Machinability of the high-strength corrosion-resistant high-ductility austenitic steel 06Kh22AG15N8M2F

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.     

Hardening in steels with a controllable austenitic γ → α transformation intended for pressing tools

The hardening of 4Kh2N5M2F2 steel is studied during plastic deformation at temperatures of 400–900°C. The strength of this steel is found to increase significantly after this treatment at temperatures below the recrystallization temperature. The vanadium carbonitrides forming in the steel at elevated temperatures decrease the grain size, decrease the sensitivity to overheating, and increase the impact toughness.     

Stability of the Transition Zones in a Steel–Vanadium Alloy–Steel Sandwich after Thermomechanical Treatment

A priority in atomic power today is to develop a new material for fuel-rod casings in fast-neutron reactors. A radiation- and corrosion-resistant three-layer composite based on vanadium alloy and stainless steel has been developed. This composite potentially meets the operational requirements on fuel-rod casings in very challenging operating conditions (high temperatures, radiation, and aggressive media). The performance of this material depends on the quality of the joint between the three layers, which is determined by the preliminary deformation and heat treatment. In the present work, the influence of tempering on the chemical composition, structure, and strength of the joint between the vanadium alloy and steel in the sandwich obtained by hot pressing a three-layer pipe blank at 1100°C is studied. The components of the pipe are 20Kh13 (Russian standard) steel for the external layers and V–4Ti–4Cr vanadium alloy in the core. The structure and chemical composition at the interfaces is investigated by optical and electronic microscopy, with X-ray spectral analysis. The strength of the steel–alloy bond is assessed in compressive tests of an annular three-layer sample with a cut; acoustic-emission measurements are employed. Pressing is found to form a transition zone of thickness 10–15 μm between the vanadium alloy and the steel, which is characterized by diffusional interaction and has a variable chemical composition. This zone consists of a series of solid solutions, without the deposition of brittle phases, and consequently the junction between the layers is strong. No pores, peeling, or defect are observed at the steel–alloy junction. However, in compressive tests of semiannular three-layer samples with a cut after hot pressing, a crack is formed in the steel layer at the tip of the cut. Annealing at 800°C improves the transition zone by increasing the thickness corresponding to diffusional interaction. Consequently, in mechanical tests, the sandwich behaves as a monolithic material, without cracking or peeling between the steel and the vanadium alloy.     

Nitrided 08Kh17T steel after high-pressure torsion

The effect of severe plastic deformation by high-pressure torsion (HPT) on the microstructure, the phase composition, the microhardness, and the thermal stability of 08Kh17T steel preliminarily subjected to high-temperature bulk nitriding followed by annealing is studied. Nitriding is performed in a pure nitrogen atmosphere at 1075°C. HPT is found to cause the formation of a homogeneous nanostructure with a grain size of 55–85 nm. The microhardness of the steel after HPT increases by a factor of 2.2–2.7, to HV 780–860 depending on nitriding conditions. Hardening is retained when the material is heated to 450°C.     

High-plasticity heat-resistant 03Kh14G16N6Yu-type steels with heat-and deformation-resistant austenite

The structure and mechanical properties of 03Kh14G16N6Yu-type austenitic steels alloyed by molybdenum, tungsten, vanadium, and zirconium are studied after normalization at 1075°C and long-term holding at 500–700°C. The chemical composition of these steels ensures the resistance of their austenite to the martensitic transformation in the temperature range from 1200 to ?196°C and during cold plastic deformation at a reduction of up to 60%. The best combination of the mechanical and technological properties is achieved in a 03Kh15G17N6YuVF steel with 0.08% W and 0.12% V. Long-term (up to 1000 h) holdings at 550–750°C do not cause the precipitation of carbide, nitride, and intermetallic phases in this steel. The long-term strength of the 03Kh15G17N6YuVF steel at temperatures up to 650°C is comparable with and its plasticity and impact toughness are higher than those of high-nickel Kh16N9M2 and Kh16N12M2 steels, which are applied in the main parts of electric power installations.     

Structure and fatigue properties of 08Kh18N10T steel after equal-channel angular pressing and heating

The structure of corrosion-resistant austenitic 08Kh18N10T steel is studied after equal-channel angular pressing (ECAP), heating, and subsequent cyclic tests. After ECAP, an oriented mainly subgrain structure with a structural element size of 100–250 nm and a high fraction of deformation twins forms in the austenite of the steel, and 42 vol % of lath martensite appears. Dynamic twinning, martensitic transformation, dynamic recovery, and even recrystallization take place in the 08Kh18N10T steel during cyclic deformation in the course of fatigue tests according to the scheme of repeated tension. The fatigue strength increases after ECAP due to the refinement and twinning of an austenite structure and the appearance of martensite. The fatigue limit is maximal after ECAP and heating at 550°C for 20 h due to a high annealing twin density in a predominantly austenitic recrystallized matrix, intense dynamic twinning, and martensitic transformation during cyclic deformation.     

