Determination of retained austenite in bearing steel

M?ssbauer effect experiments in scattering geometry were performed for gauging plates and bearings in order to measure the retained austenite content. The results, obtained from numerical calculations of Mössbauer spectra are compared with the X-ray diffraction measurements. A simple three point Mössbauer effect technique is applied in order to decrease the time of measurements in the industrial use.     

Thermodynamic characteristics of a metastable plasma

The equation of state is obtained for an ion-ion plasma which is stable with respect to recombination processes. The regions of thermodynamic stability of a nonideal plasma and of mixtures of such a plasma with an ideal plasma are determined by considering isotherms. It is shown that such a plasma-gas mixture possesses elastic properties.General Physics Institute, Russian Academy of Sciences, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 8–14, January, 1993.     

Five-parameter crystallographic characteristics of the interfaces formed during ferrite to austenite transformation in a duplex stainless steel

The crystallography of interfaces in a duplex stainless steel having an equiaxed microstructure produced through the ferrite to austenite diffusive phase transformation has been studied. The five-parameter interface character distribution revealed a high anisotropy in habit planes for the austenite–ferrite and austenite–austenite interfaces for different lattice misorientations. The austenite and ferrite habit planes largely terminated on (1 1 1) and (1 1 0) planes, respectively, for the austenite–ferrite interfaces associated with Kurdjumov–Sachs (K–S) and Nishiyama–Wasserman (N–W) orientation relationships. This was mostly attributed to the crystallographic preference associated with the phase transformation. For the austenite–ferrite interfaces with orientation relationships which are neither K–S nor N–W, both austenite and ferrite habit planes had (1 1 1) orientations. Σ3 twin boundaries comprised the majority of austenite–austenite interfaces, mostly showing a pure twist character and terminating on (1 1 1) planes due to the minimum energy configuration. The second highest populated austenite–austenite boundary was Σ9, which tended to have grain boundary planes in the tilt zone due to the geometrical constraints. Furthermore, the intervariant crystallographic plane distribution associated with the K–S orientation relationship displayed a general tendency for the austenite habit planes to terminate with the (1 1 1) orientation, mainly due to the crystallographic preference associated with the phase transformation.     

Effect of elastic excitations on the surface structure of hadfield steel under friction

The structure of the Hadfield steel (H13) surface layer forming under dry friction is examined. The deformation of the material under the friction surface is studied at a low slip velocity and a low pressure (much smaller than the yields stress of H13 steel). The phase composition and defect substructure on the friction surface are studied using scanning, optical, and diffraction electron microscopy methods. It is shown that a thin highly deformed nanocrystalline layer arises near the friction surface that transforms into a polycrystalline layer containing deformation twins and dislocations. The nanocrystalline structure and the presence of oxides in the surface layer and friction zone indicate a high temperature and high plastic strains responsible for the formation of the layer. It is suggested that the deformation of the material observed far from the surface is due to elastic wave generation at friction.     

Low-stabilty states of aluminum crystal lattice and acoustic emission under high-temperature straining

Using aluminum as an example it is experimentally established that strain accumulation under low-stability condition at the temperatures higher than 0.5 melting temperature exhibits a non-monotonic behavior and represents sharp deformation changes within a wide range of scale levels (including macroscale). The effects of this stepwise deformation are accompanied by high-amplitude acoustic emission signals. An analysis of the anomalous metal behavior and acoustic emission shows that the activation volume of an elementary deformation event under this low-stability state is exponentially increased with the deformation temperature, indicating an increased scale of cooperative atomic displacements and manifestation of low stability of the crystal lattice of this atomic configuration. The macroscopic character of this stepwise deformation provides evidence on a correlation between elementary deformation events within a volume larger than one strain band. It is assumed that the amplitude of an acoustic signal can serve a criterion of this correlation.     

