Low Alloy Structural Steel Research Articles

Evaluation of fatigue damage of structural steel based on attenuation of laser-induced surface acoustic wave

ABSTRACT In this paper, the fatigue damage degree of low-alloy structural steel is evaluated by using the attenuation characteristics of laser-induced surface acoustic wave (SAW) during propagation. Taking the typical structural steel material Q345 as an example, a cracks model of fatigue damage is established, and the finite element method is used to solve the model. The results showed that the attenuation coefficient of SAW can reflect the depth and density of fatigue cracks. The surface measurement experiments of specimens with stress cycles of 0, 50000, 100000, 150000, and 200,000 showed that with the increase of stress cycles, the attenuation coefficient of SAW increases as a whole, indicating that it is feasible to evaluate the fatigue damage degree based on the attenuation of SAW. A method of applying tensile stress to the material to improve the sensitivity of fatigue damage evaluation is proposed. The tensile stress is used to offset the horizontal amplitude of the SAW, keeping the fatigue cracks in an open state and increasing the attenuation coefficient of SAW. The attenuation coefficient measurement experiment shows that this method is feasible.

Influence of microalloying on precipitation behavior and notch impact toughness of welded high-strength structural steels

Microalloying elements such as Nb and Ti are essential to increase the strength of quenched and tempered high-strength low alloy (HSLA) structural steels with nominal yield strength ≥ 690 MPa and their welded joints. Standards such as EN 10025–6 only specify limits or ranges for chemical composition, which leads to variations in specific compositions between steel manufacturers. These standards do not address the mechanical properties of the material, and even small variations in alloy content can significantly affect these properties. This makes it difficult to predict the weldability and integrity of welded joints, with potential problems such as softening or excessive hardening of the heat-affected zone (HAZ). To understand these metallurgical effects, previous studies have investigated different microalloying routes with varying Ti and Nb contents using test alloys. The high-strength quenched and tempered fine-grained structural steel S690QL is the basic grade regarding chemical composition and heat treatment. To evaluate weldability, three-layer welds were made using high-performance MAG welding. HAZ formation was investigated, and critical microstructural areas were identified, focusing on phase transformations during cooling and metallurgical precipitation behavior. Isothermal thermodynamic calculations for different precipitations were also carried out. Mechanical properties, especially Charpy notch impact toughness, were evaluated to understand the influence of different microalloys on the microstructure of the HAZ and mechanical properties.

Tailoring the strength and low-temperature toughness of HSLA structural steel by adding trace Ce

In this study, the trade-off between strength and low-temperature toughness of high-strength low-alloy (HSLA) structural steel was solved by adding trace Ce, which increased yield strength by 5.4 % and Charpy V-notch (CVN) impact energy at −40 °C by 57.9 %. The strengthening and toughening mechanism was revealed by multi-scale characterization. The results show that the strain hardening ability is improved after adding Ce. The grain size is refined and the geometrically necessary dislocation (GND) density increases to ensure the strength improvement. The CVN impact specimens change from cleavage fracture to quasi-cleavage fracture. The grain size, inclusions and high angle grain boundaries (HAGBs) are refined and optimized, which enhances the resistance to impact crack propagation and improves the low-temperature impact toughness.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ СКОРОСТНОЙ ЭЛЕКТРОТЕРМИЧЕСКОЙ ОБРАБОТКИ НА СТРУКТУРУ СВАРНОГО СОЕДИНЕНИЯ ИЗ НИЗКОЛЕГИРОВАННОЙ КОНСТРУКЦИОННОЙ СТАЛИ

The studies’ results of the high-speed electrothermal treatment effect on the structure and hardness of various zones of welded joints made of low-alloy structural steel 10ХСНД (10KhSND) are presented. It is shown that carrying out high-speed electrothermal treatment at 950–980 °C leads to the formation of a homogeneous, fine-grained ferrite-perlite microstructure with practically unchanged hardness values in all zones of the welded joint except for the weld root, where slightly higher values of microhardness are registered.

