Structural properties of austenitic stainless steel in the initial state and after rf plasma nitriding

Mössbauer spectroscopy, TEM, electrical resistivity and magnetic measurements are used for investigation of structural changes of X5CrNi189 austenitic stainless steel sheet induced by rf plasma nitriding carried out at 400°C for 24 h. The initial structure formed by small grains of austenite and α′-martensite changes after nitriding into expanded austenite close to the surface and austenite with minor contents of ferrite/CrN in the bulk.     

Composition, structure and morphology of oxide layers formed on austenitic stainless steel by oxygen plasma immersion ion implantation

Oxygen ions were implanted in to austenitic stainless steel by plasma immersion ion implantation at 400 °C. The implanted samples were characterized by XPS, GIXRD, micro-Raman, AFM, optical and scanning electron microscopies. XPS studies showed the presence of Fe in elemental, as Fe²⁺ in oxide form and as Fe³⁺ in the form of oxyhydroxides in the substrate. Iron was present in the oxidation states of Fe²⁺ and Fe³⁺ in the implanted samples. Cr and Mn were present as Cr³⁺ and Mn²⁺, respectively, in both the substrate and implanted samples. Nickel remained unaffected by implantation. GIXRD and micro-Raman studies showed the oxide to be a mixture of spinel and corundum structures. Optical and AFM images showed an island structure on underlying oxide. This island structure was preserved at different thicknesses. Further, near the grain boundaries more oxide growth was found. This is explained on the basis of faster diffusion of oxygen in the grain boundary regions. Measurement of total hemispherical optical aborptance, α and emittance, ? of the implanted sample show that it has good solar selective properties.     

Scattering-induced attenuation of an ultrasonic beam in austenitic steel

The scattering-induced attenuation coefficient of a beam of longitudinal waves propagating through an austenitic steel plate is measured as a function of the texture angle. The experimental data were obtained by mapping the incident and the transmitted ultrasonic field, and by evaluating the energy loss experienced by each plane wave component of the beam. Contrary to the behavior of data obtained by means of conventional techniques, that of the data reported in this work agrees qualitatively with the theoretical predictions. The reasons for the disagreement between theory and data obtained by means of conventional techniques are also discussed.     

Energetic electron and ion beam generation in plasma openingswitches

In this paper, we present measurements of ion and electron flows in a nanosecond plasma opening switch (NPOS) and a microsecond plasma opening switch (MPOS), performed using charge collectors. In both experiments, an electron flow toward the anode, followed by an ion flow, were observed to propagate downstream toward the load side of the plasma during the plasma opening switch (POS) conduction. In the MPOS, ion acceleration was observed to propagate axially through the entire plasma. These results are in satisfactory agreement with the predictions of the electron magnetohydrodynamics (EHMD) theory and the results of fluid and particle-in-cell (PIC) code simulations. At the beginning of the POS opening, a high-current density (≈2 kA/cm²) short-duration (10-30 ns) axial ion flow downstream toward the load was observed in both experiments, with an electron beam in front of it. These ions are accelerated at the load side of the plasma and are accompanied by comoving electrons. In the NPOS, the ion energy reaches 1.35 MeV, whereas in the MPOS, the ion energy does not exceed 100 keV. We suggest that in the NPOS the dominant mechanism for the axial ion acceleration is collective acceleration by the space charge of the electron beam, while in the MPOS, axial ion acceleration is probably governed by the Hall field in the current carrying plasma     

Investigation of parameters of inductively coupled plasma and its use in steel nitriding

Parameters of inductively coupled plasma (ICP) discharges in a mixture of gases N₂, H₂, and Ar at a total pressure of 1.5 × 10^–3 mbar and a partial pressure ratio N₂: H₂: Ar = 2: 12: 1 are discussed. The plasma properties are analyzed using Langmuir probes and optical emission spectroscopy. The ICP discharge is used for the nitriding of specimens made of Russian grade 30ChGSA structural steel. The nitriding experiments are performed at different bias voltages V_b in the range of–200 V to +100 V with respect to the walls of the discharge chamber. The surface hardness of the treated specimens depends substantially on the bias voltage, being much higher than the initial value in all cases. The obtained results demonstrate the possibility of increasing the surface hardness up to 1000 HV (4–5 times the initial values) at the bias voltage equal to the floating potential.     

