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2021 Vol. 56 No. 12
Published: 2021-12-15
Technical Reviews
Raw Material and Ironmaking
Steelmaking
Metal Forming
Materials
Environmental Protection and Energy
Technical Reviews
1
ZHANG Jian-liang, YU Ji-yong, LIU Zheng-jian, XU Run-sheng
Current situation and trend of air pollutant emission in China′s steel industry
At present, China′s crude steel output has accounted for more than half of the world′s total output, and the development of China′s steel industry is of great significance to the world. China′s steel industry mainly adopts the long-process smelting technology of "blast furnace-converter" which uses coal as the main fuel. As a result,a large number of air pollutants,including sulfur dioxide (SO
2
),nitrogen oxides (NO
x
) and particulate matter (PM
2.5
),etc. are emitted during steel production. This paper summarizes the current status of air pollutant emissions in China′s steel industry from the sources of pollutants in the iron and steel industry, changes in the total emissions of pollutants, the characteristics of pollutant emissions from different smelting processes, the regional distribution of pollutant emissions in China′s iron and steel industry and the characteristics of pollutant emissions from iron and steel enterprises of different scales. In addition, the article also briefly reviewed the progress of ultra-low emission transformation of China′s steel industry to control air pollutants, and based on this, put forward the problems existing in the control of air pollutants in China′s steel industry and analyzed the development trend of air pollutant emission in the future of China′s steel industry.
2021 Vol. 56 (12): 1-9 [
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YANG Hong-bo, WANG Hao, ZHAO Xu, QI Wei-wei, LIU Hong-yin, SUN Jian-wei
Research progress on nano-scale interphase precipitation behavior of microalloyed high-strength steel
Increasing strength without reducing toughness is the goal that people pursue in the research and development process of high-strength steel. Compared with other strengthening methods, grain refinement can increase the strength and toughness of the material at the same time,but the minimum grain size of steel materials can be controlled to 3-5 μm now,and the strengthening effect that can be brought about is limited. A new type of ferrite-based high-strength steel has been developed in the past ten years. Through interphase precipitation,the ferrite matrix is distributed with regularly arranged nano-sized carbides,which greatly improves the toughness,formability and weldability,and is widely used in the field of construction machinery,oil pipelines,auto parts and high-rise buildings.With the development of the iron and steel industry in recent years,the understanding of the interphase precipitation has become more and more in-depth. There have been a large number of reports on the nanophase precipitation characteristics of various microalloyed steels,mainly focusing on the study of the microstructure characteristics and strength contributions of the precipitates. However,there are still many disputes about the interphase precipitation mechanism and model. It is still difficult to achieve stable interphase precipitation through process control,and the performance stability of nanophase precipitation of high-strength steel is still poor. With the development of science and technology,relevant advanced analytical instruments are also being updated, providing conditions for in-depth research on the precipitation behavior of nano-scale carbide phases in new ferrite-based high-strength steels. Based on this,the domestic and foreign research developments on the precipitation of nano-scale carbides in ferrite-based high-strength steels were reviewed,and clarifies the limitations of step theory and solute consumption theory;the composition design of ferrite-based high-strength steels was analyzed. The influence of the alloying method on the interphase precipitation behavior was revealed;the current international advanced instruments and technologies for studying the interphase precipitation behavior of nano-scale carbides were introduced. Finally,the development of the new ferrite-based high-strength steel was prospected,and the advantages of composite microalloying will be the inevitable trend of microalloying steel development in the future.
