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The results of the structure and stacking fault energy (SFE) investigations of low-carbon austenitic steels alloyed with substitutional elements are summarized. An increase in the manganese content in the range 7–20 wt % in Fe–Mn alloys is shown to make austenite stable to the γ–α transformation and unstable to the γ–e transformation. Ferromanganese steel containing 20 wt % Mn has the maximum number (50–55%) of stacking faults after deformation. The SFE of Fe–Mn alloys is inversely proportional to the manganese content at Mn < 14 wt % and directly proportional at higher manganese concentrations. A temperature dependence of the SFE on the manganese content is found for Fe–Mn alloys. The effect of chromium on the SFE depends on the manganese content. A linear dependence of the SFE on the nickel content in Cr–Ni steels with 10–25 wt % Cr is found in the concentration range 10–25 wt %.

The сrack growth characteristics are investigated in situ in a scanning electron microscope column during the tension of the welded joints of two-phase (γ + δ) and single-phase (γ) 05Kh22AG16N8M steel containing 0.36 and 0.52 wt % N, respectively. A crack in the steel with 0.36% N and its welded joint is shown to form and develop at a low load and strain due to the existence of the σ phase in the steel structure and δ ferrite in the welded joint.

The crack growth characteristics are investigated in situ in a scanning electron microscope column during the tension of nonmagnetic 04Kh18AG20 steel specimens with a overequilibrium nitrogen content (0.98 wt % N) and various vanadium contents. The character of crack nucleation and propagation in steel after quenching from 1200°С and after subsequent aging at 650°С for 5 h is shown to be the same. The critical shear crack size at the maximum load is 300 μm in vanadium-free 04Kh18AG20 steel and 120 μm in vanadium-bearing 04Kh18AG20F steel. Corrosion-resistant nickel and vanadium-free austenitic 04Kh18AG20 steel (0.98 wt % N) after quenching from 1200°C is recommended for heavy-duty nonmagnetic structures.

The works on the structure and mechanical properties of aluminum-alloyed austenitic steels are analyzed. Aluminum in aging high-nitrogen Cr–Mn–Ni–V nonmagnetic steels is shown to decrease the strength due to a decrease in the amount of dispersed VN nitrides having precipitated during aging because of the formation of coarse AlN particles hard to dissolve on quenching heating. An additional increase in the strength of aging nonmagnetic Mn–Ni–V–C steels is reached by their alloying with aluminum, which does not form hard to dissolve compounds with carbon. A significant increase in the surface hardness and the wear resistance during nitriding is reached as a result of separate or complex alloying of Mn–Ni–V steels with chromium up to 3% and aluminum up to 1.2%, which increase the nitrided layer thickness. The best combination of the properties of the nitrided layer is achieved after nitriding these steels containing 2.5–3.5% V at 700°C (12 h) in a 80% N2 + 20% HN3 medium. In this case, the hardening of the core during aging is related to the precipitation of VC carbides, and that of the nitrided layer, to the formation of VN nitrides. A significant increase in the volume fraction of strengthening phases in manganese steels is reached by complex alloying with Al, Ni, Cu, and V in the amounts that provide the simultaneous precipitation of the VC carbide and NiAl intermetallics during aging. Nonmagnetic 50G17N10Yu4F2 steel with a combined carbide–intermetallic hardening is highly competitive in strength (σu > 1600 MPa, σ0.2 > 1400 MPa) with high-strength 18Kh2N4VA ferromagnetic steels and significantly surpasses the well-known aging nonmagnetic high-nitrogen alloys.

The structure and the mechanical properties of low-carbon low-alloy 10Kh3A steel with an overequilibrium nitrogen content (0.20 wt %) are studied after heat treatment under various conditions. The quenching (950°C) and tempering (400°C) temperatures that result in significant hardening of the steel (σu = 1680 MPa, σ0.2 = 1550 MPa) at the retained plasticity (δ = 11%, ψ = 44%) that is high enough for practical application are determined. The strength of the 10Kh3A steel is higher than that of low-alloy nitrogen-free low-carbon 18Kh2N4VA steel, which is alloyed with nickel and tungsten and is widely used for heavily loaded structural members.

