Special features of the α → γ transformation in powder carbon steels

The structural state of powder steels after sintering depends on the technological regimes of their production and can markedly affect the transformations in subsequent heat treatment. The effect of the technological regimes on the nature of the transformation is investigated.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 14–16, March, 1996.     

Control of the phase composition and nitrogen content in the nitride layer in the nitriding of the steel 38Kh2MYuA

It is known that in order to obtain a high-hardness, wear- and corrosion-resistant article a nitrided layer of nitride (+)-phases should be formed on its surface. However, in some cases, for example, in nitriding high-speed die steels and steel 38Kh2MYuA, the formation of brittle nitride surface layers should be eliminated and only a zone of internal nitriding (a+ + MN) should be formed in order to provide the requisite hardness and wear resistance. The article concerns preparation of nitrided layers with different compositions on the widely used 38Kh2MYuA nitralloy.     

Kinetics and mechanism of low-pressure,high-temperature oxidation of silicon-II

The reaction of oxygen at low pressures with silicon layers on tungsten ribbons was studied. An abrupt transition was observed between a condition of passivation, in which a thin film of SiO₂ formed at low temperatures, and a steady-state combustion condition at high temperatures. The latter state is characterized by the formation of volatile SiO. The boundary between these two states has been defined in terms of the pressure-temperature relation. Oxygen consumption in the combustion state is represented by first-order reaction kinetics with an activation energy of 13 ± 1 kcal/mole. The stability of the two states has been defined by a thermodynamic analysis of the SiO₂ layer stability. The oxygen consumption dependence on temperature has been described by a kinetic model which involves a consideration of the various elementary steps in the reaction.     

High-resolution SIMS and analytical TEM evaluation of alumina scales onβ-NiAl containing Zr or Y

High-resolution SIMS and TEM have been used to evaluate growth processes and interfacial segregation occurring in -Al₂O₃ scales grown at 1200°C on -NiAl containing zirconium or yttrium.¹⁸O/SIMS shows that the extent of aluminum diffusion occurring during -Al₂O₃ growth is reduced by the presence of these alloying elements, which are seen by SIMS imaging as oxide particles within the scale. STEM/EDS of the same oxide scales show that zirconium and yttrium also segregated to the oxide-alloy interface to the extent, respectively, of 0.15 and 0.07 of a monolayer and to oxide grain boundaries (0.2 monolayer). The complementary information provided by SIMS, TEM, and STEM provides a better understanding of the role of reactive elements in modifying scale-growth processes.     

The Corrosion of Alloy Steels under Antirust Compounds in the Presence of Microbes

The kinetic corrosion characteristics of 352-, 302, and 30 steels with rust-preventive compounds applied are investigated in an industrial neutral electrolyte, depending on whether a compound is infected with microorganisms or not. The effect of microorganisms and their metabolites on the corrosion of steels greased with the compounds are assessed.     

The Influence of Ozone on the Electrochemical and Corrosion Behavior of Metals in Acid Media

The corrosion–electrochemical behavior of 092, 0817, 1017132 steels, 0628 alloy, and such metals as aluminum, chromium, and nickel are investigated in ozonized acid media. The effect of ozone on the corrosion–electrochemical properties of these metals are shown to be ambiguous.     

General laws governing variation in properties of cast alloys of the Al-Zn-Mg system

Among existing high-strength corrosion-resistant aluminum alloys, those of the Al-Mn-Zn system are most promising. They have a different phase composition, depending on the content of magnesium and Zinc: + (Al₃Mg₂), + + T(Al₂Mg₃Zn₃), + T, + T + (MgZn2) and + The majority of industrial Al-Mg-Zn alloys correspond to the phase regions + T and + T + with respect to composition. A high level of strength and satisfactory overall corrosion resistance are characteristic for these alloys. Al-Mg-Zn alloys may, however, tend to the most dangerous form of corrosion - stress-induced corrosion cracking. Using methods of experiment planning in the study, we investigated Al-Zn-Mg alloys of various compositions for the purpose of selecting alloy compositions with a high level of mechanical properties and stress-induced corrosion cracking.All-Union Scientific-Research Institute of Aviation Materials. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 24–28, December, 1994.     

Protection of Sintered Steels against Corrosion in Neutral Media with an N-M-1 Inhibitor

The effect of an N-M-1 inhibitor (a salt of cyclohexylamine and C₁₀ to C₁₆ aliphatic acids) on the corrosion of sintered powder steels 13 and 141 (with the 14 to 17% porosity) in distilled or tap water at 20 to 80°C, as well as in 0.05 M Na₂SO₄ solution, is studied by gravimetric and electrochemical methods. The protective concentration of the inhibitor is lower in distilled, than in tap water or sodium sulfate solution. The protective action decreased with an increase in temperature. In tap water or sodium sulfate solution, the corrosion-inhibiting effect is weaker for 13 than for 141.     

