 [
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Equipment Technology
143
XU Jia-qiang, SONG Zhong-hua, PAN Ni, TAN Fang-guan, XU Xue-cheng, HE Zhu
Numerical simulation on flameless combustion in U-shaped radiant tube for continuous annealing furnace
In order to ensure that the heated workpiece is evenly heated without affecting its surface quality,the metallurgical industry generally uses radiant tubes to indirectly heat the workpiece. But at the same time,due to the limited combustion space in the radiant tube,it is easy to produce a local high temperature zone,which will affect the quality of the heated product,and the high temperature will cause a large amount of NO
x
to be generated. In addition,the thermal stress generated by the large wall temperature difference will cause the tube wall damaged by creep,shortening its service life. Therefore,in order to optimize the performance of the radiant tube, a new type of radiant tube burner is proposed based on the flue gas recirculation technology,which can increase the flue gas circulation while ensuring continuous combustion. Specifically,the traditional combustion is first carried out in the radiant tube. After the temperature is higher than the auto-ignition point of the fuel,a large amount of flue gas is introduced,so that the U-shaped radiant tube reaches a flameless combustion state. At this time,the surface temperature is more uniform and the NO
x
emission is lower. Through the establishment of a mathematical model of the U-shaped radiant tube with the burner,supplemented by experimental verification,the flameless combustion characteristics in the U-shaped radiant tube were explored,including the combustion state in the radiant tube,the uniformity of surface temperature and the NO
x
emission,and the existing U-shaped radiant tube was compared and analyzed,and the influence of different smoke volume on the flameless combustion characteristics in the radiant tube was discussed. The research results show that the flameless combustion state is completely different from traditional combustion,under traditional combustion,there is an obvious local high temperature zone in the front of the radiant tube;with the introduction and further increase of the volume of cigarette smoking,the peak temperature continues to drop,and the high temperature zone. There is a phenomenon of transfer to the rear of the radiant tube. When the flameless combustion state is reached,the local high temperature area disappears;the flameless combustion greatly improves the surface temperature uniformity of the radiant tube,the extreme value of the temperature difference between the radiant tube wall is reduced from 110 K to 35 K,and the temperature uniformity coefficient is reduced from 9% to 2.9%,which is conducive to improving the actual temperature of the radiant tube. Service life;the emission of pollutant NO
x
is reduced,from the initial 0.022%to less than 0.000 1%.
2022 Vol. 57 (1): 143-150 [
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151
REN Wei-chao, ZHU Guo-ming, LI Yang-long, LI Guan-xiong, ZHOU Huan, WANG Dao-jin
Distribution model of heating output based on on-off controlled annealing furnace
The on-off controlled combustion technology is widely used in various heating furnaces because of its good dynamic response, high temperature control accuracy, low gas consumption and pollutant discharge level. For vertical annealing furnace, there are three common heating models: the proportional model, the narrow model, the normal model. In line running status, operators can choose corresponding models according to the risks of strip deviation and buckling in the radiant tube heating section,but none of these three models are unable to avoid the problems of sudden cooling and heating of the radiator tube due to frequent opening and closing of burners. It could further induce the deformation and cracking of radiation tubes,abnormal consumption of ignition electrodes and control valves and large fluctuation of gas pressure. In order to reduce the frequency of burner opening and closing times,a "stair-climbing" type heating output distribution model was established. The relationship between the controller output of strip temperature and the heating output of each column at radiant tube heating section was fitted,and the correction function of heating output distribution model for the radiant tube heating section was obtained via the interpolation. It met the requirement that the calculated values of the model was consistent with the actual values. The upper and lower limits of each column of heating output were adjusted so that the heating output was distributed in a "stair climbing" manner. The function that the burners in the inlet area of the low power heating section do not work and the burners in the outlet area always work was realized in vertical annealing furnace. A completed combustion cycle was tested. It showed that the "stair climbing" model can greatly reduce the frequency of burner opening and closing times, under a complete combustion cycle. At the condition of 89.6% strip temperature controller output at the radiant tube heating section,the burner was switched on and off for 324 times,whereas it was only 32 times for the "stair-climbing" distribution model. When the strip temperature controller output of the radiant tube heating section is 89.6%, the switching frequency of the burner under the control of the traditional model is 324 times, while that of the "stair climbing" distribution model is only 32 times.
2022 Vol. 57 (1): 151-158 [
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159
BAI Zhen-hua, LIN Wei, WANG Wei, ZHANG Wen-jun, LI Xue-tong
Development of optimization technology for disc shear process parameters of hot-dip galvanizing line
In order to study the main cutting edge quality problems such as the disc shear equipment failure due to improper setting of the cutting process parameters and the occurrence of burrs, burrs and unbalanced cut-off ratio at the edge of the strip due to improper setting of the cutting process parameters during the work. This article takes the disc shear equipment of a hot-dip galvanizing line of a steel plant as the research object, and conducts research on the equipment itself and process parameters. Through the analysis of the factors that affect the quality of the strip edges and the correlation of the input variables of the BP neural network, the four factors of the front tension, the amount of clearance, the amount of overlap, and the amount of trimming are selected as variables and the hot-rolled strip steel disc is analyzed. Based on the shearing mechanism of the blades, combined with the technological characteristics of the disc shearing equipment and the relevant parameters in the cutting process, with the goal of preventing equipment failures and improving the quality of the current edge, the different indicators of the strip edge are carried out correspondingly quantify, put forward the strip quality evaluation function, and use the calculation result as the output layer of BP neural network. On this basis, a model based on PSO-BP neural network was established, and a set of hot-dip galvanizing line trimming process optimization technology was developed. The data source, processing method and the setting method of the parameters of the PSO-BP neural network are also given. The technology trains the BP neural network based on the tens of thousands of key production process parameters of disc shears collected on site, and fits the nonlinear function on this basis. Finally, the particle swarm algorithm PSO is used to analyze the better disc shear clearance. Process parameters such as the amount of overlap and the front and rear tension have caused the trimming quality problem at the edge of the strip after the disc shears. The ratio of the total trimming kilometers is significantly lower than before, which effectively improves the trimming quality of the strip. Lays a foundation for the improvement of unit production efficiency, and at the same time creates better economic benefits for the enterprise.
2022 Vol. 57 (1): 159-166 [
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