Chromium-nickel Steels Research Articles

Elemental and Thermochemical Analyses of Materials after Electrical Discharge Machining in Water: Focus on Ni and Zn

The mechanism of the material destruction under discharge pulses and material removal mechanism based on the thermochemical nature of the electrical erosion during electrical discharge machining of conductive materials were researched. The experiments were conducted for two structural materials used in the aerospace industry, namely austenite anticorrosion X10CrNiTi18-10 (12kH18N10T) steel and 2024 (D16) duralumin, machined by a brass tool of 0.25 mm in diameter in a deionized water medium. The optimized wire electrical discharge machining factors, measured discharge gaps (recommended offset is 170–175 µm and 195–199 µm, respectively), X-ray photoelectron spectroscopy for both types of materials are reported. Elemental analysis showed the presence of metallic Zn, CuO, iron oxides, chromium oxides, and 58.07% carbides (precipitation and normal atmospheric contamination) for steel and the presence of metallic Zn, CuO, ZnO, aluminum oxide, and 40.37% carbides (contamination) for duralumin. For the first time, calculating the thermochemistry parameters for reactions of Zn(OH)2, ZnO, and NiO formation was produced. The ability of Ni of chrome–nickel steel to interact with Zn of brass electrode was thermochemically proved. The standard enthalpy of the Ni5Zn21 intermetallic compound formation (erosion dust) ΔH0298 is −225.96 kJ/mol; the entropy of the crystalline phase Scint is 424.64 J/(mol·K).

Computed Tomography for the Nondestructive Testing of Additive Manufactured Components: Opportunities and Limitations

The additive manufacturing (AM) process has grown from university research laboratories into a production process for complex-shaped components. Due to the uniqueness of the manufacturing process, new challenges have arisen regarding process control, quality assurance, and surface finishing. This paper will show how the nondestructive radiographic testing (RT) technique computed tomography (CT) can make a valuable contribution to quality assurance at each step of the AM process. The use of CT is demonstrated using an example of chrome-nickel steel nozzles manufactured using the laser powder bed fusion (LPBF) process. The surface of the nozzles is then reworked with the Hirtisation process, a trademarked part finishing technology that is based on a combination of electrochemical pulse methods, hydrodynamic flow and particle assisted chemical removal, and surface treatment. In addition to the already known use of CT for detecting internal discontinuities, CT can be used to ensure sufficient wall thickness, measure internal channel surface roughness, and gauge the geometrical correctness of parts. In this paper, it is demonstrated how to use this RT technique to optimize the design and production process during the component development phase.

Контроль якості хромонікелевих сталей за парамагнітним станом аустеніту

The subject matter of the article is the processes of monitoring and assessing the quality of austenitic chromium-nickel steels. The quality of steels and products made from them depends on the combination of physical, chemical and technological properties that are formed as a result of the phase-chemical composition and various types of processing (temperature, deformation, laser, radiation, etc.). Determination of a methodology that will supplement or replace multiple tests by measuring one parameter is highly relevant. The goal is to find a methodology for a comprehensive assessment of mechanical and corrosion properties in one parameter, which is sensitive to external factors. It is proposed to use the specific paramagnetic susceptibility of austenite c0 as an integral characteristic of the influence of various factors (chemical composition, melting conditions, deformation, temperature, etc.). Parameter c0 is a characteristic of the atomic-magnetic state of austenite and a sensitive quantity to the influence of external factors. The tasks to be solved are: to formalize the correlation between the specific paramagnetic susceptibility c0 of austenite and mechanical, corrosion properties (tensile strength sв, conditional yield stress s0.2, elongation d, corrosion rate K). The methods used are: a highly sensitive magnetometric method for determining the specific magnetic susceptibility X and the low content of the ferromagnetic phase of the samples of the studied steels in the initial state (before mechanical and corrosion tests). Mechanical indicators were determined in accordance with GOST 1497-84, the value of corrosion losses in chloride-containing solutions - in accordance with GOST 9.912-89. The following results were obtained. It has been experimentally established that the tendency of changes in the mechanical and corrosion properties of steels of the AISI 321 and AISI 304 types correlates with the magnetic nature of the paramagnetic austenite matrix, which is determined by the sum of the magnetic moments of atoms per unit mass (specific magnetization). Conclusions. It is shown that the specific paramagnetic susceptibility of austenite can be used to determine the behavior (increase or decrease in mechanical and corrosion properties). It is shown that a low content of d-ferrite can also be a measure (indicator) of the behavior of these properties.

