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2022 Vol. 57 No. 7
Published: 2022-07-15
Technical Reviews
Raw Material and Ironmaking
Steelmaking
Metal Forming
Materials
Environmental Protection and Energy
Technical Reviews
1
YANG Jian, LI Ting-ting
Research progress on inclusion control of non-oriented silicon steel with REM treatment
The magnetic properties of cold rolled non-oriented silicon steel which are highly dependent on the steelmaking technology, are affected by chemical compositions, distribution of inclusions, recrystallization structure and so on in steel. Long strip or angular inclusions usually have a greater impact on coercivity and hysteresis loss than spherical inclusions. The inclusions which have great influence on the magnetic properties of non-oriented silicon steel are mainly with the size smaller than 0.5 μm. The effects of rare earth metal(REM) treatment on inclusions in non-oriented silicon steel are summarized and analyzed, including coarsening inclusions, reducing the number of fine inclusions in steel and spheroidizing inclusions. REM have strong deoxidation ability and can effectively purify molten steel. With the addition of REM, the rare earth oxides or rare earth oxide sulfides generated in non-oriented silicon steel are usually spherical or nearly spherical. Due to the high surface activity of REM, the generated fine inclusions are easier to polymerize and grow up in the molten steel, and finally achieve the modification and coarsening of inclusions. Because the rare earth sulfides and rare earth oxide sulfides have high melting point and are difficult to form solid solution, the solid solution amount of S element can be effectively reduced during reheating process and the precipitation of fine MnS inclusions can be inhibited during cooling process. In addition, AlN and MnS inclusions are easy to precipitate on the surface of rare earth inclusions, further reducing the amount of fine precipitates. REM can improve the texture of products and has the optimal addition amount. At the same time, the technology of rare earth addition during the refining process of non-oriented silicon steel at home and abroad is analyzed. The ladle addition method is mainly used in the refining process of non-oriented silicon steel. The rare earth treatment results are ensured by adding REM under vacuum, pre-deoxidizing the molten steel by adding Al and Si elements, and injecting desulfurizer before the addition of REM, and then fully stirring the molten steel after adding REM. However, there is still the nozzle clogging problem caused by rare earth inclusions in the process of continuous casting, which needs to be studied.
2022 Vol. 57 (7): 1-15 [
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Raw Material and Ironmaking
16
LENG Chang-ming, JIANG Xin, XUE Qing-bin, LONG Fang, HUO Hong-yan, SHEN Feng-man
Effects of high proportion of acid burden on blast furnace operation and its countermeasures
Recently the proportion of acid burden (pellet and lump ore) in blast furnace (BF) of Chinese iron and steel companies increased due to the environmental considerations, especiall in the winter heating season. However, under the high proportion of acid burden, the operation performances are different due to the different resources. Some BFs got better performances, and some BFs got worse performances. Aimed to improve the proportion of acid burden and reduce the ironmaking cost, the problems caused by high proportion of acid burden were analyzed, and some countermeasures were proposed. The effects of high proportion of acid burden on the BF operation are mainly reflected in lump zone and cohesive zone of BF. The effects on the lump zone include that prosity of burden decreases due to the size difference between acid ores and sinter, difficult contolling of the burden pile due to the different packing properties, and negative effect of the powder generated by reduced lump ores on the gas permeability. The effects on the cohesive zone include that the lower melting temperature of acid burden, lower reducibility and higher FeO content in reduced ore, resulting in a higher position and wider cohesive zone in BF, and the length of coke slit increases, resulting in the increased the pressure drop. The countermeasures for the high proportion of acid burden include that reasonable select high quality of acid ores,using MgO-bearing basic pellet, relieving the negative effect on the burden pile by reasonable charge methods, and mixed charge of pellet and coke nut, effectively use the functions of bulk coke and coke nut. All the measures that improve the permeability of lump zone and cohesive zone can relieve the negative effects of high proportion of acid burden on the BF operation. The ironmaking plants can gradually take the measures, combined with the resource and operation characteristics, to improve the BF performances. The contribution of the present work is to give some references when the high proportion of acid burden is used in the BF operation.
