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2023 Vol. 58 No. 2
Published: 2023-02-15
Technical Reviews
Raw Material and Ironmaking
Steelmaking
Metal Forming
Materials
Environmental Protection and Energy
Expert Forum
Expert Forum
1
YIN Rui-yu
Essence and common law of a process-oriented manufacturing process
In the current study, from the view of the overall operation of the open dynamic system, the manufacturing process in process industries was named as an engineering system integrated by relative heterogeneous procedures/devices and a series of linking units, i.e. "interface" technology group and the integrated construction process of the dissipative structure of the manufacturing process was discussed. The physical essence and the engineering model of the dynamic operation for the manufacturing process were established and the constitutive characteristics of the dynamic operation for the manufacturing process were revealed. The concept of the combination of "virtuality" and "reality" in the engineering design of the manufacturing process and the production operation process was proposed, and its connotation of engineering philosophy was summarized. The basic idea of "taking ′flow′ as the ontology" and "thinking based on the concept of the ′flow′" was proposed.
2023 Vol. 58 (2): 1-7 [
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Technical Reviews
8
WANG Hai-feng, PING Xiao-dong, ZHOU Ji-cheng, LI Xiu-ping, LU Li-jin
Review and prospect of green development for Chinese steel industry
The green development of steel industry is an important way to promote the transformation and upgrading of steel industry and achieve sustainable development. The green development of Chinese steel industry has gone through four stages: end-of-pipe treatment,clean production,ecological industry and circular economy. Under the guidance of policies related to the green development of the steel industry,the steel industry has promoted and applied technologies such as coke dry quenching,oxygen-enriched coal injection in blast furnaces,hot feeding and hot loading of continuous casting billets,and carried out ultra-low emission renovation,pilot demonstration of clean production,eco-industrial demonstration parks,and circular economy demonstration sites. The green development of steel industry has made great progress around the three functions of steel manufacturing process: steel product manufacturing,energy conversion,waste treatment and recycling.The specific energy consumption per ton of steel (measured by coal equivalents) decreased by 71.8% from 1.93 t/t in 1981 to 0.55 t/t in 2020; the emissions of particulate pollutant and SO
2
per ton of steel decreased from 6.77 kg/t and 5.56 kg/t in 2000 to 0.36 kg/t and 0.30 kg/t in 2020,with a decrease of 94.7% and 94.6%,respectively. The NO
x
emissions per ton of steel decreased from 1.68 kg/t in 2007 to 0.87 kg/t in 2020,with a decrease of 48.2%. The chemical oxygen demand emissions per ton of steel decreased from 0.99 kg/t in 2000 to 0.02 kg/t in 2017,with a decrease of 98.2%. The utilization rate of BF slag and BOF slag has been higher than 90% since 2005. Fresh water consumption per ton of steel decreased by 90.3% from 25.24 m
3
/t in 2000 to 2.45 m
3
/t in 2020. In the future,with the evolution of the three functions of steel manufacturing process,the green development of steel industry will be promoted in the direction of low carbonization,greenization and intelligence. Through the research and application of a batch of green low carbon technologies such as short process of fully scrap-EAF,hydrogen reduction,non-blast furnace ironmaking,CCUS and intelligent technologies in steel production and enterprise decision-making,the high-quality development of steel industry will be realized.
2023 Vol. 58 (2): 8-18 [
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19
WANG Jing-zhong, YAO Hui-qin, ZHAO Ji-qing, YANG Xi-rong, YANG Gang, DING Kai-lun
Design and heat treatment of large-scale casting and forging materials for coal-fired power stations
The research status of material design and heat treatment of steel and alloy used for large castings and forgings of coal-fired power station is reviewed from the aspects of development background,development history,alloying characteristics,heat treatment process,microstructure and evolution. Advanced industries such as Europe,America and Japan have made remarkable achievements in the research,development and production of large castings and forgings for coal-fired power stations after decades of continuous investment and efforts. Our country also made large investment in this aspect,since 1980,pay attention to the study of subcritical,supercritical rotor material,to the ultra supercritical materials after 2000,2015 to present advanced supercritical materials research,on the basis of the introduction of digestion-absorption,has obtained certain achievements,began to create new steel and alloy with independent intellectual property rights,And realized the stable supply of some products. With the increase of coal steam parameters,the chemical composition of steel used for large forgings tends to be complicated,and the 10
5
h extrapolation endurance strength of steel increases continuously. In the composition design of new martensitic heat resistant steel castings,more attention is paid to the application of trace elements B and N,and the compound addition of W,Mo and Co. Domestic scholars have reported many researches on the microstructure and mechanical properties of steel for large forgings,and the researches are more in-depth and systematic. It is necessary to strengthen the creation of prototype steel grade or alloy by using the new material design method combined with the existing strong plastic processing ability in China. Sufficient attention should be paid to the research and development of generator rotor protection ring materials,which should be strengthened. The key physical properties of several typical steels for rotor,turbine cylinder and valve were compared and analyzed. The future development direction of steel or alloy materials for large castings and forgings used in ultra-supercritical power plants with high parameters is discussed based on experience.