2021 Vol. 56 (12): 10-21 [
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Raw Material and Ironmaking
22
LIANG Wang, LI Yan-jiang, ZHANG Jian-liang, GUO Xing-min, WANG Peng, WANG Guang-wei
Influence of oxygen enrichment and coal blending on fuel combustion performance in ironmaking process
The combustion performance of the fuel used for blast furnace injection is very important. The use of blast furnace injection fuel with better combustion performance is more conducive to replacing the coke ratio and reducing the cost of blast furnace ironmaking. According to the requirements of the national energy conservation and emission reduction policy, some steel companies have begun to restrict the purchase and use of coal, so semi-coke has become an effective substitute for blast furnace coal injection. The differences between bituminous coal, anthracite, and semi-coke were studied through proximate analysis and thermogravimetric analysis experiments. The changes in the combustion performance of semi-coke under different coal blending schemes and different oxygen enrichment rates were studied. The research results show that the comprehensive combustion characteristics of fuels have a certain correlation with the initial combustion temperature, final combustion temperature and combustion reaction time. Among the three fuels, bituminous coal has the best comprehensive combustion characteristics, followed by anthracite, and semi-coke has the weakest comprehensive combustion characteristics. In order to improve the combustion characteristics of semi-coke, a mixed combustion experiment was carried out on semi-coke and bituminous coal. With the increase of bituminous coal content, the comprehensive combustion characteristic parameters of the blended sample gradually increase. And in the mixed combustion reaction of semi-coke and bituminous coal, a synergistic effect was found. With the increase of oxygen enrichment rate, the combustibility of semi-coke slowly increases. When the oxygen enrichment rate increases from 0 to 20%, the comprehensive combustion characteristic parameters of semi-coke increase from 4.53×10
-14
to 6.05×10
-14
min
-2
·℃
-3
. The above results show that the addition of bituminous coal and the increase of oxygen enrichment rate can significantly improve the combustion performance of semi-coke.
2021 Vol. 56 (12): 22-27 [
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28
SHI Xian-ju, WANG Qiang, LI Guang-qiang, LIU Dai-fei, LI Jun
Characteristic evolution and corresponding influence of flux particles in sintering process
In order to study the characteristic evolution of flux particles and corresponding influence on the properties of sinter, the sampling analysis of the whole actual sintering process was carried out. The results indicated that the flux particles less than 0.5 mm were easier to adhere to the surface of core particles than iron ore particles in the mixing process, and these particles distribute uniformly within each grade of the mixture, While the flux particles larger than 0.5 mm, served as the core particles, were adhered with a certain thickness of the adhesive layer that forming new particles, and moreover the thickness of the attachment layer was less than 1 mm, there for, the diameter of the new particles only increases by no more than 2 mm on the basis of the original particles. At the same time, the original flux particles were fine, led to less flux content in the mixture larger than 5 mm after granulation. In the sintering feeding process, there was segregation of particle size, large particles were segregated downward, and the particles larger than 5 mm at the bottom layer were distributed most, resulting in segregation of flux. The increase of particles larger than 5 mm in the mixture increases the flux segregation, while the increase of 3-5 mm particles reduces the flux segregation. Therefore, segregation of particle size reduces the total flux at the bottom layer, increases the larger particle flux. The decrease of the amount of flux particles reduces the distribution point of the flux, and thus increases the uneven distribution of the flux and deteriorates the local high alkalinity environment, then increases the difficulty for liquid phase generation. At the same time, due to the segregation of particles, the large particle iron ore powder in the bottom mixture increases and more unmelted raw ore appears, which eventually leads to the poor quality of the bottom sinter.
2021 Vol. 56 (12): 28-35 [
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36
GAN Min, ZHU Liang, FAN Xiao-hui, JI Zhi-yun, SUN Zeng-qing, ZHENG Hao-xiang
Reaction behavior and influencing factors of catalytic denitration of iron ore pellets in chain grate
Under the situation of resource constraint and environmental protection pressure, in the new period, the key point of pelletizing environmental protection is to reduce NO
x
emission, and its efficient control is related to the survival of pelletizing industry. Taking iron ore pellets as the object, the effect of temperature on denitrification of different iron concentrate pellets was studied. On this basis,the catalytic denitrification reaction behavior of the down-draft drying section (DDD section) of the grating machine was studied and the influence rule of flue gas composition on denitrification in DDD section was characterized by denitrification rate and ammonia utilization, etc. The results show that the catalytic performance of hematite is better than that of magnetite and mixed ore, at the same time, the characteristics of the temperature distribution in each section of the grate machine are analyzed, and the DDD section is finally selected as the reaction zone for SCR denitration.and the optimum denitration conditions are as follows, temperature is 300-350 ℃; the volume percent of oxygen is 15%-20%, the molar ratio ammonia to nitrogen is 0.5; when SCR denitrification is carried out in the grate down-draft drying section, the volume percent of SO
2
in the flue gas is increased from 0 to 0.050%, and the reaction denitrification rate is reduced from 51.0% to 34.4%; with the increase of the water vapor(volume percent) in the flue gas, the reaction denitration rate decreases, when the water vapor(volume percent) is 9%, the denitration rate is only 44.9%. Generally speaking, the denitrification rate of about 40% can be obtained by controlling volume percent of SO
2
0.040% and the water vapor(volume percent) is less than 6%. The denitration rate is highly effective and feasible in the DDD section of the ammonia spray catalytic denitration method.