The phase composition and the mechanical properties of a 0.35-mm-thick strip made of austenitic–martensitic VNS9-Sh (23Kh15N5AM3-Sh) TRIP steel are studied after tempering at 450–900°C. The surface layer in the steel in the initial state contains almost 100% strain-induced martensite. Tempering at a temperature above 450°C is shown to cause the reverse martensitic transformation and a significant decrease in the strength properties.

Dense defect-free 10Kh3A steel ingots with an overequilibrium nitrogen content (0.1–0.17 wt %) are formed by electroslag remelting under nitrogen pressure in a DEShP 0.1 pilot furnace (All-Russia Institute of Aviation Materials). A method is developed for calculating the solubility of nitrogen in multicomponent melts, including model steels, under its atmospheric and working pressure in the furnace chamber. This method determines the nitrogen content in liquid and solid metals and can be used to form 10Kh3A steel ingots with a dense homogeneous structure. Distributions of nitrogen and other alloying elements over the ingot height and cross section are found. The calculated nitrogen solubility in the metal is in agreement with experiment one.

The microstructure and the static tensile stress–strain curve of a hot-rolled nitrogen-bearing austenitic–martensitic corrosion-resistant 27Kh15AN3MD2 steel have been studied. It is found that the curve has three straight line portions with different slopes at strains of 2–4.3% (portion I), 4.3–13.8% (portion II), and 13.8–19.5% (portion III). The intersection of the straight lines in portions I and II corresponds to the onset of the γ → α transformation at a strain of 4.3%. It is shown that strain-hardening coefficient dσ/de of the steel in portion II is significantly larger than that in portions I and III. Insignificant twinning and fragmentation of martensite crystals are observed after extension by 2%. A 25% strain leads to significant twinning intensity, refinement, and an increase in the martensite content to 90%.

Metal-matrix composite materials (CMs) are synthesized from a mixture of a metal powder (Ti, Fe, Co, Ni, Cu, Al-based alloy) and fullerenes (10 wt %). The thermobaric synthesis conditions (700–1000°C, 5–8 GPa) ensure the collapse of fullerene molecules and their transformation into superelastic carbon phase particles with an indentation hardness HIT = 10–37 GPa, an elastic modulus EIT = 60–260 GPa, and an elastic recovery of >80% upon indentation. After reinforcing by superelastic hard carbon, the friction coefficient of CM decreases by a factor of 2–4 as compared to the friction coefficient of the matrix metal, and the abrasive wear resistance increases by a factor of 4–200. Superelastic hard carbon particles are a unique reinforcing material for an increase in the wear resistance and a simultaneous decrease in the friction coefficient of CM.

The structure and the mechanical properties of high-nitrogen austenitic 05Kh21G9N7AMF (0.56% N) and 04Kh22G12N4AMF (0.49% N) steels have been studied after hot rolling. It is found that the temperatures of the onset and end of hot deformation influence the structure and the mechanical properties of these steels. The higher set of mechanical properties of steel 05Kh21G9N7AMF after rolling in the temperature range 1100–900°C is due to the formation of a lamellar and equiaxed fragmented structure.

The effect of the rolling temperature and strain on the structure and the properties of corrosionresistant austenitic–martensitic 14Kh15AN4M steel is studied. The steel is shown to exhibit high ductility: upon rolling in the temperature range 700–1100°C at a reduction per pass up to 80%, wedge steel specimens are uniformly deformed along and across the rolling direction without cracking and other surface defects. Subsequent cold treatment and low-temperature tempering ensure a high hardness of the steel (50–56 HRC). Austenite mainly contributes to the hardening upon rolling in the temperature range 700–800°C at a reduction of 50–70%, and martensite makes the main contribution at higher temperatures and lower strains. Texture does not form under the chosen deformation conditions, which indicates dynamic recrystallization with the nucleation and growth of grains having no preferential orientation.

The problems of applying a new nitrogen-alloyed martensitic corrosion-resistant 0Kh16N4AFD steel as a promising material for manufacturing car bodies are considered. The microstructure and properties of the steel after various heat treatments have been studied. It is shown that the steel is not behind 12Kh18N9T steel in the characteristics of ductility and corrosion resistance and significantly exceeds it in the static and cyclic strengths.