Viscoplastic model for the strain resistance of 08Kh18N10T steel at a hot-deformation temperature

The viscoplastic model of the strain resistance of a metal developed earlier is shown to be applied to austenitic corrosion-resistant 08Kh18N10T steel with the fcc lattice at a hot-deformation temperature of 1150°C. Metallographic examination supports dynamic recrystallization occurring at this deformation temperature.     

Corrosion properties of austenitic Cr-Mn-Ni-N steels with various manganese concentrations

The structure and corrosion properties of two high-nitrogen 05Kh20AN8MF steels additionally alloyed with 9 and 17% Mn have been studied. Metallographic, X-ray diffraction, and fractographic studies show that both steels have an austenitic structure and high plasticity properties after quenching from 1100 and 1100°C and subsequent aging at 500°C for 2 h. The steel alloyed with 9% Mn and 0.58% V exhibit a higher strength. Both steels have a higher corrosion resistance in a 3.5% NaCl aqueous solution than 12Kh18N9T steel. After aging at 400–600°C, the corrosion rate and the sensitivity to stress corrosion cracking increase.     

Estimation of the notch sensitivity of a nitrided steel by acoustic emission

The notch sensitivity of sheet corrosion-resistant 08Kh17T steel is estimated in the states before and after high-temperature (1000–1100°C) internal nitriding during tensile tests accompanied by the measurement of acoustic emission signals. A crack in the steel is shown to propagate according to a ductile mechanism is all states. As the nitrogen content increases from 0.60 to 0.85%, the ultimate tensile strength of the steel decreases by 15% in the presence of a stress concentrator and remains substantially higher than the yield strength of the sheet steel without a stress concentrator.     

Phase and structural transformations in corrosion-resistant steels upon high-pressure torsion and heating

High-pressure torsion (HPT) at a pressure of 6 GPa and room temperature is found to form a nanocrystalline structure in corrosion-resistant austenitic 05Kh15N9D2TAMF and 08Kh18N10T steels and a submicrocrystalline structure in corrosion-resistant ferritic 08Kh18T1 steel and armco iron. X-ray diffraction analysis of both austenitic steels reveals the γ → α and γ→ ?→ α martensitic transformations during HPT at room temperature. After HPT, the strain hardening in the austenitic and ferritic steels is approximately the same and mainly determined by nano- and submicrocrystalline structures, and the role of alloying and phase composition weakens. The thermal stability of the hardening in the austenitic and ferritic steels is almost the same, ～400°C. As a result of HPT, the austenitic 08Kh18N10T and ferritic 08Kh18T1 steels acquire an axial texture with the predominant 〈211〉_γ direction in austenite and the 〈110〉_α and 〈311〉_α directions in martensite and ferrite, respectively. The axial texture is retained in both steels up to a heating temperature of 750°C.     

Effect of heat treatment on the mechanical properties and the structure of a high-nitrogen austenitic 02Kh20AG10N4MFB steel

The effect of heat treatment on the mechanical properties of a high-nitrogen austenitic 02Kh20AG10N4MFB steel has been studied in the temperature region 550—1200°C. The yield strength and the ultimate tensile strength are shown to change nonmonotonically as a function of the heat treatment temperature. They sharply decrease in the annealing temperature range 850—900°C, which can demonstrate a change in the character of the structure–phase state of this steel. After annealing at 850—900°C, aging occurs with the precipitation of embrittling phases; at higher annealing temperatures, these particles dissolve and austenite recrystallizes. The study of the stress–strain diagrams makes it possible to find the laws of strain hardening of the 02Kh20AG10N4MFB steel as a function of the heat treatment temperature.     

Hot plastic deformation of 08X21H5T steel

The nonuniformity of hot plastic deformation of 08X21H5T steel is studied. Tensile tests are conducted in the vacuum chamber of the IMASH-20-75 Ala-Too machine. The samples are attached to a clamp in the chamber by means of straps. A junction of a platinorhodium–platinum thermocouple is soldered to the side surface of the sample. Air is pumped out of the chamber to a residual pressure of 5.0 × 10^–5 mm Hg (6.7 × 10^–3 Pa). The sample is heated to 800–1200°C by means of industrial-frequency current. The precision of temperature maintenance is ±5°C. The deformation of the austenite and ferrite phases is investigated as a function of the overall deformation of the steel and the temperature. The influence of these factors on the slip rate of the austenite and ferrite phases along the grain boundaries is also considered. The hot-microhardness ratio of the austenite and δ ferrite in 08X21H5T steel is investigated as a function of the temperature.     