Experimental Assessment of Mechanical Properties of Corroded Low–Alloy Structural Steel

This study investigates the mechanical properties of corroded Q355B structural steel subjected to a simulated marine atmosphere and an industrial atmosphere. The micro-morphology of corroded steel in two different environments was analyzed by SEM (scanning electron microscopy). Tension tests were performed to determine the degradation laws of the mechanical properties of corroded steel, including its yield strength, ultimate strength, elastic modulus, ultimate strain and elongation after fracture. The test results indicate that the elongation after fracture of the steel is the most severely deteriorated property after corrosion. The recommended empirical formula for limiting the maximum corrosion rate is established. It is found that when the initial elongation is 30%, the maximum allowable corrosion rate is 19.2%. Based on the achieved results, a simplified time-dependent stress–strain model of Q355B structural steel is established considering the coupling effects of corrosive environments and applied stress, which is also evaluated using relevant research. In addition, axial compression tests were conducted on corroded square stud columns to verify the effectiveness of the established model. It is indicated that the model can be used for fitness-for-purpose analyses in structural integrity assessments.

ADJUSTABLE NITROOXIDATION TECHNOLOGY FOR LOW ALLOY STEEL

The article discusses the production of a surface diffusion nitride-oxide layer on low-alloy structural steel with specified structures and properties. To develop a controlled technology for nitro-oxidation of low-alloy carbon steel, the dependences of the composition and structure of the nitrided and oxide layer on the chemical composition of the steel and the technological parameters of the process were studied. Technical iron was used as a model alloy and samples of industrial steel grades 40X, P6M5 and steel 45 were processed. Saturation temperatures were studied in the ranges above and below the eutectoid temperature for the “Fe-N” system and, accordingly, for the “Fe-O” system and it was found that the best structures are at saturation temperatures below the eutectoid

ЗАСТОСУВАННЯ МАТЕМАТИЧНОГО МОДЕЛЮВАННЯ ПРИ АНАЛІЗІ ДИЛАТОГРАМ МАРТЕНСИТНОГО ПЕРЕТВОРЕННЯ У СТАЛЯХ

The paper provides practical experience of applying mathematical modeling in the analysis of the kinetics of athermal martensitic transformation in low-alloy structural steel 30HGSA (Fe-0.30С-0.86Si-1.02Mn-0.84Сr, % wt.) using the dilatogram of the real quenching process. The change in the amount of martensite formed in the studied steel as a function of temperature during continuous quenching cooling is shown. The used technique for determining the phase ratio provides in situ correlation with the microstructural mechanisms implemented in the studied material during heat treatment. The obtained results will be used to develop parameters of heat treatment based on the principle of quenching and partitioning (Q&P) to improve the complex of properties of 30HGSA steel due to the creation of a multiphase structure.

ВИЗНАЧЕННЯ ОПТИМАЛЬНОЇ ТЕМПЕРАТУРИ ЗАГАРТУВАННЯ ЕКОНОМНОЛЕГОВАНОЇ КОНСТРУКЦІЙНОЇ СТАЛІ ПРИ РЕАЛІЗАЦІЇ ПРОЦЕСУ Q та P

The work presents practical experience of applying mathematical modeling of the multiphase structural state of low-alloy structural steel 0.30С–0.86Si–1.02Mn–0.84Сr in order to obtain improved indicators of strength and plasticity of the metal. Calculated theoretical optimum quenching completion temperature when implementing the Q&P (Quenching and Partitioning) process for the specified steel. It is shown that the optimal temperature of the completion of the quenching process should be 245 °C, when "fresh" (secondary) martensite is not formed during the final cooling, and the fraction of residual austenite reaches a maximum (approximately 27 % vol.). Austenite stabilization is known to be important in Q&P treated steels to achieve the desired combination of strength and plasticity. The obtained results will be used to develop effective modes of strengthening heat treatment of metal products of responsible purpose with the provision of increased indicators of plasticity and impact strength at ambient temperature.

ADJUSTABLE NITROOXIDATION TECHNOLOGY FOR LOW ALLOY STEEL

The article discusses the production of a surface diffusion nitride-oxide layer on low-alloy structural steel with specified structures and properties. To develop a controlled technology for nitro-oxidation of low-alloy carbon steel, the dependences of the composition and structure of the nitrided and oxide layer on the chemical composition of the steel and the technological parameters of the process were studied. Technical iron was used as a model alloy and samples of industrial steel grades 40X, P6M5 and steel 45 were processed. Saturation temperatures were studied in the ranges above and below the eutectoid temperature for the “Fe-N” system and, accordingly, for the “Fe-O” system and it was found that the best structures are at saturation temperatures below the eutectoid

ADJUSTABLE NITROOXIDATION TECHNOLOGY FOR LOW ALLOY STEEL

The article discusses the production of a surface diffusion nitride-oxide layer on low-alloy structural steel with specified structures and properties. To develop a controlled technology for nitro-oxidation of low-alloy carbon steel, the dependences of the composition and structure of the nitrided and oxide layer on the chemical composition of the steel and the technological parameters of the process were studied. Technical iron was used as a model alloy and samples of industrial steel grades 40X, P6M5 and steel 45 were processed. Saturation temperatures were studied in the ranges above and below the eutectoid temperature for the “Fe-N” system and, accordingly, for the “Fe-O” system and it was found that the best structures are at saturation temperatures below the eutectoid.