单模阶梯光纤中孤立波的弹性形变双折射及偏振色散

本文利用微扰计算综合考虑了弹性形变对孤立波在单模光纤中传输的影响,指出了即使是孤立波也存在着弹性形变双折射和偏振色散。     

Three-dimensional transient thermoelectric currents in deep penetration laser welding of austenite stainless steel

The existence of thermoelectric currents (TECs) in workpieces during the laser welding of metals has been common knowledge for more than 15 years. However, the time-dependent evolutions of TECs in laser welding remain unclear. The present study developed a novel three-dimensional theoretical model of thermoelectric phenomena in the fiber laser welding of austenite stainless steel and used it to observe the time-dependent evolutions of TECs for the first time. Our model includes the complex physical effects of thermal, electromagnetic, fluid and phase transformation dynamics occurring at the millimeter laser ablated zone, which allowed us to simulate the TEC, self-induced magnetic field, Lorentz force, keyhole and weld pool behaviors varying with the welding time for different parameters. We found that TECs are truly three-dimensional, time-dependent, and uneven with a maximum current density of around 10⁷ A/m² located at the liquid-solid (L/S) interface near the front or bottom part of the keyhole at a laser power of 1.5 kW and a welding speed of 3 m/min. The TEC formed three-dimensional circulations moving from the melting front to solidification front in the solid part of workpiece, after which the contrary direction was followed in the liquid part. High frequency oscillation characteristics (2.2–8.5 kHz) were demonstrated in the TEC, which coincides with that of the keyhole instability (2.0–5.0 kHz). The magnitude of the self-induced magnetic field and Lorentz force can reach 0.1 mT and 1 kN/m³, respectively, which are both consistent with literature data. The predicted results of the weld dimensions by the proposed model agree well with the experimental results. Our findings could enhance the fundamental understanding of thermoelectric phenomena in laser welding.     

Properties of metastable ising models evolving under the Swendsen-Wang dynamics

The behavior of the metastable nearest neighbor Ising model governed by Swendsen-Wang dynamics (SW) is investigated ind=2. The results are compared to those obtained in standard Metropolis dynamics. Both the SW and Metropolis systems are observed to decay from the metastable state via the formation of nucleating droplets. Nucleation rates are measured and found to agree with those predicted by classical nucleation theory. The growth rates of the droplets are observed to differ between the two dynamics. In addition, the dynamic critical exponentz is measured in a mean-field (Curie-Weiss) metastable Ising model at the spinodal. It is found that for SW dynamics,z=2. Since this is the same value as that obtained in the Metropolis case, this result shows that SW does not change the dynamical universality class at the spinodal.     

Formation of surface roughness on nanocrystalline aluminium samples under straining by molecular dynamics studies

The surface roughening of nanocrystalline aluminium samples was investigated by molecular dynamics simulations. Attention was focused on the fact that roughness increases with the grain size and the strain. The elastic–plastic transition was found at around 3.5% strain and a reverse Hall–Petch effect was observed under straining conditions. Then, different strain distributions in grains and grain boundaries at the sample surface were highlighted, yielding to the formation of local roughness. Finally, a linear relationship between the magnitude of roughness and the out-of-plane strain component was found.     

Softening and recrystallization of austenite in the conditions of controlled rolling of Ti microalloyed steel

Various variants of controlled rolling of Ti microalloyed steel were simulated on torsion plastometer. Softening, size and size distribution of recrystallized austenite grain between individual deformations were measured. Experiments allowed a more precise definition of physicometallurgically justified schedule of controlled rolling of the investigated steel.The authors are grateful to Dipl.-Ing. G. Backmann and Dr. A. Köthe of the Zentralinstitut für Festkörperphysik AdW Dresden for their valuable help in realizing the experimental programme.     

Estimates of the elastic characteristics of graphenes

The central and noncentral force constants have been calculated within the previously proposed model of the binding energy of carbon atoms in graphene, which is based on the Harrison bonding orbital method. The results obtained have been used to estimate the characteristic phonon frequencies and elastic constants of graphene materials.     

Kinetics of austenite decomposition upon cooling of low-alloy pipe steel from the intercritical temperature range

High-rate dilatometry is used to study the kinetics of decomposition of undercooled austenite of low-alloy pipe steel 13KhFA obtained upon heating into the single-phase γ field and the intercritical temperature range. The complex effect of the austenitizing in the intercritical temperature range on the decomposition of the undercooled austenite is revealed (the initial temperature of decomposition falls while the temperature of decomposition termination rises).     

Corrosion of weathering steel and iron under wet-dry cycling conditions: Influence of the rise of temperature during the dry period

The effect of a dry-hot period on the SO₂ corrosion of weatherig steel and pure iron under wet-dry cycling was investigated. Corrosion products were identified by Mössbauer spectroscopy and X-ray powder diffraction. The formation of an intermediate corrosion layer of spm α-FeOOH only on weathering steel was the most significant result.     