不锈钢电子束收集极的损伤能量密度阈值

对强磁场相对论返波管系统中电子束收集极损伤的主要影响因素进行了分析,通过设计并使用锥面不锈钢收集极,提高了收集极的耐电子束轰击能力。在单次实验条件下,研究了电子束能量密度对不锈钢收集极表面损伤及系统产生微波的影响,结合对无箔二极管中电子束空间密度分布的研究结果,给出了不锈钢收集极损伤电子束能量密度阈值范围。     

不锈钢电子束收集极的损伤能量密度阈值

对强磁场相对论返波管系统中电子束收集极损伤的主要影响因素进行了分析,通过设计并使用锥面不锈钢收集极,提高了收集极的耐电子束轰击能力。在单次实验条件下,研究了电子束能量密度对不锈钢收集极表面损伤及系统产生微波的影响,结合对无箔二极管中电子束空间密度分布的研究结果,给出了不锈钢收集极损伤电子束能量密度阈值范围。     

Improvement of erosion and erosion-corrosion resistance of AISI420 stainless steel by low temperature plasma nitriding

Plasma nitriding experiments were carried out with DC-pulsed plasma in 25% N₂ + 75% H₂ atmosphere at low temperature (350 °C) and normal temperature (550 °C) for 15 h. The composition, microstructure, microhardness profiles, residual stress profiles and electrochemical impedance spectrum analyses of the nitrided samples were examined. The influence of plasma nitriding on the erosion and erosion-corrosion resistance of AISI 420 martensitic stainless steel was investigated using a jet solid particle erosion tester and a slurry erosion-corrosion tester.Results showed that the 350 °C nitriding layer was dominated by ?-Fe₃N and α_N phase, a supersaturated nitrogen solid solution. However, nitrogen would react with Cr in the steel to form CrN precipitates directly during 550 °C nitriding, which would lead to the depletion of Cr in the solid solution phase of the nitrided layer. Both 350 and 550 °C plasma nitriding could improve the erosion resistance of AISI420 stainless steel under dry erosion, but the former showed better results. In both neutral and acid environment, while the erosion-corrosion resistance of AISI 420 was improved by means of 350 °C nitriding, it was decreased through 550 °C nitriding.     

Positron beam studies of void swelling in ion irradiated Ti-modified stainless steel

The void swelling behavior of heavy ion irradiated D9 steel has been investigated using variable low energy positron beam. The normalized defect-sensitive S-parameter shows up a large increase in the depth region corresponding to the maximum radiation damage as a function of irradiation temperature. From the variation of S-parameter as a function of irradiation temperature, the peak swelling temperature has been deduced and the results are discussed.     

Influence of nitrogen on the mechanism of austenitic stainless steel hardening

On the example of a C18N12M2 austenitic stainless steel, the influence of nitrogen (whose content varied from 0 to 0.45 wt.%) on the grain boundary hardening coefficient k _h entering into the Hall-Patch equation is analyzed. High values of k _h in steels with and without nitrogen are found. The data of the Auger analysis show that the hardening coefficient in the steel without nitrogen is determined by the grain-boundary segregation of carbon and oxygen. The grain-boundary hardening in the steel with nitrogen is not connected with the predominant segregation of nitrogen at grain boundaries. It is completely governed by intragranular processes—interaction of nitrogen atoms with dislocations. Omsk State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 47–52, July, 1999.     

Sound velocity anomalies near the spin glass transition in an austenitic stainless steel alloy

A cusp in the magnetic susceptibility temperature dependence of a commercial manganese austenitic stainless steel alloy, attributable to spin-glass condensation, is accompanied by anomalies in the temperature dependences of both longitudinal and transverse ultrasonic wave velocities.     

进气量对强流正离子源反向电子流的影响研究

分析了EAST-NBI离子源束引出过程中反向电子的产生及物理特性,对典型情况下的进气量对离子源的影响进行了计算和实验研究.实验结果发现,质子比受进气量影响较小,进气量与反向电子流呈明显正相关.     

