Medium Alloy Steels Research Articles

Study on the characteristics and high-temperature dissolution mechanism of eutectic carbides in medium-alloy steel

In this study, the high-temperature evolution of eutectic carbides in a medium-alloy steel was investigated as well as their precipitation mechanism. Results revealed that MC and M6C eutectic carbides in the steel appeared during the final solidification due to the segregation of Mo and V and the melt undercooling. These eutectic carbides consist of blocky shapes with varying orientations, and rod-like shapes with the same orientation. Further investigation was confirmed that the carbides (MC and M6C) exhibited an intergrowth behavior. The cooling rate had a direct influence on the secondary dendrite arm spacing (SDAS), which decreased from 180 to 130 μm as the rate ranged from 0.6 to 21.9 °C/min. After holding for 0, 25, 50, and 80 h, respectively, the volume percentage of eutectic carbides exhibited a significant decreasing trend from 2 to 0.2%. Additionaly, the carbides exhibited irregular morphology after holding for 0–50 h, respectively, and which was transformed into the rod-like shape with a small size distributed along the grain boundaries after holding for 80 h. This phenomenon was attributed to the mutual diffusion between Mo, V, and other alloying elements in the carbides and Fe element in the steel matrix.

A strategy to reduce spectral intensity uncertainty and predicted content uncertainty of low and medium alloy steel elements

This work presents a correction method for reducing the uncertainty in the spectral intensity and quantitative prediction model by incorporating plasma acoustic pressure parameters (First peak value and First attenuation slope) and validated it in order to reduce the uncertainty in the quantitative analysis of laser-induced breakdown spectroscopy (LIBS). Mo, Al, Mn, and V elements in low and medium alloy steels were analyzed using a simultaneous plasma spectroscopy and acoustic pressure signal acquisition system. The relationship between the spectra and the acoustic pressure parameters was then examined in order to analyze the spectral intensities and the uncertainty of the quantitative prediction model after incorporating the acoustic pressure parameters. The findings indicate that, in comparison to the original spectra, the average relative standard deviation (ARSD%) of the spectral intensities of the elements Mo, Al, Mn, and V incorporated in the first peak of the sound pressure were reduced by approximately 50.32%, 44.33%, 52.74%, and 41.57%, respectively, and that of the elements incorporated in the first attenuation slopes were reduced by approximately 35.82%, 29.99%, 38.38%, and 24.66%, respectively. We discovered that the quantitative laser-induced breakdown spectroscopy model based on the plasma acoustic pressure parameter correction may also successfully lower the uncertainty of the projected elemental content values through prediction model cross-validation studies.

Influence of Melt Properties on the Dendritic Structure of Steel Castings

The paper presents the experimental results on the determination of melt parameters such as the energy of the boundary, contact angle, density and kinematic viscosity of low and medium alloy steels at different temperatures, as well as the dispersion of their dendritic structure in solidified castings. The analysis of the data obtained allowed revealing using mathematical models the influence of the chemical composition and temperature of melts on their properties and the dendritic structure of castings. It was established the variation of the melt parameters depending on the particular chemical elements of steels as C, Si, Mn, O, P, V, Cr. The established analytical dependences shown that increasing density and viscosity contributes to the dispersion of the dendritic structure and viscosity is of the major effect. The derived quantitative patterns allows to evaluate structure formation of cast structural low and medium alloy steels.

Regulation Law of Tempering Cooling Rate on Toughness of Medium-Carbon Medium-Alloy Steel.

Temper embrittlement is a major challenge encountered during the heat treatment of high-performance steels for large forgings. This study investigates the microstructural evolution and mechanical properties of Cr-Ni-Mo-V thick-walled steel, designed for large forgings with a tensile strength of 1500 MPa, under different tempering cooling rates. Optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) were employed to analyze the microstructural features. The results demonstrate that the embrittlement occurring during air cooling after tempering is attributed to the concentration of impurities near Fe3C at the grain boundaries. The low-temperature impact toughness at -40 °C after water quenching reaches 29 J due to the accelerated cooling rate during tempering, which slows down the diffusion of impurity elements towards the grain boundaries, resulting in a reduced concentration and dislocation density and an increased stability of the grain boundaries, thereby enhancing toughness. The bainite content decreases and the interface between martensite and bainite undergoes changes after water quenching during tempering. These alterations influence the crack propagation direction within the two-phase microstructure, further modifying the toughness. These findings contribute to the understanding of temper embrittlement and provide valuable guidance for optimizing heat treatment processes to enhance the performance of high-performance steels in large forgings.

Dissolution Behavior of Eutectic Carbides in Medium-Alloy Steels for Heavy Forgings.