2021 Vol. 56 (12): 36-42 [
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Steelmaking
43
GUO Jing, CHEN Xing-run, HAN Shao-wei, YAN Yan, GUO Han-jie
Theory and industrial applications for improvement of ultra-thin stainless steel strip purity and inclusion plasticity by development of "two step slagging strategy"
Precision calendered ultra-thin stainless steel strip (<0.3 mm) is required with sound steel cleanness and non-inclusion plasticity to obtain high comprehensive properties and surface quality while the two aspects are in contradiction. In order to solve the conflicts between steel cleanness improvement and non-inclusion plasticity,thermodynamic analysis and laboratory-scale slag-metal equilibrium experiments were carried out for achievement of high purity for stainless steel and admirable inclusion plasticity. The results show that with the slag basicity decrease, the desulfurization and deoxidation are depressed, as well as the molten steel purity, the use of high basicity slag is a necessary condition for obtaining high purity of molten steel. The inclusion composition evolves from CaO-SiO
2
-Al
2
O
3
based system to plasticized SiO
2
-Al
2
O
3
-MnO based system with the decrease of slag basicity. The content of Al
s
in the steel decreases, and the content of Al
2
O
3
in inclusions also decreases obviously, while the plasticity becomes better. Proper MgO content addition into the slag can restrain the corrosion of lining refractory effective. It proposes a new "two step slagging strategy" based on the thermodynamic analysis, in which high basicity slag is applied in AOD to desulfurization and deoxidation, low basicity slag is employed in LF refining process to plasticized inclusions in the steel. The industrial trial results verify that the new strategy can achieve high steel cleanness and inclusion plasticity.
w
(T[O]) is less than 0.002 5%,
w
([S]) is less than 0.001 0% and inclusion is SiO
2
-Al
2
O
3
-MnO dominated silicon-manganese aluminum-garnet inclusions with an average mass percent of Al
2
O
3
lower than 20%, the plasticity is outstanding, which meets the requirement of ultra-thin stainless steel trip.
2021 Vol. 56 (12): 43-51 [
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52
XIE Xiao-yu, GU Chao, WANG Min, BAO Yan-ping, LUO Xiong-zhi, PENG Guang-jian
Manganese sulfide inclusion control technology in medium and high sulfur steel
In recent years, with the continuous upgrading of manufacturing industry, the requirement of energy saving and environmental protection becomes higher and higher. For some steels used in the manufacture of complex parts, free-cutting elements (S, Te, Pb) are usually added to steel to improve its cutting performance in order to reduce energy consumption in the manufacturing process. Adding a certain amount of sulfur is the most commonly used improvement method at present. Sulfur mainly exists in the form of manganese sulfide in steel, and its morphology and distribution control level have important influence on the mechanical properties of steel. For medium and high sulphur steel, manganese sulfide is a plastic inclusion, which is easy to aggregate during precipitation and to deform along the rolling direction during rolling to form large-size strips. Such large-size manganese sulfide can seriously destroy the transverse properties of materials. To ensure the steel properties of medium and high sulphur steels, it is necessary to control the morphology and distribution of manganese sulphide inclusions in steel. The goal is to avoid the generation of large-size manganese sulphide and to obtain spindle-like manganese sulphide inclusions with fine and uniform distribution as possible. Manganese sulfide inclusion control is a systematic problem and must be carried out in conjunction with the entire process. The influence laws of some chemical compositions and process parameters on the inclusion precipitation of manganese sulfide were summarized. And the previous manganese sulfide inclusion control practices in the whole production process, including modification treatment of refining process, compound precipitation control, solidification process control and rolling and cooling control were reviewed. It is also pointed out that for the MnS control of non-quenched and tempered free cutting steel with medium and high sulfur content, how to implement the laboratory research results in industrial production is the direction of joint efforts for the majority of researchers in the future.