Structural and phase transformations in high-nitrogen austenitic steel 05Kh20AG10N3MF during thermal action

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.     

Failure behavior of 304l stainless steel in torsion

The workability of 304L austenitic stainless steel has been investigated using torsion testing at temperatures from 20 °C to 1200 °C and strain rates of 0.01 and 10.0s ^-1 For the lower strain rate, temperature changes due to deformation heating were minimal, and failure was found to be fracture controlled at all temperatures. As for many other metals, the 304L exhibited a ductility minimum at warm-working temperatures. For the higher strain rate, failure was controlled by flow-localization processes at 20 °C and 200 °C. At these temperatures, flow softening resulting from deformation heating was deduced to be the principal cause of flow localization. A model to predict the strain at the onset of localization was developed and applied successfully to the 304L results. For high strain-rate torsion tests at 400 °C and above, failure was fracture controlled as in the low strain-rate tests, and the ductilities were shown to be correlated to those at the lower strain rate through the Zener-Hollomon parameter by employing an activation energy derived from flow-stress data.     

Study of the Interaction of Adhesion-Active Copper-Silver Alloy PSR-40 with Stainless Steel of the Austenitic Class

Interaction of molten copper-silver alloy PSR-40 with stainless steel 1Kh18N9T is studied in relation to melt temperature (700-800°C) and contact time (10-40 min). It is established that alloy components diffuse into the steel. The depth of their penetration and the degree of interaction with steel increase with an increase in temperature and contact time. As a result of this with contact of the structural components to more than 20 min and a temperature above 780°C there is formation of chemical compounds with a higher hardness at the alloy-steel interface. Therefore impregnation in air for porous carcasses made from stainless steel 1Kh18N9T fibers with molten copper-silver alloy above these parameters is undesirable.     

Fabrication of iron aluminum alloy/steel laminate by clad rolling

Laminates of an iron-aluminum alloy (20Al) and three types of steel—chromium molybdenum (CrMo), high carbon (FeCMn), and precipitation hardening steel with niobium carbide (FeCNb)—were fabricated at 600 °C and 1000 °C by clad rolling based on the compression stress ratio of 20Al to steel. The laminates fabricated at 600 °C exhibit a deformation microstructure with partial recrystallization, while those at 1000 °C reveal a refined microstructure. The 20Al layer of all the laminates exhibit a {001}〈110〉 texture, and the intensity of the texture increases with a decrease in the fabrication temperature and an increase in the reduction. The bending deformability of a laminate increases with a decrease in the compression stress ratio and by a reduction in the intensity of the {001}〈110〉 texture. The clad plate is further rolled at room temperature to a thickness of approximately 150 μm, which enables winding without damage. It is concluded that a high-strength steel at high temperatures and a high Al content in the Fe-Al alloy is beneficial for the fabrication of deformable laminates.     

Influence of heat treatment on the structure and mechanical properties of chrome steel with unstable austenite

The structure and mechanical properties of 35Kh12G3MVFDR steel are investigated. After normalization or quenching, the steel contains up to 35 vol % austenite and may be assigned to the martensitic–austenitic class. On heat treatment—tempering, isothermal holding, or isothermal quenching—the austenite is converted to martensite within 2 h. The martensite in 35Kh12G3MVFDR steel is more thermally stable: the first signs of its conversion to sorbitic structure are observed after 25-h isothermal quenching at 640°C, and its complete decomposition requires 50 h. The breakdown of martensite is accompanied by decrease in the high-temperature strength and hardness. Aging of the quenched and tempered 35Kh12G3MVFDR steel at 670–720°C lowers the hardness from 61–65 HRA to 55–60 HRA after 1600–3200 h and the yield point at 20°C from 1350 MPa to 750–850 MPa. Likewise, the yield point at 720°C declines from 310 MPa to 160–230 MPa after 600 h and then stops. The state of the martensitic structure of 35Kh12G3MVFDR steel determines its creep resistance at 700°C. For example, the martensite remains in the steel structure after relatively brief isothermal quenching (up to 24 h at 640°C), and consequently the creep limit σ^700°C _0.1%/h is no lower than after simple quenching with subsequent high tempering: 86.2 ± 9.4 MPa and 89.3 ± 8.8 MPa, respectively. At the same time, in response to the decomposition of martensitic structure as a result of prolonged aging (1600 h at 670°C), σ^700°C _0.1%/h declines to 63.9 ± 7.1 MPa. In contrast to martensite, the austenite in 35Kh12G3MVFDR steel is thermally unstable and is converted to martensite after only 1–2 h of heating, depending on the temperature.     