2023 Vol. 58 (2): 19-29 [
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Raw Material and Ironmaking
30
WU En-hui, LI Jun, XU Zhong, HOU Jing, HUANG Ping
Physicochemical properties of metallized pellets of high-chromium vanadium-bearing titanomagnetite
The iron, vanadium, titanium and chromium of high-chromium vanadium-bearing titanomagnetite can be comprehensively utilized by coal based direct reduction-electric furnace melting separation new process, which is one of the most promising non-blast furnace smelting processes. The physicochemical properties of high-chromium vanadium-bearing titanomagnetite metallized pellets have an important impact on the subsequent electric furnace melting and separation process. Based on this, the effects of reduction temperature, reduction time, coal-ore mass ratio and binary basicity on the physicochemical properties such as phase composition, metallization rate, carbon residue, resistivity and compressive strength of metallized pellets during coal based direct reduction were investigated. The magnetite and ilmenite were reduced to metallic iron and anosovite with increasing the reduction temperature and prolonging the reduction time, while higher coal-ore mass ratio and binary basicity have an adverse effect on the reduction process. The resistivity of the metallized pellets depends on the phase compositions, the content of different phase compositions and the combination form between each phase compositions of the metallized pellets. There was an obvious negative correlation between the metallization rate and resistivity of metallized pellets, while the degree of negative correlation decreased with the metallization rate increased. When the metallization rate was higher than 90%, the resistivity of metallized pellets was lower than 0.5 Ω/cm. The formation content of metallic iron and the connection form between metallic iron grains were the key factors affecting the compressive strength of metallized pellets. The increase of reduction temperature and reduction time was favorable to improve the compressive strength of metallized pellets, while the compressive strength of metallized pellets decrease with increasing the coal-ore mass ratio and binary basicity. Under the condition of reduction temperature of 1 300 ℃, reduction time of 35 min, coal-ore mass ratio of 25∶100, and binary basicity of 0.13, the metallization rate, carbon residue, resistivity and compressive strength of metallized pellets are 92.58%, 5.39%, 0.3 Ω/cm and 81.74 N/pellet respectively.
2023 Vol. 58 (2): 30-38 [
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39
ZHANG Shu-hui, SHAO Jian-nan, BI Zhong-xin, HU Qi-chen, Ly Qing, QIE Ya-na
Emission reduction ability of coke oven gas injection into blast furnace for smelting vanadium titanomagnetite
Injecting coke oven gas (COG)into blast furnace can play the adequate role of hydrogen reduction to realize the low-carbon green development of blast furnace smelting. In order to analyze the emission reduction ability of coke oven gas injected into blast furnace, the quality and energy balance model was established based on the production data and physi-chemical reactions in the blast furnace smelting with vanadium titanomagnetites to explore the effects of COG injection on the theoretical combustion temperature of tuyere and CO
2
emission of top gas. Furthermore, the operation window under certain restrain conditions was established in order to discuss the carbon and emission reduction ability of COG injection. The results show that under a certain oxygen enrichment rate, coke ratio, coal ratio and air temperature, the theoretical combustion temperature of tuyere and the CO
2
emission of top gas decrease with increasing COG injection content. The heat in the blast furnace with COG injection can be supplemented by increasing the oxygen enrichment rate under the condition of fixed air temperature and coal ratio. The oxygen enrichment rate increases with the increase of COG injection content, and the coke ratio decreases. For the vanadium-titanomagnetite blast furnace without COG injection, the tuyere theoretical combustion temperature is 2 075 ℃, and the furnace top gas temperature is at least 120 ℃ under the operating conditions of oxygen enrichment rate 3%, coke ratio 380.0 kg/t(Fe), coal ratio 130 kg/t(Fe), and air temperature 1 200 ℃. When the injection volume of coke oven gas is 55 m
3
/t(Fe), the same theoretical combustion temperature and top gas temperature as that of blast furnace without COG injection can be obtained. Correspondingly, the oxygen enrichment rate is 5.63%, the coke ratio is 371 kg/t, and the top CO
2
emission is 684 kg/t(Fe); Compared with non-injection of COG, the coke ratio and CO
2
emission are reduced by 9 kg/t(Fe) and 27.1 kg/t(Fe), respectively. When the theoretical combustion temperature is 1 900 ℃ and top gas temperature is 110 ℃, the acceptable COG injection volume content for vanadium-titanomagnetite blast furnace is increased to 185 m
3
/t(Fe) with an oxygen enrichment rate of 4.9%. In comparison with non-injection of COG, a significant effect on carbon and emission reduction is obtained with the coke ratio reduced by 49.7 kg/t(Fe)and the CO
2
emission reduced by 103.0 kg/t(Fe).
