Effect of Deoxidation Practice on the Mechanical Properties of Low Alloy Plain Carbon Steel

Purpose. Determination of the methodology for the comprehensive evaluation of the mechanical properties of high-manganese steels according to one parameter that is sensitive to the influence of external factors, which will contribute to the reduction of laboratory research costs during the selection of the best samples (melts) of steel for the production of quality-critical products of responsible mechanical engineering. Research methods. Tearing tests were carried out on the УРМ-50 machine, the relative elongation was determined according to the standard method. Microhardness was measured using a ПMT3 device at a load of 50 g by a standard method. Determination of the specific paramagnetic susceptibility c0 of austenite (before mechanical tests) was carried out on automated magnetometric scales. Results. Based on the results of experimental studies, a correlation between mechanical properties and specific paramagnetic susceptibility c0 of austenite was established. The parameter c0 is a characteristic of the atomic-magnetic state of austenite and is a supersensitive value to the influence of various external factors. That is why it is proposed to use the specific paramagnetic susceptibility of austenite as an integral characteristic to determine the influence of various factors (chemical composition, smelting conditions, deformation, temperature, etc.) on the properties of steel. Scientific novelty. The idea of a relationship between the mechanical properties of austenitic steels and the previously formed atomic-magnetic state of the austenite matrix was proposed and experimentally confirmed. Practical value. The determined correlation between the mechanical properties of high-manganese steels and the specific paramagnetic susceptibility c0 of austenite and the proposed trend correspondence matrix make it possible to perform express forecasting and quality control of steels without conducting labor-intensive mechanical tests.

Introduction: The control of the mechanical properties of structural steels is one of the main processes that regulate the service life of equipment. In most technical processes (pressure treatment, welding, rolling, thermal exposure), structure changes both in local areas and in the entire volume. Changes in the steel structure entail changes in its properties and as a result in local areas, at various stages of operation, the likelihood of the occurrence and development of critical defects increases. Its presence significantly affects the performance of the equipment, and leads to premature aging of the material and its failure. Precisely because the control of the mechanical properties of steel remains one of the urgent problems, new control methods are being developed. It is known that all properties of steel depend on the structure of the substance, however, studies on the effect of the dispersion of the structure under consideration on the mechanical properties are presented in an insignificant amount. Purpose: to analyze from a mathematical point of view the influence of the factor of different grain size, as a parameter reflecting the dispersity of the system, on the mechanical properties of structural steel. The paper studies a heat-treated planar samples of steels 15KhSND, 09G2S and St3. Methods of research: scanning electron and optical microscopes are used to study the grain structure and grain boundaries; SIAMS 700 software package is used for finding the boundaries and average data of the grain structure; portable X-ray fluorescence analyzer of metals and alloys X-MET 7000 is used to determine the chemical composition of the test samples in percentage; tensile testing machine IR-50 is used for measuring the tensile strength of samples; Vickers hardness tester is used to determine the hardness of samples. Results and discussion: it is found that there is a satisfactory correlation for the mechanical properties of structural steels (hardness and ultimate strength) and the grain size factor, which can be used to predict the hazardous states of structures and the operating time. The analysis of variance and regression of the detected dependencies is carried out. It is noted that the dropout of some values from the general regression dependence can most likely be associated with a decrease in the value of internal stresses as a result of a decrease in the distortions of the crystal lattice of steel occurring during heat treatment. It should be noted that the processes occurring and the degree of its influence on the properties of the structural steels under consideration can be different due to the presence of different amounts of alloying elements in the composition of the studied steels.