In this study, we investigate the dissolution behavior of eutectic carbides in heavy forgings. High-temperature diffusion treatment was conducted on 35Cr3Ni3MoVW2 (MoVW2) and 35Cr2Ni3MoV (MoV) steels at 1230 °C for a duration ranging from 0 to 100 h. The dissolution of eutectic carbides and its effects on the microstructure and hardness of the steels were characterized and analyzed via SEM+EBSD, ImageJ, and Thermo-Calc. The results show that the coarse eutectic carbides in both steels gradually dissolved. The distribution and morphology tend to be uniform and spherical, respectively. For holding 50 h, the hardness of both steels significantly exhibited an increasing trend, and it was attributed to the combined effects of solid solution strengthening. Thermodynamic calculations indicated that the higher W content in MoVW2 steel promoted the precipitation of M6C eutectic carbides. Moreover, both MoVW2 and MoV steels exhibited the precipitation of M7C3 eutectic carbides in the final stage of solidification, facilitated by the enrichment of C and Cr in the liquid steels.

Development of shear deformation in lath martensite of medium alloy steels under tension

Evolution of shear deformation in steel with the structure of tempered martensite was studied under active tension. Purpose of the work was to identify the patterns of deformation development at the scale-structural levels: package, plate, fragment of a package and a lath. The authors investigated the deformation relief formed at different stages of plastic deformation by optical, transmission and scanning electron microscopy. Quantitative characteristics of the deformation relief were measured: shear strength (P), distance (X) between the shear traces and their length. Statistical processing was carried out, the average values and relationship with the degree of plastic deformation were determined. It was established that development of shear deformation in the lath component of martensite occurs with the formation of two subsystems of shear traces: thin and coarse. Subsystems of thin traces are formed from the very beginning of plastic deformation. Appearance and evolution of the subsystem of coarse traces correlates with formation of the first (long) neck in the sample, and it is the main mechanism leading to the localization of plastic deformation on the sample scale. The places of localization of rough shift are the border areas of the laths and fragments of the package. Connection between localization of subsystems of coarse shear traces and formation of a fragmented dislocation structure were revealed. The values of the average shear power in thin <Pf> and coarse <Ps> traces do not depend on the degree of local plastic deformation of the sample in the entire range of deformation degrees and remain constant until destruction (<Pf> = 0.1 μm and <Ps> = 0.3 μm).

Correlation of fracture toughness with microstructural parameters and standard mechanical properties of high-strength medium-alloy steel

Fracture toughness of rolled plates of high-strength medium-alloy steel with a martensitic or martensitic- bainite microstructure can vary widely depending on the parameters of their microstructure, which depends on the specific chemical composition, rolling parameters, quenching and tempering. In previous works, the authors studied the metal of various experimental smelts. The studied materials were significantly different in the size of structural components separated by large-angle boundaries (hereditary austenitic grain, martensite packages, and bainite crystallites). The continuation of these studies is the analysis of the relationship between the fracture toughness of a metal of one smelt and the general quenching parameters and, as a consequence, with the same parameters of the microstructure formed during quenching, but with different tempering parameters. A general structural state parameter based on the obtained data, and correlated with fracture toughness is proposed.

The application of cumulating lattice to accelerate diffusion during thermal diffusion chromiing

The creation of coatings on parts with improved corrosion resistance, throughput at low and high temperatures, wear resistance makes it possible to expand the possibilities of using low and medium alloy steels. Traditional methods for creating protective coatings are various types of chemical-thermal treatment and thermal diffusion chromium plating, in particular. In recent decades, attempts have been repeatedly made to increase the efficiency of the process of thermal diffusion saturation of chromium metal, mainly due to complex saturation with vanadium, boron and other elements, as well as the use of external physical influences that accelerate diffusion. Previously, in the works of the authors, it was shown that the introduction of electron-emitter metal powder into the composition of the metal part of the filling ensures the acceleration of diffusion processes during thermal diffusion chromium plating due to the action of an internal emission field. A similar effect is also observed when replacing corundum in the separating part of the filling with powders of solid electrolytes (minerals such as serpentine and scheelite, which are emitters of electrons and anions of the oxygen when heated). An additional enhancement of the internal emission field was noted when cumula-tive nickel and molybdenum lattice were used, however, the effect of the geometric characteristics of these lattice on the magnitude of the thermal emission of electrons and oxygen anions and, as a result, the diffusion acceleration was not established. The paper presents the results of saturation of samples of steel X35CrNi2-3 at a temperature of 1000°C for 24 hours using cumulative lattice that differ in the density of holes per unit area: 20, 10 and 6 holes/cm2. The control of the elemental composition of the diffusion layer was carried out on transverse sections in the direction from the saturated surface to base metal of the sample using a JEOL JSM-6460LV universal scanning (scanning) electron microscope. X-ray phase analysis was performed on an Ultima IV diffractometer, the radiation used was Cu-Kα. The microstructure was studied using an optical microscope Axio Observer D1.m. The microhardness of the coatings was measured using an FM-800 microhardness tester. It has been established that the use of cumulative nickel lattices provides an increase in the depth of the diffusion layer in the base metal by at least 25% and additional alloying coating with a grating metal element with a hole density of 10 pieces/cm2 or more. At a lower density of perforating the lattice, the opposite effect is observed