AK STEEL 309S

Abstract AK Steel 309S is a chromium-nickel austenitic stainless steel that provides excellent corrosion resistance and heat resistance in addition to good strength at room and elevated temperatures. It is identical to AK Steel 309 except for a lower carbon content that minimizes carbide precipitation and improves weldability. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: SS-1334. Producer or source: AK Steel Corporation.

Вихретоковый контроль усталостной деградации метастабильной аустенитной стали при гигацикловом контактно-усталостном нагружении

The surfaces of parts made of austenitic chromium-nickel steels are subjected to heavy cyclically repeated contact loads, including impact loads, during operation. Therefore, the study of contact endurance and the development of methods for non-destructive testing of fatigue degradation of such steels is a relevant task. The aim of this work is to study the possibility of eddy-current testing of the fatigue degradation of the AISI 321 steel under contact loading. Mechanical testing for gigacycle contact fatigue has been conducted in accordance with the pulsing impact “plane-to-plane” contact scheme with an ultrasonic loading frequency. It has been shown that eddy-current testing of the fatigue degradation under contact loading of the AISI 321 steel is possible, but has certain limitations due to non-monotonic changes in the eddy-current device readings α depending on the number of loading cycles. Along with this, using the ascending branch it is possible to test the degree of failure of the surface layer, taking into account in the control technique the ambiguous character of the dependences of the eddy-current device readings on the number of loading cycles. The testing can be performed by measuring the eddy-current device readings at the excitation frequency of the eddy current probe f = 124 kHz. In this case, mainly surface layers are analyzed, where the processes of the fatigue degradation that affect the physical characteristics of the steel are developed intensively. The greatest influence on the value of α is exerted by the quantitative ratio of austenite to strain-induced martensite in the control zone.

Investigation of irradiated metal of WWER-type reactor internals after 45 years of operation. Part 4. Mechanical properties and fracture mechanisms

Experimental data are obtained for austenitic chromium-nickel steel of 18Cr–10Ni–Ti grade(analog of AISI 321 steel) irradiated with mixed neutron spectrum to various damage doses at temperature near 300 o C. Metal for investigations has been taken from decommissioned components of internals of WWER type reactor. On the basis of the tests of standard cylindrical specimens the strengthand the plasticity characteristics are determined over wide temperature range. The fracture mechanisms are studied by SEM examination. It is revealed that the fracture strain decreases with decrease of temperature and the transition occurs from transgranular ductile to intergranular brittle fracture. The performed review of other published works has shown that this phenomenonmay be observed for various austenitic steels irradiated with mixed neutron spectrum and for austenitic and ferritic steels with implanted helium. This phenomenon is termed as low temperature helium embrittlement (LTHE).

Consumable electrode – additional filler wire arc interaction control under surfacing (DE-GMAW)