2021 Vol. 56 (12): 52-61 [
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62
SHEN Chang, LU Qiang, GUO Jun-bo, YANG Zheng
Development and practice on forming MnS plastic inclusion in medium high carbon Al killed steel
In order to improve the fatigue resistance of medium and high carbon steel products, based on the composition characteristics of medium and high carbon steel, the process which the heterogeneous nucleation of MnS in steel takes Al
2
O
3
as nucleation particle is developed, and the brittle inclusions of Al
2
O
3
in steel is wrapped by plastic MnS, the problem of fatigue fracture caused by brittle nonmetallic inclusion is solved. The composition design of key elements in steel, the design and development of refining and continuous casting integrated process were carried out by studying the formation conditions of fine and dispersed Al
2
O
3
inclusions and the thermodynamic conditions of MnS heterogeneous nucleation and precipitation. Industrial practice shows that,the final deoxidation by aluminum with low activity oxygen can form 3-5 μm fine dispersed Al
2
O
3
inclusions, which act as the core of heterogeneous nucleation and precipitate dispersed and fine granular MnS at the solidification end of secondary dendrites; through gradient deoxidation, vacuum carbon deoxidation and protective casting, the total oxygen content in steel can be effectively controlled and the purity of molten steel can be improved,the average mass percent of T[O] of the finished product is 0.000 618%, which is 16% lower than 0.000 739% of the original process;the proportion of MnS and MnS wrapped Al
2
O
3
inclusions is more than 96% of the total inclusions in the finished product,which is equivalent to the inclusion control level of the world′s leading products, considering that the Al
2
O
3
inclusion wrapped by MnS must be thick enough for the plastic inclusion to work,the concept of "effective package rate" of MnS is established,while the maximum radius of hard inclusion was not more than 1/2 of radius of MnS wrapping part, it is considered that MnS realizes "effective wrapping" of hard phase inclusions;the average fracture toughness of the finished product is 83.47 MPa·m
1/2
, which is 24% higher than 67.31 MPa·m
1/2
of the original process.
2021 Vol. 56 (12): 62-67 [
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SONG Zhao-qi, LIU Wei, YANG Shu-feng, LI Jing-she, CHEN Yong-feng, ZUO Xiao-tan
Formation reason and control of Ds inclusions in QD08 steel
QD08 steel requires high fatigue resistance due to its special working environment, and Ds inclusions are the main reason for weakening the fatigue resistance of QD08 steel. In order to explore the reasons for the formation of Ds inclusions and control methods, and solve the problem of excessive Ds inclusions, the whole process of steelmaking, refining and continuous casting of this steel grade was sampled and analyzed. The analysis results show that the main component of Ds inclusions that affect the fatigue performance of QD08 steel is CaS-Al
2
O
3
-MgO-CaO, and its size fluctuates in the range of 15-30 μm, which mainly begin to appear after the LF refining calcium treatment operation. The Ds inclusions in QD08 steel are formed by using calcium magnesium aluminate as the core framework and wrapping CaS on the periphery. Combined with the composition distribution of inclusions, it is determined that the high calcium content in steel is not conducive to the control of Ds inclusions in QD08 steel. The modified inclusions have a low melting point, and the inclusions have strong wettability with molten steel, making inclusions difficult pass through the steel slag interface into the refined slag. In addition, the inclusions are easy to aggregate and grow in the molten steel, resulting in an increase in the size of the inclusions, which provides conditions for the formation of Ds-type inclusions. The optimization plan for the refining slag with high solubility of calcium oxide and micro-calcium treatment in the refining process was proposed, and industrial verification tests were carried out. The micro-calcium treatment ensures the necessary inclusion modification, prevents the nozzle nodules, cooperates with reducing the fluctuation of the tundish liquid level, controls the appropriate drawing speed, avoids the slag leaving from the ladle, and avoids the occurrence of slag entrapment. The process controls more inclusions to be distributed in the non-liquid zone, inhibits the collision and growth of inclusions, and reduces the level of Ds inclusions. The test results show that the Ds inclusions in QD08 steel that affect its fatigue performance have been controlled, and the initial inspection pass rate has been increased from 93.6% to 98.0%, which has brought direct economic benefits to the enterprise.
