Corrosion Resistance Of Austenitic Steels Research Articles

PREDICTION OF ELECTROCHEMICAL PROCESSES OF LOCAL DISSOLUTION OF STAINLESS STEELS. PART 1. SPECTRAL –FREQUENCY ANALYSIS OF POTENTIAL FLUCTUATIONS

The propagation of localized corrosion of stainless steels was investigated by spectral frequency analysis (HPA) of potential fluctuations in the modes of stationary and cyclic galvanostatic polarization. Corrosion-resistant austenitic and austenitic-ferritic chromium-nickel steels were studied: 12X18N10T, 10X17N13M2T, 08X22N6T, resistant to pitting corrosion, in an aqueous solution of 0.1 M NaCl with a cyanide-containing complexing agent, a corrosion stimulator - 0.01 g/l (K3[Fe(CN)6]). The studies were carried out in the range of low densities (0.5–10 µA /cm2) due to the small values of the limiting diffusion current density in oxygen. To find the time of the origin of macropittings, it is proposed to use the NAV of chronopotentiograms with their subsequent statistical processing (Fourier transform). It has been established that fluctuations in the boundary polarization regime are characteristic of the process of the origin, development and passivation of macropittings. In the mode of stationary galvanostatic polarization, frequency characteristics were studied in the range of 1.0 ± 0.5 µA/cm2. When analyzing spectral density graphs, it was found that the dominant frequency characterizes the time of formation of the macropitting, and the sections of the chronopotentiogram should be divided into sections with a duration of no more than 50-100 s. In non-stationary conditions of galvanostatic polarization in the range of 1.0-10 µA/cm2 in a cyclic mode, it was found that the processes of nucleation and passivation of macropittings can be traced with a changing value of the polarizing current. Based on the frequency range of chronopotentiograms, it was found that the average macropitting lifetime is 250-300 s (frequency range 0.033 - 0.004 Hz). The dominant frequencies are determined to identify the characteristic dependencies of the envelopes along the upper (fhg) and lower (fhg) boundaries of the potential change, based on them, an algorithm is proposed for selecting the values of the parameters of the prediction mode of the formation of macropitting processes.

Повышение качества диффузионного слоя ввысоколегированных сталях после газоциклических процессов азотирования

The study results of gas-cyclic nitriding of corrosion-resistant austenitic and martensitic steels with alternating atmospheres of ammonia and air in the mode of an isothermal process and a stepwise process with a final stage with reduced activity of the saturating atmosphere are discussed. The factors of improving the quality of the diffusion layer were determined, contributing to increased wear resistance and maximum preservation of steel resistance to shock loads due to reduced stresses at the boundary of the layer with the matrix.

Enhancing low-speed WEDM machining capabilities on Nitronic-50 with a constant frequency ultrasonic hybrid method

Nitronic-50 stainless steel is a high-strength and corrosion-resistant austenitic premium steel. It requires improved surface characteristics due to its wide use in various applications like fasteners, marine hardware, hydroelectric-power turbines, pressure vessels, etc. This work focuses on machining hard-to-machine Nitronic-50 steel is unconventionally machined using constant frequency ultrasonic-aided low-speed wire electrical discharge machining (USV-LS-WEDM) to enhance its machined surface integrity. This method achieves effective results when cutting high-strength materials with intricate shapes. Material removal rate (MRR) and surface roughness (Ra) were measured by considering inputs such as servo voltage (SV), pulse off time ( Toff), pulse on time ( Ton) and current (I) with an ultrasonic-vibration range of 20,000 Hz. The appropriate selection and usage of LS-WEDM parameters is a challenging process and is done with parametric analysis. The MRR of Nitronic-50 was enhanced with an increase in Ton and I along with a reduction in Toff and SV. Surface roughness (Ra) decreased with a gradual reduction in Ton, I, and an increase in SV. The USV-WEDM was compared with a stand-alone WEDM indicating that the MRR for USV-WEDM was improved by 12% and the Ra was decreased by 9% due to effective distribution of spark discharges, which increased material erosion and redistribution of molten metal characteristics. Machining quality for hard-to-machine Nitronic-50 steel was certainly enhanced via hybrid ultrasonic vibration with the existing LS-WEDM.