The effect of the conditions of heat treatment and plastic deformation on the structure and the mechanical properties of low-carbon martensitic nickel steel (9 wt % Ni) with an overequilibrium nitrogen content is studied. The limiting strain to failure of 04N9Kh2A steel is found to be 40% at a rolling temperature of 20°C and 80% at a rolling temperature of 900°C. Significant strengthening of the steel (σ0.2 = 1089 MPa) is obtained after rolling at a reduction of 40% at 20°C. The start and final temperatures of the α → γ transformation on heating and those of the γ → α transformation on cooling are determined by dilatometry. The specific features of the formation of the steel structure have been revealed as functions of the annealing and tempering temperatures. Electron-microscopic studies show that, after quenching from 850°C and tempering at 600°C for 1 h, the structure contains packet martensite with thin interlayers of retained austenite between martensite crystals. The strength of the nitrogen-bearing 04N9Kh2A steel after quenching from 850 and 900°C, cooling in water, and subsequent tempering at 500°C for 1 h is significantly higher than that of carboncontaining 0H9 steel used in cryogenic engineering.

Specimens with V- and U-shaped notches made of austenitic high-nitrogen corrosion-resistant 05Kh20G10N3AMF steel are subjected to impact tests in the temperature range from +20 to −196°C, and stress-strain diagrams are recorded. The test data are used to estimate impact toughness KCV and KCU, dynamic fracture toughness Jid at the stage of crack nucleation, and crack propagation energy Ap. The microrelief of the fracture surfaces is studied. As compared to forging, quenching from 1100°C is found to increase the impact toughness and the dynamic cracking resistance of the steel during impact loading and to decrease the ductile-brittle transition temperature. The steel is shown to exhibit the cold brittleness behavior characteristic of bcc materials. A model is proposed for the formation of cleavage facets in austenitic steels. It is based on easy slip along lattice planes under the low shear stress at a notch tip and the development of fracture at a stress lower than the yield strength of the material.

The static and fatigue cyclic strength of high-strength corrosion-resistant nitrogen-bearing austenitic 05Kh22AG15N8MF steel are studied in various structural states after hot rolling at 1100°C (water quenching from 1150°C, subsequent annealing at 800°C for 1 and 10 h, and cooling in air). The maximum life and a higher fatigue limit (400 MPa) are shown to be characteristic of hot-rolled samples with a finegrained austenitic structure and numerous twins. The mechanisms of fatigue crack propagation are studied.

The structural and phase transformations in high-nitrogen austenitic steel 05Kh20AG10N3MF under various thermal actions are studied. The transformations are shown to occur only in the Fe-Cr diffusion couple, and they resemble the phase transformations in an Fe-20% Cr binary alloy. At 1200°C, hightemperature phase separation is detected; at 550°C or below, low-temperature separation is detected; and at 700 and 800°C, ordering with the formation of a Laves phase is observed. The ordering-low-temperature separation phase transition in the steel differs substantially from that occurring in Fe-Cr binary alloys.

The composition and size of fullerites and the structures and fracture surfaces of superelastic hard carbon phase (SHP) particles made from them and reinforcing metal-matrix composite materials are studied by optical microscopy, X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. An inheritance relationship is shown to exist between the optically anisotropic structure of SHP formed under pressure at temperatures above the stability threshold of fullerene molecules and the structure of the original fullerites. The fractographic features of the SHP particles made from C60 fullerenes correlate with a deformed structure of fcc fullerites, whereas the particles made from a soot extract of fullerenes have a fracture surface characteristic of amorphous materials. Reinforcing with SHP particles increases the wear resistance of cobalt by several orders of magnitude and simultaneously decreases its friction coefficient. This effect is most pronounced upon reinforcing by the particles produced from a soot extract of fullerenes.

Principles of multicomponent alloying of high-temperature steels are formulated on the basis of reported and obtained experimental data. The short- and long-term strength, the structure, and the phase composition of high-temperature austenitic low-carbon steels 01Kh15N22AG2V4TYu and 02Kh18N12AG11MFB are studied in the structural states that form upon forging and aging and ensure the maximum hardening. These steels are found to have a high short-term strength and high-temperature strength. The tests of these steels performed for 8 × 103 h without failure of specimens at a temperature of 680°C and stresses of 100–120 MPa show that they are promising materials that can operate at 620–680°C for 2 × 105 h at a stress of 70 MPa in power units intended for operation at supercritical vapor parameters. The specific features of the fine structures of the steels in the forged and aged states that provide their high high-temperature strength are revealed. The evolution of structural constituents during long-term strength tests is studied, and the role of these constituents in fracture is determined.

