Variation of the yield stress and latent strain energy in the course of plastic deformation of a neutron-irradiated chromium-nickel steel

The laws of variation of the flow stress (σ) and latent strain energy (E_s) in the course of plastic deformation have been studied in the samples of a titanium-doped chromium-nickel steel (12Kh18N10T grade) before and after neutron irradiation to a dose of 5×10²²m^?2 (neutron energy E>0.1 MeV). The E_s versus σ curve can be divided into several characteristic regions, the first of which is described by a relation of the type E_s～E₀+kσ² (E₀ and k being certain coefficients). It is established that neutron irradiation shifts the E_s versus σ curve toward smaller latent energies.     

Influence of severe plastic deformation on structure and phase composition of carbon steel

Samples of Fe-1.2%C steel were subjected to high torsion straining under a quasi-hydrostatic pressure. Severe plastic deformation caused complete dissolution of the cementite phase. After large strains a highly dispersed structure with a mean particle size of 20 nm was formed, and the hardness of samples reached 11.7 GPa, which was 2.5 times higher than that in the initial state. The structure obtained was not thermally stable, and upon heating to 250°C it began to transform into a granular state with a mean grain size of about 50 nm.     

Effect of austenite deformation on crystallographic texture during transformations in microalloyed bainitic steel

Abstract

The evolution of the texture of ferrite as a function of the coiling temperature has been studied in a hot rolled Nb alloyed CMnMoCrB complex phase steel by means of electron backscatter diffraction. Coiling that steel at 720 ° C led to ferrite and pearlite, and coiling at 550 ° C produced a bainite-martensite microstructure. The presence of residual austenite in the steels coiled at 680 and 550 ° C allowed for texture measurements in γ. Analyses of texture gave fundamental information on the decomposition of γ in both the recrystallised state and the deformed state. It was found that austenite, initially deformed below the non-recrystallisation temperature T_nr, recrystallised statically d partially during the γ α and the γ ^d α _b transformations. In the specimen coiled at 680 ° C, primary ferrite and bainite could be distinguished based on the confidence indexof the diffraction pattern. A clear variant selection was observed for the γ ^d α _b transformation, as arotation of ? ₁ = 30 ° occurred inthe austenite between the ferrite and the bainite formations. The bainite was found to result mainly from the decomposition of the brass {110} 〈 112 〉 and Goss {110} 〈 001 〉 orientations of deformed austenite. The residual austenite was found to be recrystallised γ γ austenite with the cube{001} 〈 100 〉 orientation. Coiling simulations were performed in a dilatometer starting from different austenite grains sizes and deformation states. In the most deformed specimens, the deformation state of the austenite and the combined effects between the different alloying elements presentin the steel were responsible for a solute drag like effect.     

Atomic redistribution of alloying elements in nanocrystalline austenitic chromium-nickel steels obtained by strong plastic deformation

The fcc solid solution of the stable austenitic 12Cr30Ni steels has exhibited segregation during heavy cold-working ψ > 80%, T = 24 °C), that gives rise to a ferromagnetic component with a Curie temperature close to 128 °C, which may be associated with a local increase in the nickel concentration to 40%. The redistribution of the alloying elements induced by cold working is attributed, by analogy with the low-temperature irradiation, to the diffusion of the point defects generated by the deformation, to the sinks (grain or sub grain boundaries, phase interfaces, etc.) so that the sink regions have higher or lower concentrations of elements with different atomic radii. Changes that take place in the matrix during redistribution of the alloying elements are evaluated using the Mössbauer spectroscopy.     

An investigation of the relaxation of static stresses in chromium-nickel steel specimens in cyclic loading

A multifactorial experiment on relaxation of stresses in chromium-nickel steel specimens in static and asymmetric cyclic loading with frequencies of 35 Hz and 10 kHz is described. With use of the method of experiment planning mathematical models describing the reduction in stresses and accumulation of plastic deformation in relation to the maximum stress, frequency and amplitude of the cyclic load, and temperature were obtained. Certain practical recommendations on use of the results obtained in the process of technical action for the purpose of reducing residual stresses, particularly by the vibration method, are proposed.Translated from Problemy Prochnosti, No. 3, pp. 39–43, March, 1990.     

Influence of phase transformation due to temperature on cyclic plastic deformation in 304LN stainless steel

Strain controlled fatigue experiments are conducted for 304LN at room and elevated temperature of 285 °C in ambient air. Varying cyclic plasticity characterizing parameters such as cyclic hardening/softening and Masing behavior are studied. It is found that hardening along with non-Masing behavior is demonstrated at both temperatures. However the response stresses required to cause deformation are substantially higher at room temperature. Additionally the extent of deviation from masing varied considerably with temperature. Furthermore it is shown that there is a continuous distribution of yield levels at both temperatures. All alterations observed in the cyclic plastic behavior are being accounted by the absence or presence of martensite.     

Synthesized theory of plastic deformation depending on the loading rate

The synthesized theory is generalized to take into account the influence of the loading rate on plastic deformation by introducing the integral of inhomogeneity in the formula for the distance to the planes whose motion causes plastic deformation. We take into account the displacements of the planes not only in front of the stress vector but also behind it. The integral of inhomogeneity depends on the history of loading rate, which enables us to describe the processes of hardening, softening, and stabilization and the Bauschinger effect in plastically deformed materials. Technical Institute, Pedagogical University of Bydgoszcz. Bydgoszcz, Poland. “L'vivs'ka Politekhnika” State University, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 36, No. 1, pp. 39–42, January–February, 2000.     

Effect of thermomechanical conditions on the kinetics of phase transformations in austenitic metastable steel

We present the results of an experimental investigation of the —a martensitic transformation upon cyclic cooling of structurally unstable steel, taking into account such factors as time, preliminary deformation, and sustained loading of the material. We have established that the thermomechanical conditioning of the samples intensifies the phase transformation in the elastic and plastic regions. As a result of a comparative analysis of the loading of the material according to different programs, we have obtained quantitative and qualitative assessments of the martensite formation due to each of the considered factors.Translated from Problemy Prochnosti, No. 3, pp. 28–34, March, 1995.     

Phase transformations in zones of plastic deformation beneath the surface of impact fractures in steel N32T3

Impact tests are performed on steel N32T3 in the hardened and aged conditions. The mechanism of failure and martensitic transformation in zones of plastic deformation between the surface of fractures obtained over a wide temperature range is studied. It is shown that the failure mechanism for both hardened and aged steel in the stage of crack propagation depends weakly on test temperature. An increase in KCU and KCT impact strength for the steel with an increase in temperature is due to an increase in the work for crack generation and formation at the failure site of zone L whose microrelief is predominantly folded with elongated pits. Two zones of plastic deformation are detected by means of x-ray structural analysis beneath the surface of fractures in the hardened condition and one in the aged condition. It is established that within the limits of a highly deformed microzone for hardened steel the amount of martensite is constant in spite of presence of a deformation gradient, but in aged steel it decreases constantly. It is noted that for correct evaluation of the effect of phase transformations occurring in zones of plastic deformation on impact strength and failure mechanism for the steel it is necessary to consider local heating and the actual phase composition of the steel at the tip of a propagating crack.Translated from Problemy Prochnosti, No. 7, pp. 49–56, July, 1990.     

Phase transformations induced by dislocation glide in plastic deformation of alloys

It has been shown that in intense plastic deformation of alloys, dislocation glide gives rise to nonequilibrium phases or disperse structures. The phenomenon is due to the joint action of two factors: acceleration of diffusion and change in the chemical potential of the alloy components in the region of the dislocation core.