Corrosion Resistance Of Austenitic Steels Research Articles

Properties of austenitic chromium-nickel steels alloyed with nitrogen and silicon

Results of a study of austenitic corrosion-resistant steels of the Fe – Cr – Ni–N–Si alloying system are studied. The steels possess higher parameters of strength (by 25 – 30%) and corrosion resistance (by a factor of 5 – 28) as compared to chromium-nickel steels of type 18–11 serving today in strongly oxidizing media. Comparative analysis of the properties of the new steels and of steel 03Kh18N11 (GOST 5632) widely used in the chemical industry is performed.

Microstructure and composition of welds of Fe3Al intermetallic with austenitic corrosion-resistant steels

The microstructure and the element and phase compositions of the zone of deposited metal, of the fusion zone, and of the heat-affected zone in welds of Fe 3 Al intermetallic with austenitic steels are studied by methods of light and scanning microscopy, microscopic x-ray spectrum analysis, and x-ray diffraction analysis. Argon arc welding is used to obtain beads of corrosion-resistant austenitic steels 08Kh18N10, 10Kh17N13M2T, 20Kh23N13, and 20Kh23N18 on the surface of a Fe 3 Al intermetallic.

Cyclic strength of an austenitic corrosion-resistant steel with a high nitrogen content

The fatigue strength of an austenitic high-strength corrosion-resistant high-nitrogen 05Kh22AG15N8M2F-Sh steel is studied after various types of thermomechanical treatment (quenching, quenching followed by aging, rolling at a total reduction of 40%). The life and the fatigue limit (500 MPa) are shown to be maximal after rolling. After quenching or quenching followed by aging, the material has almost the same fatigue limit; however, the finite life is longer in the case of quenching. The mechanisms of fatigue crack nucleation and propagation are considered.

Maximum utilization of negative wall-thickness tolerances in pipe rolling on KhPT mills

The cold rolling of pipe on KhPT mills with the maximum possible use of negative wall-thickness tolerance is considered. Special formulas permit the calculation of the minimum permissible pipe-wall thickness for maximum metal savings. Results for the rolling of large batches of austenitic and ferritic corrosion-resistant steel pipe show that metal savings of up to 8.7% relative to the rated mass are possible in controlled pipe rolling on KhPT mills.

Formation of stress field gradients during the high cycle fatigue of an austenitic corrosion-resistant steel

The formation of long-range stress fields in an austenitic 08Kh18N10T steel during high cycle fatigue is studied by transmission electron microscopy, and their gradient character is revealed. This character manifests itself in a decrease in the stress field amplitude as the distance from the source of bending-torsion of the crystal lattice increases.

Effect of heat treatment on the structure and properties of a high-nitrogen austenitic corrosion-resistant 03Kh20AG11N7M2 steel

The structure and mechanical and corrosion properties of a high-strength austenitic 03Kh20AG11N7M2 steel after quenching and aging at 500 and 800°C are analyzed. The phase composition of the steel and the mechanism of the decomposition of austenite during heat treatment are studied by electron-probe microanalysis and transmission electron microscopy. This steel is thermally stable upon heating to 800°C for 1 h and is stable to the γ → α and γ → ɛ martensitic transformation during deformation up to tensile strains leading to fracture. The homogeneous decomposition of a supersaturated γ solid solution at 500°C leads to the formation of disperse CrN nitrides, which increase the strength of the steel and insignificantly decrease its plasticity. In this case, the stress corrosion cracking resistance slightly decreases and the passivation of the steel increases in an corrosive medium without loading.

Structure of a cast high-strength corrosion-resistant 05Kh20AG10N3MF austenitic steel containing 0.40 or 0.53% nitrogen

The phase composition and fine structure of a high-strength corrosion-resistant 05Kh20AG10N3MF austenitic steel containing 0.40 or 0.53% N are studied by X-ray diffraction and electron microscopy. In the as-cast state, this steel has a structure containing austenite, δ ferrite, and dispersed CrV(C, N) carbonitrides. The δ ferrite is represented by layers between austenite grains, the dislocation density in which is lower than in the δ ferrite. After quenching from 1100, 1150, and 1200°C, the structure of the steel with 0.53% N has no δ ferrite and the structure of the steel with 0.40% N has a low δ-ferrite content and χ-phase precipitates.