The effect of water quenching from rolling heating at 1100°C on the structure, the mechanical properties, and the static fracture toughness of corrosion-resistant austenitic high-nitrogen 0.4Cr20Ni6Mn11Mo2N0.5 steel shot-rolled at 1100–900°C is studied. It is found that, after quenching, the initially hot-deformed steel possesses a quite high fracture toughness, although quenching from 1100°C decreases its fracture toughness by 11.4%. An analysis of fracture surfaces indicates a ductile character of failed quenched steel specimens. The specimens have fracture regions close to a quasi-cleavage at the stage of stable crack growth.

Raman spectroscopy, X-ray diffraction, and microhardness and modulus of elasticity measurements are used to study the influence of compacting pressure (5, 8 GPa) on the structure and properties of the phases prepared from fullerene soot extract (mixture of C60 and C70 crystallites) in a mixture with a cobalt powder. Carbon particles synthesized during high-temperature treatment at a pressure of 5 or 8 GPa and reinforcing composite samples have a universal hardness Hu (hardness measured from the total (elastic and plastic) strain under loading) of 12 or 25 GPa, respectively. After heating of samples to 900°C, the values of Hu of the particles decrease to 9–11 GPa at elastic recovery of the phase more than 85%. The dry friction coefficients of iron- and cobalt-based composite materials in contact with tool steel are 0.08 and 0.04, respectively.

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

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

The structure and properties of high-temperature austenitic steels intended for superheater tubes are analyzed. Widely used Kh18N10T (AISI 304) and Kh16N13M3 (AISI 316) steels are found not to ensure a stable austenitic structure and stable properties during long-term thermal holding under stresses. The hardening of austenitic steels by fine particles of vanadium and niobium carbides and nitrides and γ′-phase and Fe2W and Fe2Mo Laves phase intermetallics is considered. The role of Cr23C6 chromium carbides, the σ phase, and coarse precipitates of an M 3B2 phase and a boron-containing eutectic in decreasing the time to failure and the stress-rupture strength of austenitic steels is established. The mechanism of increasing the stress-rupture strength of steels by boron additions is described. The chemical compositions, mechanical properties, stress-rupture strength, and creep characteristics of Russian and foreign austenitic steels used or designed for superheater tubes intended for operation under stress conditions at temperatures above 600°C are presented. The conditions are found for increasing the strength, plasticity, and thermodeformation stability of austenite in steels intended for superheater tubes operating at 700°C under high stresses for a long time.

Microingots (2 g in mass and 3 mm in diameter) of iron-based alloys with various contents of nickel (4.5–34.0 %) and nitrogen (0.020–0.268%) were produced by melting with induction heating in the gaseous nitrogen medium under pressure. The structure, phase composition, and microhardness of the alloys are studied. The nitrogen alloying of the Fe-Ni alloys is shown to bring about an increase in the austenite content and microhardness of the alloys. The nonequilibrium phase diagram of the Fe-Ni-N cast alloys was constructed.

The structures of Fe-Cr-N alloys are studied, and the types of chemical interactions in the Fe-Cr and Fe-N diffusion couples are determined at various temperatures. At 1200°C, austenite is shown to form in the alloys as a result of a tendency toward phase separation in the Fe-Cr and Cr-N diffusion couples. Below 1150°C, chromium nitrides form in the alloys due to ordering in the Cr-N diffusion couple.

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

Wear-resistance sliding-friction tests of high-strength corrosion-resistant nitrogen-bearing 08Kh14AN4MDB and 05Kh22AG15N8M2F steels have been performed for different structural states under sliding-friction conditions. The wear resistance of these steels depends on the intensity of the strain hardening of austenite. The martensitic-austenitic 08Kh14AN4MDB steel has a higher wear resistance if it has a high nitrogen-austenite concentration. The dependence of the weight loss of the 05Kh22AG15N8M2F and 12Kh18N10T steels on the test time is found to be linear.

The influence of thermal treatment on the structures and mechanical properties of welds of corrosion-resistant high-nitrogen austenitic 05Kh22AG16N8M-type steels is studied. In these steels, austenite is found to be highly resistant to discontinuous precipitation and the formation of σ phase and δ ferrite upon cooling regardless of the temperature of heating for quenching (from 900 to 1250°C) and the cooling conditions (water, air, furnace). Welding of these steels can produce high-strength welds with an enhanced impact toughness.

