Austenitic-ferritic Steel Research Articles

Characteristics of the Side Surfaces and Edges of Welded Wire Meshes Used in the Construction of Welded Slotted Screens.

Welded resistance slotted screens, also known as slotted screens, are a special type of screen primarily used for the filtration and separation of liquids and dust. They are characterized by slots with parallel geometry and precisely defined sizes. The quality of the side surfaces and edges of welded wires determines the durability of the slotted screens made from them. This article presents the results of tests for four types of wires: two types of working profile wires made from austenitic-ferritic steel (duplex) and two types of supporting cross wires made from ferritic steel. The wire surfaces were characterized using a profilometer and atomic force microscopy. Basic roughness parameters Ra, Rz, and SAD (surface area difference) were determined. Surface observations of the working profiles were conducted using scanning electron microscopy. These studies allowed for the characterization of the working wire surfaces used in the production of slotted screens. At work, the results of surface roughness were analyzed based on three measurement methods for wires used in the production of welded slot screens. These results allowed for the identification of the most reliable method for characterizing the surface condition of such products.

ВЛИЯНИЕ ТЕРМИЧЕСКОГО ЦИКЛА СВАРКИ НА СТРУКТУРУ И СВОЙСТВА ФЕРРИТО-АУСТЕНИТНЫХ СТАЛЕЙ 08Х22Н6Т И 08Х18Г8Н2Т

The results of researches on influence of thermal cycle of welding on structure and phase transformations in metal of heat-affected zone of welded joints of 08Cr22Ni6Ti and 08Cr18Mn8Ni2Ti steels are presented. It is shown, that at automatic submerged-arc welding of welded joints of ferrite-austenite steels the fall of plasticity is observed. It is established that the impact toughness of overheat section of heat affected zone at normal temperature has high values of impact toughness, and at test temperature of minus 20 oC values of impact toughness below 0.4 MJ/m2 were obtained.

A microstructure-based three-scale homogenization model for predicting the elasto-viscoplastic behavior of duplex stainless steels

A new microstructure-informed three-scale homogenization scheme for elasto-viscoplastic heterogeneous materials is developed. It is applied to predict the mechanical behavior of cast duplex austenitic-ferritic (AF) steels, which are widely used in primary loop of pressurized water reactors (PWR). At the first scale (microscale), the elasto-viscoplastic behavior of single crystals for both phases is modeled using linear elasticity and a viscoplastic crystal plasticity model. An “affine” type formulation based on the first moments of stresses is applied to the inelastic non-linear part of the deformation. Then, at the second scale (mesoscale), an EBSD-informed two-phase austenite/ferrite laminate structure (LS) model is developed with {110}-type habit planes (HP) in ferrite and a Kurdjumov-Sachs orientation relationship (KS-OR) between both phases. At the third scale (macroscale), the model considers a single ferritic primary grain as an aggregate of spherical two-phase laminate structure domains corresponding to the 24 KS-OR variants. The elasto-viscoplastic self-consistent scheme (EVPSC) is used through the Translated Fields (TF) method to obtain the effective behavior at this scale. The TF-EVPSC scheme is also used for an ensemble of primary ferritic grains to identify materials parameters from experimental tensile curves corresponding to as received and aged specimen. From EBSD measurements, the crystallographic data are thoroughly analyzed to physically feed the three-scale model. The results are discussed in terms of stress/strain responses in ferrite and austenite, which are correlated to the different KS-OR variants and HP orientations. The effect of primary ferritic grain crystallographic orientation and aging is also studied regarding monotonic and cyclic tests to study the possible origins of backstress in this material.

LABORATORY AND OPERATING TESTING OF HIGH-ALLOY STEEL PIPES MADE BY THE LATEST TECHNOLOGIES

The purpose of the research: evaluation of the quality and durability for pipes made of high-alloyed austenitic and ferritic-austenitic steels, which are manufactured at PJSC "CENTRAVIS PRODUCTION UKRAINE" using the latest technologies, by conducting complex laboratory studies and long-term operational tests at chemical industry enterprises. Materials and methods: the research materials were experimental pipes made of high-alloyed austenitic and ferritic-austenitic chromium-nickel-molybdenum steels of the new generation, manufactured using the latest technologies. The microstructure of the pipes was investigated by metallography and electron microscopy using developed and improved methods. Corrosive researches in laboratory terms included a test on firmness against the local types of corrosion inherent in high-alloy steels: intergranular corrosion (IGC), pitting corrosion (PC), corrosion cracking (CC) and sulfide stress corrosion cracking (SSCC). The mechanical properties of the pipes were determined by tensile and impact bending tests. Long-term operational tests of pipes were carried out in conditions of industrial production at chemical industry enterprises in apparatus for the urea and caustic soda production. Research results: A high content of special low-energy grain boundaries in the theory of coincident nodes’ lattices (SG CSL) was established in the structure of pipes manufactured according to the latest technologies (≥ 75 %); high resistance of pipes against various types of the most dangerous local corrosion compared to existing analogues, a high level of mechanical properties, as well as high corrosion resistance during long-term operational tests in environments at chemical industry enterprises. The implementation of the obtained results will contribute to increasing the efficiency of production and operation for highly alloyed steel pipes in demand on the world market and increasing the competitiveness of domestically produced pipes on the European and world markets.