Structural conversions in VT22 titanium alloy during aging

Conclusion For two-phase high-strength alloys of the VT22 type, as for -alloys of titanium, the presence of an incubation period for the formation of -phase during aging is characteristic. The signs for this process are the following: enchanced etchability of the surface of thin sections; formation of zones which do not have an interface with the matrix but differ from it in etchability (zones of presegregation of -phase); a change in the intensities of the -phase lines on the x-ray diffraction patterns. Decomposition of the -solid solution in titanium alloys of the VT22 type is a multistep process, including formation of segregates (onset of stratification of the -solid solution), regions of the Guinier—Preston zone type, various intermediate states, coherent states of the formed -phase, and finally the appearance of isolated -phase, having an interface with the matrix -solid solution.Pskov Filiate of St. Petersburg State Technical University. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 33–37, August, 1992.     

New Protective Coatings for Replacing Cadmium Coatings on Steel Parts

Works aimed at solving the problem of replacing toxic cadmium coatings used for protection of aircraft steel parts are reviewed. Numerous electrolytic alloys based on zinc and zinc-bearing coatings of the Colsil and Dacromet types are suggested for the purpose. A VIAM-designed coating based on a Zn – Sn alloy in combination with a modified phosphate coating is considered. It is shown that the protective properties of the combined coating are close to those of a cadmium coating, and the former is recommended for commercial use.     

Thermal and thermomechanical hardening of steel 40G2S using quenching from the intercritical temperature range

Conclusions The level of mechanical properties of steel 40G2S after hardening at - and (+)-region temperatures is governed not only by the ratio of phases in the structure, but also by the presence of generally fine inhomogeneous structure. Variation of the amount of ferrite or bainite in the martensitic matrix should be carried out so that the possibility is provided for occurrence of accommodiating deformation in these phases. In view of this the amount of ferrite or bainite in the steel structure should be small (5–7%), and the size of inclusions of these phases in the martensite matrix should be small (1–2 m).Institute of Steels and Alloys, Moscow (MISiS). Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 27–30, July, 1987.     

Correlation Between Diagrams of Isothermal and Anisothermal Transformations and Phase Composition Diagram of Hardened Titanium Alloys

A brief review of works devoted to phase transformations in titanium alloys and published by the authors during a long period and of recent publications on the topic is presented. When plotting phase diagrams of hardened titanium alloys (metastable diagrams) the authors used as a basis their relationship to the equilibrium diagrams and the transformations of the -phase of various compositions during hardening from the -range temperatures. After studying the structure of hardened alloys they investigated their transformations during aging, isothermal treatment, and continuous cooling from the -range temperatures. Using the interrelation between the phase diagrams of hardened alloys and the phase transformations of -phase under various kinds of heat treatment the authors developed theoretical diagrams of isothermal and anisothermal transformations, which were later confirmed by experimental diagrams for pilot and commercial alloys. The suggested classifications of diagrams of isothermal and anisothermal transformations are applicable to titanium alloys of various structural classes with allowance for the coefficient K of stabilization of the -phase.     

Developing Concepts of Chromium Functions in the Passivation and Pitting of Fe–Cr Alloys

The passivability and pitting resistance of Fe–(0–100)Cr alloys in deaerated acidic sulfate environments (at a concentration of sulfate ions of 0.1 to 1.0 mol/l and pH from 0.5 to 1.8) and neutral borate buffer solutions with a chloride concentration of 0.003 mol/l and pH 7.3 are studied with the use of steady-state and pulse electrochemical methods. Four critical alloy compositions corresponding to the sharp changes in the passivability, repassivability, and pitting resistance of the alloys are discussed: 6.5; 11; 17; and 27% Cr. Based on considering the alloys as purely mechanical mixtures with no sign of any order so that a chromium atom can occupy any lattice point with a probability proportional to the bulk chromium content, the following hypothesis is put forward. It is the crystallographic and electronic structure of Fe–Cr alloys that forms the main reason for the existence of the mentioned critical concentrations. Upon reaching certain critical compositions, chromium atoms either occupy positions in each coordination sphere (6.5% Cr), each elementary cell of an scc lattice (11% Cr), or each quasirhombohedral pore (17% Cr); or a superlattice compound appears (27% Cr).     

Dynamic recrystallization of beta-phase in titanium alloy

Conclusion Dynamic recrystallization of cast -grain in alloys type VT-6S, which proceeds most actively at high temperatues (1200°C) and high rates of deformation (10 sec^–1), causes refinement of cast grain and reorientation of crystallites.DeceasedA. A. Baikov Institute of Metallurgy. TsNIIKM Prometei. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 34–36, September, 1991.     

