Journal of Iron and Steel Research International最新文献

The effect of vanadium (V) element on the microstructure and mechanical properties of anchor steel was explored by microstructural characterization and mechanical property tests of anchor steels with different V contents. The results indicated that the trace addition of V element can generate dispersed VC nanoparticles in the anchor steel and then refine microstructure by inhibiting austenite grain growth. The increase in V content leads to the formation of a larger amount of smaller VC nanoparticles and more refined microstructure. Moreover, the increasing V content in anchor steel causes the volume fraction of ferrite to increase and that of pearlite to decrease continuously, and even leads to the formation of bainite. Accompanied by the microstructure change, the V-treated anchor steels exhibit higher strength compared with the anchor steel without V addition. However, the increased hardness difference between ferrite and pearlite results in poor coordination of deformation between them, leading to a decrease in their plasticity. The impact toughness of anchor steel first increases but then significantly decreases with the increase in V content. The improvement in impact toughness of trace V-treated anchor steel benefits from the enhancement in the band structure after hot rolling, which consumes more energy during the vertical crack propagation process. However, when the V content further increases, the hard and brittle bainite in the anchor steel can facilitate crack initiation and propagation, ultimately resulting in a reduced toughness.

Pursuing green, low-carbon ironmaking technology primarily aims to reduce fuel ratios, especially coke ratios. Simultaneously, the reduction in coke ratios causes the coke layer in the blast furnace (BF) to become thinner, deteriorating the gas and liquid permeability of the burden column. This exacerbates coke degradation, significantly impacting the smelting process and increasing the demand for high-quality coke. To investigate the existence state of coke in the hearth, a 2500 m³ BF in China was taken as the research object, and three sets of samples at different heights of the hearth were obtained during planned outage. The results indicate that coke undergoes a significant degradation upon reaching the hearth. The proportion of coke particles smaller than 50 mm ranges from 81.22% to 89.50%. The proportion of coke particles larger than 20 mm decreases as the distance from the centerline of the tuyere increases, while the proportion of particles smaller than 10 mm increases with this distance. Additionally, the closer the bottom of the furnace is, the smaller the coke particle size becomes. The composition of slag filling the coke pores is similar to that of the final slag in the blast furnace, and the graphitization of coke is comparable to that of the final slag. The graphitization of coke starts from the surface of coke and leads to the formation of coke fines, and the graphitization degree of − 74 μm coke fines is the highest. The temperature has an effect on the reaction rate of coke solution loss, and the higher the temperature is, the faster the reaction rate is.

304 stainless steel (SS)/Q235 carbon steel (CS) bimetallic composite shafts were prepared by the cross wedge rolling (CWR). The bonding interface welding mechanism was investigated through CWR rolling experiments and finite element simulation, as well as element diffusion, microstructure analysis, and mechanical property tests. According to simulation studies, the bonding interface is primarily subjected to three-directional compressive stresses at the tool–workpiece contact zone. As compression ratio increases from 0.25 to 0.35, the interface of the stress penetration area increases, while the diameter and wall thickness of CS/SS bimetallic shaft decrease, and hence, thickness-to-diameter ratio remains unchanged, which is conducive to the coordinated deformation of inner and outer metals and the interface of welded joints. The microstructure analysis of the interface shows that there are no obvious defects and cracks in the attachment, and that the microstructure on CS side is dominated by ferrite and martensite phases. Caused by the decarburization effect, Q235 steel microstructure features coarse ferrite, accompanied by a carburized layer with a thickness of about 20 μm on SS side near the interface where grains are refined. As radial compression ratio increases, the diffusion distance of Cr, Ni, and other elements increases, the average thickness of the decarburized layer decreases, the interfacial bonding strength increases from 450 to 490 MPa, and metallurgical bonding at the interface is thus improved. The study demonstrates that it is feasible to use 304 SS and Q235 CS for cross wedge rolling composite shafts.

The hardenability of steel is crucial for its durability and performance in engineering applications, significantly influencing mechanical properties such as hardness, strength, and wear resistance. As the engineering field continuously demands higher-performance steel materials, a deep understanding of the key influencing factors on hardenability is crucial for developing quality steel that meets stringent application requirements. The effects of some specific elements, including carbon (C), vanadium (V), molybdenum (Mo), and boron (B), as well as heat treatment process parameters such as austenitizing temperature, austenitizing holding time, and cooling rate, were examined. It aims to elucidate the interactions among these factors and their influence on steel hardenability. For each influencing factor, the heat treatment procedure, characteristic microstructure resulting from it, and corresponding Jominy end quench curves were discussed. Furthermore, based on the continuous development of big data technology in the field of materials, the use of machine learning to predict the hardenability of steel and guide the design of steel material was also introduced.

Metallurgical dust (MD) was used as raw material to prepare rare earth Ce-doped Fe-based catalysts. The results show that the Ce_0.1/AMD-300 °C catalyst prepared from acid-modified diatomite (AMD) with m_Ce/m_MD = 0.1 (m_Ce and m_MD are the mass of Ce and MD, respectively) after being roasted at 300 °C can reach 99% NO_x removal rate in the wide temperature range of 230–430 °C and exhibits excellent SO₂ and H₂O resistance. The MD effectively removes alkali metal elements by the modification process, increases the specific surface area and optimizes the pore structure of MD. The doping of Ce element makes Fe-based catalysts have more surface adsorbed oxygen O_α and a higher Ce³⁺/Ce⁴⁺ ratio. Through ammonia temperature-programmed desorption and hydrogen temperature-programmed reduction, it was found that the strong interaction between cerium and iron promotes the formation of more oxygen cavities in the catalyst, thereby generating more active and easily reducible oxygen species and promoting the transformation of Brønsted acid site to Lewis acid site. The research results provide a theoretical basis for the preparation of efficient and inexpensive Fe-based catalysts from MD.

