A. I. Uvarov

Structure and mechanical properties of the nitrogen-containing austenitic plate steel 04Kh20N6G11AM2BF

Structure and mechanical properties of the nitrogen-containing austenitic plate steel 04Kh20N6G11AM2BF with a thickness of 20 and 40 mm after hot rolling, quenching from different temperatures, and final strengthening by cold or warm deformation have been studied. For these large-section plates, sufficiently high mechanical properties were obtained, namely, the yield stress σ0.2 ≥ 690 MPa, the relative elongation δ ≥ 20%, the relative reduction ϕ ≥ 50%, and the impact toughness KCV+20 ≥ 100 J/cm2. This complex of strength and plastic properties of hot-rolled steel was produced after the quenching of the plates from 1150°C and subsequent strengthening warm (600°C) or cold (20°C) rolling with a reduction of up to 15%. These properties of steel were due to several causes, namely, the presence of nitrogen in the fcc solid solution, an increased density of dislocations (≈ 1010 cm−2), the precipitation of nanocrystalline vanadium nitrides with sizes of 2–4 nm, and the absence of large amounts of coarse near-boundary particles.

Evolution of the microstructure and microstresses in the 40Kh4G18F2 steel upon carbide aging

Structural mechanism of aging of the 40Kh4G18F2 steel at 600 and 700°C (precipitation of clusters and VC carbide particles) has been clarified, and its effect on the magnitude of the elastic microdeformation of the lattice of an austenitic matrix and, consequently, on the magnitude of microstresses, has been analyzed.

Specific features of low-temperature phase transformations in nitrogen-Containing Cr-Mn-based steels

Physical and mechanical properties of nitrogen-containing austenitic steels of different alloying systems have been studied at temperatures from −196 to 700°C in the quenched state. It has been found that nitrogen-containing Cr-Mn-based steels undergo a paramagnetic to antiferromagnetic ordering (with a manifestation of invar properties), the ΔE effect, and a resistivity anomaly. It has been shown that the behavior of the temperature dependence of the yield stress in nitrogen austenite is determined by several factors. Along with specific features of the dislocation structure determined by a low energy of stacking faults, the strengthening of nitrogen austenite is influenced by its magnetic state.

Effect of preliminary plastic deformation on the structure and physicomechanical properties of aging invar alloy N30K10T3

The invar alloy N30K10T3 after water quenching from 1150°C (austenite, γ phase) has the temperature of the start of martensitic transformation Ms ≈ −80°C and the Curie temperature TC ≈ 200°C. The effect of aging-induced phase decomposition in a deformed supersaturated solid solution on its hardness HV, electrical conductivity σ, magnetic permeability μ, and linear expansion coefficient β has been studied. It has been shown that cold plastic deformation of the alloy (at 20°C) to 30–50% increases its hardness, virtually does not change the conductivity, and decreases permeability. Aging of the deformed invar results in increasing HV and σ and decreasing μ. At room temperature, the deformed invar has a low linear expansion coefficient; its magnitude grows the faster, the greater the aging temperature Ta. Plastic deformation increases the density of dislocations, which form a banded substructure in austenitic grains. Besides, a metastable martensitic phase has been observed, which undergoes a reverse martensitic transformation into austenite upon heating in the temperature range from 550°C to 650°C. This transformation causes a decrease in the linear expansion coefficient β(T) of the deformed material. In samples aged at Ta = 700°C (after deformation), an athermal aging-induced martensite (αa phase) appears after cooling them to 20°C. The appearance of the αa phase is due to an increase in the temperature of the start of the martensitic transformation to above the room temperature caused by aging. In the samples containing the αa phase, there is observed a decrease in β in the temperature range from 350 to 670°C, which is due to the reverse transformation of the aging-induced martensite into austenite (αa → γ).

Effect of structure of aging metastable austenitic steels on the signal from an eddy-current transducer

Eddy-current parameterf0 of the N26T3 steel has been studied as a function of both the aging temperatureTag=20–800°C and the time τ of exposure to a constant temperature of 550 and 600°C up to 6h. In the initial state, the steel had two phases: (1) cooling-induced martensite+austenite (α+γ) or (2) strain-induced martensite+austenite (α′+γ). The parameterf0 drops monotonically as τ increases, and this drop is the faster, the higherTag. The parameterf0 changes nonmonotonically with the aging temperature. In addition to the initial two-phase structures, the one-phase γ structure has also been studied. The parameterf0 grows monotonically with the plastic cold strain and changes nonmonotonically with the aging temperature (20–800°C). Observed changes inf0 have been explained.

