Low-carbon Low-alloy Steel Research Articles

Producing Nanobainite on Carburized Surface of a Low-Carbon Low-Alloy Steel

Producing Nanobainite on Carburized Surface of a Low-Carbon Low-Alloy Steel

Effect of Quenching and Tempering on Mechanical Properties and Impact Fracture Behavior of Low-Carbon Low-Alloy Steel

Conventional quenching and tempering were employed to achieve the optimal strength and toughness of low-carbon low-alloy steel. The fracture behavior (crack initiation and propagation) of the steel in the impact process was also analyzed. It was found that the microstructures of the steel after different tempering treatments were mainly composed of martensite, and its mechanical properties were dependent on the tempering temperature. With the increase in tempering temperature, martensitic laths merged and coarsened. Moreover, recovery occurred, causing a decrease in dislocation density. Subsequently, the strength of the steel gradually decreased, and the impact energy increased. When the tempering temperature was 600 °C, the optimal yield strength (557 MPa) and the impact energy (331 J) were achieved. In addition, high angle grain boundaries (HAGBs) affected the impact energy and crack propagation. Cracks were easily deflected when they encountered high angle grain boundaries, and linearly expanded when they encountered low angle grain boundaries (LAGBs).

Simulation of the Crystallization Process in Low-Carbon Low-Alloy Steels

Simulation of the Crystallization Process in Low-Carbon Low-Alloy Steels

Excellent tensile local deformability and toughness of a tempered low carbon-low alloy steel with multilevel boundaries

The tempered low carbon-low alloy steel achieves excellent strength, plasticity, local deformability and toughness. The impressive local deformability and impact toughness are mainly due to the impediment to crack propagations of multilevel boundaries and dispersed fine carbides, demonstrating the intrinsic relationships between the toughness and local formability in tensile testing.

APPLICATION OF EXPERIMENTAL PLANNING METHODS IN EVALUATION OF СТ3ГПС STEEL QUALITY ASSESSMENT

Introduction. Low-carbon low-alloy steels are widely used in construction. Therefore, despite the existence of a significant number of methods and ways to assess their quality criteria, the task of operational forecasting of these criteria is urgent. Difficulties in predicting the quality criteria of metal products from steels lie in the complexity of the technology of their production. If the parameters of the technology deviate from the normative documents, the properties of the material can differ significantly. In this regard, it is proposed to apply the method of experimental planning to estimate the tensile strength of low-carbon steel. Materials and methods. Samples of steel of ordinary quality Ст3Гпс made of a circle with a diameter of 24 mm were studied. The chemical composition of steel and its strength indicators varied within the normative documents in accordance with ГОСТ 380 and ДСТУ 2651. In the state of factory supply, the steel structure was ferritic-pearlitic. The content of the pearlite component, depending on the amount of carbon in the steel ranged from 11,2 to 17,6 %, the remaining fraction fell to ferrite. The results of the experiment. At the first stage of research the analysis of influence of each chemical element of steel on limit of its durability was carried out. To this end, with the help of the program "Expert", implemented on a computer, obtained one-factor models of strength forecast. In the second stage of research, the number of rows was reduced from 32 to 16 by implementing the matrix of experimental planning using the technique of small replicas. This approach significantly reduces the cost of experiments. The obtained multifactor (X1…X5) model for predicting the strength limit of steel St3Gps is adequate according to Fisher's and Cochren's criteria. According to Fisher's criterion, the coefficient of convergence of the results was 1,029 with a critical value of 2,400. The model is also adequate according to the Cochren test of 0,335 with a critical value of 0,547. At the third stage of research, based on the results of the analysis of the coefficients of the multiparameter model, histograms of complex assessment of the influence of chemical composition elements on the strength of steel are constructed. Conclusions. An adequate model for predicting its strength and histograms of the effect of its chemical composition on Ст3Гпс Steel was obtained. It makes sense to use the obtained results for the operational forecast of the strength of low-carbon steels in the state of factory delivery.

