Phase Composition Of Steel Research Articles

Исследование влияния длительной высокотемпературной эксплуатации на структуру и свойства аустенитной хромоникельмолибденовой стали

The effect of long-term operation at a temperature of 515°C on the structure and properties of steel 08Cr16Ni11Mo3 (grade 316) is studied. Data on the structure and phase composition of the steel were obtained using optical and scanning electron microscopy. The phase composition of steel in the equilibrium state was determined by thermodynamic modeling in the FactSage software package. As a result of the study, it was found that there are the structure changes with the formation of secondary phases initiated by the precipitation of elements with limited solubility from the supersaturated solid solution during operation at a temperature of 515°C for 195 000 hours in steel 08Cr16Ni11Mo3 (grade 316). The presence of the following secondary precipitates in the structure of the solid solution of austenite was revealed: carbide of the М23С6 type (M — Cr, Mo), ferrite (α), intermetallic phases. Based on a comparison of the thermodynamic modeling data and the experimental determination of the phase composition, it was found that the structure of steel is close to equilibrium. The results of static tensile tests have shown that a change in the phase composition during heat aging leads to embrittlement of steel, i. e. a decrease in ductility. In general, the mechanical properties of the material in the state after operation are close to the original ones. The tensile strength at room temperature is 5 % higher than the initial one, and in the range of elevated temperatures of 350 – 600°С it is 5 –10 % lower than the initial level. The yield strength at temperatures of 20, 500 and 600°С after operation increases by 5 –10 % of the initial level, and at temperatures of 350 and 550°С it practically does not change. In the temperature range 350 – 600°C, the ductility values of steel 08Cr16Ni11Mo3 (grade 316) decrease by 5 –17 % from the initial level. The main contribution to the change in the mechanical characteristics of steel is made by secondary precipitates of carbide and intermetallic phases.

Phase Composition of Austenitic Stainless Steels in Additive Manufacturing: A Review

Additive manufacturing (AM) is among the novel industrial technologies for fast prototyping of complex parts made from different constructional and functional materials. This review is focused on phase composition of additively manufactured chromium-nickel austenitic stainless steels. Being produced by conventional methods, they typically have single-phase austenitic structure, but phase composition of the steels could vary in AM. Comprehensive analysis of recent studies shows that, depending on AM technique, chemical composition, and AM process parameters, additively manufactured austenitic stainless steels could be characterized by both single-phase austenitic and multiphase structures (austenite, ferrite, σ-phase, and segregations of alloying elements). Presence of ferrite and other phases in AM steels strongly influences their properties, in particular, could increase strength characteristics and decrease ductility and corrosion resistance of the steels. Data in review give a state-of-art in mutual connection of AM method, chemical composition of raw material, and resultant phase composition of AM-fabricated Cr-Ni steels of 300-series. The possible directions for future investigations are discussed as well.

Effect of the γ→ε Phase Transition on Transformation-Induced Plasticity (TRIP) of Nickel-Free High Nitrogen Steel at Low Temperatures

The deformation behavior, mechanical properties, and microstructure of Fe-Cr-Mn-0.53%N austenitic stainless steel were studied at a temperature range of 77 up to 293 K. The dynamics of the steel elongation were non-monotonic with a maximum at 240–273 K, when peaks of both static atom displacements from their equilibrium positions in austenite and residual stresses in the tensile load direction were observed. The results of X-ray diffraction analysis confirmed that the only stress-induced γ→ε-martensite transformation occurred upon deformation (no traces of the γ→α′ one was found). In this case, the volume fraction of ε-martensite was about 2–3%. These transformation-induced plasticity (TRIP) patterns were discussed in terms of changes in the phase composition of steel as the root cause.

Service Life Effect on Structure and Phase Composition of DIN 14MoV63 Steel

The paper studies the structure and phase composition of steel 0.12C–1Cr–1Mo–1V–Fe (grade DIN 14MoV63) after a long-term operation using the transmission electron microscopyю Investigated are the nontreated specimen (not subjected to operation) and specimens after a long-term operation with and without fracture. The phase composition and morphology of the steel structure are determined for each specimen. It is found that the steel servicing leads to the destruction of lamellar perlite, intensive fragmentation of ferrite, redistribution of the carbide component and elastic distortion of the crystal lattice.