Investigation of the change in wettability properties and corrosion behavior of AISI 304 after laser surface texturing

Stainless steel is a widely used material in industry, architecture, and medical instruments. However, after various thermal processing of stainless steels, chromium carbides can be formed, which locally depletes the chromium available to form a passive film and reduces the corrosion performance. Laser surface treatment can change the surface chemistry of the steel and improve some electrochemical characteristics. However, these characteristics are influenced by the laser power, pulse width, distance between the lines, scanning speed, etc., which all change the surface chemistry and characteristics of laser surface texturing. Simultaneously, the ability to repel liquids that cause corrosion actions could combine to enhance corrosion performance. Since the wettability of a solid surface depends both on its topography and chemical nature, the micro structuring of an austenitic steel surface is an effective way of fabricating hydrophobic or super hydrophobic corrosion-resistant surfaces. For this reason, this study discusses the effect of laser power in the impact zone and the distance between raster lines on the microstructure, wettability, and corrosion resistance of austenitic steel (AISI 304) when exposed to nanosecond fiber laser radiation. The results indicate that parameter-controlled micro structuring can be used to form both hydrophilic and hydrophobic surfaces with different electrochemical performances.

The Influence of Heat Treatments in Corrosion Resistance of Austenitic Steels

Abstract This paper presents the results of laboratory research on the influence of heat treatment on the corrosion resistance of austenitic steels (Cr-Ni, Cr, Mn, Cr-Mn-Ni), research that may extend under certain conditions and ferrites steels and semi-ferrites chrome steels.This type of intercrystalline corrosion was observed in other alloy systems due to media containing chloride ions.The experimental results consist in comparing structural changes and corrosion rate for different types of austenitic steels that were made experimental research.

Влияние фрикционной обработки и жидкостной цементации на сопротивление общей коррозии хромоникелевых аустенитных сталей

Currently, to increase the hardness, strength and wear resistance of thermally non-hardenable austenitic chromium-nickel steels, such methods as frictional treatment with a sliding indenter and liquid carburizing have been used. However, along with an effective increase in mechanical characteristics, the application of these types of treatment may be accompanied by a decrease in the corrosion resistance of austenitic steels. Therefore, it is reasonable to study the influence of frictional treatment and liquid carburizing on the general corrosion resistance of Cr–Ni austenitic steels. In this work, the surface microhardness of the 12Cr18Ni10Ti and AISI 321 steels was determined using the recovered indentation method after electropolishing, mechanical grinding, frictional treatment, and liquid carburizing at a temperature of 780 °C. Using scanning electron microscopy and optical profilometry, the authors studied steel surfaces subjected to the specified types of treatment and determined their roughness. The corrosion resistance of steel was studied by testing for general corrosion using the gravimetric method. When testing for general corrosion, it was found that hardening (up to 710 HV 0.025) frictional treatment leads to an increase in the corrosion rate of the 12Cr18Ni10Ti austenitic steel compared to the electropolished state (from km=0.35 g/(m2·h) to km=0.53–0.54 g/(m2·h)). The corrosion rate of the ground steel is km=0.58 g/(m2∙h), while mechanical grinding does not provide a significant increase in the microhardness of the steel under study (from 220 to 240 HV 0.025). It is shown that the corrosion behavior of 12Cr18Ni10Ti steel subjected to various types of treatment is determined by the following factors: the presence/absence of strain-induced α'-martensite in the structure, the quality of the formed surface and, apparently, the dispersion of the formed structure. Liquid carburizing of the AISI 321 austenitic steel leads simultaneously to an increase in its microhardness to 890 HV 0.025 and a certain increase in corrosion resistance compared to fine mechanical grinding. This is related to the fact that carbon embedding atoms stabilize the electronic structure of iron (austenite and martensite), thereby increasing its corrosion resistance.