Microalloying of Low-Carbon Low-Alloy Steels with Titanium

Microalloying of Low-Carbon Low-Alloy Steels with Titanium

Effect of High Temperatures on the Mechanical Properties of the Weld Metal in the Welded Joint of Low-Carbon Low-Alloy Steel

Effect of High Temperatures on the Mechanical Properties of the Weld Metal in the Welded Joint of Low-Carbon Low-Alloy Steel

INVESTIGATION OF THE INFLUENCE OF TEMPERATURE INCREASE ON THE STRUCTURAL STATE OF LOW-CARBON LOW-ALLOY STEEL

Problem statement. The development and implementation of low-carbon low-alloy steels of high strength in the structural elements of blast furnaces, which will operate in conditions of heating to high temperatures is an urgent problem and can give a significant effect during the operation of buildings and structures.. Purpose of the article. establishing changes in the structural state of low-carbon low-alloy steels depending on the temperature rise. Conclusion. Conventionally, the temperatures at which the studied steels can be operated can be divided into two levels: the temperature below which no significant structural changes are detected; temperature at which significant structural changes are observed, which lead to a decrease in the reliability of structures. The presence of two levels associated with both the development of diffusion processes and the ability of the structural state to resist the effects of temperature stresses (structural stability). The structural stability of steel with increasing temperature is due to the processes that bring the system closer to the position of thermodynamic equilibrium compared to low temperature (structural state at room temperature), which is usually optimal in terms of performance. Such changes include the processes of recrystallization, coagulation of secretions and other phase transformations that lead to changes in the macro- and microstructure that impair the performance properties of the material. At relatively high temperatures, these processes occur at a significant rate, as a result of which they are crucial in limiting the possibility of using this material.

Methodological features of microstructural heterogeneity estimation by the thickness of steel plates

The relationship of anisotropy coefficients estimated both by textural analysis and direct measurements has been studied using the example of low carbon low-alloy plate steel for Arctic application. The parallel between the anisotropy coefficients values and visual assessment of the structural inhomogeneity has been established, and also use cases of anisotropy coefficients to search for the “structure-property” relationships have been discussed. All the investigated coefficients with different accuracy describe the basic trends of heterogeneity changes by the thickness of the plate, but only the coefficient found by textural analysis makes it possible to evaluate the heterogeneity at any thickness point of the plate adequately, and this is always uniquely coincided with the visual assessment. The volume fraction of the coarse structural constituents with the highest anisotropy of ferritic-bainitic steel, estimated by direct measurements, can also be useful when searching for the “structure-properties” relationships.

Outstanding impact toughness of low-alloyed steel with fine lamellar microstructure

A low-carbon low-alloyed steel subjected to tempforming exhibited high strength and outstanding impact toughness (KCV). The latter surprisingly increases from 412 J cm−2 at room temperature to 426 J cm−2 at 183 K. Such an unusual behaviour is attributed to delamination toughness, which is provided by the ultrafine lamellar microstructure. Namely, the rapid delamination crosswise to the impact direction blunts the crack and significantly increases the impact toughness.

Dependence of Surface Profile on Diamond Impregnation Characteristics

The paper presents the results of studies of the profile of the impregnated diamond surface depending on the grain size and initial roughness of the matrix. The experiments were carried out by impregnating powders of different grit size into a matrix made of low-carbon low-alloy steel with HB180 hardness using a ball indenter. The roughness parameters were measured using a contact profilometer. The height and step parameters of roughness and the curve of the profile bearing length were evaluated. In studying the effect of grain size on the surface profile, it was found that the optimal grain size should be 0.5...0.8 of the initial surface mean spacing profile irregularities. The shape of the Abbott-Firestone curve in this case corresponds to a flat profile. Experiments carried out with varying the initial roughness of the samples confirmed the dependence of the optimum grain size on the mean spacing of the profile irregularities. The developed research procedure can be used to design technological processes of hardening parts, tools and accessories by diamond impregnation.

The influence of grain boundaries on the development of deformation in low-carbon low-alloy steels