2022 Vol. 57 (7): 16-25 [
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26
DOU Ming-hui, SUN Yang, HAN Jia-wei, SUN Zhang, LIANG Ying-hua
Solution loss characteristics of cokes in H
2
O+CO
2
atmosphere
To study the solution-loss reaction characteristics of cokes in hydrogen-rich blast furnace, a homemade coke reactivity measurement device with continuous water inflow was developed to carry out coke solution-loss experiments by CO
2
(N
2
) carrying H
2
O vapor with different percentages (0-30%), which provided H
2
O+CO
2
(gas mixture of H
2
O and CO
2
)and H
2
O+N
2
(gas mixture of H
2
O and N
2
)atmosphere. The Boudouard reaction(C+CO
2
=2CO)kinetics and water gas (C+H
2
O=CO+H
2
)reaction kinetics of cokes in H
2
O+CO
2
atmosphere were studied using real-time recording the mole percent of CO and H
2
in the outlet gas through infrared gas analyzers. The results show that carbon loss ratio and solution-loss rate of cokes increase with the increase of H
2
O percentage in the H
2
O+CO
2
reaction atmosphere. Furthermore, with the increase of H
2
O percentage the water gas reaction rate and carbon loss ratio increase gradually, while the Boudouard reaction rate and carbon loss ratio decrease gradually, which indicates that there is a strong competition between the reactions of H
2
O and CO
2
with coke. The analysis for fitting slopes of linear relationship between carbon loss rate and H
2
O percentage shows that the slopes of the Boudouard reaction and water gas reaction for cokes in H
2
O+CO
2
atmosphere are less than the ones in single atmosphere, and an inhibition factor (
α
) based on the difference of reaction rate constant is proposed to
evaluate the degree of inhibition, which can characterize the influence degree of interaction for H
2
O and CO
2
on carbon dissolution reaction and water gas reaction. The inhibition factor
α
<
sub>
CO
2
/H
2
O of CO
2
to water gas reaction is 0.253, and the inhibition factor
α
<
sub>
H
2
O/CO
2
of H
2
O to Boudouard reaction is 0.179.
α
<
sub>
CO
2
/H
2
O:
α
<
sub>
H
2
O/CO
2
is 1.41. The inhibition degree of CO
2
on water gas reaction is stronger than that of H
2
O on carbon solution reaction.
2022 Vol. 57 (7): 26-33 [
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34
CHEN Shuai, LI Jia, LUO Shi-yuan, CAI Tian, ZHANG Zheng-dong, GUO Hong-wei
Design optimization and numerical simulation of blast furnace cooling column
When the cooling stave of blast furnace is completely damaged in the later stage of furnace service, the cooling column is generally used to repair it, but the installation quantity and installation position of cooling column almost depend on the practical experience of on-site technicians. Aiming at the arduous problem that how to determine the quantity and position of blast furnace cooling column installed on a furnace shell, an optimized installation method was put forward through analyzing the relationship between installation quantity and position and cooling effect to make full use of cooling performance of cooling column. Firstly, based on the basic principle that the total heat exchange area of cooling column was greater than the total heat exchange area of original cooling stave, by calculating the heat exchange area of cooling column and original cooling stave, the set number of cooling columns installed on a furnace shell was determined to be 11. Secondly, taking the central coordinates of installation positions for 11 cooling columns as the design variables, the optimization mathematical model for calculating the maximum cooling area was established by basic principle of grid method. After setting the constraints, it was solved in MATLAB software by genetic algorithm, and 91.68% of cooling coverage area of cooling columns and the central coordinates of 11 cooling columns were obtained. Finally, a three-dimensional steady-state heat transfer model was established by central coordinates of installation positions for 11 cooling columns, and the model was analyzed by FLUENT software. After full iteration, the temperature field of blast furnace cooling column was obtained, and the surface temperature fields for three types of arrangement of furnace shells were compared. The results showed that the maximum surface temperature and the average temperature of blast furnace shell with optimized arrangement were 73.34 ℃ and 54.29 ℃, respectively. Compared with the other two arrangements, the maximum temperature was reduced by 14.69% and 30.21% respectively, and the average temperature was reduced by 13.33% and 17.42% respectively, which effectively improved the cooling performance and utilization efficiency of cooling column.