The state of the problem of grinding the grain structure and improving the mechanical properties of low-alloy structural steels has been studied. The state of the problem of grain structure refinement and improving the mechanical properties of low-alloy structural steels has been studied. The role of nanodispersed additives is reduced to the creation of additional artificial crystallization centers in the melt. They must be consistent with the critical radiuses of the embryos. According to our calculations, for the grinding of primary austenite grains in castings, the size of the introduced particles should be 40–50 nm. Output and modified castings of 09G2 and 09G2S steels were subjected to severe plastic deformation by equal-channel angular pressing followed by low-temperature annealing at 350 °C. In the initial state, cast steels 09G2 and 09G2S had a ferrite-pearlite structure with an average primary austenite grain size of 30 μm; after modification and deformation, the grain size was 10 μm. After quenching and cooling in water, the structure has changed insignificantly - ferritic-reed, with an average grain size of ~ 8...10 microns. After cooling the quenched samples in a solution of 20 % NaCl in water, the structure of packet martensite was obtained. In the initial state, the studied steels have insufficiently high property values: microhardness Нμ up to 3000 MPa, yield point σ 0,2 up to 800 MPa. When quenching in water, the hardness somewhat increases, the most significant increase is observed when the samples are cooled in a NaCl solution. Due to the significant grinding of martensite crystals, accelerated cooling provides a greater increase in hardness. A nanodispersed powder of titanium carbonitride Ti (CN) with a fraction of 50...100 nm was obtained by the method of plasma-chemical synthesis, the process technology was developed. Intensive plastic deformation of 09G2 and 09G2S steel castings was carried out. The structure and properties of steels before and after treatments have been studied. As a result of the combination of hardening methods, the grain size of the steels was reduced by 3 times and the yield strength increased from 3000 to 4000 MPa. Nanodispersed powder of titanium carbonitride Ti (CN) with a fraction of 50...100 nm was obtained by the method of plasma chemical synthesis, and a process technology was developed. Intensive plastic deformation of castings of 09G2 and 09G2S steels was carried out. The structure and properties of steels before and after treatments were studied. As a result of a combination of hardening methods, grinding of steel grains by 3 times and increasing the yield strength from 3000 to 4000 MPa was achieved

Effects of cooling rates (annealing and normalizing) on the tensile properties and microstructure of plain carbon (0.10% C) and Ni-Mo steel were investigated. Samples of the steels were annealed and normalized by Radio Frequency (RF) Generator from their respective heat treatment temperatures. Specimens undergoing two cooling rates reveal various microstructure and tensile properties. The results show that tensile strengths are better at higher cooling rate (normalized) than slower cooling rate (annealed). Ni-Mo content steel shows the better tensile strength but poor ductility than plain carbon steel in the both heat treatments. Microstructures of all specimens were examined by an optical microscopy.

Carbide-free bainitic (CFB) steels with a matrix of bainitic ferrite and thin layers of retained austenite, to reduce the manufacturing costs, usually do not contain alloying elements. However, a few reports were presented regarding the effect of alloying elements on the properties of these steels. Thus, this study evaluates the effects of vanadium and rare earth (Ce-La) microalloying elements on the structure, phase transformation kinetics, and mechanical properties of carbide-free bainite steel containing silicon fabricated by the casting and austempering procedure. Optical and scanning electron microscopy (OM and SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) were used to study the microstructure and phase structure. The transformation kinetics were examined by a dilatometry test. Hardness, tensile, and impact tests evaluated the mechanical properties. Due to adding alloying elements, the fracture toughness and change in matrix phases relation was studied by the crack tip opening displacement (CTOD) test and SEM fractography. The microstructure of the silicon added sample was completely carbide-free bainite. The test results showed vanadium helped CFB formation, even in continuous cooling. The primary austenite grain (PAG) size grew by vanadium addition. The EBSD phase map illustrates an increment in the percentage of retained austenite by vanadium. In contrast, the addition of 0.03 wt% rare earth reduced the primary austenite grain size and reduced the retained austenite content. The results of the dilatometry test confirmed that vanadium and rare earth addition both reduced the critical cooling rate of the bainite transformation. Vanadium leads to an earlier cessation of bainite transformation, while rare earth elements postpone this transformation. Mechanical tests showed that the tensile strength of carbide-free bainite steels was strongly influenced by the morphology and volume fraction of austenite. Retained austenite, when transformed to martensite during the transformation-induced plasticity (TRIP) phenomenon, leads to increased tensile strength and fracture toughness, or retained austenite with a film-like shape prevents the growth of cracks by blinding the crack tip. The result of the CTOD test exhibited that retained austenite plays the leading role in increasing crack resistance when TRIP occurs.

. Introduction . The incompleteness of formal axiomatics in identifying the structure of many materials is a consequence of the complex geometric shape of its elements. For adequate approximation of the structure elements, it is not enough to use standard techniques that are based on Euclidean geometry. The use of the language of fractal geometry allows to partially eliminate the incompleteness of formal axiomatics through the use of fractal (fractional) dimensions. Materials and techniques . The object of the study was Ст3пс mild steel. The composition, structure and properties of steel are given. A method for calculating the fractal dimension developed by the authors is described. Results and its discussion . An algorithm is proposed for fractal modeling of the structure and properties of Ст3 low carbon steel, which is based on establishing the limits of self-similarity of the structure; calculation of the spectrum of dimensions of the elements of the structure; determining the sensitivity between the quality criteria of the metal and the dimensional characteristics of the structure; formalization of the results. Conclusions . The regularities of the influence of the fractal dimension of the Ст3 structure elements on the mechanical properties are established. The developed models make it possible to predict the properties of mild steel depending on the transformations of its microstructure due to the effects of heat treatment.