ОБОСНОВАНИЕ КОРРЕКТИРУЮЩИХ ВОЗДЕЙСТВИЙ, КОМПЕНСИРУЮЩИХ ПОНИЖЕННОЕ СОДЕРЖАНИЕ УГЛЕРОДА В СТАЛИ ПРИ ПРОИЗВОДСТВЕ ХОЛОДНОКАТАНОГО ЛИСТОВОГО ПРОКАТА ДЛЯ ШТАМПОВКИ

The relevance of the work. There are situations in the practice of metallurgical production when steel melting with a chemical composition intended to complete the determined order is reassigned to the production of rolled metal from another steel grade. With the formal accordance of chemical composition of melted steel to the requirements for a different steel grade, crucial control parameters of process that are traditionally used for a new grade of steel, may turn out to be inappropriate for structural and phase transformations in steel with real chemical composition. To prevent the re-lease of non-conforming products is necessary to develop and apply operational corrective actions. The purpose of the work is selection and rationale of operational corrective actions in the production of cold rolled sheet products of quality classes CQ, DQ and DDQ of mild quality steel to compensate for the reduced carbon content in meltings assigned to complete the respective orders. Microscopy methods were used to study the structure and phase composition of steel with a carbon content of 0,008 – 0,04 % in hot-rolled and cold-rolled states. Data on the mechanical properties of hot-rolled and cold-rolled steel were obtained by standardized tensile test methods. Based on the test results, re-liable multiple approximations of influence of control characteristics of the technology on properties of cold-rolled steel were constructed, which were subsequently used in optimization of thickness of semi finished rolled product for cold rolling as a compensating effect at the fluctuations of carbon content within the above limits. The novelty of the work lies in the identification and rationale of corrective actions for a technological system in which cold rolling is carried out on a continuous four-stand mill with roll feed. The results of the work consist in determining the temperature of the end of rolling and the increment of the thickness of the semi finished rolled product as operation-al compensating effects at assigning steel meltings with a low carbon content for rolling into a tech-nological system with a continuous four-stand mill with roll feed. The practical significance of the work is to prevent the yield of non-conforming products at using the proposed solution in the pro-duction of cold-rolled steel of quality classes CQ, DQ and DDQ 0,6–2,0 mm thick.

Effects of high energy on steel structure in deformation

The author of the article investigates how microwave radiation affects the processes of active deformation and mechanical stress relaxation in stressed stainless steel specimen under the electric current and when vector E (of microwave radiation) moves in different directions along the axe of the specimen. When vector E of microwave radiation was oriented in a longitudinalis way and electric current was passed, the softening of metal increased from 22 to 30 %. Multi-criteria analysis of steel samples with electric current and samples with no electric current was made. Analysis findings showed that external energy deposition influenced greatly on deformation of steel crystals. The action of high-density electric current pulses and microwave radiation on a sample loaded above the yield strength increases the ductility of stainless steel, and its strength characteristics, the microstructure is modified. Phase composition of steel was also investigated. The studies showed that the content of martensitic and austenitic phases in steel changed significantly. Moreover, the results showed that there was an additional mechanism of electroplastic deformation in the crossed fields of microwave radiation and magnetic field of current.

Influence of Phase Composition of Steel on a Damage Rate from Bio-Corrosion

The complex research of influence of a structural condition of metal on resistance to corrosion destruction of the low-alloyed steel, operated in biocorrosion environments, is conducted. It is established that the ferritic component of a structure resists better in the environment modeling conditions of impact of biogenous gases on metal under the exfoliated anticorrosive covering. Ferrite – carbide mix, in the form of beynit, has a bigger resistance in the environment reproducing conditions of lack of biogenous factors. Existence in beynitny structure of a martensitic component leads to the largest resistance of biocorrosion in the environment modeling conditions of anaerobic corrosion with biogenous gases.