2022 Vol. 57 (7): 34-42 [
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Steelmaking
43
CHANG Li-zhong, SU Yun-long, ZHANG Long-fei, ZHU Chun-li, XU Tao, SHI Xiao-fang
Influence of power frequency on cleanliness of electroslag ingot during electroslag remelting process
In the process of electroslag remelting, low-frequency power supply can improve power factor, reduce power consumption and realize three-phase balance of power system. However, the influence of power frequency on the metallurgical quality of electroslag ingot, especially the cleanliness, is still lack of sufficient data support. Based on the small-scale low-frequency electroslag remelting experiments in the laboratory, the effects of different power supply frequencies, especially low supply frequencies on the cleanliness of ingot were studied and the effect lows of power frequencies on chemical composition, oxygen and nitrogen content, inclusion distribution in the 304 austenitic stainless steel and GCr15 bearing steel electroslag ingots were analyzed in detail. The results show that compared with power frequency electroslag remelting, when low frequency (2, 1, 0.4, 0.1 Hz) electroslag remelting is adopted for both stainless steel and bearing steel (other experimental parameters such as the composition and weight of slag, smelting current and voltage, remelting atmosphere etc, are exactly the same), the oxygen content in electroslag ingots increases greatly, both between 0.010% and 0.013%. But the frequency variation has little effect on nitrogen content. The content of aluminum in electroslag ingot also increases significantly, while other chemical compositions change little. Correspondingly, the number of inclusions in low frequency electroslag ingot also increases significantly, and the increased inclusions are mainly alumina. However, the inclusions are mainly small inclusions less than 10 μm, the large inclusions increase slightly, but the number is very small. The main reason for increase of oxygen content is that the DC effect of low-frequency power supply causes the electrolysis of alumina in the remelting slag pool (30% Al
2
O
3
+70% CaF
2
slag system) which leads to the increase of aluminum and oxygen content. The total oxygen content of ESR ingot increases when the aluminum and oxygen formed by alumina electrolysis enter the molten metal pool. With the cooling and solidification of metal pool, oxygen and aluminum form alumina inclusions, which remain in the electroslag ingot. The DC electrolysis effect of low-frequency power supply in industrial production needs to be further analyzed.
2022 Vol. 57 (7): 43-53 [
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54
DU Yi-nuo, GUO Lei, YANG Yang, ZHANG Shuai, YU Han-zhang, GUO Zhan-cheng
Numerical simulation of inclusions floating behavior under supergravity field in liquid steel
Supergravity can significantly increase the gravity difference between solid-liquid phases, and the removal rate of inclusions in molten metal can be greatly accelerated. The study was based on the supergravity metallurgy device to establish computational fluid dynamics model of solid inclusions in the liquid steel in different gravity fields, according to the dynamic mesh and flow-solid interaction. The model simulated the floating motion state of inclusions in the gravity fields with different gravity coefficients, and studied the influence of factors such as the supergravity coefficient and size of inclusions on the floating behavior and flow field distribution. The simulation results indicate that the inclusions tend to be steady movement after a short acceleration with the constant gravity coefficient, the extension of supergravity field will cause the increase of floating speed of inclusions and the liquid steel near the inclusions will be “push away” quickly, then the flow state of liquid steel has been changed. Inclusion particles with
d
=1, 10 μm are still satisfied with the Stokes flow law under the certain supergravity field since the size of particle is small. The large size inclusions of
d
=100 μm only compliant with the Stoke flow Law when the gravity coefficient is below ten times. With the lager gravity field is applied, the nearby flow field changes from laminar flow to turbulent flow, and the Stokes float law is no longer suited. When studying the model of inclusion floats in gravity fields with different gravity coefficients, it is found that the change of floating velocity for
d
=1 μm inclusions is directly proportional to the change of gravity coefficient when the coefficient changes with time. After the lager inclusions such as
d
=10, 100 μm are not consistent with the laminar flow field, the floating velocity is no longer in a linear relationship with the gravity field.
