Effect of Strain Rate on Discontinuous Flow and Mechanical Characteristics of High-Nitrogenous Steel

Experimental study on the effect of strain rate on discontinuous flow and mechanical characteristics of the high-nitrogenous steel Kh23AG19F has been performed. Within the range of strain rates from 4.62 · 10^-5 to 1.85 · 10 ^-4 s^-1, discontinuous flow, reflected by serration on the tensile diagram, is chiefly determined by intergranular deformation mechanisms. Under strain rates over 1.85 · 10^-2 s^-1, combined deformation modes prevail, which cause a change in the character of discontinuous flow and transform a serrated tensile diagram into a wavy graph, with the yield stress of steel increased significantly.     

Statistical modeling of a medium in amorphous and crystalline states

A simple statistical mechanical model of condensed molecular medium has been developed on the basis of the thermodynamic-functional method and the Rott correlation function method of conditional distributions. The short-range and long-range orders, pressure, and chemical potential are investigated with due regard for the correlation in the filling of microvolumes by particles of the medium (in the presence of vacant microcells). Two solutions are found in the range of volumes typical of the crystalline state. These solutions correspond to a splitting of the pressure isotherm and the chemical potential of the system into crystalline and amorphous branches.     

Structure and wear resistance of electron-beam nitrous coatings

The paper deals with the study of the tribological properties of nitrogen-containing austenite coatings deposited by electron-beam facing during abrasive wear and the sliding friction of a VK6 hard alloy indentor. The abrasive wear resistance of the nitrous coatings deposited by the electron-beam facing of steel 60Kh24AG16 powder in quartz sand is lower than that of the steel 65G coatings after hardening; it increases with increasing mass share of the filler. At contents of nitrided ferrovanadium of 10?C30 wt % the abrasive wear rate increases by 30?C50%, respectively. It is found that under a certain load applied to the VK6 ball indentor the friction coefficient and the shear resistance of the surface layer diminish. It is shown that under heavy specific loads applied to the ball indentor the nitrous coating faced from steel 60Kh24AG16 powder and composite nitrous coatings have wear resistance exceeding that of steels 110G13 and Kh18N10 by more than two and seven times, respectively. Based on the results of structural studies an explanation of the observed behavior of the nitrous coatings is proposed.     

Structure and properties of the fusion zone formed due to electron beam facing of a coating from nitrogen-alloyed chromium-manganese iron on low-carbon steel

The structure, properties, and residual stresses in the fusion zone formed due to electron beam facing of a wear-resistant coating from chromium-manganese iron with nitrogen-alloyed austenitic matrix on thin-wall articles fabricated from low-carbon steel are studied. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 19–22, February, 2007.     

Molecular-statistical description of the specific heat of crystals with thermal vacancies. 2. numerical calculations of the contribution of the vacancy subsystem to the lattice specific heat of crystals

The earlier proposed single statistical model of a condensed molecular system with pairwise interaction of molecules described by the intermolecular Lennard-Jones potential has been applied. In using an analytical expression for the addition to the vibrational specific heat of a perfect crystal, in which the presence of thermal vacancies under real conditions is taken into account, numerical calculations have been carried out and an analysis of the results obtained has been made.     

Structure and Mechanical Properties of Nitrogen Austenitic Steel after Ultrasonic Forging

Electron microscopy and X-ray diffraction have been used to investigate a nitrogen 07Kh17AG18 steel with an austenitic structure after the surface deformation treatment—ultrasonic forging. During ultrasonic forging, an austenitic structure transforms into a new structure with an elevated concentration of deformation-induced stacking faults, a lot of deformation microtwins, ε-martensite crystals. The austenite lattice parameter is found to be decreased in the surface layer. After ultrasonic forging, nitrided steel exhibits enhanced strength properties with retained high plasticity.     

Residual stresses in electron-beam coatings with a nitrogen-austenite matrix and structural mechanisms of their relaxation

The structure, distribution of elastic microdeformations related to the effect of residual stresses of the 1st and 2nd kind in nitrogen austenite coatings prepared by electron-beam overlaying and the mechanisms of relaxation of residual stresses in the substrate-coating system have been investigated. The state of stress is characterized by a change in sense over the coating thickness. An analysis of experimental data shows that the relaxation of residual stresses results in the formation of a structure with an enhanced density of dislocations. The main mechanism of relaxation of residual stresses in overlaid coatings is microtwinning and γ → ɛ transformation.     

Structure,mechanical, and tribotechnical properties of an austenitic nitrogen steel after frictional treatment

The features of the structure and the mechanical and tribotechnical properties of an austenitic nitrogen steel (Cr16.5, Mn18.8, C0.07, N0.53, Si0.52 wt %, and Fe for balance) after frictional treatment have been studied. It has been shown that, along with twinning, the nitrogen austenite upon frictional treatment undergoes a γ → stacking fault → ε transformation. The strengthening of the steel by the frictional treatment manifests in a delay of the onset of the plastic flow. In the structure of the surface layer with a thickness of 5 μm, a high concentration of stacking faults has been detected. The mechanical properties depend on the orientation of the acting stresses relative to the direction of the frictional treatment. Upon the sliding friction of a ball made of hard alloy (94%WC + 6%Co) on the strengthened surface, an anomalously low coefficient of friction of 0.13 is observed. The coefficient of friction in the presence of abrasive particles in the form of wear debris increases to 0.50; however, the wear rate is almost two times lower compared to the same characteristic for a nonstrengthened surface of the nitrogen steel tested under the same conditions.