2021 Vol. 56 (12): 68-74 [
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75
LI Wei-gang, CHUN Li-liang, LI Yang, YI Cheng-xin
Research and application of optimal control model for slab width of stainless steel
The accurate control of slab width is one of the important factors to ensure slab quality in the continuous casting process. The slab width is too wide or too narrow will bring adverse effects to the rolling process. At present,the slab width is mainly controlled by adjusting parameters of the secondary cooling zone online by manual experience,which has the problems of low qualified rate and large fluctuation. Therefore,it is very important to realize automatic optimization control of slab width for stainless steel. Aiming at the characteristics of high dimension and nonlinear and multivariable coupling in the process control of slab width for stainless steel,an optimal control model of slab width based on the random forest and differential evolution(RF-DE) algorithm is proposed. Firstly,the factors affecting the slab width are selected from a large number of composition and process parameters based on expert experience,and then a data-driven prediction model of slab width is established by the random forest algorithm. Secondly,taking the secondary cooling process parameters of continuous casting as the decision variable,taking the absolute error between the predicted width of the prediction model and the target width of the slab as the objective function,the optimal control model of slab width with process constraints is constructed,and the differential evolution algorithm is used to optimize the above model,obtain the secondary cooling process parameters of continuous casting. Finally,the model is verified by the actual production data of a steel plant,and the experimental results show that compared with gradient boosting decision tree,support vector regression,multilayer perceptron and other models,random forest model has strong generalization ability and high accuracy, and is more suitable for the prediction of slab width,the mean absolute error is 0.047 2 mm. Moreover,the qualified rate of slab width for stainless steel is increased,and the proposed model has high control precision.
2021 Vol. 56 (12): 75-84 [
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Metal Forming
85
SUN Jian-liang, YAN Ming-ze, LI Ming-yuan, HAO Tong-tong
Analysis on flatness about support axle group deformation in 20-high mill
The capacity and quality of sheet and strip is a momentous mark of the industrial development level, especially the copper strip. SUNDWIG 20-high mill is the key equipment for cold rolling of copper sheet and strip. The bending deformation of its outermost A and D support axle group is one of the most important means to affect the flatness. The change of the saddle displacement can bend the core shaft of the support axles, the deformation will be reflected on the support roller and transferred to the intermediate rolls and the work roll in turn, and ultimately affect the plate thickness and flatness. The traditional calculation method of support axle group deformation such as hypothetical broken line method and statically indeterminate beam method which considers the support axle and support roller as a whole, but the influence of the deformation between them on the support axle group deformation deformation is ignored. The bending deformation of each section of the support roller based on the finite element method was simulated and fitted to obtain the bending deformation of the whole support axle group,and then evaluated the influence of the deformation on the plate flatness with the flatness prediction model based on the elastic deformation model of roll system and the metal plastic deformation model. The results show that the thickness and flatness distribution doesn′t change locally but in the total width direction after applying different displacement combinations to four saddles in the upper roll system. Four saddles have different adjustment effects on shape and thickness. With the same displacement applied, the influence of the middle saddle on the flatness and thickness is greater than that of the side saddle. In addition,even if symmetrical saddle shift are applied in the saddle of the upper roll system,the influence on the thickness and flatness is asymmetric.
2021 Vol. 56 (12): 85-95 [
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96
BAI Zhen-hua, WANG Nan, CUI Xi-ying, ZHANG Ya-zhen
Optimization of lubrication system for flatness control process in cold tandem rolling
In the process of strip speed rise and fall of tandem cold rolling mill, the rolling speed will fluctuate frequently and greatly, and the friction coefficient in the rolling deformation zone will fluctuate greatly, causing the rolling pressure to fluctuate back and forth, resulting in the problem that the shape in the speed rise and fall stage is significantly worse than that in the stable stage. The optimization of process system is very effective for the shape problem caused by friction coefficient. Therefore, firstly, this paper analyzes the shape change process of strip steel in the process of speed increase and decrease under different emulsion concentration, initial temperature and flow rate. In view of the shape defects in the speed up and down stage, the strip steel is divided into several strip elements along the transverse and longitudinal directions by using the piecewise discrete method, the transverse and longitudinal objective functions of the shape in the speed up and down process are proposed, and then the dynamic change objective function of the shape in the speed up and down process is constructed to realize the comprehensive control of the shape fluctuation in the transverse and longitudinal directions in the rolling process. Since the emulsion concentration and initial temperature cannot be changed in the rolling process, combined with the shape objective function, the optimal setting function of emulsion concentration and initial temperature is proposed under the constraints that the strip does not slip and heat scratch and the rolling force of each stand does not exceed the limited rolling force; The emulsion flow optimization can effectively control the frequently changing local wave shape defects. Therefore, the emulsion flow generally changes nonlinearly with the rolling speed. Taking the minimum fluctuation of outlet plate shape as the control function, and taking no slip and thermal scratch and the total amount of emulsion in each frame as the constraint conditions, the emulsion flow following speed optimization function is proposed. Finally, the optimization model is applied to the tandem cold rolling mill of a domestic steel plant. According to the rolling force distribution before and after optimization and the cloud diagram of strip shape, it can be seen that the field application effect is good.