Problem statement. Most modern materials have a polycrystalline structure. Their most important property − mechanical strength − is determined by the defective structure of the crystals. Under the defective structure should be understood not only the concentration and distribution of point defects, dislocations, packaging defects, but also the grain boundaries. The development of such processes as diffusion, recrystallization, plasticity, creep, fragility, cracking and corrosion resistance depends on the grain boundaries. The degree of this influence is directly related to the peculiarities of the atomic structure of boundaries and their interaction with other defects. Therefore, the study of the influence of interfacial and intraphase boundaries on the development of plastic deformation in modern materials is an urgent task. Purpose of the article. Investigation of the influence of the type of polycrystalline boundaries on the kinetics of propagation of plastic deformation in low-carbon low-alloy steel 06Х1. Conclusion. Investigation of the influence of the type of polycrystalline boundaries on the kinetics of propagation of plastic deformation in low-carbon low-alloy steel 06Х1. Conclusion. For low-carbon low-alloy steel 06Х1 the influence of the type of polycrystalline boundaries on the kinetics of plastic deformation propagation is investigated. The relationship between the propagation of plastic deformation and the type of interfacial and intraphase boundaries is established. The proposed physical model takes into account the ability of structural components to block plastic deformation. Keywords: propagation of plastic deformation; boundaries of a special type; boundaries of a general type

Features of the ferrite-bainite structure low-alloy low-carbon steel after heat hardening and subsequent tempering

Problem statement. In recent decades, there has been a tendency to increase the mechanical properties of low-carbon, low-alloyed steel plate iron by using controlled rolling or hardening heat treatment of finished steel parts. At the same time, for welded parts, the most suitable is a metal having a ferrite-bainite (or bainite) structure. The work investigated the features of the ferrite-bainite structure of low-carbon and low-alloyed steel 15ХСНД for the production of connecting pipeline parts. Purpose of the article. To establish the laws of formation of a ferritic-bainitic structure in low-carbon low-alloy steels depending on the parameters of heat treatment. Determine the effect of heat treatment parameters on the properties of the connecting parts of pipelines made of these steels. Conclusion. The regularities of the influence of heat treatment parameters on the structure, mechanical properties and topography of fractures of impact samples of 15ХСНД steel with a ferrite-bainitic structure are established. Keywords: stamped-welded connecting parts of man pipelines; heat treatment; microstructure; bainite;mechanical properties; fractography

Effect of prior annealing on the microstructure and mechanical properties of thermo-mechanically treated TRIP steel

Low-carbon low-alloyed high strength steel 0.2C-1.5Al-0.5Si-2Mn-0.06Nb (in weight %) was forged into bars and annealed at 1050 °C with either 2-hour hold and furnace cooling to room temperature or with 20-min hold and controlled cooling by 1 °C/s. These various holds and coolings created two different initial microstructures, banded ferritic-pearlitic one for the long hold and bainitic-ferritic for the shorter hold and quicker cooling. Samples with those microstructures then underwent the same thermo-mechanical treatment (TMT) typical for TRIP (transformation induced plasticity) steels. Very different microstructures and mechanical properties were obtained for both initial states even after the application of the same TMT schedules. Light and scanning electron microscopy was used to characterize obtained microstructures and tensile tests were applied for the determination of mechanical properties.

Mathematical model of forecast of strength of low carbon steel

Introduction. The use of different mathematical approaches to assessing and forecasting the quality characteristics of materials for different purposes is always relevant. The urgency of solving problems and problems of modern materials science with the use of methods of mathematical modeling allows to optimize technological processes of production, to determine in a short period of time the set parameters with minimal time and material costs. In the work using the method of regression analysis, the strength criteria of low-carbon low-alloy steel depending on the characteristics of the structure were evaluated. Materials and methods. Samples of Ст3пс steel grade made of a circle with a diameter of 24 mm were selected as the material for the study. The structure and mechanical properties were investigated at three reference points: at a distance of 0 mm from the center of the sample, 6 mm from the center of the sample and 12 mm from the center of the sample. The steel was investigated in the state of factory delivery, and after two modes of heat treatment to obtain ferritic-perlite and bainite structure. The following properties were determined: microhardness, tensile strength and yield strength, hardness and toughness at room temperature. The results of the experiment. Models for estimating mechanical properties were obtained using regression analysis. Models describing the relationship between the microhardness of pearlite and its area (R2 = 0.8366) in the state of factory delivery have a relatively high correlation coefficient; the score and the ultimate strength (R2 = 1.0) and yield strength (R2 = 0.8669) of steel after cooling in an oil medium; hardness and area of pearlite after hardening steel in the pearlite region (R2 = 0.7215). Conclusions. The practical significance of the work performed is the ability to perform a rapid analysis of the properties of rolled metal from steel Ст3пс based on determining the area of the structural elements and their scoring. However, it should be noted that the existing discrepancy between the results of the experiment and the forecast using the obtained models may be due to the influence of other factors. Such factors include the influence of chemical composition, incompleteness of formal axiomatics, which occurs when estimating the geometry of complex structural elements.
 Keywords: low-alloy steel; structure; chemical composition; mechanical properties; regression model; properties forecast