2022 Vol. 57 (7): 54-62 [
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63
GUO Shuai, ZHU Hang-yu, ZHOU Jie, DONG Shuai, LIANG Yin
Effects of inclusions on stress field in low-density steel under compressive loading
Crack initiation and growth are usually caused by non-metallic inclusions (NMI) during the rolling process, and it is necessary to study the effects of NMIs on the mechanical properties of low-density steel. The influences of typical NMIs such as single Al
2
O
3
, MnS, AlN, TiN and Al
2
O
3
-AlN、AlN-MnS complex NMIs on the stress field in low-density steel were investigated using Abaqus software, and then the effects of type, size, direction, distribution of NMIs on stress field were also studied. The results show that the deformability, shape, and size of NMIs significantly affect the distribution of stress field, and the maximum stress value caused by NMIs and nearby matrix are TiN, AlN, Al
2
O
3,
and MnS in descending order. The maximum stress value and range of stress field are positively associated with the size of NMI. Moreover, the angle between the longitudinal axis of NMI and loading direction affects the crack initiation location and propagation direction. As for TiN and AlN inclusions, the sharp corner located in the loading direction can inhibit the stress concentration. In addition, the aggregated NMIs are more likely to cause the stress concentration, and the maximum stress value has a negative correlation in the distance of NMIs. For Al
2
O
3
-AlN complex inclusion, the internal Al
2
O
3
could prevent deformation of complex inclusion and increase the stress value, and increase the harmfulness of AlN. However, for AlN-MnS complex inclusion, the stress concentration in corner of AlN could be relieved by externally wrapping with MnS inclusion, and the harmfulness of AlN could be decreased. Therefore, to decrease the harmfulness of NMIs on properties of low-density steel, the number and size of brittle NMIs and aggregated AlN should be controlled, and the damage of AlN inclusion to be reduced by AlN-MnS complex inclusion.
2022 Vol. 57 (7): 63-72 [
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73
SHANG Ting-rui, WANG Wei-ling, KANG Ji-bai, ZHU Miao-yong, LUO Sen
In situ observation of solidification under transient and average cooling rate of 20CrMnTi continuous casting
Wide hardenability band and large-size TiN precipitates seriously endanger the product quality of 20CrMnTi gear steel. The key basis for its control is to master the behavior mechanism of solidification structure evolution during continuous casting. The traditional high temperature laser confocal scanning microscopy(HT-CSLM) in situ observation and research usually sets the cooling rate of mushy zone as a fixed value,which can not effectively reflect the change of cooling rate during continuous casting solidification. Therefore,20CrMnTi 160 mm×160 mm billet was the research object. Through the two-dimensional slice solidification heat transfer calculation,the thermal history,transient and average cooling rate of the paste area 20,40 and 60 mm below the inner arc surface were determined,and then the heating and cooling scheme of HT-CSLM experiment was designed. Then,HT-CSLM experiments under the conditions of transient and average cooling rate in the mushy zone at these locations were carried out to reveal the solidification process of 20CrMnTi under different cooling conditions δ grain growth kinetics and peritectic phase transformation mechanism. Finally,the effect of cooling conditions on solidification structure size was investigated by electron probe microanalysis(EPMA). The results show that due to the compensation of solidification latent heat,the cooling rate at the position of 20,40 and 60 mm under the inner arc is small in the initial solidification stage,and gradually increases in the middle and later stages of solidification,and becomes more significant with the deeper into the billet. The average cooling rates at these locations are 102.81,44.63 and 34.93 ℃/min,respectively. δ grain precipitates first from the liquid steel,and its average growth rate increases with the increase of cooling rate. Under the condition of transient cooling rate,instantaneous growth rate increases with the progress of solidification,but decreases slightly under the condition of average cooling rate. This is because under the condition of transient cooling rate,the cooling rate of mushy zone changes from slow to fast,which continuously compensates the latent heat of solidification,at the same time,the number of initial nucleation is small,the growth space is large,and the influence of solute undercooling is relatively weak. When the melt temperature decreases to the critical temperature of peritectic phase transformation,δ grain transition to γ grain rapidly,that is,massive transformation occurs,leading to a rapid increase in the solid fraction,accompanied by some γ grain polymerization rapidly. On the whole,the critical temperature of peritectic phase transition decreases with the increase of cooling rate,but it is also affected by the initial content of solute. After that,the remaining liquid phase transitions to the γ phase until complete solidification. The grain radius decreases with the increase of cooling rate,and it is smaller under the condition of average cooling rate than that under the condition of transient cooling rate,which depends on the number of nucleation in the initial solidification stage.