2021 Vol. 56 (12): 96-102 [
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Materials
103
SU Hang, PAN Tao, LI Hao
Quality capability ranking of material production lines —Theory and practice
Traditional quality evaluation standard is whether it is "qualified" or not, and the quality difference above the threshold is ignored,which is an important factor causing the quality dilemma of winning the bid at a low price in recent years. Quality capability ranking of material production lines is to change the standard threshold evaluation into quality capability ranking evaluation, which may give top level enterprises a new quality target after 100% qualified,and meet the differentiated needs of users. By establishing quality capability ranking evaluation model including value function, process evaluation and quality inheritance model with the support of expert experience, quality capability ranking of material production lines adopts the key quality factors evaluation and product big data, so that the quality differences of "qualified" products can be distinguished, which may truly and comprehensively reflect the product quality capability of different production lines. The key technologies include three groups of models,in which value function model changes the traditional pass-or-not evaluation into continuous evaluation,process evaluation model extends the traditional sample evaluation to process capability evaluation,and quality inheritance model introduces the role of raw materials which is missing in traditional evaluation. Objective data are used in all models. At present,quality capability ranking has been carried out for many kinds of steel products according to the requirements of users,such as medium heavy plate,and T/CISA association standards have been released as the first standards about quality capability ranking. Quality capability ranking is first proposed and applied in the field of iron and steel materials. It has good applicability to the typical production process of products with raw materials and supporting production processes. Quality capability ranking can be further extended to the raw material industry and equipment manufacturing industry other than iron and steel materials.
2021 Vol. 56 (12): 103-108 [
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109
PENG Wei, GAO Xin-qiang, FAN Zeng-wei, BAI Jia-xin, WEI Xi-cheng, DONG Han
Characteristics and high purification development of pure iron
Discovery of iron and the use of iron tools promote the progress of human civilization and the rapid development of industry. Research work on the high and ultra-pure iron have always been performed in developed countries, which can offer high and ultra-pure iron commercial products. However,this work has been done less in our country and it is urgent to further research on high and ultra-high pure iron,with a view to attracting the relevant scientific researchers in this field of sufficient attention. Focusing on iron and pure iron,from the production of China′s first industrial pure iron to the relevant research on the preparation of high-purity iron and ultra-pure iron in the relevant countries, the relevant production technology of pure iron was discussed, and the fact that high-purity iron and ultra-pure iron cannot be produced on a large scale was pointed out. The promotion can improve the sensitivity of its yield and tensile strength to the strain rate,improve its corrosion resistance and DC soft magnetic properties in the simulated atmospheric environment,and also briefly describe the application of pure iron after high purification from the point of view of raw materials and materials. As raw materials,high and ultra-pure iron can improve the quality and performance of steel materials,amorphous materials,and semiconductor materials,etc. As materials,it can be the good soft magnetic material,magnetic shielding material,shaped charge liner material and damping material. Innovations such as materials,technology and equipment rely on the progress of basic research,and China′s research work on high-purity iron and ultra-pure iron is not in-depth,seriously restricting the development of high-performance steel materials,hindering the progress of China′s high-end equipment manufacturing industry,therefore,high-purification of pure iron can not only achieve the iron-based new materials in the field of filling plate and deriving new materials,but also promote industrial strong foundation,with the necessity of the times.