2023 Vol. 58 (2): 39-46 [
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Steelmaking
47
ZHANG Li-feng, REN Ying
Concept of inclusion capacity of slag and its application
The parameter of the difference between the original concentration and the saturation concentration of inclusions in the refining slag divided by slag viscosity (Δ
C
/
η
) was retrieved from literatures and the disadvantages of the parameter were discussed, including its dimensional feature and the ignorance of the size of inclusions. Similar to the dimensionless Grash of number used to the natural convection of the fluid flow, the inclusion capacity of the refining slag was proposed (the dimensionless number of
Zh
). The dimensionless dissolution rate of inclusions in the slag (
R
y
) was proposed. The expression between the inclusion capacity of the slag and the dimensionless dissolution rate was obtained. The inclusion capacity of the slag, the
Zh
number, can be used to predict the dissolution rate and dissolution time of inclusions in the refining slag, to calculate the rate constant of the dissolution reaction and the diffusion coefficient of inclusions in the slag, and to calculate the removal time of inclusions from the molten steel. With the increasing of the
Zh
number and the increasing of inclusion size, the dissolution time of inclusions became longer. With the increasing of inclusion size, the average removal time of less than 500 μm inclusions increased while the maximum removal time decreased. At the temperature of 1 600 ℃, for the dissolution of Al
2
O
3
in the CaO-Al
2
O
3
-SiO
2
slag, the dissolution reaction rate constant was 5×10
-6
-10×10
-6
m/s and the diffusion coefficient of Al
2
O
3
in the CaO-Al
2
O
3
-SiO
2
slag was 2.5×10
-10
-4×10
-10
m
2
/s, and the two parameters varied with the composition of the slag.
2023 Vol. 58 (2): 47-60 [
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61
CAO Jian-qi, CHEN Chao, XUE Li-qiang, LI Zhou, ZHAO Jian, LIN Wan-ming
Analysis of inclusions in whole smelting process of non-oriented silicon steel DG47A
For a high grade non-oriented silicon steel DG47A(Fe-2%Si-0.36%Al-0.26%Mn),clustered Al
2
O
3
-MgO spinel inclusion with a length of 50 μm, which may influence the product property in the sequent process, is found in a hot rolled sheet produced by a steelmaking plant. By analyzing the samples taken from the BOF→RH→tundish→continuous casting slab production process and thermodynamic calculation, the evolution of inclusions in the smelting process of this steel grade are studied. The morphology, size and type of inclusions were analyzed by scanning electron microscope and energy dispersive spectrometer analysis (SEM-EDS). The formation condition of Mg-Al spinel inclusion was calculated by thermodynamics. In addition,the mechanism of precipitation phase during solidification process was calculated by PANDAT software. The results show that SiO
2
is the main inclusion after RH decarburization. There are Al
2
O
3
and a small amount of SiO
2
inclusions after 3 minutes of adding aluminum in RH. Afterwards, Al
2
O
3
-MgO and MnS-containing composite inclusions are formed after adding alloys of ferro-silicon and manganese in RH treatment. CaS-containing composite inclusions are formed after adding desulfurizers. There are no single Al
2
O
3
inclusions before the content of CaS and MnS in the composite inclusions tended to increase, and MgO remained at about 25%. CaS and AlN inclusions are wrapped around the outer edge of Al
2
O
3
-MgO inclusions. The AlN and MnS inclusions were found in slab. After adding aluminum in RH, the average size of the inclusions is about 20-25 μm, and decreased to about 2-5 μm before tapping of RH. In the tundish and the slab, with the cooling of the molten steel,the second phase precipitated on the surface of the inclusions, and the average size of the inclusions slightly increased to around 3-6 μm. The thermodynamic calculation results show that, at 1 873 K, when the Mg content in the molten steel is greater than 0.000 26%, Al
2
O
3
-MgO inclusions are formed. During the cooling process of molten steel, AlN and MnS inclusions precipitated successively with the decrease of temperature.