2022 Vol. 57 (7): 73-85 [
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86
CHEN Bin, LI Hai-bo, JI Chen-xi, LIU Guo-liang, ZHOU Hai-chen
Influence of casting parameters on level fluctuations and its industrial application
The level fluctuations behavior of the molten steel in the steel slab continuous casting mold is the result of the combined effect of the molten steel flow in the mold,the mold itself vibration,and the fluctuation of the molten steel in the slab when rollers squeeze the slab. The stability of level fluctuations of the mold has a great effect on the behavior of slag entrainment in the continuous casting slab process. In industrial practice of steel slab continuous casting,the level fluctuations is detected in a certain zone of the top surface (such as the middle of the mold width direction) using a radioactive source or an eddy current sensor to represent the overall level fluctuations. In the current study,the effects of casting parameters on the top surface level profile of the mold were studied through the three-dimensional numerical simulation of the gas-liquid two-phase flow. The casting parameters include casting speed,argon flow rate,out-port angle of submerged entry nozzle(SEN)and mold width. The results show that the fluctuation amplitude at different positions of the top surface of the mold was different,and it changed with the variation of casting parameters. With the increasing of the casting speed and argon flow rate,the difference between the peak and the trough of the top surface level profile increased near the narrow face and the SEN,respectively. When the out-port angle of SEN was 15°,the surface level was higher near the SEN and the narrow face. When the out-port angle of SEN was 45°,large surface level was only observed near the SEN. The results show that it was necessary to arrange the level detection equipment near the SEN and the narrow face for mold level detection when using the conventional SEN with 15° out-port angle and the mold width was larger than 800 mm,ensuring more fully reflected the real behavior of level fluctuations of the mold,which can enhance the guidance of the surface quality of the rolled coils and effectively improve the control level of the continuous casting process. When using the SEN with 45° out-port angle,the arrangement of the original level detection remained unchanged.
2022 Vol. 57 (7): 86-94 [
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Metal Forming
95
KANG Yong-lin, ZHU Guo-ming, JIANG Min, WANG Guo-lian, LIU Peng-tao, XU Hai-wei, XIE Cui-hong, WEI Yun-fei, SHEN Kai-zhao, LIU Yang
Slab continuous casting by big roll heavy reduction and extra thick plate rolled by low compression ratio
In recent years, the heavy reduction technology at solidification end of continuous casting developed at home and abroad has achieved good effect on reducing porosity and segregation in thick slab, while there are also some deficiencies, for instance, when the thick slab is pressed by the small rolls of segment, the strain is difficult to penetrate into the core of slab, which is not conducive to ameliorate the central porosity. Obtaining high-quality thick slab with high efficiency, low cost as well as low energy consumption and rolling high-quality thick slab with low compression ratio are still the direction of further exploration and development. In order to solve the problems of central porosity and segregation defects in the solidification process of thick slab continuous casting more effectively, a new technical of wide-thick slab continuous casting by big roll heavy reduction(BRHR) was proposed and the BRHR equipment was developed. The BRHR equipment had been installed, commissioned on the wide and thick slab continuous casting line and operated for more than two years. Meanwhile, the process prediction and control system and secondary cooling water process optimization control technology were developed. The research proves that developed BRHR equipment and technology for continuous casting are conducive to make the reduction strain penetrate into the core of slab. Using the large gradient temperature field which is larger than 500 ℃ or 400 ℃ formed at the end of solidification or just complete solidification (
f
s
=1.0) on the continuous casting line to implement large diameter roll for large reduction can significantly reduce the central defects of wide and thick slab. The production practice proves that shrinkage, porosity and segregation in 400 mm thickness specification wide and thick continuous casting slab have been significantly ameliorated by BRHR equipment and technology. Combined with the optimization of rolling process, the high-quality extra thick slab with thickness of 150-200 mm is produced with very low compression ratio of 1.90-2.53, which has great significance for low cost and short process production of high-quality extra thick products as well as energy conservation and emission reduction.