Improving the corrosion resistance and reliability of austenitic and austenitic-ferritic steel pipe

Methods of improving the production technology for austenitic and austenitic-ferritic corrosion-resistant steel pipe are considered. The proposed modifications improve the resistance to intercrystallite and pitting corrosion, the thermal stability, and the operational reliability. Hence, the pipe produced is more competitive in the marketplace.

Structure formation in metastable austenitic steel 03Kh14N11K5M2YuT under the action of deformation

High-strength corrosion-resistant austenitic steel 03Kh14N11K5M2YuT with deformation-unstable austenite is studied. Regular features of the evolution of the substructure of the steel are investigated. The anomalously high ductility of the steel is shown to be explainable by the joint action of uniform slip, microtwinning, and martensitic transformations responsible for formation of subfine martensite crystals.

Ab initio development of a high-strength corrosion-resistant austenitic steel

A new austenitic steel alloyed with carbon + nitrogen is developed based on ab initio calculations of the electronic structure, which were carried out using the local density functional theory, and on experimental studies by means of conduction electron spin resonance. It is shown that alloying of CrMn austenite with carbon + nitrogen increases the concentration of conduction electrons and assists their more homogeneous spatial distribution, which results in short-range atomic ordering and, consequently, in a higher thermodynamic stability of iron-based face-centered cubic solid solutions. The developed CrMnCN steel is characterized by a yield and ultimate strength of 600 and 1000 MPa, respectively, in combination with an extremely high fracture energy. The notch-impact toughness exceeds 400 J. The resistance to impact wear is comparable with that of Hadfield steel. Corrosive properties are in some corrosive media similar to those of austenitic Cr18Ni10 steel. Possible applications of the developed steel are discussed.

Machinability of the high-strength corrosion-resistant high-ductility austenitic steel 06Kh22AG15N8M2F

The machinability of the high-nitrogen corrosion-resistant austenitic steel 06Kh22AG15N8M2F during turning is studied. The specific features of the structure of the surface layers in steel workpieces after turning are revealed. The cutting conditions that provide the lowest wear of VK8 alloy cutting tools upon turning are found: the cutting speed is 21–74 m/min, the feed is 0.15–0.60 mm/rev, and the cutting depth is 0.15–0.75 mm. The presence of a large amount of Cr2N-type chromium nitrides in the structure of the steel annealed at 800°C for 2 h and a high nitrogen content in the austenite of the steel quenched from 1100°C increase the wear of the cutting tools. As to turning of the forged steel, the wear resistance of the cutting tools upon turning of the 06Kh22AG15N8M2F steel is higher than that upon turning of 08Kh18N10T steel, in which deformation martensite forms (in surface layers) during turning.

Viscoplastic model for the strain resistance of 08Kh18N10T steel at a hot-deformation temperature

The viscoplastic model of the strain resistance of a metal developed earlier is shown to be applied to austenitic corrosion-resistant 08Kh18N10T steel with the fcc lattice at a hot-deformation temperature of 1150°C. Metallographic examination supports dynamic recrystallization occurring at this deformation temperature.

Radiation swelling of modified austenitic steels

Problems of synthesis of radiation-resistant austenitic steels for nuclear reactors now in operation and those of new generations to be used in future are considered. An analysis of the state-of-the-art and prospect for solving this problem demonstrates that, despite significant efforts of researchers all over the world, the economically required levels of operation of nuclear reactors have not yet been achieved. This is determined to a large extent by the insufficient radiation resistance of the main structural materials, namely, of corrosion-resistant austenitic steels. The main problem of supplying materials for modern nuclear power engineering and that to be used in future is a study of microstructural evolution and its influence on degradation of the initial physical-mechanical characteristics. The influence of the structural state of alloyed steels on the radiation resistance is examined.