Влияние термической обработки и содержания вольфрама на структуру, фазовый состав и коррозионную стойкость высокоэнтропийных сплавов системы Fe – Cr – Ni – Mo – W

The effect of heat treatment (diffusion annealing, quenching, low-temperature and high-temperature tempering) on the structure, phase composition and corrosion resistance of high-entropy 35 Fe – 30 Cr – 20 Ni – 10 Mo – 5 W and 30 Fe – 30 Cr – 20 Ni – 10 Mo – 10 W alloys has been studied. High-entropy alloys of the Fe – Cr – Ni – Mo – W system with different concentrations of tungsten were obtained by sintering mechanically alloyed powders in a vacuum furnace. It was revealed that the total and pitting resistance of the obtained high-entropy alloys to aqueous solutions of NaCl is higher than that of industrially produced austenitic corrosion-resistant steel 316 L used in the oil and gas industry.

Strength and fracture mechanism of nanostructured metal materials for medical applications

In this paper we study titanium Grade4, magnesium alloy Mg-Zn-Ca, corrosion-resistant austenitic steel 08Kh18N9 for medical applications. The mechanical properties in tension, torsional strength, and cyclic crack resistance under different types of loading of steels are investigated. The results are compared for two states of steels: the initial coarse-grained (CG) state and ultrafine-grained (UFG) state produced by severe plastic deformation processing via equal-cannel angular pressing (ECAP). It is demonstrated that the ultrafine-grained materials have essentially better strength and lower sensitivity to cyclic overloads. It is concluded that all the studied UFG materials are more promising compared to CG ones for the manufacture of medical devices for various purposes, which experience various static and cyclic loads during operation.

Simulation of the Dynamic Recrystallization of Austenitic Corrosion-Resistant Steel during the Formation of a Complex Section by High-Temperature Thermomechanical Treatment

Simulation of the Dynamic Recrystallization of Austenitic Corrosion-Resistant Steel during the Formation of a Complex Section by High-Temperature Thermomechanical Treatment

Effect of Thermo-Physical Properties of the Tool Materials on the Electro-Discharge Machining Performance of Ti-6Al-4V and SS316 Work Piece Materials

Electro-discharge machining (EDM) is a useful non-conventional machining operation frequently applied to make different complex geometries in any conducting material. The objectives of the present paper are to study the effect of a variation of thermo-physical properties (TPP) of three different tool materials on EDM performances. The different performances compared in this paper are: material removal rate (MRR), tool-wear rate (TWR), surface roughness (SR), radial overcut (ROC), surface-crack density (SCD) and surface hardness. Two of the most widely used work piece materials, such as corrosion-resistant austenitic stainless steel (SS316) and high strength corrosion-resistance titanium alloy (Ti-6Al-4V), are machined with the help of three different tools by varying input current and maintaining constant pulse-on time, pulse-off time and flushing pressure. Microstructural studies of the tool tip surface after machining have also been carried out. It is found that among these three tool materials, the copper tool showed the best machining performance with respect to material removal rate, radial overcut, surface finish and surface-crack density. This work will help industry personnel to choose a suitable tool for a specific work piece material.

Efficient Multi-Material and High Deposition Coating including Additive Manufacturing by Tandem Plasma Transferred Arc Welding for Functionally Graded Structures

Market demands coating processes with high-performance, high reliability, high flexibility for processing of complex geometries and multi-material depositions, as well as increased deposition rates. The systematic coupling of two plasma transferred arc welding systems that interact in the same melt pool to form a tandem Plasma Transferred Arc (PTA) system accomplishes these tasks. Previous research has shown that the deposition rate with the tandem PTA method reaches 240 percent when comparing to the conventional single torch PTA method. Within one layer, up to four different powders and powder fractions can be combined at the same time. This allows for the creation of multi-material coatings that are suitable for sustaining high mechanical loads and wear- and temperature-resistant surfaces by use of tungsten carbides (WC). This study examines and analyzes defined functionally graded structures made from super duplex steel 1.4410 and corrosion resistant austenitic steel 1.4404. The mechanical-chemical properties of the tandem PTA system can be precisely controlled by changing the powder feeding positions. Furthermore, an additively manufactured specimen from previous studies is examined and evaluated. A direct comparison with conventional single torch PTA was performed to demonstrate the benefits of the tandem PTA-process.