Introduction. Arc surfacing through feeding an additional filler wire heated by an additional arc burning between the filler wire and the electrode wire is considered. Under the conditions of such surfacing, the minimization of the input of the remelted substrate metal into the weld metal is studied. The research objectives are to examine the conditions providing self-regulation of this advanced arc surfacing process, and to evaluate control capabilities of the heat impact power on the metal and on the weld metal flow. Materials and Methods. In solving a wide range of welding and surfacing tasks, it is advisable to use engineering analysis methods based on physicomathematical modeling of processes and phenomena. These include: self-regulation of the arc process under joint melting of the electrode and the filler wires; assessment of the possibilities to control the heat impact power on the metal and on the weld metal flow during the formation of the weld The features of the arc surfacing of anticorrosive chromium-nickel steels on low-alloy steel are considered in the paper. Results. New mathematical dependences are proposed that describe physical phenomena under surfacing with an arc interaction between the electrode and filler wire. A physicomathematical model of the joint melting of the electrode and filler wire is developed. It provides determining the values of the control parameters. In addition, you can find out how much heat affects the substrate from: heat release in the main arc, droplet flows of the weld electrode and filler metal, arc plasma Discussion and Conclusions. It is established how the current and the lengths of the main and additional arcs are affected by the supply voltages. The feed rate of the electrode and filler wire with a diameter of 1.6 mm and 1.2 mm made of Inconel 625 alloy is determined. It is shown what thermal effect the substrate undergoes in this case. It is noted that due to the larger value of the main arc current, the diameter of the electrode wire should be larger than that of the filler wire. The heat flow in the substrate is created mainly by the flow of the weld metal droplets.

AK STEEL 309

Abstract AK Steel 309 is a chromium-nickel austenitic stainless steel. It is typically used for elevated temperature applications. Its high chromium and nickel contents provide comparable corrosion resistance, superior resistance to oxidation, and the retention of a larger fraction of room temperature strength than the common austenitic stainless steels, such as type 304. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: SS-1333. Producer or source: AK Steel Corporation.

Study of the effect of the deformation martensite on the corrosion resistance of NPP equipment and pipelines made of austenitic steels

Austenitic stainless steels are widely used in nuclear and thermal power engineering due to their high mechanical, corrosion and technological properties. We present the results of studying the effect of deformation martensite on the corrosion resistance of chromium-nickel steels of the austenitic class. Samples of heat exchange tubes of steam generators, tube bends, plates (constituents of steam turbines), safety valves used in NPP equipment were studied. The tests were carried out using metallographic, X-ray diffraction, atomic emission and atomic absorption spectral analyses. Electron microscopy was used to determine the content of the ferrite phase. It is shown that irregular dark gray spots located along a line parallel to the sample axis contain iron oxides. The appearance of such defects observed only on the outer surface of the products is attributed to the technology of their manufacture. It is also shown that severe plastic deformation which occurs during production or operation leads to formation of the deformation martensite which is subject to corrosion at this the corrosion cracking is accompanied by stress. The absence of δ-ferrite in the metal of samples is also revealed. The deformation martensite formed during operation of the product at the point of contact with a harder material leads to appearance of a large number of microcracks, which develop according to the fatigue mechanism under cyclic loading. The results obtained can be used to assess the probability of the formation of deformation martensite in chromium-nickel austenitic steels.

Effect of Medium-Energy Ar+ Ion Irradiation on the Structure of Austenitic Chromium–Nickel Steel

Effect of Medium-Energy Ar+ Ion Irradiation on the Structure of Austenitic Chromium–Nickel Steel

Mechanisms of plastic deformation and fracture of austenitic chromium-nickel steel irradiated during 45 years in WWER-440

The test results of tensile round bars from austenitic stainless steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated during 45 years in Pressure Water Reactor of WWER-440 type with various damage doses are represented over wide temperature range. The standard mechanical properties including the fracture stress and the fracture strain are determined, and the fracture mechanisms are studied. A phenomenon of decrease in the fracture strain with decrease of temperature is revealed that is accompanied by transition to intergranular brittle fracture. This phenomenon is termed as low temperature helium embrittlement (LTHE). On the basis of the analysis of other published works it has been concluded that LTHE is sufficiently common phenomenon that is revealed for various austenitic steels irradiated with mixed neutron spectrum.It is shown that the strain-induced martensite and low cohesive strength of grain boundary (GB) due to the helium accumulation on GBs are two necessary factors which cause LTHE of the irradiated austenitic steels. Mechanism of microcrack nucleation on weakened GB is proposed that takes into account the morphology of the strain-induced martensite formed near GB.Some features of plastic deformation over the temperature range of LTHE are revealed and explained as follows: (i) a running neck and large yield drop; and (ii) a difference in the true stress-strain curves for the cross-section with the originally arisen neck and for other cross-sections of tensile round bar over initial plastic strain range.