Corrosion resistance of microfuel elements in air during contact with austenitic steel fuel-assembly components

A problem arising in the development of light-water reactors with a microfuel-based core is guaranteeing safety in accident regimes where the temperature of the outer surfaces of the microfuel elements reaches 1200-1400°C [1-3]. It has been determined experimentally [4] that unirradiated microfuel elements with a silicon carbide outer protective layer possess high corrosion resistance and integrity in a vapor-gas medium at temperatures up to 1600°C and have successfully passed heat-resistance tests by preheating in air up to 800-1600°C followed by rapid cooling in water. However, these tests were performed with no contact with the structural materials of fuel assemblies, while during a serious accident the chemical interaction between the metal and microfuel elements can destroy the protective outer layer of silicon carbide. Investigations of the interaction of sintered silicon carbide with zircalloy, austenitic steel, and oxides of various elements which are constituents of steel (FeO, Fe 3 O 4 , Cr 2 O 3 , MnO, and others) in air at high temperature 1450-1800°C established that silicon carbide is unstable under conditions where it comes into contact with type 316 austenitic steel at its melting temperature of 1450°C [5]. However, calculations have shown [1] that the most likely maximum temperature in a reactor core during a loss-of-coolant accident is ∼1200°C (for nominal VVER-1000 parameters). At the present time, there were no data on the behavior of the outer silicon carbide coating of microfuel elements in oxidative media in the case of contact with austenitic corrosion-resistant steel at the indicated temperature. It should also be noted that the structure and physical properties of sintered silicon carbide differ substantially from those of the carbide obtained by chemical gas phase deposition in a fluidized bed [5]. In this connection, investigations were performed on the corrosion resistance and integrity of silicon carbide coatings on microfuel elements coming into contact with austenitic stainless steels 08Kh18N10T and EI-847 (05Kh15N16M3B) in air at 1100-1200°C. In addition, the corrosion resistance of this steel under the same conditions was evaluated. Microfuel elements from two batches with different uranium oxide kernel diameters (300 and 500 μm) and multilayer cladding consisting of pyrolytic carbon and silicon carbide were chosen for the investigations. The outer protective silicon carbide coating on the microfuel elements was -50 pm thick in the first batch and -140 μm thick in the second batch. The nominal characteristics of the microfuel elements are presented in [4].

The effect of the chemical composition of a nitrogen austenitic steel on its forgeability

Nitrogen-bearing corrosion-resistant austenitic steel is a new product of some metallurgical works; it has a high strength, forgeability, impact toughness, corrosion resistance, and a low nickel content [1]. The properties of nitrogen-bearing corrosion-resistant steels were studied in [2], and the thermodynamics and kinetics of nitrogen dissolution in a metallic melt were considered in [3, 4]. At present, the methods for the optimization of the production of high-nitrogen corrosion-resistant steel and the problem of its quality control are being analyzed. Alloying elements in steels of this class exhibit a strong tendency toward micro- and macrosegregation, which causes nonuniform mechanical properties across an ingot and several types of defects. 12Cr18Mn18N steel is used to produce retaining rings and has a significant potential for use in other fields of engineering. The OOO OMZ-Spetsstal company has a great deal of experience in making steel of this grade. The steel under study was melted in a 50-t arc furnace; its chemical composition was finished in an outof-furnace unit; and two 22-t and one 9-t ingots were poured. After cutting the sinkheads of the 22-t ingots, their face ends were fettled, and they were then remelted to produce 18-t ingots in an electroslagremelting setup. The 9-t ingot was forged to produce an electrode and it was then remelted in the electroslagremelting setup at the OAO Mechel company to form a 5-t ingot. After electroslag remelting the ingots were heat-treated and forged to yield sleeve-tube workpieces. When retaining rings were produced, the forgeability of the 12Cr18Mn18N steel was found to be insufficient. To improve the forgeability of the ingots, we will study the causes affecting their forgeability and determine the possibilities for controlling their quality. Forgeability is known to be related to the presence of different phases, which serve as stress concentrators, in the bulk of the metal. These phases for the steel under study are nonmetallic inclusions and a ferrite phase forming along grain boundaries [5]. These defects form due to various technical factors, one of which is the chemical composition of the metal. To determine the effect of the chemical composition on the plastic properties of the steel, we used group and regression analyses to process experimental data. These results indicate the causes of the low forgeability of the steel. To estimate the effect of the chemical composition of the 12Cr18Mn18N steel on ingot forgeability, we compared the averages and dispersions of two statistical samples at different ductilities (see table). The first statistical sample consists of the chemical compositions of twelve ingots whose forgeability during forging was insufficient. The second sample consists of the chemical compositions of eleven ingots whose forgeability during forging was sufficient. The averages were compared using Student’s test; the dispersions were compared using Fishsher’s variance ratio; and the confidence level in both cases was 95%. In the ingots with a sufficient forgeability, the aluminum concentration and the Mn/Cr ratio are higher than those in the ingots with an insufficient forgeability. Our results indicate that the cause of the low forgeability of the steel is a nonoptimal composition of nonmetallic inclusions, which is determined by the aluminum content in the metal. A second factor is the presence of a ferrite phase in the steel, which depends on the ratio of the concentration of austenite-forming elements to the concentration of ferrite-forming elements [6].