­Microstructural Evolution and Mechanical Properties of Functionally Graded Austenitic–Ferritic Steel Produced Via Directed Energy Deposition

­Microstructural Evolution and Mechanical Properties of Functionally Graded Austenitic–Ferritic Steel Produced Via Directed Energy Deposition

SMOOTH AND REDUCED OIL AND GAS PIPES WITH INCREASED CORROSION RESISTANCE

Formulation of the problem. Corrosion of pipes used in the oil and gas industry leads to significant economic losses, therefore, increasing their corrosion resistance and durability is an urgent task. Purpose: generalization of results of developments of technologies of manufacturing and research of qualitative characteristics of oil and gas pipelines (smooth) and pump-compressor (threaded) pipes of the increased and high corrosion resistance and giving recommendations on their application in oil and gas industry in environments of various corrosion aggressiveness. Methodology. The microstructure of tubular steels and protective coatings was studied by light metallography and electron microscopy. Complex corrosion studies included laboratory tests of samples in model chloride and hydrogen sulfide-containing media, the resistance to sulfide corrosion cracking under stress (SCCS) and hydrogen cracking (НС) according to the methods of NACE TM 0177 and NACE TM 0284 as well as operational tests at the oil fields of Ukraine. Mechanical properties for stretching and impact bending of samples by standard methods. Results. The results of the development of production technologies and the study of the qualitative characteristics of oil and gas pipelines and tubing with increased and high corrosion resistance in aggressive oil and gas production environments are summarized. The influence of the chemical composition of steels and protective coatings, as well as pipe manufacturing technologies on their microstructure, corrosion resistance in various media, and mechanical properties is shown. Scientific novelty. For the first time, the presence of special low-energy boundaries in the ferrite of low-alloy ferrite-pearlite and high-alloy ferritic-austenitic steels was established, their number and energy level were estimated. The high operational reliability of threaded pipes with a protective coating is substantiated. Practical value. The results of the work and recommendations for the rational use of oil and gas pipes with increased corrosion resistance can be used to increase the economic efficiency of production in the oil and gas industry.

Effect of alloying elements on structure, metastability and properties of Fe-Cr-Mn (Ni-free) corrosion-resistant austenitic-ferritic steels

Investigated was chromium influence within 15-21.4 wt.% and manganese influence within 8-11.4 wt.% upon phase transformations, formation of structure and mechanical properties of corrosion resistant nickel-free (Fe-Cr-Mn) steels of austenite-ferrite structural class. It was found out that by the variation of chromium and manganese content it was possible to modify efficiently the content of ferrite and austenite in the structure, the degree of deformation metastability of austenite and control the mechanical properties of steels. An improved complex of strength, plasticity properties and impact toughness is reached at optimal content of alloying elements (Cr, Mn) in new nickel-free steels, it can be explained by positive impact of deformation induced martensite γ→α’ transformation at testing during their formation.

Slurry Erosion Behavior of Cast 25 Cr Austenitic-Ferritic Steel with Niobium Addition for Subsea Pipelines

Austenitic-ferritic steel, as suggested by its name, has an equal fraction of austenite and ferrite phases, also known as duplex stainless steels (DSS), are one of the highly used materials for subsea pipelines applications. The presence of slurries is inevitable in subsea pipelines. This technical work elucidates the slurry erosive wear behavior of duplex stainless steel and the impact of the addition of niobium (Nb) on the phenomena. Vacuum induction melting was used to produce duplex stainless steel, and its Nb added casts. The aim of the work is to compare both castings' for erosive wear behavior using a slurry jet erosion tester. Computational thermodynamic software Thermo-calc was used to investigate the presence of numerous phases in the system. X-ray diffraction (XRD) has confirmed the formation of niobium carbide in the steel, indicated by Thermo-calc. The effect of slurry velocity (30, 40, and 50 m/s) and impingement angle of slurry (30°, 45°, and 90°) on wear characteristics of these castings were analyzed using volume loss measurements, optical profilometry, and scanning electron microscopy (SEM). The erosion rate of both the materials increased with increasing velocity, whereas erosion was more at shallow angles of impact and increased significantly at the slurry jet's normal incidence. Refinement of austenitic grains in the ferritic pool hints at an increase in heterogeneous nucleation in Nb-doped samples; at the same time, the samples have shown increased hardness and superior erosion resistance against the slurry jet impact.