Choosing Accumulation and Preliminary Heat Treatment Modes for Making Forged Ingots of Medium-Carbon Medium-Alloy Steels

Choosing Accumulation and Preliminary Heat Treatment Modes for Making Forged Ingots of Medium-Carbon Medium-Alloy Steels

Thermodynamics Analysis and Pilot Study of Reusing Medium and High Alloy Steel Scrap Using Induction Melting and Electroslag Remelting Process

The annual cumulative quantity of high and medium alloy steel scrap has exceeded 10 million tons. Using the traditional smelting process involving electric arc refining in a smelting furnace for these scraps causes high percentages of alloy losses, which decreases the value of the alloy steel scrap and poses environmental threats. Existing studies have rarely focused on separate smelting of the scrap and oxidation behaviors of the alloying elements. Therefore, this study proposes an induction melting and electroslag remelting scheme to process the scrap. Based on this scheme, the effects of the temperature, oxygen content, and element contents on the recovery percentages of the alloying elements were investigated using pilot experiment and thermodynamic analysis. The experimental results showed that the alloying elements (tungsten, chromium, nickel, molybdenum, and vanadium) exhibited recovery percentages of 97.36%, 94.62%, 97.63%, 95.09%, and 89.49%, respectively; furthermore, the impurity content did not increase during smelting. The thermodynamic analysis indicated that an increase in carbon content improved the oxidation resistance of the alloying elements except for nickel, whereas the increases in the contents of oxygen and alloying elements increase their oxidation. Steam partial pressure and air suction dramatically increase the concentrations of nitrogen, hydrogen and oxygen. This scheme is an alternative for smelting medium and high alloy steel scrap, and the thermodynamic analysis provides a theoretical understanding of the oxidation behaviors of the alloying elements in the steel scrap and the control of impurity.

Material and processing optimization on disc cutter of tunnel boring machine for failure prevention

During the excavation process of hard rock tunnel by tunnel boring machine, rock breakage is mainly realized by the disc cutter, of which the cutter ring is in direct contact with the rock and therefore is prone to failures like wear, distortion and fracture. In this paper, in order to prevent the frequently-occurred failure of the cutter rings made of H13 medium-alloy steels, the properties of the specimens that were made of 42CrMo low-alloy steel and had undergone different heat treatment processes were investigated, including chemical composition, impact absorbed energy, hardness and wear resistance. The results pointed out that the combination of quenching at 850 °C and tempering at 180 °C and 230 °C was the optimum process, through which increased impact absorbed energy, equivalent hardness and wear amount was achieved in comparison with that of the H13 specimen. Achievement of this paper will facilitate both failure prevention and cost reduction for the disc cutter of tunnel boring machine.

Methodology of scientific selection of accumulation modes and preliminary heat treatment of forgings made of medium carbon medium alloy steels

This article considers issues related to the forgings from medium-carbon medium-alloyed steel grades. It is necessary to take into account the processes of phase and structural transformations when assigning modes of accumulation of ingots after forging and preliminary heat treatment (PHT). The main provisions of the appointment of PHT modes were analyzed. The paper formulates their limited application when using diagrams of isothermal transformation of austenite, built according to standard techniques.

Prediction of Cr, Mn, and Ni in Medium and Low Alloy Steels by GA-BP Neural Network Combined with EDXRF Technology

Prediction of Cr, Mn, and Ni in Medium and Low Alloy Steels by GA-BP Neural Network Combined with EDXRF Technology