2023 Vol. 58 (2): 61-71 [
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72
WANG Jia-hui, ZHANG Hua, FANG Qing, ZHOU Jia-chao, XIE Xu-qi, NI Hong-wei
Physical simulation on optimization of flow field in a tundish by top-swirling turbulence inhibitor
A top-swirling turbulence inhibitor(TI) was proposed to generate a rotating velocity filed of molten steel in the tundish impact zone,which could effectively weaken the strength of molten steel returning to steel-slag interface,reduce the turbulent kinetic energy,avoid slag entrapment and secondary oxidation of molten steel,so as to purify the molten steel in the impact zone. To validate the metallurgical superiority of the designed top-swirling TI in each tundish operation periods,the multiphase flow behaviors in a single-strand slab tundish during steady-state casting,start-up operation and ladle changeover process with different TIs (without a TI,with an ordinary TI and with a top-swirling TI) were compared and analyzed by water model experiments. The results showed that the top-swirling TI had no negative effect on the flow field at steady-state casting of tundish,while revealed obvious metallurgical advantages at the transient casting periods. Compared with the case of without a TI,when using the top-swirling TI,the average residence time of molten steel was prolonged from 308.5 s to 327.4 s,and the volume percent of dead zone was reduced from 9.67% to 4.13%,and the response time was increased from 69 s to 109 s,which would effectively avoid the occurrence of short-circuit flow. The exposed areas of molten steel under the cases of without TI and with ordinary TI were about 115 cm
2
and 55 cm
2
during start-up operation,and the exposed area were about 90 cm
2
and 50 cm
2
during ladle changeover,respectively. While the molten steel would not be exposed to air when using the designed top-swirling TI during both start-up operation and ladle changeover process,and it could effectively reduce the fluctuation of the steel-slag interface compared with the ordinary TI. The top-swirling TI can effectively improve the flow state of molten steel in the tundish,avoid slag entrapment and secondary oxidation of molten steel during transient casting periods,improve the steel cleanness and metal yield,and ensure remarkable service life without obvious cost increasing,which possesses high value of promotion and application.
2023 Vol. 58 (2): 72-82 [
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83
LI Yong-chao, YANG Yu-dan, LU Cai-ling, LI Cai-qing, WANG Wei
Evolution behavior of oxide inclusions in spring steel deoxidized by silicon during hot rolling
Large non-deformable oxide inclusion is the main cause of spring fatigue failure. The negative effect of inclusion can be alleviated by reducing the size of oxide inclusion after hot rolling by obtaining low melting point plastic inclusion with good deforming properties. In order to study the evolution behavior of oxide inclusion in industrially produced silicon deoxidized spring steel during rolling process, The morphology, composition, size and density of oxide inclusions in continuous casting bloom, rolled billet and wire rod were analyzed by SEM+EDS. The results show that SiO
2
-Al
2
O
3
and SiO
2
-Al
2
O
3
-CaO were spherical inclusions in the continuous casting bloom, which were basically in the low melting point region. SiO
2
-Al
2
O
3
and SiO
2
-Al
2
O
3
-CaO inclusions in the rolled billet were long strip shape, and the tadpole-like SiO
2
inclusions were also found. There were five kinds of inclusions in the wire rod, four of which were long strip shape inclusions, in addition to SiO
2
-Al
2
O
3
and SiO
2
-Al
2
O
3
-CaO inclusions,also include SiO
2
-CaO-MgO and SiO
2
-Al
2
O
3
-CaO-MgO inclusions with high content of CaO and MgO. From the bloom to the rolled billet, the width less than 3 μm inclusions density increased from 1.1 /mm
2
to 3.2 /mm
2
, and the proportion increased from 50% to 80%. In the wire rod the width less than 3 μm inclusions almost reached 100%. The width less than 3 μm inclusions in each stage were mainly composed of SiO
2
-Al
2
O
3
、SiO
2
-Al
2
O
3
-CaO、SiO
2
. During the rolling process, the aspect ratio of SiO
2
-Al
2
O
3
and SiO
2
-Al
2
O
3
-CaO inclusions increased continuously, and their deformation index was higher than other types of inclusions. Meanwhile, due to the compression ratio, the deformation index of all inclusions in the rolled billet was higher than those in the wire rod. According to the morphology and composition evolution of the inclusions, combined with the crystallization behavior of the inclusions during heating, it is reasonable to speculate that the crystalline phase precipitated in the continuous casting bloom inclusions during high temperature heating, and the crystalline phase was separated in the subsequent rolling process, forming SiO
2
inclusions and high CaO and MgO content composite inclusions.
2023 Vol. 58 (2): 83-89 [
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470
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Metal Forming
90
ZHANG Qiang, LI Hong-bo, CHEN Gang, ZHANG Jie, ZHANG Peng-wu, WANG Wu-zhou
Analysis and control of hot-rolled strip crown for cold-rolled middle-wave control
The middle-wave flatness defect happens during the production of electro-galvanizing steel in a cold rolling mill. It is found that the cold-rolled strip with middle-wave flatness defect is related to the hot-rolled strip crown after the industrial data tracking and analyzing. In order to obtain the relationship between the hot-rolled strip crown control status and the cold-rolled strip middle-wave flatness defect, he industrial hot-rolled strip crown was statistical analyzed. It was found that the
C
40 values of the hot-rolled strip which was led to the cold-rolled strip middle-wave flatness defect, ere over 50 μm. And the ratio of the over 50 μm
C
40 value was 44.07%. It is proposed that the larger
C
40 value of the hot-rolled strip was a major cause for cold-rolled middle-wave defects. The influence rule of the data processing and calculation process of the hot-rolled strip profile gauge on the measured crown value is analyzed afterwards. The online crown measured value and the off-line crown measured value by manual measurement are compared. All the off-line crown measured values are larger than the online crown measured value, the difference is about 10 μm. So it is proposed that the error in the data processing process of the hot-rolled strip profile gauge, which lead to the actual larger strip crown than the measured value, is another major cause for cold-rolled middle-wave. To solve the larger strip crown problem, and considered the production stability, the transient process, a "small crown" control strategy is propose and put into industrial practice. It changes the hot-rolled strip target crown from 50 μm to 30 μm, the crown of hot-rolled strip is effectively controlled. The real production data is counted respectively before and after the "small crown" control strategy put into industrial practice. The re-grading rate of cold-rolled strip due to the defects of middle wave is reduced from 4.46% to 0.68% per month, the industrial practice got a good result. The research result shows a research idea and practical experience for the coordination control for the strip profile in the hot and cold strip rolling process.