Formulation of the problem. Predicting the mechanical properties of structural carbon steels is of great scientific and practical importance. Along with the physical-mechanical methods of evaluating the properties of steels, mathematical methods are being actively implemented, which allows to save money and time for conducting cost exams. The relevance of this work is due to the difficulties that arise in assessing the accuracy of the prediction of real and model data. This is due to the multifactorial carbon steel manufacturing technology where even a slight change in the technology parameters can lead to a significant change in the quality criteria of the target product. The paper proposes to investigate the influence of elements of chemical composition and structure on the mechanical properties of structural steel 15пс using the methods of mathematical analysis. Method. Constructional steel 15пс (sheet thickness 14 mm according to ГОСТ 16523) was selected as the steel for the study. The technique of planning experiments at the levels of factors +1 and 1 is used to evaluate the mechanical properties of steel 15пс in the state of factory delivery on the basis of the analysis of the influence of elements ofchemical composition and structure. Results of the experiment. As a result of the implementation of the experiment planning matrix, dependencies were obtained describing the influence of the elements of the chemical composition and ferrite-pearlitic structure of the steel on the properties. The pairwise correlation coefficients of R2for predicting the tensile strength based on the effect of the elements of the chemical composition are 0,89, a relative elongation of 0,82. When forecasting mechanical properties based on the influence of ferrite-pearlite structure 0,77 and 0,75 respectively. The calculated Fisher and Cochran criteria confirm the adequacy of the obtained results of mathematical modeling of properties. Conclusions. Using the experiment planning matrix, a mathematical model for estimating the mechanical properties of 15пс steel was constructed. Based on the analysis of the coefficients of the equations, histograms were obtained describing the influence of the elements of the chemical composition on the properties of the metal. This approach will allow, without additional funds, to predict the tensile strength and elongation of steel 15пс not only at the end of the main technological cycle, but also in the process of production of rolled metal within the standard technology and regulatory documents.

Carbide is the binary compound that formed by carbon and the elements with less or similar electronegativity (except hydrogen). Carbide is one of the important precipitated phases in special steels, which plays an important role on the properties of steel. In this chapter, the definition and classification of carbides are presented, and the instruments and technologies for the analysis of carbides in special steels are introduced. Through the thermodynamic analysis and experimental study on the formation of carbides in many typical special steels, it is found that inevitable microsegregation in the solidification process is the key reason for the precipitation of primary carbides. These primary carbides have large size and the high content of alloying elements, which significantly reduce the processing and mechanical properties of special steels. By improving the solidification process, modification and heat treatment, the processing and service properties of special steels could effectively promote the breaking and dissolution of primary carbides. The secondary carbides in special steel mainly generate in the annealing process. Optimizing the heat processing of steel and adding alloying elements could significantly refine the secondary carbides, and consequently improve mechanical properties of steel.

The article aims to investigate the mechanical properties of C45 steel with a previously constituted bainitic structure, due to its widespread use in the machine industry.The input ferritic-pearlitic structure of steel was subjected to heat treatment in the form of quenching and tempering in order to obtain a bainitic structure. Tempering was carried out at different temperature and time values. It allowed various properties of the steel samples to be obtained, which were subsequently subjected to tensile strength and hardness testing. In addition, metallographic images of the resulting structures were taken.The results obtained from the tests were compiled in tabular form. Based on the results, correlations were observed in the tensile strength and hardness of the tested steel relative to various parameters of the hardening and tempering processes.The strength properties testing of C45 steel with a bainitic structure was limited to determining the yield strength Re, tensile strength Rm, elongation A, and microhardness HV0.5.The tests confirmed the possibility of controlling heat treatment process parameters to achieve the desired mechanical properties of the steel. This may contribute to the practical control of the steel’s properties due to economic aspects and functional requirements.The article is primarily addressed to industrial practice, i.e., manufacturers of machine parts made of medium-carbon steel, due to the reduction in heat treatment time and energy consumption costs while maintaining the steel’s machinability and strength properties.