COMPARATIVE ANALYSIS OF THE INFLUENCE OF THE COMPOSITION OF THE ALLOYING COVERING ON THE CHANGE IN THE STRUCTURE AND MICROHARDNESS OF STAINLESS STEEL 12KH18N10T

The article is devoted to the experimental analysis of the influence of the process of laser pulsed alloying in a layer of alloying mixture on the qualitative and physical and mechanical characteristics of the modified surface of stainless chromium-nickel steel of the austenitic class 12Cr18Ni10T. It was found that the use of graphite paste as an alloying compound leads to a significant increase in microhardness, a change in micromorphology, and the formation of a heat hardening zone in the near-surface layer of steel. The smoothing of the boundaries of structural changes is revealed and the effect of surface hardening is determined when a finely dispersed powder of titanium dioxide (anatase) is added to the alloying coating. According to the data obtained, a comparative analysis of the dependence of the microhardness of the modified surface on the voltage of the pump lamp and the diameter of the laser pulse spot is carried out. The maximum microhardness value, equal to 9,56 GPa, was achieved as a result of laser processing of a series of samples, where graphite paste was applied as a preliminary surface preparation. Rational technological modes of laser modification of the surface of 12Cr18Ni10T steel that have previously undergone abrasive blasting, modes of laser pulsed alloying in a layer of graphite coating and laser pulsed alloying of steel in a layer of coating consisting of graphite paste and anatase powder in a ratio of 4:1, respectively, are recommended.

Высокотемпературная коррозия сталей в растворах кислот. Ч. 3. Ингибиторная защита сталей азотсодержащими гетероциклическими органическими соединениями и неорганическими окислителями. Обзор

The literature and patent data on the protection of steels in high-temperature acid solutions by nitrogen-containing heterocyclic organic compounds and inhibitors of oxidative type were summarized. Composite inhibitors based on substituted triazoles can provide effective protection of low-carbon and chromium-nickel steels in these environments (200 °С). The mechanism of the protective action of these inhibitors is based on the ability of substituted triazoles to form on the steel surface in acid solutions the protective layers chemically bonded to the metal surface. Often these protective layers are basically composed of a polymer complex compound containing triazole molecules and Fe cations (in the case of nickel-chromium steels — Ni and Cr). It is noted that oxidizing additives can be used to protect steels which are in high-temperature acidic media at a passive state. Using the example of corrosion of chromium-nickel steel in H3PO4 solutions (130 °C), it is shown that additives of oxidants (Cu(II) and NO3–) stabilize the passive state of the metal in this medium, preventing the possibility of its active dissolution. Based on analysis of the literature data, a conclusion was made about the prospects of using compositions based on nitrogen-containing heterocyclic compounds for protecting steels in high-temperature acidic environments. These compositions are superior in important technological parameters to mixed inhibitors based on unsaturated organic compounds.

Effect of Nanosecond Ultraviolet Laser Radiation on the Structure and Adhesion Properties of Metals and Alloys

t—The effect of ultraviolet (UV) laser radiation on the structure and adhesion properties of materials such as chromated bronze, stainless refractory austenitic chromium-nickel steels, and copper, has been experimentally studied. It has been shown that the surface microstructuring of elements of a diffusion-bonded joint improves its mechanical properties as to its tensile strength and tensile strain. Some results are presented for the laser perforation of a copper interlayer and the laser surface microstructuring of ceramic blanks which provide improvement in the mechanical properties of a Si3N4/Cu/Si3N4 welded joint.