Effect of the parameters of the plasma channel produced by a high-current relativistic electron beam in dense gaseous media on the beam transportation stability

Results are presented from experimental studies of the time evolution of the plasma channel produced by a high-current electron beam (with an electron energy of E _e = 1.1 MeV, a beam current of I _b = 24 kA, and a pulse duration of t = 60 ns) in helium, nitrogen, neon, air, argon, krypton, xenon, and humid air (air: H₂O) at pressures from 1 to 760 Torr. It is shown that, in gases characterized by a small ratio of the collision frequency to the gas ionization rate u _i , the electron beam produces a broad high-conductivity plasma channel, such that R _b/R _p < 1, where R _b and R _p are the beam and channel radii, respectively. As a result, large-scale resistive hose instability is suppressed.     

Dependence of the nitriding rate of ferritic and austenitic substrates on the crystallographic orientation of surface grains; gaseous nitriding of Fe-Cr and Ni-Ti alloys

Gaseous nitriding of ferritic Fe–Cr and austenitic Ni–Ti solid solutions reveals that the extent of the uptake of dissolved nitrogen depends on the crystallographic orientation of the surface grains of the substrate. In both ferritic and austenitic substrates, the surface nitrogen concentration and the nitriding depth decrease upon increasing the smallest angle between the surface normal and the normal of a {1?0?0} plane of the surface grain considered. This phenomenon could be ascribed to the residual compressive macrostress developed during nitriding which varies as a function of crystallographic orientation of the (surface) grains due to the elastically anisotropic nature of ferrite and austenite solid solutions investigated in this study.     

Strain rate and cold rolling dependence of tensile strength and ductility in high nitrogen nickel-free austenitic stainless steel

The tensile strength and ductility of a high nitrogen nickel-free austenitic stainless steel with solution and cold rolling treatment were investigated by performing tensile tests at different strain rates and at room temperature. The tensile tests demonstrated that this steel exhibits a significant strain rate and cold rolling dependence of the tensile strength and ductility.With the increase of the strain rate from 10~(-4)s~(-1)to 1 s~(-1), the yield strength and ultimate tensile strength increase and the uniform elongation and total elongation decrease. The analysis of the double logarithmic stress–strain curves showed that this steel exhibits a two-stage strain hardening behavior, which can be well examined and analyzed by using the Ludwigson equation. The strain hardening exponents at low and high strain regions(n_2and n_1) and the transition strain(εL) decrease with increasing strain rate and the increase of cold rolling RA. Based on the analysis results of the stress–strain curves, the transmission electron microscopy characterization of the microstructure and the scanning electron microscopy observation of the deformation surfaces, the significant strain rate and cold rolling dependence of the strength and ductility of this steel were discussed and connected with the variation in the work hardening and dislocation activity with strain rate and cold rolling.     

Effect of the current rise rate in a relativistic electron beam pulse propagating in the ion focusing regime on the dynamics of ion hose instability

The effect of the current rise rate in a relativistic electron beam pulse propagating in the ion focusing regime on the spatial dynamics of the ion hose instability is considered. Numerical analysis of the formulated equations shows that the lower rate of current rise in the beam pulse at the linear stage of evolution of the instability noticeably reduces the amplitude of hose oscillations.     

Microstructure and corrosion behavior of austenitic stainless steel treated with laser

Surface modification of AISI316 stainless steel by laser melting was investigated experimentally using 2 and 4 kW laser power emitted from a continuous wave CO₂ laser at different specimen scanning speeds ranged from 300 to 1500 mm/min. Also, an investigation is reported of the introduction of carbon into the same material by means of laser surface alloying, which involves pre-coating the specimen surfaces with graphite powder followed by laser melting. The aim of these treatments is to enhance corrosion resistance by the rapid solidification associated with laser melting and also to increase surface hardness without affecting the bulk properties by increasing the carbon concentration near the surface. Different metallurgical techniques such as optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize the microstructure of the treated zone. The microstructures of the laser melted zones exhibited a dendritic morphology with a very fine scale with a slight increase in hardness from 200 to 230 Hv. However, the laser alloyed samples with carbon showed microstructure consisting of γ dendrite surrounded by a network of eutectic structures (γ+carbide). A significant increase in hardness from 200 to 500 Hv is obtained. Corrosion resistance was improved after laser melting, especially in the samples processed at high laser power (4 kW). There was shift in I_corr and E_corr toward more noble values and a lower passive current density than that of the untreated materials. These improvements in corrosion resistance were attributed to the fine and homogeneous dendritic structure, which was found throughout the melted zones. The corrosion resistance of the carburized sample was lower than the laser melted sample.