2023 Vol. 58 (2): 90-95 [
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96
JI Ya-feng, WANG Xiao-jun, MENG Yuan, WANG Hai-shen, LIU Yu, LI Xu
Prediction of hot deformation behavior of 2205 duplex stainless steel based on PSO-BP
Aiming at the problem that the constitutive equation established by traditional mathematical and statistical methods cannot accurately reflect the hot processing properties of materials, a hot deformation prediction model with machine learning combined with optimization algorithm was proposed. A single-pass hot compression test was conducted using a Gleeble-3800 thermal simulation test machine to study the rheological behavior of 2205 duplex stainless steel under the heating temperature of 900-1 100 ℃ and the strain rate of 0.01-10 s
-1
. The Arrhenius model considering strain correction and the improved BP neural network model based on particle swarm algorithm(PSO-BP) were constructed,and the predicted values of the PSO-BP model were used to draw the hot processing diagram based on dynamic material model (DMM). The prediction ability and stability of the two models were evaluated by calculating the mean square correlation coefficient(
R
2
), root mean square error(
RMSE
) and average relative error(
AARE
). The results show that the PSO-BP model has better performance in predicting the flow properties of 2205 duplex stainless steel with
R
2
,
RMSE
and
AARE
of 0.999 79, 1.138 7 and 1.43%, respectively, which is a 2% improvement in
R
2
and a 10.147 6 MPa and 4.979% reduction in
RMSE
and
AARE
, respectively, relative to the strain-compensated Arrhenius constitutive model. Moreover, the drawn hot processing map is in good agreement with the experimental hot processing map, and the optimal processing intervals are from 1 000 to 1 100 ℃ for processing temperature and 3.5 to 10 s
-1
for strain rate. Therefore, the proposed PSO-BP model has strong reliability and applicability, can accurately describe the hot deformation characteristics of 2205 duplex stainless steel, and provide theoretical guidance and technical support for the forging, rolling and other processes of 2205 duplex stainless steel.
2023 Vol. 58 (2): 96-103 [
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104
WANG Fei-xue, ZHANG Jing-yan, WANG Ze-kun, LI Fei-fei, ZANG Xin-liang
Contral strategy and mechanism of compensation of thickened wall thickness on ends of pierced billet
Aiming at the thickening defects on the seamless pipe ends during tension reducing,basing on the compensation scheme of the wall thickness on pipe ends and the head and tail sharpening technology,the sharpening parameters of the sharpened pierced billet are pre-designed. With the help of ABAQUS finite element software,the whole process simulation model of tension reduction was established and its accuracy was verified by field test. The effects of different sharpening amount and sharpening length on the cutting loss length of the ends of pipe and the law of compensation of thickening wall were studied by single control variable method. Establishing the judgement basis of "full compensation area","over compensation area" and "unreasonable area" with different compensation effects. Considering the characteristics of long process and multi-process of seamless pipe production process and the genetic characteristics of pipe size under different processes,different passes and different tools,a control strategy of sharpened pierced billet compensation of multi-process joint control of tandem rolling-tension reducing is proposed. The design criterion of cutting parameters for pierced billet is given and the prediction model of effective value range of sharpening amount is derived basing on a large number of wall thickness data. The compensation control model of the head and tail sharpening of the sharpened pierced billet is established during the whole process of tension reduction,biting steel-steady rolling-casting steel. The section shape and dimensional accuracy of seamless pipe before and after compensation are compared and analyzed. The results show that the compensation control strategy for the sharpened pierced billet has significant suppression effect of defects. The strategy is extended to the pipe process of tension reduction with different specifications and extension coefficients,the applicability of the head and tail sharpening compensation control method is verified. Taking the length of pipe end cutting loss reduced by 60% as the measurement standard,there exists an effective value range for the sharpening amount of tensioning products of various specifications. The research has important guiding significance and industry practical value for improving the quality stability and yield of seamless pipe products.