Physical methods of research and monitoring

The main magnetic parameters sensitive to the structure of steels are the parameters of their saturation loop of magnetic hysteresis: the coercive force Hcs and remanent magnetization Mrs. The saturation magnetization or saturation intensity Mr is most sensitive to the phase composition of steels. The variety of steel grades and modes of technological treatment (e.g., heat treatment, mechanical load) determined the use of magnetic structurescopy and magnetic characteristics — the coercive force Hc, remanent magnetization Mr , and specific hysteresis losses Wh on the subloops of the magnetic hysteresis of steels — as control parameters in diagnostics of the stressed and structural states of steel structures and pipelines. It has been shown that changes in Hc, Mr , and Wh are more sensitive to structural stresses and structures of steels than the parameters of the saturation hysteresis loop of magnetic hysteresis (Hcs, Mrs, and Mrs). The formulas for calculating Hc, Mr and Wh are presented to be used for estimation of changes in the parameters upon heat treatment of steels. Features of the structural sensitivity of the subloop characteristics and expediency of their use for magnetic structural and phase analyzes are determined. Thus, the range of changes in Ìr attributed to the structural changes in steels upon gradual Hm decrease is many times wider compared to the range of possible changes in Mrs under the same conditions. Conditions (relations between the magnetic parameters) and recommendations regarding the choice of the field strength Hm are given which provide the justified use of Hc, Mr and Wh parameters in magnetic structurescopy

Study of a Welded Joint of 12Kh18N10T Steel Using Acoustic and Magnetic Methods

The paper presents results from studies on the influence of plastic deformation on magnetic and acoustic characteristics of a welded joint material of 12Kh18N10T (analogue AISI 321) austenitic steel. We have shown that an inhomogeneous structure in the heat-affected zone causes a nonuniform distribution of acoustic parameters and magnetic properties of the welded joint material. The formation of the martensitic phase occurs upon plastic deformation, which influences the properties of the whole material and has elastic moduli differing from that of the original austenitic phase. The increase in the volume fraction of martensite leads to the decrease in the elastic moduli of the material and, as a consequence, to the decrease of ultrasonic waves velocity. The variation of ultrasonic waves velocities leads to significant errors upon measurements of the material parameters under study, for instance, of a sheet thickness using ultrasonic thickness measurement. The formation of martensite changes also the magnetic properties of the material. We have found the dependence of the shear ultrasonic wave velocity on a parameter governed by the change in the phase composition of the austenitic steel upon plastic deformation. We have developed an algorithm for the determination of the thickness of the welded joint metal undergoing pressure forming and plastic deformation upon operation of constructions. We have shown that the additional measurement using the magnetic method of the parameter governed by the change in the phase composition of the steel upon deformation substantially decreases the errors of the thickness measurement of the welded joint metal.

Parameters of Models of Structural Transformations in Alloy Steel Under Welding Thermal Cycle

A mathematical model of structural transformations in an alloy steel under the thermal cycle of multipass welding is suggested for computer implementation. The minimum necessary set of parameters for describing the transformations under heating and cooling is determined. Ferritic-pearlitic, bainitic and martensitic transformations under cooling of a steel are considered. A method for deriving the necessary temperature and time parameters of the model from the chemical composition of the steel is described. Published data are used to derive regression models of the temperature ranges and parameters of transformation kinetics in alloy steels. It is shown that the disadvantages of the active visual methods of analysis of the final phase composition of steels are responsible for inaccuracy and mismatch of published data. The hardness of a specimen, which correlates with some other mechanical properties of the material, is chosen as the most objective and reproducible criterion of the final phase composition. The models developed are checked by a comparative analysis of computational results and experimental data on the hardness of 140 alloy steels after cooling at various rates.

Phase Composition and Microhardness of Surface Layers 34CrNi1Mo Steel after Electrolytic-Plasma Processing

Present work is devoted to phase composition research, structure and microhardness of structural steel 34CrNi1Mo after electrolytic-plasma processing in a cathode heating mode. Technology of electrolyte-plasma hardening provides reliable quality and the required mechanical properties of the products which are often subjected to wear and temperature-force actions. Results of microscopic researches and X-ray structure analysis are presented in this work. It is established that microstructure of steel detail modified layer being processed in electrolytic plasma at a temperature of 850 °C during 5 minutes, is generally represented by martensite quenching. The phase composition of steel 34CrNi1Mo after electrolytic-plasma carburization is presented by structure of α-Fе phase and carbide phases Fe2C, Fe3C. Surface microhardness increases more than by 2.5 times in comparison with a reference value.

OAO Uralmashzavod software for the simulation of solidification and mild compression

Software for simulating complex technological processes in the continuous casting of steel has been developed. Cristall (Cristall 2D, Cristall 3D), Dinamika (Dinamika-DSVO), and Cristall-Pora software permits the calculation of the temperature fields and phase composition of steel in offline and online modes and hence may be used in the predesign, design, debugging, and operation of industrial continuous-casting systems. In addition, Cristall-Pora software permits calculation of the hydrodynamic processes in the two-phase zone and accordingly may be used in the development of mild-compression equipment. Practical examples are presented.