2022 Vol. 57 (7): 95-105 [
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106
YU Meng, WANG Chun-hai, ZHANG Xiao-feng, WEN Jie, WANG Yong-qiang, ZHANG Qing-dong
Shape warping behavior of stainless steel/carbon steel clad plate during temper rolling
Aiming at the behavior that stainless steel/carbon steel clad plate is prone to non-uniform extension and warpage during temper rolling,a finite element numerical simulation model for the temper rolling process of stainless steel/carbon steel clad plate was established, and the uneven deformation behavior of the temper rolling process of the stainless steel/carbon steel clad plate that has been industrialized and mass-produced and its possible lead to warpage Numerical simulation study of defects. On this basis, the heredity and evolution of the shape of homogeneous plate, asymmetric stainless steel/carbon steel clad plate and symmetrical stainless steel/carbon steel/stainless steel clad plate during temper rolling were compared and analyzed, and it was found that only asymmetric stainless steel/carbon steel clad plate is very prone to warpage defects in the process of temper rolling. At the same time, the effects of tempering and conventional rolling on the warpage defects of asymmetric stainless steel/carbon steel clad plates after rolling are compared and analyzed. The thickness-wise delamination characteristics of stainless steel/carbon steel clad plates and the influence of clad plate size parameters, leveling process and equipment parameters of leveling machine, etc. on the warpage defects of the plate shape are revealed. Afterwards, the warp height is proportional to the thickness ratio. For the skin-passing process, when temper rolling with equal tension, the warpage height after skin-passing is proportional to the tension; when temper rolling with unequal tension, the change of pre-tension has a great influence on the warpage defects after skin-passing; the warpage height after that is inversely proportional to the friction coefficient of the roll and the carbon steel layer surface. For the parameters of the leveling equipment, the warpage height after leveling is proportional to the diameter of the roll contacting the surface of the carbon steel layer, the lifting height of the anti-wrinkle roll on the entry side, and the distance from the contact roll on the surface of the stainless steel layer to the entry side. Finally, the numerical simulation results were verified by rolling experiments, which proved the accuracy of the temper rolling model of the clad plate. Based on the above research results, corresponding technological countermeasures are proposed, which provide a theoretical basis for the control of flat warpage during temper rolling of metal clad plates.
2022 Vol. 57 (7): 106-114 [
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115
LI Song-song, LI Wei, YUE Heng-quan, GAO Tian, WANG Hai-jun, YU Hui
Analytical model of mean roll radius in alloy steel bar rolling
In alloy steel bar rolling, oval and round pass play a decisive role in the dimensional accuracy and quality defects of finished bar. When calculating the rolling process specification, the mean roll radius is generally used to replace the roll radius of groove profile change. Therefore, the reliability of mean roll radius calculation model plays an important role in the reasonable selection of rolling process (rolling speed, reduction, rolling force, etc.) and the improvement of geometric dimension accuracy of products. On the basis of existing mean roll radius model, considering the influence of spread for different alloy steels, the calculation formulas of section shape and rolling critical point of deformed rolled piece were deduced using the prediction model of pass rolling surface profile. A method for calculating the equivalent rectangular average height using the section area and critical average width of export rolled pieces was proposed. A new calculation model for the mean roll radius of oval and round pass was given and verified by rolling experiments. The rolling experiment results show that, compared with the existing model, the new calculation model improves the calculation accuracy of mean roll radius to a certain extent. At the same time, based on the influence coefficient of alloy composition, the corresponding relationship of critical point distribution after rolling deformation of different alloy steels is explored. Taking into account the existence of straight lines on the side walls of pass, the rolling contact state of round pass is divided into stages. When the alloy composition coefficient is small (carbon structure steel and pearlitic-martensitic steel), the rolling critical point falls on the arc groove, and all calculation models are valid. When the alloy composition coefficient exceeds 1.33 (austenitic steel and ferritic steel), the rolling critical point extends to the straight line of side wall, the original model calculation fails, and the rolling process parameters are solved by the new calculation model. The critical distribution of alloy steel grade rolling based on the new model has important guiding significance for the rapid formulation of process parameters for bar rolling steel grade transformation.
2022 Vol. 57 (7): 115-124 [
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Materials
125
ZHENG Kai, CAO Wen-quan, YU Feng, WANG Cun-yu, ZHONG Zhen-qian, XU Hai-feng
Research status and progress of high temperature stainless carburized bearing steel
Aviation bearing steel is developing towards high temperature resistance, corrosion resistance, high load bearing and long service life. The M50 bearing steel on service has the problems of high strength but insufficient toughness and corrosion resistance. Although the toughness of M50 NiL carburized bearing steel is improved by reducing C content and adjusting alloy composition, it still can't meet the development needs of aeroengines with high thrust weight ratio in future, and the problem of insufficient corrosion resistance has not been solved. Although high chromium stainless bearing steel BG-42 and high nitrogen bearing steel cronidur30 have good corrosion resistance, their surface hardness and core toughness are still insufficient. High temperature stainless carburized bearing steel represented by CSS-42L steel has high strength, toughness and excellent corrosion resistance. It not only has great competitive advantages in aviation bearing application, but also can be applied to gears, shafts and fasteners used in high temperature or corrosive environment. However, relevant research work at home and abroad is still insufficient and lack of systematicness. Therefore, it is particularly important to summarize its research and development status. Based on the development history of aviation high temperature bearing steel, the research and development background and alloy composition design idea of high temperature stainless carburized bearing steel at home and abroad are introduced in detail. The effects of main alloy elements such as Cr, Co, Mo, Ni, V and W elements on microstructure and properties are reviewed. Although the addition of Co element does not directly participate in precipitation strengthening, it can inhibit precipitation δ-ferrite formation and have a special effect of promoting dispersion precipitation. The effects of heat treatment process on microstructure, strength and toughness were revealed from two aspects: surface carburization and core material. In view of the shortcomings of the research on the basic theory and manufacturing process of the high temperature stainless carburized bearing steel at home and abroad, the research and development directions of optimizing alloy composition, breaking through carburizing heat treatment technology, and researching microstructure evolution, fatigue damage and failure mechanism under different working conditions are put forward.