2023 Vol. 58 (2): 104-112 [
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Materials
113
ZHANG Shao-long, ZHOU Wen, HU Feng, WU Kai-ming, PAN Xian-ming
Effect of Mn on tempering stability of retained austenite in bainite steel
In order to study the effect of Mn mass percent (0.1% and 1.5%) on the tempering stability of retained austenite (RA) in carbide-free bainite steel,scanning electron microscopy (SEM),electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to study the stability and mechanical properties of retained austenite. The results show that the hot-rolled microstructure of 0.1Mn steel is mainly composed of granular bainite (GB)+lath bainite (LB),while the hot-rolled microstructure of 1.5Mn steel is mainly lath bainite,and the content of retained austenite in 1.5Mn steel is higher,and the yield strength and tensile strength are better than 0.1Mn steel. After tempering at 300-500 ℃,the volume fraction of RA gradually decreases to complete decomposition,and the yield strength and tensile strength increase first and then decrease,but the elongation increases gradually. The best tempering performance is obtained at 300 ℃. The main reason is that during the tempering of retained austenite at 300 ℃,the block retained austenite decomposes into supersaturated martensite/bainite,and the carbon diffuses from the supersaturated martensite/bainite to the adjacent retained austenite to increase its content,so that the thermal stability is improved,and TRIP effect is produced in the process of stretching,so that the strength and plasticity of the test steel is improved. The mechanical properties of 1.5Mn steel is obviously better than that of the 0.1Mn steel,mainly because Mn and C can have synergistic effect to promote the stability of austenite and improve the elongation. In addition,the increase of Mn content increases the carbon equivalent,so that the strength of the test steel is enhanced. Based on the modified C-J model,the work hardening behavior of two test steels during tensile process is characterized. It was found that the strain hardening index of the 1.5Mn steel is always greater than that of the 0.1Mn steel,and the test steels showed three-stage strain hardening characteristics.
2023 Vol. 58 (2): 113-125 [
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126
WANG Jin-jian, CHEN Run-nong, HU Hui-chao, LIU Jing, CAO Yan-guang, LI Zhao-dong
Effect of Al on microstructure and weathering resistance of 4Cr1.5Ni weathering steel
Weathering steel has good atmospheric corrosion resistance, but traditional weathering steel cannot be used in high-humidity and hot marine atmospheric environment, relevant reports pointed out that it has accelerated corrosion after 8 years of exposure to the sun in Wanning. To meet the needs of marine engineering development, it is particularly important to optimize traditional weathering steel or develop new weathering steel. Two new weathering steels, 4Cr1.5Ni and 4Cr1.5Ni0.8Al, were designed based on traditional low-carbon steel composition and considering laterite nickel ore resources. The indoor accelerated dry-wet cyclic corrosion test was used to simulate the high humidity and heat Marine atmosphere environment. The microstructure and weatherability of the new weather-resistant steel were studied by combining OM, SEM, EDS, XRD, XPS and electrochemical methods. The effects of aluminum addition on microstructure, morphology of initial corrosion rust layer, phase composition and protection ability of test steel were analyzed emphatically. The relevant results can provide a reference for the development of new weathering steel suitable for the high-humidity and heat marine atmospheric environment. The results show that the microstructure of 4Cr1.5Ni steel is ferrite and martensite, and that of 4Cr1.5Ni0.8Al steel is ferrite and a little pearlite. The addition of aluminum can promote the formation of ferrite. The addition of aluminum reduces the corrosion rate, rust layer thickness and corrosion current density of 4Cr1.5Ni steel, and increases the corrosion potential and rust layer resistance. The α/γ(α-FeOOH/γ-FeOOH) value of 4Cr1.5Ni0.8Al steel is 2.5 times that of 4Cr1.5Ni steel, and the protection ability of the rust layer is enhanced. The presence of aluminum in the rust layer in the form of +3 valence (AlOOH and Al (OH)
3
), and at the same time promotes the formation of FeCr
2
O
4
which is thermodynamically more stable in the initial rust layer. In particular, the distribution area of aluminum and chromium in the rust layer of 4Cr1.5Ni0.8Al steel is the same, that is, there is a synchronous enrichment phenomenon, indicating that there is a synergistic effect of aluminum and chromium.