Effect of prior austenite grain size on the formation of carbide-free bainite in low-alloy steel

ABSTRACT

Inconsistencies exist in literature regarding the effect of prior austenite grain size (PAGS) on the extent and kinetics of bainite transformation. Attempts have been made in the present work to address these issues in a low-alloy carbide-free bainitic steel using dilatometry, over a range of PAGS. The bainite transformation kinetics in the above-mentioned conditions have been analysed quantitatively using established kinetic model to extract information related to the transformation mechanisms in such conditions. Greater obstruction from grain boundaries in fine-grained austenite restricts sheaves of bainite to develop completely and thereby reduces the volume fraction of bainite in comparison with coarse-grained austenite. Initial nucleation rate of bainite transformation increases with decreasing PAGS due to an increase in the nucleation site density. However, the maximum nucleation rate decreases consistently with decreasing PAGS due to gradual reduction in the autocatalytic factor.     

Cumulative second-harmonic analysis of ultrasonic Lamb waves for ageing behavior study of modified-HP austenite steel

The cumulative second-harmonic analysis of ultrasonic Lamb wave has been performed to study the precipitation kinetics and microvoid initiation of ferritic Cr–Ni alloy steel during the ageing process. Ageing of ferritic Cr–Ni alloy materials have been done at 1223 K and 1173 K for different degradation time intervals and air cooled. The results show that the normalized acoustic nonlinearity of Lamb wave increases with the formation of fine precipitates at the early stage of ageing till about 1000 h and keeps as a plateau with the precipitates dynamic balance for a long-term ageing, and then decreases gradually at the final holding time with the coarsening of precipitates and initiation of microvoids. The results also show that the variation of nonlinear Lamb wave follows the same trend as that of hardness in materials. Therefore, the cumulative second-harmonic of ultrasonic Lamb waves has been found to be strongly sensitive to the precipitates behavior and microstructure evolution during the thermal ageing of ferritic Cr–Ni alloy steel.     

Deformation and properties of heterophase metastable steels under high hydrostatic pressures

Abstract

This paper shows the possibility to control the strength and plasticity properties of heterophase metastable steels based on the Fe-Mn solid solution as a result of purposeful alteration of the phase composition and fault structure by varying the hydroextrusion process parameters. Practical means of realization of high-strength states (б_0.2 ? 1000… 1400 MPa) in 05G20S2 and I4G20K2F steels using the hydroextrusion are proposed.     

Light-induced drift of neon under optical excitation from a metastable state

A running light wave, resonant with the neon transition 1s₅-2p₂, has been found out to affect the spatial distribution of neon atoms in a positive discharge column. The effect has shown an antisymmetric dependence (typical of the light-induced drift) on the tuning out of the radiation frequency relatively the absorption line centre, as well as on the direction of the light wave vector.     

On the elastic characteristics of graphene and silicene

Analytical expressions for the central k ₀ and noncentral k ₁ force constants of two-dimensional (graphene, silicene) and three-dimensional (diamond, silicon) structures have been obtained within the previously proposed model of the binding energy of carbon atoms in graphene. The Kleinman internal displacement parameter of the two-dimensional structure has been determined. It has been shown that the ratio k ₀/k ₁ depends only on the dimension of the structure.     

Mossbauer analysis of deformation dissolution of the products of cellular decomposition in high-nitrogen chromium manganese austenite steel

Methods of Mossbauer spectroscopy and electron microscopy analysis of high-nitrogen chromium manganese steel FeMn₂₂Cr₁₈N_0.8 have been used to investigate the processes of dissolution of the products of cellular decomposition in austenite matrix upon severe deformation under the conditions of dry sliding friction and shear under pressure in Bridgman anvils. Deformation-induced redistribution of nitrogen from the chromium nitrides to interstitial positions of the quenched and preliminary aged steel has been determined. According to the data of Mossbauer analysis the depth of dissolution of chromium nitrides and the increase of content of nitrogen in steel matrix upon friction is 10?μn and more. Aging decreases the amount of nitrogen which transfers to the solid solution under deformation. This is a factor of the enhanced adhesive wear in the aged samples.