The contact-reactive brazing of Al_0.3CoCrFeNi high-entropy alloys with a Nb interlayer was researched. The effects of Nb thickness and brazing temperature on the interfacial microstructure and mechanical properties of Al_0.3CoCrFeNi joints were investigated. The results show that with Nb thickness increasing from 10 to 100 μm, the average width of Al_0.3CoCrFeNi joints is increased from 127 to 492 μm and the erosion volume of Al_0.3CoCrFeNi base metals (BMs) by face-centered cubic-Nb eutectic liquid is enlarged accordingly. With increasing brazing temperature from 1280 to 1360 °C, the intergranular penetration of eutectic liquid into Al_0.3CoCrFeNi BMs becomes more severe and lamellar Laves phase is broken-up and spherized. The shear strength of joint is increased gradually from 374 to 486 MPa and then decreased to 475 MPa. The maximum shear strength value of 486 MPa is obtained when brazing at 1340 °C for 10 min, reaching about 78% of the shear strength of Al_0.3CoCrFeNi BMs. Besides, the brazing mechanism was analyzed in details.

To address the challenge of visualizing internal defects within castings, ultrasonic nondestructive testing technology has been introduced for the detection and characterization of internal defects in castings. Ultrasonic testing is widely utilized for detecting and characterizing internal defects in materials, thanks to its strong penetration ability, wide testing area, and fast scanning speed. However, traditional ultrasonic testing primarily relies on one-dimensional waveforms or two-dimensional images to analyze internal defects in billets, which hinders intuitive characterization of defect quantity, size, spatial distribution, and other relevant information. Consequently, a three-dimensional (3D) layered characterization method of billets internal quality based on scanning acoustic microscope (SAM) is proposed. The method starts with a layered focus scanning of the billet using SAM and pre-processing the obtained sequence of ultrasonic images. Next, the ray casting is employed to reconstruct 3D shape of defects in billets, allowing for characterization of their quality by obtaining characteristic information on defect spatial distributions, quantity, and sizes. To validate the effectiveness of the proposed method, specimens of 42CrMo billets are prepared using five different processes, and the method is employed to evaluate their internal quality. Finally, a comparison between the ultrasonic image and the metallographic image reveals a difference in dimensional accuracy of only 2.94%. The results indicate that the new method enables visualization of internal defect information in billets, serving as a valuable complement to the traditional method of characterizing their internal quality.

304H austenitic stainless steel wire was investigated, emphasizing microstructural deformation, martensite phase transformation, and residual magnetic properties during drawing. Utilizing several microstructural observation techniques, the volume fraction of martensite, modes of grain deformation in distinct regions, and the phase relationship between austenite and martensite were comprehensively characterized. In addition, a finite element simulation with representative volume elements specific to different zones also offers insights into strain responses during the drawing process. Results from the first-pass drawing reveal that there exists a higher volume fraction of martensite in the central region of 304H austenitic stainless steel wire compared to edge areas. This discrepancy is attributed to a concentrated presence of shear slip system {111}<110>γ crystallographic orientation, primarily accumulating in the central region obeying the Kurdjumov–Sachs path. Subsequent to the second drawing pass, the cumulative shear deformation within distinct regions of the steel wire became more pronounced. This resulted in a progressive augmentation of the volume fraction of martensite in both the central and peripheral regions of the steel wire. Concurrently, this led to a discernible elevation in the overall residual magnetism of the steel wire.

To achieve the new strategy of low cost and outstanding property, friction stir welding (FSW) was used to join AA2219-T6 alloy and AA2195-T8 alloy. The relationship between macro/microstructure and nanomechanical properties was established by using a nanoindentation instrument. During FSW, the grains in stir zone were refined by recrystallization, and the main mechanism of recrystallization was continuous dynamic recrystallization and geometric dynamic recrystallization. The overall micro-hardness value of AA2195 alloy was higher than that of AA2219 alloy due to the strength of the material, and the decrease in hardness value is attributed to the dissolution and coarsening of precipitation. Each zone of the dissimilar joint showed obvious indentation size effect, and the highest nano-hardness values of 2219-base metal (BM) and 2195-BM zones were 1.42 and 1.71 GPa, respectively. The nano-hardness is closely related to the precipitation behavior and follows the same law as the distribution of micro-hardness. The creep mechanism was mainly dislocation slip. The combined action of grain boundary, dislocation, and coarse precipitation can affect creep resistance, in which coarse precipitation plays a dominant role.

The permeability of the sintering process can be significantly improved by the pellet sintering, but the excessive permeability will impact the heat accumulation of the sinter bed. Thus, it is very essential to clarify the influence of the pellet particle size on the heat transfer process of sintering. Therefore, pilot-scale sinter pot tests of pellet sintering with manganese ore fines of different particle sizes were conducted, and traditional sintering was compared to reveal the heat transfer process of sintering and its impact on the microstructure of sintered ore. The results indicate that under suitable pellet sizes (8–12 mm), the heat transfer efficiency and the heat accumulation effect between the layers of sinter bed are strengthened by the pellet sintering, as well as the highest temperature in the combustion zone and the duration of high-temperature zone. This also leads to the further growth of ferrotephroite or hausmannite in liquid phase and its more reasonable crystal distribution. Ultimately, compared with the traditional sintering process, the total solid fuel consumption can be reduced by 20%–30%, and the productivity can be increased by 11.71%–16.21%.