O. V. Rybal’chenko

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→ ɛ→ 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.

Formation of a submicrocrystalline structure in austenitic 08Kh18N10T steel during equal-channel angular pressing followed by heating

The structure and mechanical properties of austenitic 08KhN10T steel subjected to equal-channel angular pressing (ECAP) at room temperature (ɛ = 3.2) and subsequent heating are studied. In the course of ECAP, the steel undergoes a martensitic transformation; the martensite content reaches 45%. Upon heating, martensite (ferrite) transforms into austenite. The partly submicrocrystalline oriented structure of the 08Kh18N10T steel in the austenitic (55%)-martensitic (45%) state (formed upon ECAP) provides its high strain hardening (σ0.2 = 1315 N/mm2), as compared to the initial state (σ0.2 = 250 N/mm2), and high plasticity δ = 11%. After heating to 550°C, the steel has a predominantly submicrocrystalline austenitic (80%)-ferritic (20%) structure, σ0.2 = 1090 N/mm2, and δ = 11%.

Effect of torsion conditions under high pressure on the structure and strengthening of the Zr–1% Nb alloy

The effect of temperature and degree of deformation upon severe plastic deformation by torsion under a high pressure on the structure, phase composition, and microhardness of the industrial zirconium Zr–1% Nb alloy (E110) has been studied. The high-pressure torsion (HPT) (with N = 10 revolutions) of the Zr–1% Nb alloy at room temperature results in the formation of grain–subgrain nanosize structure with an average size of structural elements of 65 nm, increase in the microhardness by 2.3–2.8 times (to 358 MPa), and α-Zr → β-Zr and α-Zr → ω-Zr phase transformations. The increase in the HPT temperature to 200°C does not lead to a decrease in the microhardness of alloy owing to the increase in the fraction of ω-Zr phase, though the average size of structural elements increases to 125 nm. The increase in the temperature to 400°C during HPT with N = 10 revolutions leads to the grain growth in the α-Zr grain structure (~90%) to 160 nm and a decrease in the microhardness to 253–276 HV.

Effects of silica and titania modification additions on the microstructure of sintered alumina

The way in which silica and titania modification additions are introduced into alumina is shown to have a strong effect on the microstructure of sintered Al2O3-SiO2-TiO2 materials. By combining molecular layering and mechanical mixing, materials with a controlled pore structure can be obtained.

Effect of Shear Strain on the Structure and Properties of Chromium-Nickel Corrosion-Resistant Steels

The structure and properties of metastable austenitic steel 08Kh18N10T and stable austenitic steel ASTM F138 under shear deformation implemented by torsion under hydrostatic pressure (THP) at T = 300 and 450°C and by equichannel angular pressing (ECAP) at T = 400°C are studied. The THP yields an ultrafine-grain structure in a fully austenitic matrix with grain size 45 – 70 nm in steel ASTM F138 and 87 – 123 nm in steel 08Kh1810T. The ECAP at 400°C yields a grain-subgrain structure with structural elements 100 – 300 nm in size in steel 08Kh18N10T and 200 – 400 nm in size in steel ASTM F138.

Effect of the Removal of a Surface Layer on the Mechanical Properties and the Static Stress–Strain Curves of an Austenitic–Martensitic Sheet TRIP Steel

The influence of the removal of a surface layer with a high strain-induced martensite content on the mechanical properties and the shape of stress–strain curves of austenitic–martensitic VNS9-Sh TRIP steel is studied by room-temperature tests. The removal of a surface layer 5–20 μm thick by electropolishing is shown not to decrease the mechanical properties of this steel and not to change the shape of its stress–strain curves, which have a developed yield plateau. This effect can be related to the presence of a long (up to 1%) stage of microyield in this steel. The existence of a yield plateau in the stress–strain curves of VNS9-Sh steel in the initial state and after the removal of a surface layer can also be explained by the simultaneous operation of three plastic deformation mechanisms, namely, slip, twinning, and martensitic transformation, during deformation.

Effect of the phase composition of the surface layer on the mechanical properties of 23Kh15N5AM3-Sh TRIP steel sheets

The static and cyclic mechanical properties of cold-rolled corrosion-resistant VNS 9-Sh (23Kh15N5AM3-Sh) TRIP sheet steel from two batches having different deformation martensite contents in the surface layer are studied. An increase in the deformation martensite content is shown to cause an increase in the strength properties, a certain decrease in the plasticity, and an increase in the fatigue limit at 107 cycles.

Effect of the removal of the surface layer of a TRIP steel sheet on its phase composition after static tension at various strain rates

The effect of the removal of the surface layer of a thin strip made of austenitic–martensitic VNS9-Sh (23Kh15N5AM3-Sh) TRIP steel on the phase composition of the strip surface is studied after static tension at various strain rates. An increase in the strain rate is shown to increase the austenite content in the surface layer of the metal. The removal of a 10-μm-thick surface layer by electropolishing results in an increase in the austenite content due to the initial nonuniform phase composition of the thin TRIP steel strip across its thickness after cold rolling.