2022 Vol. 57 (7): 125-136 [
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137
ZHOU Nai-peng, SHE Chang-lian, CHAI Feng, LUO Xiao-bing, LI Jian
Advances in corrosion research of low alloy steel in high humidity and high temperature marine environment
The 21 st century is the century of oceans,the improvement of marine engineering materials plays a critical role in the implementing the national oceans strategy. With the development of the “One Belt and One Road” policy and the exploration of natural resources,the South Sea has attracted a great number of attentions. The extreme environment of the South Sea,characterized by high temperature,high humidity,high salinity and high irradiation has extremely high corrosivity then other marine environments. And the harsh corrosion environment raises a claim of long service and high reliability of the hull steel. There is no doubt about the growing importance of the investigation of the corrosion behavior and mechanism in the harsh marine environment in the South Sea. And there is a serious lack of the corrosion data of hull steel in the South Sea. The evaluation methods and improvement methods for corrosion resistance of the hull steel in tropical marine environment was fundamentally introduced. The evaluation method consisted the simulated corrosion test which was mainly characterized by the dry/wet cyclic test and the correlation study between results acquired form the simulated corrosion test and the outdoors exposure test. The existing problem of the disagreement of the experimental parameter such as the test solution,the temperature and the humidity has been mentioned. The role of the alloying element optimization,the inclusion modification and the control of microstructure evolution on the corrosion resistance improvement was illustrated. The effect of the addition of Ni,Cr,Cu,Sb,Sn and other alloy elements on the corrosion behavior has been summarized. Also the application prospects of the Inclusion modification and the control of microstructural evolution in the South Sea has been proposed. And a reference for the further research and application of the hull steel in the high humidity and high temperature environment of the South Sea was provided.
2022 Vol. 57 (7): 137-145 [
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146
CHEN Guang-xing, XU Xiao-chang
Microstuctures and aging impact properties of 15CrMoR steel
In order to explore the influence of primitive microstuctures on the low-temperature impact performance of 15CrMoR steel during aging process and to clear the primitive microstuctures of 15CrMoR steel with high aging impact performance stability,three primitive microstructures of 15CrMoR steel were obtained by controlling the cooling method after austenitization. The microstructure and aging impact properties at low temperature of 15CrMoR steel were investigated by means of OM,SEM,EPMA,EBSD and low temperature impact test.The results show that cooled to room temperature by furnace cooling,air cooling and wind cooling after austenitizing respectively,the microstructures of 15CrMoR steel are coarse ferrite + lamellar pearlite,ferrite + degraded pearlite,and granular bainite. The carbides in the lamellar pearlite microstuctures are mainly lamellar, while mainly intermittent short rod and granular like in the lamellar pearlite microstuctures. And the carbon-rich M-A islands in granular bainite microstuctures are mainly distributed along the grain boundary.The precipitation and growth of carbides at grain boundary occurred during the cyclic aging process of the three kinds of 15CrMoR steel with different primitive microstructures,which led to the continuous deterioration of low-temperature impact performance. When the grain boundary carbides are distributed in chains,the low-temperature impact performance of 15CrMoR steel is poor. The coarse ferrite + lamellar pearlite microstructure has a small grain boundary area,which leads to a chain-like distribution of grain boundary carbides. And the carbon-rich M-A islands mainly distributed along the grain boundary in granular bainite can also lead to the chain-like distribution of grain boundary carbides easily.Therefor,15CrMoR steel with the ferrite+ degraded pearlite primitive microstructures has good impact performance stability during the cyclic aging process,which average impact absorption energy at -10 ℃ is still as high as 196 J after 6 cycles of aging.However,the average impact absorption energy at -10 ℃ of both 15CrMoR steel with ferrite + lamellar Pearlite primitive microstructures and with granular bainite normalized microstructures is only 18 J after 4 cycles of aging,which owing to the carbides at grain boundary has formed a chain-like distribution.