К ВОПРОСУ О МОДЕЛИРОВАНИИ ОПЕРЕЖАЮЩЕЙ ТРЕЩИНЫ ПРИ ВИБРОТОЧЕНИИ

The work objective is to consider the possibility of creating conditions for appearing a leading crack by adjusting the modes of vibratory turning, regardless of the properties of the machined materials.
 The problem to which the paper is devoted. The paper is devoted to modeling vibration turning for developing stresses in the machined material to create conditions for appearing and maintaining a leading crack and in the cutting area during vibratory turning, the search for optimal modes to create conditions for its existence. 
 Research methods. Modeling was carried out by the finite element method in Deform software application. The starting point for modeling was the results of field experiments on vibratory turning of corrosion-resistant austenitic steel 12X18H10T.
 The novelty of the work lies in the application of the finite element method to define the modes of vibratory turning in order to create a certain area of internal stresses in the processed material in a given direction for forming a leading crack. 
 Study results. As a result of modeling, optimal turning modes are defined during vibration cutting, which will create conditions for appearing a leading crack and exhausting the plasticity margin of the machined material. 
 Conclusions: The creation of a leading crack and the exhaustion of the plasticity margin of the machined material contributes to the chip control, the formation of microgeometry of the machined surface during vibratory turning, the reduction of cutting forces when turning hard-to-machine materials and built-up surfaces.

Влияние нормальной силы на сглаживание и упрочнение поверхностного слоя стали 03Х16Н15М3Т1 при сухом алмазном выглаживании сферическим индентором

Introduction. Sliding burnishing minimizes roughness and hardens of the steel surface. Quality of the formed surface and strength characteristics of the surface layer are determined by the burnishing speed, force and feed. Due to the danger of the surface micro-destruction during burnishing, the problem of selecting the favorable value of the normal force at a given feed arises. The current investigation aims to study the effect of normal force during dry diamond burnishing with a spherical indenter on smoothing the surface microprofile and strain hardening of the 03Cr16Ni15Mo3Ti1 austenitic steel surface layer. Research methods. Profilometry, scanning electron microscopy (SEM), microdurometry are used. Results and discussion. As the result of dry burnishing of deformation-stable austenitic steel 03Cr16Ni15Mo3Ti1 with a spherical indenter with a 2 mm radius made of natural diamond at a sliding speed of 10 m/min and feed rate of 0.025 mm/rev, it is found that in the investigated variation range of the burnishing normal force (100...200 N) the value of the smoothing coefficient of the initial steel surface microprofile after finish turning is 79...90 %, the greatest smoothing with a decrease in the average roughness parameter Ra from 1.0 to 0.1 µm is achieved at a force of 150 N; during diamond burnishing the initial (after finish turning) surface is hardened by 15...43 % (up to 382...444 HV), as the burnishing force raises from 100 to 175 N, a non-monotonic increase of the average microhardness from 409 to 444 HV 0.05 takes place; burnishing with a load of 175 N forms a gradient-hardened layer with a thickness of 300...350 μm with the appearance of individual microfractures in the form of beadings and micro-cracks on the surface, the maximum hardening is caused by the formation of a highly dispersed surface layer of 30...40 μm thick with a structure of highly dispersed austenite and the corresponding activation of grain-boundary and dislocation strengthening mechanisms. The results can be used when selecting the diamond burnishing parameters of parts made of corrosion-resistant austenitic steels according to the criteria for obtaining low surface roughness without significant microfractures and effective strain hardening of the surface layer.