Effect of heat and thermomechanical treatments on the structure and physical and mechanical properties of the N30K10T3 invar

Invar alloy N30K10T3, whose austenite is metastable with respect to the martensitic γ → α transformation that occurs upon cooling below the martensitic point (Ms = −80°C), has been studied. The following six ways of the alloy strengthening have been tested: (1) aging (a) in a temperature range of ΔTa = 20–700°C; (2) liquid-nitrogen cooling (lnc) of the material preliminarily hardened by aging under the aforementioned conditions (route 1) (a + lnc); (3) preliminary phase-transformation-induced hardening (ph) (γ → α → γph) and aging in the temperature range of ΔTa (ph + a); (4) liquid-nitrogen cooling of the material preliminary hardened via route 3 (ph + a + lnc); (5) preliminary cold deformation (to 30%) at room temperature and aging in a temperature range of ΔTa (cd + a); and (6) liquid-nitrogen cooling of the material preliminary hardened via route 5 (cd + a + lnc). The six ways of hardening were found to affect the hardness, electrical conductivity, magnetic permeability, and temperature dependence of the thermal expansion coefficient.

Adjusting the linear expansion coefficient Lin Fe-Ni-Co-Ti invars by aging and phase hardening

The N30K10T3 and N40K10T3 invars with the Curie points θC ≈ 200°C and θC ≈ 310°C and the martensite temperatures Ms ≈ −80°C and Ms < −196°C, respectively, have been studied. The two alloys were hardened by quenching in the range of temperatures from 100 to 750°C. In addition, the first alloy was hardened by a combination treatment including phase-transformation-induced hardening and aging. The method of phase hardening consisted in the use of a forward (γ → α) and a reverse (α → γph) martensitic transformations. It has been shown that the temperature dependences of the linear expansion coefficient and the dependences of the hardness on the temperature and time of aging are considerably different for both alloys upon decomposition of the supersaturated solid solution. Both the ordinary and the double aging have been studied.

Effect of the Structure of Aging Invars with a Metastable Austenite on the Frequency Dependence of Their Magnetic Permeability

The effect of the generator current frequency f on the magnetic permeability μ of the N30K10T3 invar is studied for its various structural states formed upon the following treatments: phase naklep (i.e., the phase-transformation-induced hardening of austenite), cold plastic deformation, and cooling in liquid nitrogen. The ferromagnetic austenite of the alloy is metastable with respect to the γ → α martensite transformation upon cooling to temperatures below the temperature of the onset of the martensite transformation (Ms ≈ −80°C) and represents a supersaturated solid solution ageable during heating. The types of treatment are shown not to change the linear character of the μ(f) dependence in the frequency range under study (15–50 kHz) and to decrease μ to a certain extent.

A study of cellular decay in austenite alloys using an applied eddy-current transducer

The eddy-current parameter f0 of the N36K10T3 invar has been studied in the range of aging temperatures from 600 to 900°C. The maximal drop in f0 has been observed at the temperature Tag = 800°C, and the drop in this parameter was the larger, the longer the aging process. The drop in this parameter is caused by the cellular decay process in the solid solution, which depletes the austenite of nickel and titanium. The parameter f0 increases notably (from 4 to 46 kHz) when crystals of lowtemperature martensite (α-phase) are generated in samples of the N26T3 steel with 100% cellular decay. This high value (f0 = 46 kHz) persists at Tag < 400°C and drops by a factor of 4.5 over the interval 400 < Tag < 600°C because the ferromagnetic α-phase transforms to the paramagnetic phase-hardened austenite (α → γph). Aging of the phase-hardened austenite in the steel with cellular decay at Tag = 700°C increases the parameter f0 by a factor of two (from 10 to 20 kHz) because the ferromagnetic α-phase is generated when the aged phase-hardened austenite transforms to the martensite (γph → α) as a result of cooling the steel from the aging to room temperature.

Effect of plastic strain and aging of N36K10T3 invar on the output of an applied Eddy-current transducer

Eddy-current parametersf0 andx0 as functions of the plastic strain in the N36K10T3 Invar have been studied. It has been proven that parametersf0 andx0 decrease monotonically as the strain degree rises to ∈=50%. Higher temperatures and longer times of aging (annealing) of the strained Invar lead to higherf0 andx0, whereas no changes in the eddy-current parameters have been detected in the case of an unstrained (quenched) Invar. Feasibility of deriving the strain, the temperature, and duration of isothermal aging of strained Invars with fcc lattices from the eddy-current parametersf0 andx0 has been demonstrated.