The effect of deformation on the structure and related chemical properties of an austenitic 0Kh18N2A alloy with an overequilibrium nitrogen content has been studied. Cold plastic deformation at an 8–11% reduction before aging at 350°C is shown to halve the corrosion rate of the alloy as compared to the undeformed state. A thermoplastic treatment by the schedule quenching + aging at 350°C + 20% reduction is found to be more effective: the corrosion rate decreases by an order of magnitude as compared to the undeformed state.

The kinetics of development of fatigue microcracks in a high-strength 08Kh14AN4MD steel is studied when a cantilever specimen with several notches is subjected to rotational bending tests. The specific feature of the tests consists in the fact that, when the specimen is loaded at a constant load, different stress amplitudes are realized in different notches. As a result, after the sample has failed across the section with the maximum stress, a longitudinal polished section of the specimen contains fatigue cracks having nucleated in the mouths of the other notches at lower stress amplitudes. A relation between inflection points in the fatigue curve and the conditions of local and developed yield in a notch has been established. Fatigue fracture mechanisms at a superhigh number of loading cycles are studied, and their relation to the structure near a crack is found. A rapid method for estimating the fatigue limit at a superhigh number of loading cycles is proposed.

The phase composition, lattice parameters, and residual stresses in the α and γ phases of steels containing 0.14–1.2 wt % N are determined by high-temperature X-ray diffraction at 20–1200°C. A procedure is proposed for the in situ quantitative study of the Cr2N nitride dissolution kinetics and austenite grain growth when diffraction patterns are taken at high temperatures. The temperature boundaries of the decomposition of the α and γ phases and the temperature of complete dissolution of nitride phases are found. The formation of interphase residual stresses during thermal treatment is considered.

The possibilities of the maximum decrease in the nickel content in an AISI 316 (0Kh17N12M2-type) steel via partial substitution of nitrogen for nickel and the corresponding correction of the contents of other alloying elements are analyzed. The corrected chemical composition of an AISI 316L-based steel is ≤0.02% C, 0.1–0.3% N, 17.5–18.5% Cr, 2.2–2.7% Mo, 3–4% Mn, and 0.1–0.5% Si. Calculation of the chromium equivalents of martensite formation and ferrite formation using the Potak-Sagalevich structure-phase diagram shows that, after quenching, these steels should have a purely austenitic structure without martensite or ferrite.

The effect of hot-rolling conditions on the structure, strength, ductility, fracture toughness, and technological properties of the nonmagnetic steel 05Kh22AG15N8M2F-Sh containing 0.55% N has been studied. A homogeneous and fine-grained austenitic structure forms in the steel upon rolling at 1000–1050°C and a reduction of more than 60–70%. This structure provides the following properties: σ0.2 = 1044 N/mm2, σu = 1172 N/mm2, δ = 32%, ψ = 64%, and KCV = 1.06 MJ/m2 at −70°C. The possibility of recrystallization of the hot-rolled steel (deformed at 10–90% reductions) is checked upon its subsequent heating to 850–1200°C followed by water quenching. The steel is shown to have high strength, ductility, and fracture toughness and to retain an austenitic structure without cracks or exfoliation upon hot plastic deformation by rolling up to a 90% reduction.

The structure and hardening of austenitic steels subjected to shock-wave treatment have been studied. This treatment is shown to form a structure whose cell size decreases with increasing pressure. The treatment-induced hardening of the steels can be estimated using the Hall-Petch relation. At the same degrees of residual deformation, shock-wave treatment results in a significantly higher degree of hardening of the austenitic steels as compared to cold rolling. The degree of hardening increases with decreasing stacking-fault energy in austenite.

The structure of the Fe18%Cr alloys with 0.6, 0.9, 1.1 and 1.3%N quenched from different temperatures was studied using electron microscopy and X-ray analysis. It was shown that the temperature of quenching and N concentration in alloys determine which structure is formed after quenching: austenite only, austenite + martensite; austenite + CrN or ferrite + CrN. The type of the quenched structure determines the character of the alloys decomposition during ageing. The decomposition of the austenite begins with CrN mixed zones formation and simultaneously γ-α transformation. Further, the mixed zones transform into CrN with a tetragonally distorted B1 structure of the NaCl type. Nitrides present in the quenched structure (martensite or ferrite) result in further coarsening during ageing.