Study of the durability of ferritic - austenitic steel samples after cyclical fatigue impact

The purpose of this article is to investigate the fatigue strength of corrosion resistant ferritic austenitic steels used in marine equipment. Two groups of sheet steel samples were prepared: the first group were reference parts and the second group of samples were welded. The fatigue tests were performed with specially developed vibrating equipment. The destroyed surfaces were examined by optical microscopy, and the phase composition by X-ray diffraction analysis. Fatigue strength was evaluated by the number of cycles needed for a crack at a certain alternating load. Fatigue tests show how multi-cyclical fatigue affects the formation and development of a fatigue crack, and metallographic and X-ray diffraction analysis shows the phase changes occurring in the structure of SAF 2507 steel.

Increasing service life and reliability of centrifugal separators by applying new materials

This paper analyzes stress-strain behavior and bearing capacity of a rotor in a self-discharging separator, diameter 500 mm, manufactured from parts that underwent a hardening cycle. Three variants of the rotor were studied having the same design but differing in body materials: austenitic steels 06X17H13M3-BД, ALIII-23-43-02 and austenitic-ferritic steel 10X26H5M, ALIII-23-24. Research results allow recommending austenitic-ferritic steel for manufacture of separator rotors, as they provide necessary margin of safety for the design.

Tensile behavior of ultrafine-grained low carbon medium manganese steel by intercritical annealing treatment

The intercritical annealing treatment at 650 and 700 °C results in two ultrafine-grained (UFG) dual-phase ferrite–austenite steels. The two steels exhibit different and special discontinuous yielding and pronounced Luders-like strain phenomena with large yielding strain which are related to their retained γ-austenite (RA) volume fractions and RA stabilities. The steel annealed at 650 °C shows an absent or very small strain hardening, while the steel annealed at 700 °C shows an obvious strain hardening upward curvature with increasing strain. The results show that before and during straining, the steel annealed at 650 °C exhibits a mixture of equiaxed and elongated UFG α-ferrite and austenite phases; however, the steel annealed at 700 °C exhibits only elongated UFG α and γ phases. It was found that most of the γ-austenite to α′-martensite transformation occurred at the initial deformation stage and very small or almost no transformation occurred afterward. This demonstrates that the strain-induced martensite (SIM) transformation (γ–α′) or transformation-induced plasticity (TRIP) effect dominates only at the initial deformation stage. RA remained stable, and no TRIP effect was observed at the final deformation stage. The load–unload–reload test was performed to evaluate the back stress (σb) hardening effect. It is believed that the pronounced strain hardening behavior at the later deformation stage is mainly associated with σb enhancement induced by the strain partitioning between the soft and hard phases due to SIM transformation during tensile deformation.

Influence of Copper Addition on Sigma Phase Precipitation during Hot Deformation of Duplex Steel.

The paper presents an experimental study on microstructure changes in duplex steel after hot deformation. Duplex steels and cast steels are characterized by a multiphase microstructure. They are relatively new materials with great contributions to the many fields of industries. Due to the fact of deforming two different phase austenite and ferrite those materials have a complex plasticity. This work is a continuation and complementation of previous works and is a significant supplement to information presented in them. The article concerns precipitation phenomena and changes in the microstructure of two grades of ferritic-austenitic steels: X2CrNiMoN25-7-4 and X2CrNiMoCuN25-6-3. Those steels have a very similar chemical composition, differing by only 2.5% copper content. An important aspect presented in the work is we observed that adding 2.5% copper prevented precipitation of the destructive sigma phase during the hot deformation.

The Study of Structure Formation Evolution at High Pressure with a Shear in a Corrosion-Resistant Austenitic-Ferritic Steel 03Kh14N10K5M2YuT with Different Initial States

The article presents results of studies of phase transformations and structure formation that form the necessary complex of physical and mechanical properties of austenitic-ferritic steel with a structural ratio of 50:50. The structure formation at high pressure with a shear of steel 03Kh14N10K5M2YuT with different initial states is studied. After the action of intense plastic deformations, a submicrocrystalline structure arises. This causes interest in these deformations.