Understanding the Structure and Electrochemical Behavior of the Rust Layer Formed on a High-Strength Low-Alloy Structural Steel under Cyclic Exposure to Polluted Marine Atmosphere

Understanding the Structure and Electrochemical Behavior of the Rust Layer Formed on a High-Strength Low-Alloy Structural Steel under Cyclic Exposure to Polluted Marine Atmosphere

CAST HOLLOW BILLET STRUCTURE SIMULATION MODELING FOR OIL GRADE PIPES

Simulation modeling of hollow billet casting processes for the production of seamless oil grade pipes was performed. The aim of the work was to study the influence of geometric shape on the quality and properties of a continuously cast pipe billet. Modeling parameters, initial and boundary conditions were selected taking into account the conditions of the current production. The object of the study was a pipe billet with a diameter of 210 mm. When modeling the process of casting and solidification of billets, low-alloy structural chromium-molybdenum steel was used. For the simulation processes, three-dimensional models of billets were created, as well as models of shapes. Several factors were taken into account when modeling continuous casting and crystallization of a hollow billet: casting speed, chemical composition of the alloy being poured; casting temperature; geometric dimensions of the billet section. Modeling of hollow billet casting in the «LVM Flow» software package predicted the non-shrinking structure formation a decrease in microporosity (more than 0.85 according to the Niyama criterion) of the billet. As a result of simulation modeling, the improvement of the structure is theoretically confirmed when using a hollow steel billet as a starting point for the production of seamless hot-rolled pipes. There were no signs of shrinkage and microporosity on the hollow billet exceeding the permissible value according to the Niyama criterion. Keywords: hollow billet, steel, modeling, pipe, 25CrMoV.

Development of Interparticle Bonding during Sintering of Metal Powders with the Addition of Carbon

Introduction. Publications on sintered metal powder parts consider interparticle bonding in hot-deformed materials and features of low-alloy structural steels, as well as the use of carbon-containing materials. The authors of the presented article have previously investigated sintering in relation to structural changes in the material, described changes in physical and mechanical properties, reduction of oxides, recrystallization, etc. This paper shows the relationship of mechanical properties of powder steels with the parameters of intracrystalline bonding. The kinetics of its development during sintering is demonstrated for the first time. The study objective is to find out how sintering affects the interparticle bonding and structure of powder alloys with iron and carbon. The task is to study the technological modes of sintering samples from alloyed and pure iron powder to achieve the best mechanical characteristics.Materials and Methods. The powders of the Höganäs company were sintered at a temperature of 900-1150 ºС for 0.5–2.5 hours. The protective gas medium (dissociated ammonia) made it possible to prevent oxidative and other sintering reactions. For static cold pressing, a hydraulic press 2PG-125 with a maximum force of 1250 kN was used.Results. For the first time, the presence of intracrystalline bonding mechanisms with different intensity during sintering has been experimentally established. The dependences of the increment of the relative area of the contact surface on the duration of the isothermal exposure were constructed. With an increase in the sintering temperature to 1150 ºС and a holding time of more than 80 minutes, the contact surface area gradually increased. It was shown that the samples from the powder grades under consideration formed an intracrystalline bonding on the entire contact surface at 1150 ºС. Therefore, this technology can be recommended for practical use. The addition of graphite to the charge slows down the growth of the contact surface. At the same time, the molds from pure powder ABC100.30 and from Distaloy HP-1 powder showed differences. In the first case, with the addition of graphite to the charge, the contact surface developed more intensively than in the second one. The obtained results were recorded in the photo and visualized in the form of graphs.Discussion and Conclusion. According to the results of mechanical tests, it is possible to estimate the proportion of the contact section of the molding with intracrystalline bonding. Its feature is the structural correspondence of the interparticle surface of the splice and the intergrain boundary. The value of this boundary is determined by comparing the relative area of the contact section with the intracrystalline bonding and the relative area of the contact surface. The possibilities of improving the quality of bonding of powder steels by increasing the temperature and time of their exposure during sintering are determined.