Effect of cooling rate on the microstructure and mechanical properties of a low-carbon low-alloyed steel

Heavy plate steels with bainitic microstructures are widely used in industry due to their good combination of strength and toughness. However, obtaining optimal mechanical properties is often challenging due to the complex bainitic microstructures and multiple phase constitutions caused by different cooling rates through the plate thickness. Here, both conventional and advanced microstructural characterization techniques which bridge the meso- and atomic-scales were applied to investigate how microstructure/mechanical property-relationships of a low-carbon low-alloyed steel are affected by phase transformations during continuous cooling. Mechanical tests show that the yield strength increases monotonically when cooling rates increase up to 90 K/s. The present study shows that this is associated with a decrease in the volume fraction of polygonal ferrite (PF) and a refinement of the substructure of degenerated upper bainite (DUB). The fine DUB substructures feature C-rich retained austenite/martensite-austenite (RA/M-A) constitutes which decorate the elongated micrograin boundaries in ferrite. A further increase in strength is observed when needle-shaped cementite precipitates form during water quenching within elongated micrograins. Pure martensite islands on the elongated micrograin boundaries lead to a decreased ductility. The implications for thick section plate processing are discussed based on the findings of the present work.

On Microstructure and Mechanical Properties of a Low-Carbon Low-Alloy Steel Block Fabricated by Wire Arc Additive Manufacturing

In this study, wire arc additive manufacturing process is employed to fabricate a low-carbon low-alloy steel block, using an ER70S-6 solid wire. Three sets of samples with different orientations, including perpendicular (Vertical), parallel (Horizontal), and 45° (45-degree) relative to the deposition plane, were prepared in order to investigate the anisotropy in mechanical properties and microstructure of the fabricated part. Both Horizontal and 45-degree samples showed a uniform microstructure containing mostly ferritic grains with a small volume fraction of pearlite at their grain boundaries. Differently, a periodic microstructure was detected in the Vertical sample, consisting of a combination of acicular ferrite, bainite, and allotriomorphic ferrite formed in the interlayer regions in addition to polygonal ferrite within the melt pools’ center. Moreover, the uniaxial tensile and Charpy impact results exhibited isotropic tensile, yield, elongation, and impact properties for both Horizontal and 45-degree samples; however, the Vertical sample showed a lower mechanical performance. The improved mechanical properties of the Horizontal and 45-degree samples were correlated to their uniform ferritic microstructure.

Correlation of structure parameters and performance characteristics of alloy steels for shipbuilding

The article presents the results of a study of the relationship between strength and performance (temperatures of ductile-brittle transition Tdb and zero plasticity NDT, critical opening at the crack tip CTOD at a test temperature of —40°C) on the structure parameters of thick plate products made of low-carbon low-alloy steels with different contents of basic alloying and microalloying elements.

Влияние высоких температур на механические свойства металла шва сварного соединения малоуглеродистой низколегированной стали

The mechanical properties of the seam metal of a low-carbon low-alloy steel welded joint of the 22K type (Russian standard) have been investigated when testing for uniaxial tension in the temperature range from room temperature to 1200 °C. A comparative analysis of the changes in the structure, the strength and plastic properties of base metal and weld seam metal in the selected temperature range was carried out.

Effect of thermomechanical treatment on the microstructure and mechanical properties of a low-carbon low-alloy steel

The effect of thermomechanical treatment on the microstructure, tensile strength and impact toughness of low-carbon low-alloy steel is considered. The developed microstructure is characterized by grain elongation along the rolling direction. Both the yield strength and the ultimate tensile strength increase with a decrease in test temperature. The ultimate strength at room temperature is 797 MPa, and at 77 K the ultimate strength increases to 1198 MPa. The steel samples subjected to tempforming exhibit impact toughness of KCV = 410 J/cm2 at room temperature. A decrease in the test temperature to 233 K leads to a slight decrease in the KCV value to 340 J/cm2. It should be noted that the impact specimens are not completely fractured even at a test temperature of 233 K, suggesting higher real values of impact toughness.