Effect of titanium and tungsten carbide on the formation of the structure and the properties of composite coatings. Part 1: the structure and phase composition of steel R6M5–(WC+TiC) coatings

The results of investigations of the special features of the formation of the structure and phase composition of R6M5 steel–(WC+TiC) composite coatings in relation to the content of tungsten monocarbide in the initial charge are presented. It is shown that the amount of retained austenite in the composite coating depends on the tungsten carbide content in the total volume of the added hardening phase. The maximum amount of austenite (75%) in relation to the total volume of the matrix was observed in the coatings containing 20% of the carbide component.

Thermodynamic simulation of the formation of carbonitrides in steels with Nb and Ti

Available thermodynamic data on the Fe-Nb-Ti-C-N system have been analyzed and a self-consistent thermodynamic description of the system and its constituent subsystems has been suggested. Using the constructed thermodynamic description, calculations of phase equilibria have been performed for this system and some features concerning the effects of the alloy composition on the phase composition of steels alloyed with niobium and titanium have been considered.

Investigation of phase composition of high temperature chromium steels and chromonitriding process in austenitic alloys

The creep resistance of 9% chromium high temperature steels is determined by the alloy content and structure resulting from heat treatment. This paper describes the analysis of the phase composition using CALPHAD numerical modelling methods, of known modifications of 9% high temperature chromium steel: 9Cr–0·1C, 0·9Mo, 0·21V, 0·1Nb, 0·04N (P91) and 9Cr–0·1C, 2W, 0·5Mo, 0·21V, 005Nb, 0·05N, 0·005B (P92). The effect of alloying elements on the phase composition of the steel and the mutual effect of the composition on the nature and quantity of the phases Me23C6 and Me(CN) in the temperature range 570–620°C is described. On the basis of calculated data and experimental results, a composition for new high temperature steels with additional Co alloying (up to 3%) and varying carbon contents in the range 0·02–0·10% is proposed. Results are shown for investigations on high temperature chromium steels containing cobalt, including: effect of complex alloying with tungsten, molybdenum, and cobalt on the service properties and structural composition of steels; heat treatment processes for alloy variants and kinetics of structural change during creep and prolonged thermal aging. Data have been obtained comparing calculated and experimental data for the phase composition in chromium steel, also the effect of the phase composition on creep characteristics. On the basis of a complex laboratory investigation and industrial pilot heats, optimal composition variants for the alloy content of high temperature Cr–Mo–V–Co steels have been determined for practical applications. CNIITMASH has developed a chromonitriding technology for improving the corrosion, wear and scratch behaviour, as well as for protection against self-welding and other service characteristics of austenitic steel components and nickel alloys. Chromonitriding technology includes saturation of the component surface with chromium and nitrogen. The technology is intended for strengthening valves and bushings, water pump components, and components operating in liquid metal, burnt fuel residue, and other aggressive environments. The conditions governing the formation of the strengthening layers, consisting of an austenitic matrix (γ solid solution) and containing Cr2N with a depth of up to 250 μm and a hardness of 750–950 HV have been determined. Thermodynamic analysis of phase formation conditions during the chromising and subsequent nitriding process over a wide range of temperatures and saturating media has been carried out. The technology has been optimised for process and media composition leading to a structure with maximum surface properties.

Thermodynamic simulation of the Fe-V-Nb-C-N system using the CALPHAD method

A critical analysis of available thermodynamic data for the Fe-V-Nb-C-N system has been performed. Based on the CALPHAD method, a self-consistent thermodynamic description of this system has been suggested. Using the constructed thermodynamic description, calculations of phase equilibria of the system under consideration have been performed and some peculiarities of the effect of the alloy composition on the phase composition of steels alloyed with vanadium and niobium have been considered.

Analysis of the structural and phase sensitivity of the relaxation magnetization of steels

A formula for calculating relaxation magnetization \(M_{H_r }\) of steels from their saturation magnetization and remanent magnetization is used to analyze the structural and phase sensitivity of \(M_{H_r }\). The conditions under which \(M_{H_r }\) has a high sensitivity to changes in the structural state and phase composition of steel are established.

Wear of alloy tool steels under impact conditions

The impact wear rate depends on the impact energy, ductility, hardness, and phase composition of steels.