The influence of the structure and properties of 30KhGSA steel on the shaping of round-shaped blanks using the method of plastic bending is studied. Bending of the initial steel rod sample results in the sample fracture. Methods of mechanical tests and metallographic analysis used in the study showed that the steel sample in the initial satate has a structure of lamellar perlite. A comparative evaluation of the structure and properties of the steel samples prior to and after additional heat treatment (spheroidizing annealing) revealed that annealing enhanced the plastic properties of the sample and changed the sample structure from lamellar to globular perlite. Formation of the granular perlite structure indicates to the devision of the plates into smaller particles and their further spheroidization due to transferring carbon through the surrounding solid solution. Thus, additional cyclic heat treatment of steel in the state of delivery, allowed us to solve the problem of the rod fracture upon subsequent plastic bending. As a result of the research, the values of the mechanical properties of steel were obtained experimentally, which ensure the process of bending the rod into a round shaped blank without destroying it. The proposed mode of cyclic heat treatment (spheroidizing annealing) can be used to improve the plasticity characteristics of the metal upon shaping by the method of plastic bending.

The use of heat straightening to repair damaged steel structures has gained popularity in recent years. However, applications have been limited because of concerns related to degradation of material properties after repair. Most research has been limited to small undamaged plate specimens where only one to three heats were applied. The purpose of this paper is to report on a study in which structural members were damaged and completely repaired by heat straightening, after which material properties were investigated. The research data indicate that heat straightening does affect mechanical properties of steel. Yield stress may increase by as much as 20%, especially in the vicinity of the apex of vee heats. Tensile strength also increases but at only half the rate of yield stress. The ductility as measured by percent elongation may decrease by one-third, and the modulus of elasticity may decrease by over 25% in some heated regions. Damage with maximum strains up to 100 times the yield strain were repaired, and material properties were compared to members damaged with much smaller strains. The degree of damage had a minimal effect on the material properties of heat-straightened steel. Some members were damaged and completely heat straightened more than once to evaluate the effect of repetitive damage on the material properties of heat-straightened steel. Changes in material properties were small after two cycles of damage and repair. However, additional cycles produced a more brittle material and, in some cases, resulted in fracture of the material. In summary, heat straightening is a viable alternative for the repair of damaged structural steel. However, the user should be aware that some material properties will be changed during the process.

The deformation microstructures formed by novel multistage high-temperature thermomechanical treatment (HTMT) and their effect on the mechanical properties of austenitic reactor steel are investigated. It is shown that HTMT with plastic deformation at the temperature decreasing in each stage (1100, 900, and 600 °C with a total strain degree of e = 2) is an effective method for refining the grain structure and increasing the strength of the reactor steel. The structural features of grains, grain boundaries and defective substructure of the steel are studied in two sections (in planes perpendicular to the transverse direction and perpendicular to the normal direction) by Scanning Electron Microscopy with Electron Back-Scatter Diffraction (SEM EBSD) and Transmission Electron Microscopy (TEM). After the multistage HTMT, a fragmented structure is formed with grains elongated along the rolling direction and flattened in the rolling plane. The average grain size decreases from 19.3 µm (for the state after solution treatment) to 1.8 µm. A high density of low-angle boundaries (up to ≈ 80%) is found inside deformed grains. An additional cold deformation (e = 0.3) after the multistage HTMT promotes mechanical twinning within fragmented grains and subgrains. The resulting structural states provide high strength properties of steel: the yield strength increases up to 910 MPa (at 20 °C) and up to 580 MPa (at 650 °C), which is 4.6 and 6.1 times higher than that in the state after solution treatment (ST), respectively. The formation of deformed substructure and the influence of dynamic strain aging at an elevated tensile temperature on the mechanical properties of the steel are discussed. Based on the results obtained, the multistage HTMT used in this study can be applied for increasing the strength of austenitic steels.

Improving the impact wear properties of medium carbon steel by adjusting microstructure under alternating quenching in water and air

In recent years, high-strength steel (HSS) is finding increasing applications in building construction due to its excellent strength and durability properties. However, structures, incorporating HSS, exhibit lower fire resistance due to rapid deterioration of their mechanical properties at elevated temperatures. For evaluating the fire resistance of steel structures, high-temperature properties of steel are to be specified as input data. The properties of steel not only vary with temperature but also the extent of variation is influenced by the type and grade of steel. This paper presents a state-of-the-art review on temperature-dependent properties of HSS. The available data and relations for thermal, mechanical, and deformation properties of HSS are compiled. Using these data, the variations in the elevated properties of HSS are established and the reasoning for such variation is explained. Finally, the critical properties to be considered for evaluating the fire resistance of structures, incorporating HSS, are discussed.

The comparison on tribological properties of ion sulfuration steels under oil lubrication