Influence of silicon, boron and rare-earth metals on corrosion resistance of austenitic chromium-nickel steel

The effect of silicon (in range 0.14 – 0.78 wt. %), boron, and rare-earth metals (REM) on the corrosion resistance of low-carbon austenitic chromium-nickel steel of 03Kh18N11 (AISI 304L) grade was studied. It is shown that all steels in quenched state when tested in boiling 56 and 65 % HNO3 solutions have comparable corrosion rates, which do not exceed the critical norm (0.5 mm/year) in accordance with GOST 6032 – 2017 (State Standard). Testing samples in boiling 27 % HNO3 + 4 g/l Cr+6 solution are susceptible to intergranular corrosion (IGC). The corrosion rate and the penetration depth of IGC increase with increasing silicon concentration from 0.14 to 0.78 wt. %. Study of the effect of nitric acid concentration and test temperature has shown that steel with 0.78 wt. % Si has significant corrosion losses exceeding the critical ones when testing in 56 and 65 % HNO3 solutions with temperature of 120 and 130 °С. But steel with high silicon content (0.78 wt. %) and low carbon concentration (0.020 – 0.022 %) after quenching in a range of 1080 – 1150 °C and tempering at 650 °C does not exceed the critical norm on average corrosion rate. Only 0.01 wt. % increase in carbon concentration leads to a significant (more than 30 times) increase in corrosion rate of sensitized steel. It is shown that microalloying with REM does not impair corrosion resistance of sensitized steel. In contrast to REM, alloying chromium-nickel steel with even a small addition of boron (0.0015 %) reduces steel corrosion resistance by an order of magnitude. Corrosion rate inverse dependence on quenching temperature is observed when, with increasing temperature, corrosion rate of 02Kh18N11GS0.38R steel increases. The effect of silicon (in range 0.14 – 0.78 wt. %), boron, and rare-earth metals (REM) on the corrosion resistance of low-carbon austenitic chromium-nickel steel of 03Kh18N11 (AISI 304L) grade was studied. It is shown that all steels in quenched state when tested in boiling 56 and 65 % HNO3 solutions have comparable corrosion rates, which do not exceed the critical norm (0.5 mm/year) in accordance with GOST 6032 – 2017 (State Standard). Testing samples in boiling 27 % HNO3 + 4 g/l Cr+6 solution are susceptible to intergranular corrosion (IGC). The corrosion rate and the penetration depth of IGC increase with increasing silicon concentration from 0.14 to 0.78 wt. %. Study of the effect of nitric acid concentration and test temperature has shown that steel with 0.78 wt. % Si has significant corrosion losses exceeding the critical ones when testing in 56 and 65 % HNO3 solu tions with temperature of 120 and 130 °С. But steel with high silicon content (0.78 wt. %) and low carbon concentration (0.020 – 0.022 %) after quenching in a range of 1080 – 1150 °C and tempering at 650 °C does not exceed the critical norm on average corrosion rate. Only 0.01 wt. % increase in carbon concentration leads to a significant (more than 30 times) increase in corrosion rate of sensitized steel. It is shown that microalloying with REM does not impair corrosion resistance of sensitized steel. In contrast to REM, alloying chromium-nickel steel with even a small addition of boron (0.0015 %) reduces steel corrosion resistance by an order of magnitude. Corrosion rate inverse dependence on quenching temperature is observed when, with increasing temperature, corrosion rate of 02Kh18N11GS0.38R steel increases.

Влияние имплантации ионов аргона и кислорода на физико-химические и коррозионно-электрохимические свойства хромоникелевой стали 14Х17Н2