Structure formation in high-strength nitrogen-bearing steel on hot deformation

The resistance to deformation of nitrogen-bearing Cr–Ni–Mn steel at 800–1200°C is investigated by means of the Gleeble 3800 system. By analysis of the deformation diagrams—in particular, determination of the threshold strain for dynamic recrystallization—the temperature and strain corresponding to the onset of dynamic recrystallization are established as a function of the strain rate, and optimal temperatures for hot stamping, forging, and rolling are recommended for industrial conditions. With true strain e = 0.9, the dynamic recrystallization in the steel at strain rates of 10^–2–2 s^–1 occurs at temperatures no lower than 900°C. Metallographic data confirm the experimental results and show that the structure formation in the steel on isothermal deformation at different rates is different above 900°C. With increase in temperature and decrease in strain rate, relaxation processes are more developed. At a strain rate of 0.01 s^–1 (stamping on a press), dynamic recrystallization begins at around e = 0.1 (relative reduction around 10%) in the range 1100–1200°C. Strain of around 20 and 30%, respectively, is required with decrease in temperature to 1000 and 900°C. With increase in strain rate to 0.1 s^–1 (forging), dynamic recrystallization begins with around 20% strain above 1100°C, 28% at 1000, and 35% at 900°C. At a strain rate of 1–2 s^–1 (rolling), dynamic recrystallization begins at around 30% strain in the range 1000–1100°C. In that case, the threshold strain is 36% at both 900 and 1200°C.     

Structure and mechanical and corrosion properties of new high-nitrogen Cr-Mn steels containing molybdenum

The structure, mechanical properties, and pitting corrosion of nickel-free high-nitrogen (0.8% N) austenitic 06Kh18AG19M2 and 07Kh16AG13M3 steels have been studied in various structural states obtained after hot deformation, quenching, and tempering at 300 and 500°C. Both steels are shown to be resistant to the ?? ?? ?? and ?? ?? ? martensite transformations irrespective of the decomposition of a ?? solid solution (06Kh18AG19M2 steel). Austenite of the steel with 19 wt % Mn shows lower resistance to recrystallization, which provides its higher plasticity (??₅) and fracture toughness at a lower strength as compared to the steel with 13 wt % Mn. Electrochemical studies of the steels tempered at 300 and 500°C show that they are in a stable passive state during tests in a 3.5% NaCl solution and have high pitting resistance up to a potential E _pf = 1.3?C1.4 V, which is higher than that in 12Kh18N10T steel. In the quenched state, the passive state is instable but pitting formation potentials E _pf retain their values. In all steels under study, pitting is shown to form predominantly along the grain boundaries of nonrecrystallized austenite. The lowest pitting resistance is demonstrated by the structure with a double grain boundary network that results from incomplete recrystallization at 1100°C and from the existence of initial and recrystallized austenite in the 07Kh16AG13M3 steel. To obtain a set of high mechanical and corrosion properties under given rolling conditions (1200?C1150°C), annealing of the steels at temperatures no less than 1150°C (for 1 h) with water quenching and tempering at 500°C for 2 h are recommended.     

Influence of the Chemical Composition and Heat Treatment Modes on the Phase Composition and Mechanical Properties of the ZK51A (ML12) Alloy

The objects of investigation are ZK51A (ML12) alloy samples containing from 3.5 to 5.5 wt % Zn and 0.5–0.8 wt % Zr. The influence of Zn and Zr content on phase transition temperatures and the phase composition in equilibrium conditions and when using the Scheil–Gulliver solidification model is established using the calculation of phase diagrams in the Thermo-Calc program. It is shown that a significant increase in the liquidus temperature of the alloy occurs at a zirconium content in the alloy higher than 0.8–0.9 wt %, and an increase in the melting temperature above 800°C is required, which is undesirable when using steel crucibles. The equilibrium content of alloying components in the magnesium-based solid solution at various temperatures is calculated. The microstructure of as cast and heat-treated alloys with various concentrations of alloying components is investigated using scanning electron microscopy. The distribution of Zn and Zr in a dendritic cell of the as cast and heat-treated alloy is investigated. Zinc is concentrated along the dendritic cell boundaries in the as cast state, but its concentration in their center becomes higher than along the boundaries after heat treatment (HT). Zirconium is concentrated in the center of dendritic cells. It is shown that the two-stage solutionizing mode gives the largest increment of this characteristic: 330°C, 5 h + 400°C, 5 h. The influence of the aging temperature (150 and 200°C) on the sample hardness is investigated. It is revealed that it is higher in the case of aging at 200°C, and its maximum is observed under holding for 8?10 h. The HT of the alloy, including solution treatment (330°C, 5h + 400°C, 5 h) with subsequent quenching and aging (200°C, 8 h), made it possible to attain an alloy ultimate strength of 285 ± 13.5 MPa and a elongation of 11.4 ± 1%.