The Influence of 1 wt.% Cr on the Corrosion Resistance of Low-Alloy Steel in Marine Environments

In this study, the effects of 1 wt.% Cr addition on the corrosion behavior and mechanisms of low-alloy structural steel in a marine environment were investigated through immersion experiments, corrosion product analysis, and electrochemical experimental systems. The results demonstrate that the addition of 1 wt.% Cr significantly enhances the corrosion resistance of low-alloy steel in marine environments. The influence of Cr addition on the corrosion product layer was analyzed through rust layer morphology, cross-sectional morphology, elemental distribution, and electrochemical systems. Cr addition effectively promotes the densification of the corrosion product layer on the surface of low-alloy steel in marine environments, hindering the penetration of corrosive ions and thus improving corrosion resistance. This study’s findings can promote the optimization of corrosion resistance in low-alloy steel in marine environments and enhance its application prospects in marine environments.

Corrosion Resistance of Steel S355MC in Crude Glycerol

Corrosion is the degradation of materials in oxidizing environments. In aqueous solutions, it is initiated by the surface reaction of the metallic material with the surrounding electrolyte. The corrosion rate of metals can be significantly reduced by the presence of organic compounds. Crude glycerol is an organic by-product of biodiesel, soap, and fatty acid production. It is produced in substantial amounts through transesterification. Crude glycerol contains several impurities and has low economic value. Its disposal in the environment is unwanted and potential applications need to be explored. In the present short communication, steel corrosion in crude glycerol has been investigated for the first time. The corrosion behavior of low-alloy structural steel S355MC in non-purified crude glycerol was studied by electrochemical methods. The results were compared with the use of tap water. The open-circuit potential (OCP) of S355MC in crude glycerol was more negative compared with that of tap water. The OCP was stable over time, indicating the rapid passivation of the steel substrate. The corrosion resistance was further studied by electrode polarization. On the polarization curve of S355MC in crude glycerol, a wide passivation region was found. Furthermore, the corrosion rate was 2.2 times smaller compared with that of tap water. The surface exposed to tap water was significantly degraded by red rust. The surface of S355MC after exposure to crude glycerol, on the other hand, was less affected by corrosion and covered with a protective layer. The results demonstrate a significant corrosion-inhibiting activity of crude glycerol that could be utilized in various technologies.

Changes in the microstructure of selected structural alloy steel grades identified after their simulated exposure to fire temperature

Results of research on changes in microstructure of selected steel grades used in construction, observed in cooled state after prior exposure to fire temperature are presented in this paper. The following steel grades have been analyzed in detail: S355J2+N, X20Cr13, X6CrNiTi18–10 and X2CrNiMoN22–5–3. These grades are considered to be representative for classic low alloy structural steel of ferritic-pearlitic structure, and several special grades of stainless steel varying in microstructure: martensitic, austenitic and mixed, austenitic-ferritic of duplex type. Analysis of post-fire susceptibility to initiation and unconstrained propagation of brittle failure was the basic purpose of this research. This property seems to be the key one in the context of potential post-fire continued service of these steels when subjected to load. The presented results seem to correlate well with the results of toughness test conducted on the same steels (presented in [6]). The scenarios of sample heating and long term keeping up in the high temperature, and in particular the temperature levels assumed by the authors have been intentionally selected to enable or exclude the chance of expected structural changes occurring in the material subjected to experiment. The varied effective cooling modes have been designed to simulate the slow cooling in the open air or alternatively, rapid cooling during firefighting action conducted by fire brigade.

Investigations on microstructural and mechanical properties of BSK 46 steel weldments

BSK 46 is a low alloy structural steel with excellent mechanical and corrosion properties and is widely used in many applications, including tipper bodies of heavy-duty trucks. Optimizing the welding parameters to reduce defects and improve productivity is critical for the users. The present work addresses optimizing the welding process parameters to improve productivity with adequate weld quality during the pulsed gas metal arc welding (P-GMAW) process. Three BSK 46 weldments (weld-1, weld-2 and weld-3) were fabricated by varying the root gap, root face, filler pass and heat input. The metallographic and mechanical characterization of P-GMAW weldments were done through microstructures, Vickers micro-hardness, transverse tensile strength, Charpy toughness and three-point bend test. Subsequently, a correlation has been developed between the microstructural features and mechanical properties of the weld joints. The hardness was found to be incremental in nature from the base metal to the fusion zone. Maximum hardness of 215.81 ± 10 HV was observed in the weld-3 fusion zone. Tensile test results reveal that weld-3 weldments exhibit a higher tensile strength of 547.48 ± 2 MPa than weld-1 (537.46 ± 7 MPa) and weld-2 (533.67 ± 9 MPa) weldments. Maximum impact toughness of 136.33 ± 14 J was observed in the weld-3 weldments. Post-bend testing showed no cracks on the weld surfaces, indicating defect-free weld joints with good ductility. It is observed that weld-3 showed relatively better mechanical properties than weld-1 and weld-2 in lesser welding time and lower welding cost