The effect of argon and oxygen ion implantation both in separate and joint was carried out. Physical and chemical structure of the surface and corrosion-electrochemical behavior of 14Cr17Ni2 chromium-nickel steel was studied. Methods of potentiometry, atomic force microscopy, X-ray photoelectron spectroscopy, and microhardness measurement were used. It was found that the initial chromium-nickel steel exhibits high corrosion resistance in the medium of a borate buffer solution with the addition of a local corrosion initiator — potassium sulfate. However, steel was found to be susceptible to local (pitting) corrosion in this environment. It is shown that the implantation of argon and oxygen ions changes the nature of the corrosion-electrochemical behavior of chromium-nickel steel. Treatment with Ar+ ions enriched the sample surface with Cr atoms and reduces the overall corrosion losses of steel, but is characterized by the maximum value of local corrosion. Treatment with O+ ions provide optimal results in terms of reducing local and general corrosion. It was found that in this case, the sample surface is intensively oxidized to a depth of more than 20 nm, resulting in the formation of mixed oxides that are resistant to corrosion. There is a process similar to electropolishing of the sample surface due to partial dissolution of steel. Defects in the structure of the sample surface, on which pitting corrosion began, are “healed”. Joint treatment with Ar+ ions and O+ ions does not give noticeable advantages compared to separate implantation with these ions. Corrosion losses for samples treated only with O+ ions and Ar+ ions together with O+ ions did not exceed those for the original sample, although there are practically no passivation regions on the potentiodynamic curves. Microhardness of the samples after ion implantation coincides with the microhardness of the original sample. Result of ion implantation is no significant for change in the structural and phase structure of the surface layers of chromium-nickel steel. Ion implantation will not negatively affect the physical and mechanical properties of studied steel. The research shows that it is advisable to choose the type of implantable ions and the optimal process parameters depending on the steel grade and its application. For these purposes, the research methodology proposed in this article will be useful.

Dynamic Theory of the Effect of a Strong Magnetic Field on the Martensitic Transformation in Steels with Austenite Grain Sizes Close to a Critical Value

In the dynamic theory of martensitic transformations, temperature Ms of the start of transformation corresponds to conditions that are optimal for generating waves by nonequilibrium d electrons that control the growth of a martensitic crystal. The recognition of relative damping $${{\Gamma}}_{{\text{e}}}^{'}$$ of s electrons plays a substantial role in this case. A general analysis that has made it possible to propose, for the first time, an analytical formula for critical size Dc $$\left( {{{\Gamma}}_{{\text{e}}}^{'}} \right)$$ of austenite grains is used to interpret the results for chromium–nickel steels, in which the transformation is initiated by strong magnetic fields. Under conditions of positive bulk magnetostriction, a magnetic field with intensity H lowers the chemical potential of electrons. As a result, the Dc( $${{\Gamma}}_{{\text{e}}}^{'},$$ H) value decreases and austenite with a grain diameter of D, which was stabilized by condition D < Dc( $${{\Gamma}}_{{\text{e}}}^{'},$$ 0) in the absence of a field, becomes destabilized, since inequality D > Dc( $${{\Gamma}}_{{\text{e}}}^{'},$$ H) is fulfilled. The dynamic theory predicts a sharp increase in the Dc( $${{\Gamma}}_{{\text{e}}}^{'},$$ 0) value at $${{\Gamma}}_{{\text{e}}}^{'}$$ → 1. This is evidenced by value Dc $$\left( {{{\Gamma}}_{{\text{e}}}^{'}} \right)$$ ≥ 1 mm for steel 67Kh2N22, which is three orders of magnitude larger than Dc( $${{\Gamma}}_{{\text{e}}}^{'},$$ 0) ≈ 1 μm for the Fe–31Ni alloy. Other peculiarities of the effect of magnetic field on the martensitic transformation are also discussed.

Investigation of the impulse impact effect in the process of additive manufacturing of metal products by plasma cladding