2022 Vol. 57 (7): 146-153 [
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154
ZHU Xiao-xiang, YANG Geng-wei, ZHAO Gang, HAN Ru-yang, FU Zhi-xiang, BAO Shuang
Impact abrasive wear behavior of hot-rolled medium manganese martensitic wear-resistant steel
The impact abrasive wear behavior of hot-rolled medium manganese martensite wear-resistant steel under the impact energy of 1 J, 2.5 J and 5 J was systematically studied by MLD-10 dynamic load abrasive wear tester, and compared with that of Hardox450 steel. With the help of optical microscope (OM), scanning electron microscope (SEM) and Brinell hardness tester, the microstructure, mechanical properties, wear surface layer and sub-surface layer of the test steel were analyzed, and the wear mechanism was discussed. The results show that the microstructure of the experimental steel is lath martensite. Compared with Hardox450 steel, the Brinell hardness of the experimental steel is higher, and the impact absorption energy at -40 ℃ is lower, which is 503 HB and 15.3 J respectively. Under the same working conditions, the wear weight loss of the test steel is obviously smaller than that of Hardox450 steel, and the wear rate corrected based on the effective wear time increases first and then decreases with the increase of impact energy. When the impact energy is 2.5 J, the wear rate is the highest and the grinding loss is the largest. The reason are as follows. When the impact energy is low, the wear of the test steel is mainly furrow, accompanied by a small amount of embedded abrasive particles, resulting in less wear loss; When the impact energy is 2.5 J, the cutting of the worn surface is intensified, and the plastic deformation makes a large number of abrasive grains to embedded in the matrix, resulting in stress concentration, which leads to fatigue cracks in the repeated impact process, and then extends to the surface of the experimental steel, resulting in increased fatigue wear and spalling of the matrix, obvious spalling pits in the worn sub-surface, and significantly increase in weight loss. When the impact energy is 5 J, the plastic deformation of the worn surface increases, the work hardening is obvious, fatigue wear dominates, the hardness of the worn surface is higher, the furrows and abrasive grains are less embedded, the worn sub-surface layer is more even, the weight loss decreases, and the wear rate decreases.
2022 Vol. 57 (7): 154-161 [
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Environmental Protection and Energy
162
LONG Hong-ming, DING Long, TAO Jia-jie, QIAN Li-xin
Analysis on resource utilization of spent V
2
O
5
-WO
3
/TiO
2
catalyst produced in sintering flue gas
In 2019, the "Proposal on promoting the implementation of ultra-low emissions in the steel industry" was presented by Chinese government, aiming to convert more than 80% of China's iron and steel capacity enterprises into ultra-low emission transformation by the end of 2025. Currently, NO
x
emission reduction from sinter flue gas has become the focus. Selective catalytic reduction with ammonia (NH
3
-SCR) based on vanadium-tungsten-titanium catalyst has become one of the mainstream technologies for sinter flue gas denitrification and has been widely used in iron and steel enterprises. However, as the catalysts reach the end of their life, spent catalysts are increasing year by year. It is estimated that the spent catalysts produced by sinter flue gas denitrification will reach 100 000 m
3
per year in 2027 in China. Vanadium-tungsten-titanium spent catalysts contain V
2
O
5
, which have strong biological toxicity and have been classified as "HW50" hazardous waste in the new National Hazardous Waste List. With the increasingly stringent environmental requirements, the effective disposal of spent catalysts has become a key common problem that needs to be solved in iron and steel industry. The current status of spent catalyst disposal was summarized in terms of disposal concepts and technical methods. The main treatment methods include valuable element extraction, spent catalyst recycling and harmless disposal. The corresponding technical approaches of valuable element extraction include leaching, extraction, precipitation, hydrothermal synthesis and carbon thermal reduction. Spent catalyst recycling includes the mixing of spent catalysts to make new catalysts. Harmless disposal includes solidification/stabilization before landfill disposal. Based on the new development concept of "solid waste does not leave the factory" in iron and steel enterprises, the research ideas related to the resource utilization of spent catalysts as a titanium resource in the steel production process are analyzed. Finally, the prospect of efficient and clean utilization of spent catalysts in iron and steel enterprises is presented.
2022 Vol. 57 (7): 162-178 [
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