Austenitic Chromium-nickel Steels Research Articles

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.

Effect of plastic deformation on the phase composition and electromagnetic characteristics of the 321N austenitic steel (08Kh18N10T)

The changes in the phase composition and electromagnetic properties of the 321N chromium-nickel austenitic steel under plastic deformation by uniaxial tension are studied. As strain increases from 0 to 0.37, the content of ferromagnetic α′-martensite in the steel increases monotonically to 60%. The electrical resistivity and the initial magnetic permeability increase monotonically by factors of 1,25 and 18, respectively. To monitor the strain state and the content of α'-martensite in products made of the 321N steel, it is preferable to use initial magnetic permeability rather than electrical resistance. The skin layer thickness of the deformed 321N steel for frequencies from 5 to 1000 kHz is calculated from the experimental values of initial magnetic permeability and electrical resistivity. Eddy current diagnostics of the state of the surface of products made of this steel, hardened by surface plastic deformation, is proposed to be performed at frequencies ranging between 100 and 200 kHz.

Effect of Diamond Burnishing on Fatigue Behaviour of AISI 304 Chromium-Nickel Austenitic Stainless Steel.

The disadvantages of widely used austenitic stainless steels are their low hardness and relatively low fatigue strength. Conventional chemical-thermal surface treatments are unsuitable for these steels since they create conditions for inter-granular corrosion. An effective alternative is a low-temperature surface treatment, creating an S-phase within the surface layer, but it has a high cost/quality ratio. Austenitic steels can increase their surface micro-hardness and fatigue strength via surface cold working. When the goal is to increase the rotating bending fatigue strength of austenitic chromium-nickel steels, and the requirements for significant wear resistance are not paramount, diamond burnishing (DB) has significant potential to increase the fatigue strength and, based on the cost/quality ratio, can successfully compete with low-temperature chemical-thermal treatments. The main objective of this study is to establish the effect of DB on the rotating fatigue strength of AISI 304 L chromium-nickel austenitic steel. The influence of DB parameters on the surface integrity (SI) characteristics was studied. Optimal DB parameters under minimum roughness and maximum micro-hardness criteria were obtained. Rotating bending fatigue tests of the diamond burnished (in a different manner) and untreated specimens were performed. DB implemented via parameters providing maximum micro-hardness increased fatigue limit by 38% compared to untreated specimens.

Structural Transformations in Cold-Rolled Austenitic Chromium-Nickel Steel Studied by Synchrotron X-Ray Diffraction and Peak Profile Analysis

Structural Transformations in Cold-Rolled Austenitic Chromium-Nickel Steel Studied by Synchrotron X-Ray Diffraction and Peak Profile Analysis

Mechanical Properties Degradation Modeling of Austenitic Chromium-Nickel AISI 304 Steel After Thermal Ageing

Austenitic chromium-nickel steel AISI 304 is used as a structural material for heat exchange equipment. Long-term operations result in degradation of mechanical properties of material due to formation of chromium carbides at grain boundaries. The influence of various thermal ageing modes of AISI 304 steel on mechanical properties with metal fragments of reactor plant on fast neutrons of RP BN-600 taken as an example after long-term operation has been investigated.

Peculiarities of stress corrosion fracture of sensitized and neutron irradiated chromium-nickel austenitic steel

The results of SEM studies of fracture surfaces for the 12Cr18Ni9 austenitic steel ruptured under a fixedtensile load in FeCl3 water solutionand in air are presented. The samples of austenized, sensitized at 650° and irradiated with neutrons (to 1020n/cm2) steel were examined. It was shown thatirradiation hardening and sensitizing annealing increased the susceptibility of steel to intergranular cracking in corrosive solution. Structural features of formation of the strain-induced α’-martensite and its reinforcing effect on fracture in various environments are discussed.

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.

Mechanisms of Stress Corrosion Cracking of Irradiated Austenitic Chromium–Nickel Steels Used for WWER and PWR Vessel Internals

Mechanisms of Stress Corrosion Cracking of Irradiated Austenitic Chromium–Nickel Steels Used for WWER and PWR Vessel Internals

CARTECH 321

Abstract CarTech 321 is a titanium-stabilized chromium-nickel austenitic stainless steel that was developed to provide the performance of an 18-8 austenitic stainless steel with improved intergranular corrosion resistance. Since titanium has a stronger affinity for carbon than chromium, titanium carbide tends to precipitate randomly within the grains instead of forming continuous patterns at the grain boundaries. 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, machining, and joining. Filing Code: SS-1338. Producer or source: Carpenter Technology Corporation.

CARTECH 303

Abstract CarTech 303 is a free-machining austenitic stainless steel. The addition of sulfur to this 18-8 chromium-nickel austenitic stainless steel, which is ordinarily tough and difficult to machine, enhances the alloy’s machinability to the degree that it can be readily utilized for producing parts on automatic screw machines at about 70% of the speed of SAE 1212. This sulfur modification has led to widespread acceptance and use of this grade in the screw machine industry. 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, machining, and joining. Filing Code: SS-1337. Producer or source: Carpenter Technology Corporation.

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

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

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).

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.

Electron-Microscopy Investigation of Excess-Phase Precipitates Affecting the Intergranular Corrosion of Chromium–Nickel Austenitic Steels

Electron-Microscopy Investigation of Excess-Phase Precipitates Affecting the Intergranular Corrosion of Chromium–Nickel Austenitic Steels

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.