High-strength austenitic stainless steel

Based on the studies of carbon and nitrogen effects on the electron structure, short-range atomic order, and thermodynamic stability of iron solid solutions, a physical concept for alloying steels with carbon and nitrogen is proposed. The concept is used for the design of a cost-effective austenitic corrosion-resistant steel of super-high strength and fracture toughness.

Control of the safe operating period of equipment and pipelines in reactor facilities which are in operation or under construction

The basic assumptions for ensuring safe operation of the components of nuclear facilities, based on controlling service lifetime characteristics, are presented. It is shown up for the Du300 RBMK-1000 pipes, which were made of corrosion-resistant austenitic steel, that this technology can be used effectively in operating power generating units. The complex of measures, developed and validated in the last few years, for monitoring and assessing the technical state of weld seams in pipelines, using the safety concepts “leak before rupture” and “prevention of failure” as well as methods for suppressing the proneness of weld seams to form cracks by the corrosion cracking method under stress, has made possible not only safe operation of Du300 pipelines but it is also a basis for optimizing the volumes and periodicity of operational nondestructive monitoring.

Structure and mechanical properties of a nonmagnetic high-nitrogen corrosion-resistant 05Kh22AG15N8M2F cast steel produced by high-gradient directional solidification

The structure and properties of an austenitic high-nitrogen corrosion-resistant 05Kh22AG15N8M2F cast steel produced by high-gradient directional solidification (HGDS) and equiaxed-grain solidification (ES) have been studied and compared. In contrast to ES, HGDS allows one to substantially decrease the degree of dendritic segregation of alloying elements, to eliminate porosity, and to increase the strength and plasticity of the steel.

Corrosion-resistant analogue of Hadfield steel

The concept of alloying austenitic steels with carbon+nitrogen is used for the development of a corrosion-resistant austenitic CrMn steel having an impact wear resistance close to that of the Hadfield steel. A higher stabilization of the austenitic phase by C+N, as compared to carbon or nitrogen alone, is substantiated by ab initio calculation of the electron structure, measurements of the concentration of free electrons and calculations of the phase equilibrium. Based on these results, the compositions (mass%) Cr18Mn18C0.34N0.61 and Cr18Mn18C0.49N0.58 were melted and tested along with Hadfield steel Mn12C1.2. Mechanical tests have shown that, as compared to the Hadfield steel, the experimental steels possess a higher strength, plasticity, hardness and the same resistance to impact wear. TEM studies of the surface layer after impact treatment revealed a mixture of the amorphous phase, nanocrystals and fine-twinned austenite. At the same time, using Mössbauer spectroscopy of conversion electrons, the ferromagnetic ordering was found in the surface layer of up to 10μm in depth, which is the sign of the strain-induced martensitic phase. The hypothesis of a transition from the low-spin to the high-spin state of the iron atoms within the thin twins in austenite was proposed in order to interpret the discrepancy between TEM and Mössbauer studies. Potentiodynamic measurements and immersion tests show that the CrMnCN steels possess a significantly higher pitting potential and resistance to general corrosion in comparison with Hadfield steel.

Исследование процесса получения высокопрочной проволоки из стали 12Х18Н10Т волочением с электролитно-плазменной обработкой поверхности

Purpose of the paper is to investigate technology of strain hardening of corrosion-resistant austenitic 12X18H10T steel by drawing method using electrolyte-plasma machining (EPM) as an auxiliary operation. Structure and properties of material surface layer after drawing have been examined. It has been ascertained that there are scores and micro-cracks on the material surface that make it difficult to carry out subsequent drawing drafts. In order to eliminate these drawbacks it is proposed to apply EPM between drawing stages. The developed drawing modes using EPM allow to reduce number of drafts while obtaining special hard- drawn wire and improve service life of the tool.