PROSPECTS OF APPLICATION OF TUBES MADE OF DUPLEX STEELS OF A NEW GENERATION IN THE HEAT EXCHANGING EQUIPMENT OF NUCLEAR POWER PLANTS

Prospects of using tubes produced by Centravis Production Ukraine JSC of ferritic-austenitic (duplex) steels of a new generation according to the developed innovative technology in the heat exchanging equipment of nuclear power plants (NPP) were scientifically substantiated based on analysis of scientific and technical literature and the results obtained in comprehensive studies. Comparative corrosion studies of the tubes made of austenitic Cr-Ni and Cr-Ni-Mo steels and 02Cr22Ni5NМo3 (UNS S 31803) duplex steel have shown a substantially improved resistance of the latter to intercrystalline, pit and crevice corrosion, corrosion cracking and erosion. Presence of special low-energy γ-γ, α-α grain boundaries and α-γ interphase boundaries characterized by an increased corrosion resistance and a contribution to the growth of steel durability as a whole was found for the first time in the structure of ferritic-austenitic steels.

STUDY OF THE CORROSION RESISTANCE OF STRUCTURAL MATERIALS WORKING IN CONDITIONS OF SULPHATE SOLUTIONS OF COKE-CHEMICAL PRODUCTION

The article presents the results of the study of the corrosion resistance of austenitic and austenitic-ferritic steels in the environments of the sulfate department of PJSC “Zaporozhkoks”. Now in the coking industry, the problem of corrosion protection of welded joints in the equipment of sulfate sections is most acute. Aggressive medium sulfate compartments are mother liquors, which include: sulfuric acid, ammonium sulfate, chlorides. In the mother solution with the acidity of 3-6%, the following ions are present, g/l: sulfates – 400-450; chlorides – 0.2-2.8; cyanides – 0.065-0.16; rodanid – 0.1-1.2; total iron – 0,002-0,05; pyridine bases – 10-20. The presence of pyridine bases in the working solutions of the sulfate separation somewhat reduces the aggressiveness of the solutions. However, at a concentration of 10-20 g/l in 6-10% H2SO4 at 60°C, their protective effect does not exceed 50-60%. According to researchers, the content in process solutions of mineral salts and in coke oven gas with the almost complete absence of O2 makes it difficult to form protective passive films on the surface of nickel-chromium steels, leading to the occurrence of local types of corrosion damage (ulcers and pitting). In addition, the occurrence of corrosion processes stimulates increased temperature and velocity of movement of the solutions.It has been established that the corrosion resistance of materials depends on the acidity of the mother liquor and when applying strong sulfuric acid in these zones, it is necessary to use lined materials, enameled pipes or steels of alloy type 943 (0Х23Н28М3Д3Т) capable of withstanding increased acidity (10-15%) of the mother liquor. Avesta 254 SMO stainless austenitic steel containing slightly more than 6% molybdenum (Mo) – (АКС 254 SMO (X20Н18AM6D) shows the highest corrosion resistance in sulphate separation environments.

Methods and Devices of Control of Phase Composition, Electrical and Magnetic Properties of Chromium-Nickel Steels

Данная работа посвящена вопросам фазового анализа и контроля содержания фазовых составляющих в коррозионно-стойких хромоникелевых сталях аустенитного и аустенитно-ферритного классов, широко используемых в различных отраслях современной промышленности и машиностроения. В первой части работы приведены результаты исследований связи между электрическими свойствами и фазовым составом образцов исследуемых сталей в исходном состоянии и после их пластической деформации. С помощью сканирующего зондового микроскопа методами атомно-силовой и электросиловой (метод зонда Кельвина) микроскопии получены изображения поверхности исследуемых образцов. Анализ данных изображений позволяет определить изменения фазового состава аустенитных и аустенитно-ферритных сталей после пластической деформации. Также установлено, что распад фазы аустенита вследствие деформационных воздействий и последующее образование фазы мартенсита деформации приводит к изменению удельного электрического сопротивления образцов, по величине которого можно судить о количестве образующегося мартенсита деформации. Во второй части статьи представлены новые приборные разработки, предназначенные для экспрессного (в том числе неразрушающего) контроля электрических и магнитных свойств сталей на основе аустенита. Своевременный и достоверный контроль этих свойств необходим для проведения качественной и количественной оценки фазового состава изделий как после их изготовления, так и во время эксплуатации.