Elastic-hereditary errors of fixation of non-rigid box blanks

The literature review has shown that so far no studies have been carried out on the elastic deformations of open box blanks during installation and fixation in machine tools. In the analysis of the installation of non-rigid axisymmetric blanks, it is indicated that the existing shape error of the base surface elastically changes its shape during fastening, and the processed surface gets the correct shape, which, after removing the clamping force, is distorted, and the base surface is not restored to its original shape due to the removal of the allowance layer. Typical operations of preliminary shaping of an open box-shaped workpiece obtained from medium-alloy steel 30HGSA with increased strength are described. The workpiece has errors in the relative position of the elements up to ± 0.3 mm. In production conditions the elastic-hereditary errors of fixing non-rigid box blanks were determined when compensating for the initial position of the deformed wall of the blank, by monitoring with the built-in sensor of the machine. It has been determined that such compensation is insufficient. For theoretical justification of the new proposals, the calculation of the stress-strain state of the construction using finite element analysis was made, which showed the deviation values of the side walls of the blank. Errors that most affect the deviations of the side walls when processing blanks of reduced rigidity are noted. A method of fixing and processing of thin-walled body blanks is proposed, in which the base side of the blank is measured using an RMP40 sensor before clamping force and after it, followed by adding value difference compensations in the control program for processing on a CNC milling machine. A comparative analysis of the dimensional deviation under the action of clamping force and after release from the clamps was made. A trial batch of blanks was processed, confirming the results of theoretical studies.

Material Characterization of Follower Assembly of G5 155mm Gun Howitzer Breach Mechanism Block

Medium alloy steel is widely used as a material for guns and rocket launchers due to its high strength and excellent machinability characteristics. The purpose of this study is to determine the material properties of the follower assembly used in a breech block gun launcher which is significantly important f or t he future product improvement. The microstructure and the effect of alloying elements in the follower assembly is evaluated in this study. The SPECTRO Optical Emission Spectroscopy (ES) method is used to analyse the chemical composition of the material and the Field Emission Scanning Electron Microscope coupled with Energy Dispersive X-Ray (FESEM-EDX) were used to analyse the inclusions of the sample. Results of the ES chemical composition analysis found that Nickel (Ni) is the major alloying elements beside Molybdenum (Mo), Chromium (Cr), Manganese (Mn), Silicon (Si), Sulphur (S), and Carbon (C) while chemical mapping and line scanning analysis of FESEM-EDX on inclusions distributed in the material microstructure identified as a compound of Manganese Sulphur(MnS). Fine dendritic microstructure arrangement and distribution in the microstructure analysis showed that the sample had been quenching in the heat treatment process, which also played a significant role in the material characterization. From the analysis, it is found that the material can be defined as medium alloy steel that is also typical for high strength material for ballistic application.

ОБОСНОВАНИЕ ЦЕЛЕСООБРАЗНОСТИ ПОВТОРНОГО НАГРЕВА В АВТОМАТИЗИРОВАННОЙ ЛИНИИ ДЛЯ ИЗГОТОВЛЕНИЯ КОЛЬЦЕВЫХ ЗАГОТОВОК

Features and requirements to the use of reheating of ring blanks in the conditions of production on the automated line are considered. An assessment is given for a technological temperature state of ring blanks at various stages of production under conditions of the automated line. For assessment of rational for reheating at production of ring blanks, a classification of ring manufacturing technology is proposed with the production of a pressed non-core blank in an open die, with the production of a pressed profile blank in a closed die, with the production of a pressed profile blank in a stamp with reverse extrusion. The technology of ring rolling with the production of a pressed non-core blank in an open die is the most economical and does not require the use of reheating in the manufacture of rings made of medium-alloy steels. The technology of ring rolling of a profile blank obtained in a closed die does not require the use of additional heating after pressing, in the case of manufacturing rings with a simplified profile on the outer or inner diameters of the ring. In the manufacture of rings with a more complex profile on the outer and inner diameters of the ring, as well as rings made of high-alloy steels, the final decision on the need for additional heating is made depending on the temperature of the end of intensive plastic deformation for the selected steel grade of the ring. The technology of ring rolling with the production of a pressed profile blank in a die with reverse extrusion requires the use of reheating after the pressing operation before the ring rolling operation, and is recommended for the manufacture of rings from medium- and high-alloy steels with a complex profile section on the outer and inner diameters, wall thicknesses, with a ratio of wall thickness to outer diameter D within h / D = 0.011...0.016 and with a ratio of wall thickness to ring height L within h / L = 0.020...0.041. The proposed recommendations are intended for use in the development of technological support for the operation of the automated ring-rolling complex at OJSC “BELAZ”.