2023 Vol. 58 (2): 126-136 [
Abstract
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137
ZHU Li-guang, MA Chen-yu, WANG Qi, ZHENG Ya-xu, XIAO Peng-cheng, GUO Zhi-hong
Effect of welding process on microstructure and properties of heat affected zone of marine steel
The third generation oxide metallurgy technology with Mg treatment is adopted to produce 70 mm thick EH420 marine steel through hot metal pretreatment→converter→LF refining→VD refining→CC→TMCP process. In order to study the effect of "welding pass" and "line energy" on the microstructure and properties of heat affected zone (HAZ),thick plates were welded with large line energy. The welding processes were three wire submerged arc two pass welding with 170 kJ/cm line energy and three wire submerged arc single pass welding with 250 kJ/cm line energy. The results show that compared with the upper surface of 170 kJ/cm,the original austenite grain size at 170 kJ/cm
T
/4 increases from 58.60 μm to 75.22 μm due to "two pass welding". The number of M-A components is close,but the average size of island M-A components increases from 0.96 μm to 1.26 μm,and the average size of strip M-A components increases from 1.89 μm to 2.44 μm. The impact toughness at low temperature is deteriorated,and the average impact energy at -40 ℃ is reduced from 205 J to 156 J. Compared with the 170 kJ/cm upper surface,the original austenite grain size on the 250 kJ/cm upper surface increased from 58.60 μm to 74.75 μm due to the "increase of linear energy". The number of M-A components decreased,but the size of M-A components increased significantly. The average size of island M-A components increased from 0.96 μm to 1.52 μm,and the average size of strip M-A components increased from 1.89 μm to 2.87 μm,which worsened the low-temperature impact toughness,and the average impact energy at -40 ℃ decreased from 205 J to 187 J. After high line energy welding,there are composite inclusions in the coarse-grained region with MgO as the core and Ti(N,C) attached to the periphery. These inclusions can induce the precipitation of acicular ferrite (IAF),which is helpful to improve the impact toughness. Compared with 170 kJ/cm
T
/4,the size of M-A components on the upper surface of 250 kJ/cm is similar,but the number remains low,so the impact toughness on the upper surface of 250 kJ/cm is higher. Compared with multi pass welding,appropriately increasing the linear energy and reducing the welding passes can not only improve the impact toughness,but also improve the welding efficiency.
2023 Vol. 58 (2): 137-146 [
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147
HU Lei, ZHANG Li-qin, HU Feng, YIN Chao-chao, CHEN Teng-sheng
Effect of multi-scale cross section microstructure on strength and toughness of quenched and tempered marine steel
During rolling and heat treatment, due to the cooling rate and transformation kinetics from surface to center of large thickness marine steel are greatly different, which makes it difficult to completely reach the critical cooling rate on the cross section of the thick plate, thus forming martensite and bainite multiphase structure. Effect of multi-scale LM/LB substructure on strength and toughness of test steel by cross section microstructure of ultra-heavy plate observation and statistical analysis. The test results show that the tensile strength and yield strength are slightly lowered from the surface to the center, but the low temperature impact properties of the thick plate at different positions of the section are significantly different. (the average value of impact energy of the surface, 1/4 thickness(1/4
θ
(
θ
represents thickness)) and center at -40 ℃ were 139, 204.7 and 172 J, respectively). Due to the higher density lattice defects of martensite in the EBSD band slope (BS) diagram shows the characteristics of lower image quality, in combination with the Gaussian multi-peak fitting technique to quantitatively determine the mixed structure of 1/4
θ
lath martensite (LM) and lath bainite (LB) (68.3%LM+ 31.7%LB), two-phase mixture makes 1/4
θ
to achieve a high large-angle grain boundary ratio and lowest Kernel average misorientation (KAM) distribution、Geometrically necessary dislocation (GND) densities, making the 1/4
θ
have better impact toughness. Martensitic non-diffusive transformation is greatly affected by nucleation rate, while bainite transformation is jointly affected by nucleation rate and atomic diffusion rate, the cross-section effect of thick plate changes the nucleation rate and atomic diffusion rate, further affecting the multi-scale LM/LB substructure size. The Hall-Petch equation is introduced to describe the influence of LM/LB sub-structures at different scales on yield strength and impact toughness. The correlation coefficient
R
, between sub-structure size and strength and toughness is obtained by linear fitting numerical analysis. The larger the
R
-value is, the greater the influence of sub-structure on strength and toughness of materials is. Therefore, it is determined that lath and block are effective control units to determine the yield strength and toughness of quenched and tempered marine steel, respectively.