Additive technologies (AT) or layered synthesis technologies are one of the most dynamically developing areas of “digital” production. A common problem of additive technologies is ensuring the proper microstructure of the synthesized material and the eliminating defects. The use of filler wire as a working material eliminates the problems associated with the low productivity of existing methods, the high cost of the equipment used, the limited types of materials used, due to the use of powder systems. Products made of stainless chromium-nickel steels are widely used in various industries. The main problem of additive technologies is to ensure the properties of the laminates are not lower than those obtained by traditional methods. Characteristic defects of laminated materials obtained by surfacing are increased porosity, non-metallic inclusions, a decrease in ductility, and for high-alloy steels, a loss of special properties. This predetermined the development of research in the field of additional technological measures to improve the final properties of the product. This paper presents the results of a study of the effect of ultrasonic vibrations on the structure and properties of the deposited steel 12Cr18Ni10Ti. For welding was used the wire 12Cr18Ni10Ti, process was carried out by plasma arc in a protective argon gas. It was found that ultrasonic treatment has an effect on the final grain size, structure formation and hardness, as well as on the geometry of the deposited layer. Studies show that the use of ultrasonic vibrations in the process of surfacing can be applied in the design of equipment for the implementation of processes of additive production.

ВЛИЯНИЕ НАНОСТРУКТУРИРУЮЩЕЙ ФРИКЦИОННОЙ ОБРАБОТКИ НА МИКРОМЕХАНИЧЕСКИЕ И КОРРОЗИОННЫЕ СВОЙСТВА СТАБИЛЬНОЙ АУСТЕНИТНОЙ ХРОМОНИКЕЛЕВОЙ СТАЛИ

Friction treatment is an effective method to increase the strength and wear resistance of austenitic chromium-nickel steels. Previously, the authors identified that the high level of mechanical properties of metastable austenitic steels is achieved at the intensive development of deformation γ→α'-transformation. However, the presence of deformation martensite in the austenitic steel structure can negatively affect its anti-corrosion properties. The search for ways to improve the strength characteristics of stable austenitic chromium-nickel steel while maintaining high resistance to corrosion destruction is the up-to-date line of research. In this paper, to evaluate the mechanical properties of 03Cr16Ni14Mo3Ti steel in the hardened condition and after friction treatment, the authors applied the technique of measuring the hardness using the restored print and the method of instrumental micro-indentation, which allows recording the indenter loading and unloading diagrams. The corrosion failure resistance of steel was studied in general corrosion tests. The authors compared the corrosion rate of austenitic steel after grinding, electropolishing, and friction treatment; using scanning electron microscopy and optical profilometry, studied steel surfaces subjected to these treatments and determined their roughness. Nanostructuring friction treatment provides surface hardening of stable austenitic steel up to 570 HV 0.025. The study showed the high efficiency of friction treatment application to increase the strength characteristics and resistance of steel surface layer to elastic and plastic deformation. The authors identified that austenitic steel is characterized by similar corrosion rates km=(3.26–3.27)∙105 (g/cm2∙h) after electrolytic polishing (the structure of large-crystal austenite) and after frictional treatment (sub-micro/nanocrystalline austenite structure), while mechanical grinding leads to a twofold increase in the corrosion rate of 03Cr16Ni14Mo3Ti steel due to the occurrence of microcracks and metal breakouts on the polished surface. The research justified the determining role of the quality of the surface formed by various treatments (roughness, the presence of continuity defects) in ensuring the corrosion resistance of stainless steel.

Influence of Process of Straightening Ship Hull Structure Made of 316L Stainless Steel on Corrosion Resistance and Mechanical Properties

Abstract The AISI 316L type steel belongs to the group of chromium-nickel stainless steels. They are determined according to European standards as X2CrNiMo17-12-2 and belong to the group of austenitic stainless steels. Steels of this group are used for elements working in seawater environments, for installations in the chemical, paper, and food, industries, for architectural elements, and many others. The chemical composition of corrosion-resistant austenitic steels provides them with an austenite structure that is stable in a wide temperature range, under appropriate conditions for heating, soaking, and cooling. 316L steel plate was subjected to a technological treatment of hot straightening with an oxy-acetylene torch, which is not commonly used for this type of steel, mainly due to the lack of objective assessment of whether the austenitizing temperature has been achieved and the stability of the heat treatment process is ensured. The single-phase structure of austenite with high corrosion resistance, without precipitation of carbides, steel is obtained by supersaturation in water from 1100°C. The purpose of the presented research was to determine the usefulness of the flame straightening process for a ship structure made of 316L steel.