Cast High-Strength Wear- and Corrosion-Resistant Austenitic Nitrogen Steel for Fittings Used in Shipbuilding

The paper presents the results of studies of a new cast high-strength austenitic corrosion-resistant steel, which can be successfully used in shipbuilding for the manufacture of fittings. The authors included data on the structural-phase state of steel, the results of evaluating the mechanical properties, wear and corrosion resistance of the metal of castings in the cast and heat-treated state. The mechanical properties of steel are considered in detail in a wide temperature range. The impact strength was considered at low temperatures and static strength at 20 to 350 ° C. It is shown that steel has higher mechanical and corrosive properties in a wide temperature range than those of traditional stainless steels. The corrosion resistance of steel is considered. This is intergranular and pitting corrosion; the main types of corrosion are peculiar for shipbuilding. It has been shown that cast steel is superior to traditional corrosion-resistant steels in pitting corrosion resistance estimated by the pitting coefficient PREN and the critical temperature of pitting. The new cast steel has the same wear resistance as Hadfield steel.

On the formation of recrystallization nuclei in austenitic nitrogencontaining steel under hot deformation

This article presents the results of studying the structure of high-strength corrosion-resistant austenitic nitrogen-containing steel formed as a result of hot deformation. It was found that, depending on the temperature, degree and rate of deformation, the mechanism of formation of nuclei of dynamic recrystallization changes. At temperatures above 1100°C, nuclei are formed due to bending and subsequent migration of grain boundaries; however, with a decrease in temperature and an increase in the degree and rate of deformation, subgrains become centers of recrystallization near the initial boundaries.

Влияние термической обработки на свойства коррозионностойкой стали, легированной серебром и титаном

The field of application of corrosion-resistant austenitic steel is wide due to its resistance to corrosion and oxidation, durability, high strength and ductility. Austenitic corrosion-resistant steel is of particular importance for medicine. Medical instruments and products are made from it. However, the environment is very corrosive to metals and can lead to protein adsorption, biofilm formation (attachment of microorganisms/bacteria to the surface of the material), and corrosion or itself become a source of bacterial contamination. Recent studies have shown that the addition of Ag and Ti to corrosion-resistant steels can impart antibacterial properties to them without the need for surface modification. The article is devoted to the study of the structure and mechanical properties of a new antibacterial corrosion-resistant steel. The structure was studied by light optical microscopy and X-ray diffractometry. The mechanical properties were studied by stretching the samples on a tensile testing machine. The effect of homogenizing annealing and ingot rolling on the structure of corrosion-resistant steel is shown. According to the test results, it has been established that heat treatment of steel makes it possible to increase the ductility of steel. After rolling, the plates have a fine-grained structure. Normalization at 900 °C and 1000 °C relieves internal stresses and reduces the proportion of ferrite in the structure.

Durability Aspects of Chloride-Affected Cracked Concrete Structures Reinforced with 1.4003 Rebars

The protection of reinforced concrete components exposed to chlorides is often ensured by coating systems, which are usually associated with high maintenance costs over the service life. A possible alternative is the use of high-alloy, stainless steel reinforcement. Through smart selection in areas subject to particularly high stresses and the possibility of using mixed reinforcement with black steel, this type of reinforcement can also be used for economical construction. In many areas, it is sufficient to use significantly cheaper chromium steel rebars instead of very expensive, highly corrosion-resistant austenitic chromium-nickel steels. An industrial research project was carried out at Munich University of Applied Sciences in which the resistance of a chromium steel reinforcement with material number 1.4003 in chloride-exposed separation cracks of RC-specimens was investigated. The results obtained formed the basis for the development of design variants for underground parking garages. Structural tests on a large number of existing structures show how a long service life can be achieved with such reinforcement even under high chloride loads.