Increasing the construction strength of petroleum pipes operating in agressive environment

Purpose. Questions about ways to increase the structural strength of oil country tubular goods are considered. Alloying and heat treatment of medium-alloy steels should ensure: pro-carbonization to the structure of martensite and lower bainite with a minimum carbon content (C ≤ 0.3 %), high resistance to brittle fracture and hydrogen embrittlement, the formation of uniformly distributed finely dispersed carbides and sulphides of a round shape to reduce diffusion mobile hydrogen is absorbed by steel. Propose modes of thermal treatment of casing pipes that provide the required level of mechanical and operational properties. Methodology. We used standard techniques for determining the mechanical properties in tension, dynamic bending tests and fracture studies. Results. The modes of heat treatment of casing pipes of strength category E, L are proposed, which provide the required level of mechanical and operational properties and an increase in structural strength. Originality. A systematic analysis of the influence of various factors on the structural strength of oil country tubular goods operating in an aggressive environment has been carried out. The highest degree of correlation between the value of the impact toughness and the tough component in the fracture is shown. Cooling of pipes with a nozzle sprayer of the design of the Department of Heat Treatment of Metals of NMetAU, which provides high resistance to brittle fracture by increasing the proportion of the viscous component and changing the microrelief of the cup fracture. Practical value. The proposed technology of heat treatment of oil pipes, working in an aggressive environment, provides the required level of mechanical properties and resistance to hydrogen sulfide cracking. Keywords: structural strength; oil country tubular goods; alloying; heat treatment; strength categories;temperature and deformation parameters; hydrogen sulfide cracking; brittle fracture resistance

Selected Properties of Hardfacing Layers Created by PTA Technology

The paper presents research results on the quality of hardfacing layers made during the renovation of unheated mold surfaces designed for injection of aluminum alloys using the plasma transferred arc (PTA) technology. As mold material, the medium alloy steel X38CrMoV5-1 (H11) was used. For the formation of functional layers, three types of additives in the form of powder were applied: two types on an iron basis with the designation HSS 23 and HSS 30 and one type on a nickel basis with the designation DEW Nibasit 625-P. The hardfacing layers were made on a 120 × 350 × 50 mm plate in two layers on the plasma hardfacing machine PPC 250 R6. The quality of the layers was evaluated by means of nondestructive and destructive tests. The surface integrity of the layers was assessed using visual and capillary tests. The samples passed these tests. The impact of the parameters used and the mixing of the hardfacing metal with base material, as well as the structure analysis, were assessed by means of light and electron microscopy (SEM). The chemical composition of the elements was determined by energy-dispersive X-ray spectroscopy (EDX) analysis using a SEM microscope. The hardness of the individual layers was evaluated. Since, during operation, molds are subjected to significant wear due to friction, the friction coefficients for selected temperatures were determined by the equipment for the evaluation of tribology properties. Based on the experiments conducted, all three types of additives can be used for renovation. However, from a tribology perspective, the additive DEW Nibasit 625-P on a nickel alloy basis is recommended for renovation.

On the importance of mathematical calculations in the study of structure characteristics and the physical and mechanical properties of 30XGSA steel, smelted on a different charge

The article considers the influence of the quality of the initial charge on the structure and physical and mechanical properties of the structural medium-alloy steel 30KhGSA. It was found that the 30KhGSA steel (smelters No. 3-4) cast in cast-iron molds (ingot weight 2.6 t) has a significant chemical heterogeneity and liquation in carbon and the main alloying elements (Cr and Mn), and in the melting on the semi-product of the boiling slag layer, the liquation is more pronounced. Starting from the tempering temperature of 500∘C, the structure of both melts (the fluidized slag layer and the ordinary metallized charge) becomes more uniform and the mechanical properties are aligned. Microstructural studies have established that with an increase in the annealing temperature at a single exposure, the chemical inhomogeneity decreases, but not significantly. Starting from 1000 ∘C, when the annealing temperature increases, the steel grain diversity and the growth of austenitic grains appear, especially in the melting on the semi-product of the boiling slag layer. Different grain sizes adversely affect the mechanical properties of steel: grain enlargement reduces the resistance of steel to brittle fracture, worsens the service characteristics of the metal. Elimination of chemical and structural heterogeneity can be achieved by conducting a ho-mogenizing annealing (annealing at 950 ∘C for 8 hours). An increase in the annealing temperature leads to an intensive grain growth, especially in steel smelted on the original charge. It is shown that 30XGSA steel, which is melted on a semi-product of a boiling slag layer, in an improved state with equal hardness and strength characteristics, has increased plastic properties and especially impact strength in comparison with steel on a conventional metallized charge. Apparently, this should also determine the higher operating characteristics of steel obtained with the use of pure primary charge.

Resistance of High-Strength Medium-Alloy Steel to Brittle Fracture and Its Connection to the Structural State Parameters

Resistance of High-Strength Medium-Alloy Steel to Brittle Fracture and Its Connection to the Structural State Parameters