2023 Vol. 58 (2): 147-158 [
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159
ZHENG Ce, LI Ying-ju, TAO Wen-zhe, LUO Tian-jiao, YANG Yuan-sheng
Hot deformation microstructure and behavior of silicon steel solidified under low voltage pulsed magnetic field
In order to refine the microstructure of silicon steel ingot and improve its processability, the effect of low voltage pulsed magnetic field (LVPMF) on the solidification structure of silicon steel was investigated, and the hot deformation behavior and microstructure of different as-cast microstructures were compared. The fine grains are obtained by employing the low voltage pulsed magnetic field during the solidification of silicon steel. With the increase of frequency of LVPMF, the ratio of equiaxed grains (area of equiaxed grains to whole area) and average grain size of equiaxed grains was increased firstly and then decreased. In addition, the ratio and average grain size of equiaxed grains increased with the voltage of LVPMF. The average size equiaxed grain is refined to half of grains without LVPMF, and the ratio of equiaxed grains increased from 10% to 100% under optimal LVPMF parameter with frequency of 5 Hz and voltage of 200 V. Hot compression experiments (deformation temperature of 950 ℃, strain rate of 0.01 s
-1
and 0.1 s
-1
) and hot rolling experiments (blooming temperature 1 100 ℃) were carried out for columnar grains solidified without LVPMF and equiaxed grains solidified with LVPMF (frequency of 5 Hz, voltage of 200 V). A small amount of recrystallization grains occurs and strip-shaped grains are formed in the samples solidified without LVPMF with columnar grains after hot compression. The strip-shaped grains are hard to eliminate and deteriorate processing performance of the alloy. The samples solidified with LVPMF with equiaxed grains can be fully recrystallized after hot compression. Therefore, fine recrystallization grains are acquired with average size of 670 μm. By comparing the microstructure and texture of hot-rolled sheets, it is found that the samples with LVPMF with equiaxed grains are more prone to recrystallization during hot rolling, resulting in weaker texture intensity and anisotropy.
2023 Vol. 58 (2): 159-167 [
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168
YONG Xi, LIU Zhen-bao, WANG Chang-jun, NING Jing
Construction and application of genome database management platform of ultra high strength steel
The "material genome project" is mainly to change the "trial and error" mode of material research. Through the collection and sorting of previous experimental data,combined with simulation computing technology and information technologies such as big data and blockchain,it can establish the basic database,big data management platform,high-throughput simulation computing,experiment and analysis platform of materials,and introduce advanced AI technology such as machine learning to provide effective data support for the rapid development of high-performance new materials. According to the data processing requirement in ultra-high strength steel research,the genome database of ultra-high strength steel and its management platform are established based on the basic data collection and high flux simulation calculation of ultra-high strength steel. It presents the structural framework of database system and the overall architecture of genome data management platform,and shows some applications developed on this platform,such as integrating experimental data to form experiment report,parsing computing data to form customized visualization,and so on. This platform can accommodate various data type,including numeric,text,rich text,table,function,image,etc. and support the storage and management of TB-level mass data and the index and retrieve of million-level data records. It can implement the intelligent management of the whole process from online collection,normalized processing,storing and managing to retrieving and analyzing,so as to provide requisite data supporting for the research work of ultra-high strength steel. As a result,the platform can effectively improve the data utilization and analysis capability of research group and provide high-quality data services for developing new ultra-high strength steel.
2023 Vol. 58 (2): 168-172 [
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164
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Environmental Protection and Energy
173
ZHANG Qi, SHEN Jia-lin, JI Yang-mei
Analysis of carbon emissions in typical iron- and steelmaking process and implementation path research of carbon neutrality
The blast furnace-blast oxygen furnace (BF-BOF) steel production process is a typical iron and steel process,and also is typical iron-coal chemical process with high energy consumption and large carbon emissions,which is in a key area for Chinese iron and steel industry to achieve the goal of carbon neutrality. In 2020,the production of steel produced by this process accounted for over 90% of the national crude steel production,and the BF-BOF steel process is an important source of CO
2
emissions in the iron and steel industry. Therefore,the carbon emission calculation and carbon neutralization path research of companies based on the typical BF-BOF steel process has attracted attention. At present,there are a variety of calculation methods for carbon emissions of iron and steel companies at home and abroad,but different CO
2
calculation boundaries and methods have great differences in the results of companies′ CO
2
emissions,and the influencing factors are also different. The carbon emission characteristics of the steel production process are introduced. Taking a typical production process as an example,it analyzes the carbon emission,carbon emission accounting methods,and influencing factors of the whole steel process from the perspective of system boundary,and calculates the carbon emissions of 3.9 million tons and 5.5 million tons of iron and steel companies under different methods,and compares the differences between different calculation methods. The results show that the proportion of CO
2
emissions in the pre-iron process of company A and company B to the total carbon emissions is 60.99% and 54.12%,respectively. Coking,sintering and ironmaking processes should be given priority to reduce CO
2
emissions in the iron- and steelmaking process. The factors affecting the emission reduction in the iron- and steelmaking process mainly include the consumption of fossil fuels,the recovery rate of energy,the proportion of self-generated electricity and the selection of carbon emission factors. Among them,the consumption of fossil fuels accounts for more than 80% of the total CO
2
emissions,which is the largest source of CO
2
emissions from the iron- and steelmaking process. Meanwhile,the application effects and carbon emission reduction paths of different technologies and measures are analyzed with the goal of carbon neutrality of the whole steel process,which is to provide a theoretical basis for iron and steel companies to achieve the carbon peak-carbon neutrality goal and a useful reference for companies to formulate a carbon neutrality roadmap.
2023 Vol. 58 (2): 173-187 [
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