Strength and Fracture Mechanism of an Ultrafine-Grained Austenitic Steel for Medical Applications.

In this paper, we study the corrosion-resistant austenitic steel Fe-0.02C-18Cr-8Ni for medical applications. The microstructure and mechanical properties (tensile mechanical properties, torsional strength, impact toughness, and static and cyclic crack resistance) under different types of loading of the steel are investigated. The results are compared for the two states of the steel: the initial (coarse-grained) state and the ultrafine-grained state produced by severe plastic deformation processing via equal-channel angular pressing. It is demonstrated that the ultrafine-grained steel 0.08C-18Cr-9Ni has essentially better properties and is very promising for the manufacture of medical products for various applications that experience various static and cyclic loads during operation.

Strength and fracture mechanism during torsion of ultrafine-grained austenitic steel for medical applications

The article considers evaluation of torsional strength and fracture of austenitic corrosion-resistant steel 08Kh18N9 with an ultrafine-grained (UFG) and coarse-grained (CG) structure, widely used in medicine for the production of plates, screws, rods for bone osteosynthesis and other medical products. The structure of the CG steel was studied using an Axiovert 40 MAT metallographic microscope, and the fine structure of the UFG steel was investigated with a JEM-2100 transmission electron microscope. Torsion tests of the cylindrical samples with a diameter of 10 mm were carried out at a temperature of 20 °C on MK-50 installation. JEOL JCM-6000 scanning electron microscope was used for the microfractographic studies of fracture surfaces. The analysis of the “Torque - torsion angle” diagrams showed that the torsional ultimate strength (τt) and yield strength (τ0.3) of UFG steel increase by 1.3 - 3.8 times, and the relative shear (g) decreases by 2.4 times in comparison with CG steel. High values of torsional strength properties of UFG steel make it possible to provide high torque without destroying the product. Consequently UFG steel 08Kh18N9 in comparison with CG steel is a more promising material for the manufacture of medical screws and other medical products that experience significant loads during the torsion process. Three areas were identified on the surface of all fractures: fibrous central part, transitional (middle) part, and a relatively smooth peripheral part. Fracture begins with the formation of shear pits in the middle and peripheral parts, which, with further rotation of the sample, are completely rubbed out (in case CG steel), or remain (in case of UFG steel). Final failure occurs under the action of normal stresses in the central part of the sample.

Strength and Fracture Mechanism during Torsion of Ultrafine-Grained Austenitic Steel for Medical Applications

The article considers evaluation of torsional strength and fracture of austenitic corrosion-resistant steel 08Kh18N9 with an ultrafine-grained (UFG) and coarse-grained (CG) structure, widely used in medicine for the production of plates, screws, rods for bone osteosynthesis and other medical products. The structure of the CG steel was studied using an Axiovert 40 MAT metallographic microscope, and the fine structure of the UFG steel was investigated with a JEM-2100 transmission electron microscope. Torsion tests of the cylindrical samples with a diameter of 10 mm were carried out at a temperature of 20°C on MK-50 installation. JEOL JCM-6000 scanning electron microscope was used for the microfractographic studies of fracture surfaces. The analysis of the torque–torsion angle diagrams showed that the torsional ultimate strength (τt) and yield strength (τ0.3) of UFG steel increase by the factor of 1.3–3.8, and the relative shear (g) decreases by the factor of 2.4 in comparison with CG steel. High values of torsional strength properties of UFG steel make it possible to provide high torque without destroying the product. Consequently, UFG steel 08Kh18N9 in comparison with CG steel is a more promising material for the manufacturing of medical screws and other medical products that experience significant loads during the torsion process. Three areas were identified on the surface of all fractures: fibrous central part, transitional (middle) part, and a relatively smooth peripheral part. Fracture begins with the formation of shear pits in the middle and peripheral parts, which, with further rotation of the sample, are completely rubbed out (in case CG steel), or remain (in case of UFG steel). Final failure occurs under the action of normal stresses in the central part of the sample.