Age hardening of VT35 titanium alloy

VT35 alloy belongs to -titanium alloys that preserve the body-centered lattice of the -phase in hardening from the -region. In an equilibrium state this alloy has an + structure. After hardening, VT35 alloy has a high ductility and a low strength. The subsequent single- or double-stage aging in the biphase region promotes considerable strengthening of the alloy due to segregation of a second phase. VT35 titanium alloy is hardened to a pure -phase by cooling from the single-phase region in water, in air, or with the furnace (at a rate of at least 3 -4 deg/min). This special feature of the alloy is caused by its chemical composition (Ti - 3% Al -15% V - 3% Cr - 3% Sn), which provides a high coefficient of -stabilizationK = 1.5. The present paper concerns the processes of age toughening of a hardened VT35 alloy and the kinetics of the structural transformations in such a treatment.     

Effect of rapid cyclic electrothermal treatment on the structure of nickel steel

Conclusions The high dislocation density of austenite undergoing the transformation is due to the influence of fresh dislocations that occur during the transformation in virtue of its martensitic character and to dislocations inherited from the original phases.Since the increase of the dislocation density in austenite causes an increase in the number of martensite crystals, it can be assumed that the increase in the number of phase nuclei is due to an increase in the density of fresh dislocations. In this case the refining of martensite is due to an increase in the number of nuclei and to the barrier effect of elements of the substructure. The formation of atmospheres of impurity atoms at dislocations in alloys with carbon stabilizes the austenite and intensifies recrystallization processes. Cementite particles in phase are not inherited by austenite with heating to the transformation temperature.Institute of Metal Physics, Academy of Sciences Ukrainian SSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 20–23, January, 1975.     

Formation of elemental silicon inclusions in the sulfide scale on Cu-Si alloys

The sulfidation of Cu-Si alloys in liquid sulfur resulted in an enrichment in the metallic substrate in silicon with the simultaneous formation of the phase, whereas within the inner layer of the scale elementary silicon occurred in a dispersed form. The formation of the phase in the surface layer of the metallic substrate results from the supersaturation of vacancies generated at the alloy/scale interface. The formation of silicon inclusions results in the selective sulfidation of copper when the phase moves toward the inner layer of the scale.Formerly of Institute of Materials Engineering, Academy of Mining and Metallurgy, Cracow, Poland.     

Role of kinetic effects on metal partition at the alloy-scale interface during the oxidation of alloys

An alternative mass balance at the alloy-scale interface is proposed for the Wagner theory of binary alloy oxidation. A simple relation between the bulk composition of the alloy and the scale composition at the alloy-scale interface, , is derived in terms of the transport properties of the scale and the limit of application of the relation defined. There is good agreement between calculated and measured values of .Supported by a Science Research Council grant.     

Peculiarities of the Effect of Perchlorate Ions on Electrodeposition of Cadmium in Aqueous–Acetonitrile Electrolytes

It is shown that, depending on the composition of aqueous–acetonitrile solvent, either acetonitrile (AN) molecules or perchlorate anions predominantly adsorb on the electrode. The highest surface concentration of AN and the lowest rate of cadmium electroreduction are observed in the mixture with the most loosened structure (x ₂ 0.4). The salting-out action of mixed solvent in the domains of its structure stabilization primarily manifests itself in an increase in the adsorption activity of ClO^– ₄ anions and a corresponding promotion of Cd²⁺ discharge as a result of " effect. The maximum process rate is observed in the domain, where the AN structure is ordered by monomeric water molecules.     

Structural formation of high-speed steels during crystallization

Conclusions The L+ peritectic transformation in tungsten-molybdenum high-speed steels goes to completion prior to the start of the eutectic reaction (L+K), which may precede segregation of austenite from the liquid (with a high carbon content). In this case, the eutectic is crystallized on the base of the metastable M₂C carbide. Conditions for the formation of thermodynamically more stable MC and M₆C carbides are created during slow cooling characteristic for the central zones and upper horizons of an ingot. Eutectics based on these carbides begin to crystallize at comparatively high temperatures, when the peritectic transformation has yet to go to completion. In a certain temperature interval, these transformations occur simultaneously; in this case, they can be suppressed by the eutectic crystallization owing to the characteristic features of the peritectic transformation. As a result, -ferrite (the products of its decomposition) is present in the steel.The mechanism responsible for the peritectic transformation in tungsten-molybdenum highspeed steels is characterized by the penetration of austenite into the depths of the -crystals during steady contact between the liquid and both the austenite, and the -phase, and by the absence of solid-phase pericrystallization. Diffusion processes are carried out via a network of channels connecting the thin liquid interlayer at the -transformation front with the interdendrite melt. This dictates the high rate of the peritectic transformation, and also the possibility of the suppression of its eutectic crystallization of the liquid in the channels.Decreases in the macro-, micro-, and submicroheterogeneity and increases in the technological plasticity can be attained with this effect on crystallization, which prevents overlapping of the regions of the peritectic and eutectic transformations. The amount of residual -ferrite and skeletal eutectic, and the chemical heterogeneity of the austenite should be reduced in this case.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 23–30, November, 1982.