2021 Vol. 56 (12): 109-118 [
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119
WANG Hong-zhong, ZOU Zong-yuan, LI Yin-xiao, LIU Dou-dou, ZHAI Dong-lin, CHEN Lei
Martensitic transformation characteristics and its effect of steel Fe-19Cr-0.2Ni-5Mn-0.2Si under cyclic loading
Transformation induced plasticity(TRIP) duplex stainless steel has great potential for industrial application because of its excellent strength and plasticity and economic efficiency. The effect of martensite transformation during cyclic deformation on cyclic mechanical properties of TRIP duplex stainless steel is the basis of promoting its further development and industrial application. Thus the cyclic properties and transformation characteristics of TRIP duplex stainless steel Fe-19Cr-0.2 Ni-5Mn-0.2Si were studied. The tensile mechanical properties and cyclic softening/hardening properties under symmetrical cyclic loading test with 0.6% strain amplitude of the tested steel were determined by INSTRON test machine,respectively. In the process of cyclic loading,the martensitic transformation was measured by ferrite measuring instrument at different cycles,and the characteristics of martensitic transformation were analyzed. Transmission electron microscopy (TEM) was used to observe the microscopic structures of transformation martensite and dislocation under typical cycles. Furthermore,the mechanism of martensitic transformation and dislocation structure evolution on cyclic softening and hardening properties was studied. The results show that the test steel shows obvious TRIP effect under tensile condition. The martensite transformation rate is fast at the early stage of cycling,and then the transformation rate gradually decreases and tends to zero. Cyclic softening and hardening can be divided into three stages: initial cyclic hardening,cyclic softening and secondary cyclic hardening. The hardening effect caused by the proliferation of dislocations in the two phases plays a leading role in the initial cyclic hardening. The subsequent cyclic softening is dominated by the softening effect caused by the low energy dislocation structure in ferrite. In the secondary cyclic hardening stage,the transformation martensite plays a leading role in the hardening of the material. Although transformation martensite has little effect on the cyclic softening and hardening properties of the tested steel at the early stage of cyclic loading,it has a great effect on the properties at the later stage of cyclic loading.
2021 Vol. 56 (12): 119-125 [
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126
CHU Shuang-jie, JIN Xin-yan, BI Wen-zhen
Influence of internal oxidation on coating/substrate interface of hot dip galvanized high strength steel sheet
Due to the selective oxidation of Si and Mn during the annealing process of Si-Mn added high strength steel which significantly deteriorates the wettability of strip with liquid zinc,the galvanizability of hot dip galvanized high strength steel is still a challenge. To improve the coating adhesion of hot dip galvanized high strength steel,characterizations of the inhibition layer on coating/substrate interface and the internal oxidation in the subsurface of hot dip galvanized 0.2%C-1.8%Si-1.8%Mn high strength steel sheets with different coating adhesion were conducted by GD-OES,SEM,FIB and TEM. Annealing simulation experiments were used to study the effect of annealing atmosphere dew point on the formation of internal oxidation. The correlation between dew point,internal oxidation thickness,inhibition layer coverage and coating adhesion was revealed. The coating adhesion is determined by the inhibition layer on the coating/substrate interface,good coating adhesion can be obtained when the coverage of inhibition layer is greater than 80%. There exists a critical internal oxidation thickness which is approximately 0.58 μm. When the internal oxidation thickness gradually increases from 0 to 0.58 μm,the inhibition layer coverage increases from 10% to 80% approximately. When it further increases from 0.58 μm to 3.85 μm,the inhibition layer coverage increases slightly in the range of 80%-90%. The internal oxidation is promoted when the dew point of the annealing atmosphere is increased. When it is annealed at 800 ℃ and 870 ℃ and soaked 120 s in an atmosphere of N
2
-5% (volume percent)H
2
,the internal oxidation thickness increases from 0 to 3-5 μm as the dew point increases from -40 ℃ to +10 ℃. Therefore,it is suggested to control the dew point of annealing atmosphere in the range of -20 ℃ to -10 ℃ to get a favorable internal oxidation thickness.
2021 Vol. 56 (12): 126-133 [
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Environmental Protection and Energy
134
YE Heng-di, ZHOU Hao-yu, WANG Ye-feng, LI Qian, LU Xing-fu, LIU Qian
Exploration and research on key technologies of multi-layer heat supplying and H
2
-rich sintering
In order to manage the environmental problem caused by greenhouse effect, China aims to peak its carbon dioxide emissions before 2030 and achieve carbon neutrality by 2060. The iron and steel industry ranks second just after the thermal power industry in terms of the carbon emission. Therefore, reducing carbon emission in iron ore sintering is an irresistible trend. In the conventional sintering, it is hard for the solid fuel particles to disperse more in the upper bed and less in the lower bed which is essential due to the heat auto-accumulation effect. Consequently, it is inevitable that the reducing atmosphere is locally present which brings about extra CO in the flue gas and adverse impacts on the sintering process, and the uneven heat pattern impairs the sinter quality and the energy efficiency. All these restrict the improvement of energy-saving and low-carbon emission in sintering process. Based on the analysis of the effects of the fuel form and fuel distribution on the sintering process, the "multi-layer heat supplying and H
2
-rich sintering" idea was proposed, which provided a new heat supplying method for upper, middle and lower layer in deep bed sintering condition. With the new method, the upper bed is heated up by the oxygen-rich ignition and solid fuel combustion, the middle bed by the combustion of H
2
-rich gas and solid fuel while the lower bed by the steam injection and solid fuel combustion. The low carbon combustion mechanism as well as the key technologies of the new method were elaborated. The solution to the possible deterioration of the wet layer in the application of the technologies was also put forward. The integration application of these technologies would help to reduce energy cost, carbon as well as other pollutants emission,and improve the sinter quality.