New approach to development and manufacturing technologies of duplex steel

We conducted a brief review of current production and application of duplex and super duplex steels for manufacture of equipment exposed to the hazard of sulphide stress-corrosion cracking, sea water and other corrosive environment. The super duplex steel with enhanced corrosion-mechanical characteristics in comparison with the known steels of austenitic-ferritic class was developed. Based on the concepts of formation of a special structure of two-phase austenitic-ferritic steels in the process of crystallization, the possibilities of compositional, technological, thermal and special impact techniques are considered and advanced ways of controlling physical, chemical, structural homogeneity and properties of super duplex steels are developed. Electroslag remelting with the application of low-frequency alternating current provides effective control over the length of the two-phase area, the size of the primary dendrites of the austenitic and ferritic phases, the average distance between their axes, the parameters of the crystallizing cell, the development of liquation phenomena and the size of the growing non-metallic phases. Within framework of the proposed approach, the thermodynamic and kinetic conditions for the formation and growth of hardening phases are assessed, a new composition and a complex technology for the manufacture of corrosion-resistant super duplex steels for gas and oil production equipment has been developed. Thermodynamically stable, having sizes of 30-300 nm, niobium nitrides and carbonitrides are located inside the grains of the ferritic phase. At the same time, the sigma phase and chromium carbide precipitates at the intergrain boundaries are not observed. The results of the determination of mechanical and corrosion properties in accordance with the NACE TM 0177 standard (method A), tests of corrosion witness-samples in field conditions demonstrate the advantages and prospects of using new super duplex steel for the manufacture of oil and gas production equipment operating in an environment with high H2S content and CO2 under significant mechanical loads, without the risk of brittle fracture.

Effect of interlayers and scanning strategies on through-thickness residual stress distributions in additive manufactured ferritic-austenitic steel structure

A total of five different types of specimens were additively manufactured by directed energy deposition (DED) process. The specimens have a functionally graded material (FGM) structure, which has been deposited with variation of chemical composition of ferritic and austenitic steel powders in each interlayer on a steel substrate. Residual stress distributions were experimentally measured through the thickness of the specimens by the contour method, neutron diffraction, and deep/incremental center hole drilling. Neutron diffraction provided three orthogonal stress components in each FGM part and the results were compared to the two-dimensional stress map obtained by the contour method and confirmed its criticalities from the highly spatial resolved depth profile by the hole drilling method. Significant variations from tension to compression (up to 950 MPa) in the sine-wave stress profile were alleviated to about 430 MPa when the FGM were deposited with orthogonal or island DED scanning strategies with interlayers. Gradual changes (16.3–12.1 × 10−6/°C) of the thermal expansion coefficient were measured among the inserted DED FGM parts and grain structure with defects along the interface was three dimensionally examined by neutron tomography.

Effect of the Heat Treatment on the Corrosion Resistance of Duplex Stainless Steels

Duplex stainless steels (DSS) are biphasic austenitic-ferritic steels in which the best combination of mechanical and corrosion resistance properties is achieved for an almost equal volume fraction of the phases. In this work, the effect of secondary phases precipitation on the corrosion resistance of four DSS grades (2101, 2304, 2205 and 2507), after isothermal aging in the critical temperature range 750-900 °C, was studied. The corrosion resistance was investigated by potentiodynamic polarization tests in both 0.6 M NaCl solution (pH 7) and in an acid chlorinated solution (pH 3) at room temperature. Moreover, the critical pitting temperature was determined according to ASTM G150. The results showed that secondary phases precipitation mainly influenced the resistance to corrosion of the lean duplex grades.

ANALYSIS OF THE STRUCTURE AND TRIBOLOGICAL PROPERTIES OF SINTERED STAINLESS STEELS

Increasing development of civilization encourages the search for modern engineering materials. At present, very interesting and promising materials are sintered stainless steels that are considered to be the most rapidly developing group of materials, which is related to the demand for materials with good mechanical properties and high resistance to corrosive agents. Taking into account sintered austenitic–ferritic steels, it is possible to obtain a structure with different proportions of the two basic structural components. The main problem limiting the applicability of sintered stainless steels is porosity, which deteriorates not only the strength properties but also the usability as compared to their cast and materials after plastic working. Extremely valuable factors influencing tribological properties are the chemical composition, proportion of individual powders and sintering conditions. In this study, the microstructure and tribological properties of sintered stainless steels obtained by sintering in different proportions of 316L austenitic steel and 409L ferritic steel were compared. The abrasion wear resistance test for individual sintered steels was performed by pin-on-disc method.