ІМПУЛЬСНІ СТАБІЛІЗАТОРИ ГОРІННЯ ДУГИ ПРИ ЗВАРЮВАННІ ЗМІННИМ СТРУМОМ ПРОМИСЛОВОЇ ЧАСТОТИ

The work deals with the development of AC welding arc stabilization devices that provide a qualitatively different level of functionality to industrial frequency welding transformers. It is shown that despite the rapid spread and use of inverter sources of direct current for arc welding of metals, welding with alternating current, using simple and unpretentious welding transformers, which work at the frequency of the current of the industrial power supply network, continues to be relevant. With regard to manual arc welding with coated electrodes and a non-fusible electrode on alternating current of industrial frequency, the problem of increasing the stability of arc burning is solved thanks to the use of impulse stabilizers of arc burning. Thepurpose of the study is to increase the energy efficiency of industrial frequency alternating current welding power sources due to the development of arc stabilization devices at the modern level.The choice of the polarity of the pulses significantly affects the parameters of the stabilizing device and the AC welding process. Studies of the influence of the pulse polarity on the parameters of the pulse arc stabilizers themselves have been carried out. The schematic implementation of stabilization devices using stabilizing pulses, the polarity of which is opposite to the polarity of the arc current, is considered.The experience of using the developed stabilizers allows us to conclude that they provide sufficiently high stability of arc burning from an alternating current welding transformer during manual arc welding of low-alloy structural steels covered with electrodes, arc welding of stainless and other special steels, arc welding of cast iron, during non-fusible argon arc welding electrode of stainless steels, aluminum and its alloys with the contact method of initial ignition of the arc

Determination of optimal conditions for hardening by pulsed plasma flows of low-alloy structural steels with different carbon content

Increasing the wear-resistance of materials is an urgent task of modern materials science, which is most economically and efficiently solved by modifying only the surface of products. Consequently, studies of changes in the microhardness of low-alloy structural steels with different carbon content after irradiation of samples with pulsed plasma flows have been carried out. The chosen processing method is considered the most perspective now. As a result, optimal hardening conditions were determined, in which the maximum microhardness of the surface layer was achieved, and the effect of alloying components on the calcination thickness was also established.

Влияние термической обработки на образование соединения MNS в низкоуглеродистой конструкционной стали 09Г2С

Introduction. The properties of steels are determined by many factors, including the manufacturing process and subsequent treatment. Some features of these processes lead to the fact that in steel, apart from alloying elements added to obtain a certain level of physical and mechanical properties, there are also foreign impurities that enter it at various stages. Foreign elements can not only dissolve in the matrix, but also participate in the formation of particles of nonmetallic inclusions acting as defects. Its presence significantly affects the performance characteristics of the material. That is why it is necessary to understand the processes that lead to the appearance of nonmetallic inclusions and affect its shape. Purpose: to consider the effect of heat treatment, leading to the appearance of a ferrite-martensitic structure, on the shape and size of nonmetallic inclusions; to determine its influence on the physical and mechanical properties of the material. In the work, samples of rolled steel 09Mn2Si after heat treatment are studied. Research methods. To study the properties and structure of steel 09Mn2Si, the following methods were used: scanning electron microscopy – to study the structure of the material, chemical composition in the local area and the site under study and to determine the accumulation of impurities; SIAMS 800 software and hardware complex – to compare the structure of the material with the atlas of microstructures, to determine the score of the grain structure, differences in the structural and phase composition occurring during heat treatment; portable X-ray fluorescence analyzer of metals and alloys X-MET 7000 - to determine the chemical composition of the samples under study in percentage terms; Vickers hardness tester with a preload of 20 kg – to measure the hardness of the samples under study. Results and discussions. It is found that in the low-alloy low-carbon structural steel 09Mn2Si in most cases there are nonmetallic inclusions of the type of manganese sulfide formed during its manufacture. When this steel is heated to the temperatures of the intercritical transition, this compound is formed in the area of grain boundaries in the form of spherical inclusions. The presence of these inclusions significantly affects the strength and corrosion properties. Manganese sulfide acts as the point of the corrosion process initiation.