2021 Vol. 56 (12): 134-141 [
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142
PAN Jian, MA Wen-zhuo, ZHU De-qing, TIAN Hong-yu, YANG Cong-cong, WANG Ying-yu
Desulfurization and denitrification performance of activated carbon prepared by one-step method from low-rank coal
Activated carbon method is a flue gas treatment technology that can realize comprehensive control of multiple pollutants,such as sulfur dioxide and nitrogen oxides generated in the sintering process. However,its popularization and application in sintering flue gas multi-pollutant purification field are limited because of its high production and use costs. Based on the coupling effect among pyrolysis of low-rank coal,gasification reaction of semi-coke and reduction of iron oxides,the low-stage coalification and activation were completed through a one-step method which using low-rank coals as carbon resource and oxidized pellets as activating agent,and the activated carbon (SF AC) was manufactured. Furthermore,the proximate analysis,specific surface area,iodine adsorption value,desulfurization and denitrification performance as well as regeneration performance of activated carbon were also conducted for comparison with those of the commercial activated carbon (ZJ AC). The results show that the desulfurization breakthrough capacities of SF AC and ZJ AC in separate desulfurization are 368.11 mg/g and 73.58 mg/g,respectively. And the denitration breakthrough capacities in separate denitration are 250.39 mg/g
and 14.99 mg/g,respectively. The SF AC with iodine adsorption value of 695.13 mg/g and specific surface area of 370.42 m
2
/g has a better adsorption property than the ZJ AC with iodine adsorption value of 530.54 mg/g and specific surface area of 157.50 m
2
/g. In addition,the desulfurization and denitrification performance of regenerated ZJ AC and SF AC both show a decrease tendency,while the regenerated SF AC still has a better desulfurization and denitrification performance than that of regenerated ZJ AC. Compared with the separation process of desulfurization and denitrification,process of simultaneous desulfurization and denitrification will cause an increased desulfurization property and decreased denitrification property. The adverse effects can be improved by catalytic reduction of NH
3
under low temperature.
2021 Vol. 56 (12): 142-152 [
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153
DAI Xiao-tian, CHEN Qian-ye, QI Yuan-hong, YAN Ding-liu
Pilot plant test of BF gas deep desulfurization technology
In BF gas, the content of organic sulfur, which is mainly COS, is high while the content of inorganic sulfur is comparatively low, so that BF gas is difficult to desulfurize. Aimed at above difficulty, a BF gas deep desulfurization process, a dry process before gas combustion, was developed and tested in pilot plant scale at a metal company in Shandong province. The process scheme was as follows. The desulfurization test equipment was mounted at downstream direction of the blast furnace TRT module, and BF gas was connected to the desulfurization test equipment from the blast furnace′s gas pipe line through the bypass. The hydrolysis and desulfurization reactors were both packed beds, and designed as two-stage series connected type, which were "primary hydrolysis + desulfurization" and "secondary hydrolysis + desulfurization" modules. The hydrolysis and desulfurization reactors were filled with an improved Al
2
O
3
based low-temperature hydrolysis catalyst and ferric oxide based desulfurizer, respectively. The hydrolysis catalyst promoted the reaction of COS with water vapor to produce H
2
S in BF gas, and then the desulfurizer reacted with H
2
S to produce Fe
2
S
3
. Thus, sulfur was removed from BF gas. In the pilot plant test, the gas flow rate was 400 m
3
/h, the gas temperature was about 80-100 ℃, the volume percent of COS and H
2
S were about 70% and 25%, respectively, and the total sulfur content of BF gas was 145 mg/m
3
. After more than 300 h of continuous running, pilot tests show that after processing, there is no waste water discharged, the converting rate of COS into H
2
S is about 99%, desulfurization rate is more than 96%, and the density of sulfur dioxide in exhausted gas (after combustion) is less than 10 mg/m
3
.
2021 Vol. 56 (12): 153-159 [
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