Effects of the composition and low-temperature thermomechanical treatment on the mechanical properties of structural steels

Conclusions The investigation of the effect of thermomechanical treatment on the mechanical properties of steels with different compositions makes it possible to put in evidence the effect of alloyed elements. The addition of up to 1.2–1.5% Si (particularly with vanadium) makes it possible to increase the tempering temperature to 350°C without significantly decreasing the strengthening effect of low-temperature thermomechanical treatment. An increase of the concentration of chromium from 1.5 to 3–5% also increases the resistance of the steel. In steel containing 3–5% Cr and also molybdenum, vanadium, and tungsten, the effect of low-temperature thermomechanical treatment is retained after tempering at temperatures up to 500°C, the plasticity remaining rather high. Low-temperature thermomechnical treatment of batches 8 and 10 followed by tempering at 500°C resulted in the following mechanical characteristics: _b=240–255 kg/mm² when =10–13% and =30–35%; after tempering at 350°C _b=255–265 kg/mm², ₅=8–12%, and =28–36%.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 36–40, April, 1963     

The properties of structural steels at −196°C

Conclusions 1. After quenching and high-temperature tempering, the steels investigated have a fairly high strength and plasticity at –196°C, and therefore can be recommended as structural materials for nonwelded parts of air-fractionating apparatus with stress concentrations not higher than K_t=4.VNIIKRIOGENMASh. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 8–11, March, 1969.     

Electrotempering of quenched Fe−N alloys

Conclusion Phase transformations during tempering of quenched Fe–N alloys with induction heating (200 deg /sec) occur in the same manner as in heating at the rate of 5–10 deg/min, although the temperature range of the transformations is 50–80° higher.Kiev Polytechnical Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 63–64, February, 1974.     

About structural changes in the YuNDK35T5AA alloy upon magnetic annealing

The lattice parameters of α′ and α phases with a “slightly tetragonal” structure, which are formed in YuNDK35T5AA single crystals grown from the melt, have been determined. Magnetic annealing of the single crystals was shown to result in an increase in the degree of tetragonality of both phases. The difference between the lattice parameters a of the phases increases substantially; the unit-cell volume of the α phase increases, whereas that of the α′ phase decreases slightly. X-ray diffraction patterns obtained for the modulated structure formed in the YuNDK35T5AA single crystals in the as-grown state, after high-temperature annealing followed by cooling in air, and after magnetic annealing were compared; the modulation periods were determined.     

Highly Anisotropic Powders of Alloys of Nd - Fe - B System with Magnetic Energy of Up to 27 MG · Oe Obtained by the Method of Hydrogenation-Dehydrogenation

The effect of additives of Nb, Ga, Co, Zr, Al, and Dy and of the temperature of hydrogen treatment on magnetic properties of powders of alloys based on the Nd₂Fe₁₄B compound and fabricated by the method of cyclic hydrogenation-dehydrogenation is investigated. Powders of an alloy with additives of Nb, Ga, and Dy fabricated in an optimum mode have maximum magnetic energy of 27 MG · Oe (216 kJ/m³). Plastomagnets from these powders with an epoxy binder have magnetic energy of 16 MG · Oe (128 kJ/m³) at residual induction B _r = 8.35 kG, _J H _c = 14 kOe, and _B H _c = 7 kOe.__________Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 30 – 33, April, 2005.     

The oxidation of Co−Nb alloys under low oxygen pressures at 600–800°C

The oxidation of two Co–Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800° C in H₂–CO₂ mixtures providing an oxygen pressure of 10^–24 atm at 600°C and 10^–20 atm at 700 and 800°C, below the dissociation pressure of cobalt oxide. At 600 and 700°C both alloys showed only a region of internal oxidation composed, of a mixture of alpha cobalt and of niobium oxides (NbO₂ and Nb₂O₅) and at 700°C also the double oxide CoNb₂O₆, which formed from the Nb-rich Co₃Nb phase. No Nb-depleted layer formed in the alloy at the interface with the region of internal oxidation at these temperatures. Upon oxidation at 800°C a transition between internal and external oxidation of niobium was observed, especially for Co–30Nb. This corrosion mode is associated with the development of a single-phase, Nb-depleted region at the surface of the alloy. The corrosion mechanism of these alloys is examined with special reference to the effect of the low solubility of niobium in cobalt and to the relation between the microstructures of the alloys and of the scales.     

Improvement of the magnetic properties of nanocomposite permanent magnetic alloys with Dy and Ga substitutions

The Dy and Ga substituted NdFeB nanocomposite permanent magnetic alloys with high magnetic properties have been prepared by appropriate wheel speed of melt-spinning and post-annealing treatment. Under optimal conditions, compared with the best magnetic properties of ternary NdFeB alloy of J_r=1.18 T, H_ci=379.5 kA/m and (BH)_max=119.5 kJ/m³, the best magnetic properties of the alloy with Dy and Ga substitutions are J_r=1.16 T, H_ci=580.5 kA/m, and (BH)_max=162.7 kJ/m³. The XRD and TEM results showed that each of two alloys consists of hard magnetic 2:14:1 phase and soft magnetic α-Fe phase. The grain size of the 2:14:1 phase is about equal in the two alloys. The grain size and content of α-Fe phase in Dy and Ga substituted alloy are finer and lower, respectively.     

The oxidation of Ni-Nb alloys at low-oxygen pressures at 600–800°C

The oxidation of two Ni–Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800° C in H₂–CO₂ mixtures providing an oxygen pressure of 10^–24 atm at 600° C and 10^–20 atm O₂ at 700 and 800° C, these pressures being less than the dissociation pressure of nickel oxide. The scales formed on both alloys at 600 and 700° C show only a region of internal oxidation composed of a mixture of alpha nickel and niobium oxides (Nb₂O₅ or/and NbO₂), which formed from both the metal phases present, i.e., Ni₈Nb and Ni₃Nb. Only small, or even no, Nb depletion was observed in the alloys close to the interface with the zone of internal oxidation at these temperatures. On the contrary, samples of both alloys corroded at 800° C produced a continuous external scale of niobium oxides without internal oxidation. The corrosion mechanism of these alloys is examined with special reference to the effect of the low solubility of niobium in nickel.     

Mechanical and magnetic properties of cast irons VCh 50-2 and KCh 50-5 after temper hardening

Conclusion After heat treatment cast iron changes both its mechanical and magnetic properties, which is connected with structural transformations in the matrix. Thus, from results of the change in magnetic properties for cast iron, it is possible to estimate the amount of heat treatment, i.e., to establish the structural and phase condition of the cast iron, and to estimate the completeness of transformations occurring during quenching and tempering.As parameters for monitoring the heat treatment of HCSG and PMC in the tempering range 600–750°C, it is possible to use and µ₃₀₀, and µ₃₀₀ is to be preferred. In the range t_tem=500–600°C should be used.Results of these studies have been used in developing an electromagnetic structurescope by means of which measurements have been made of differential dynamic magnetic permeability for monitored and reference articles located in continuous eddy-current converters.Test for a structurescope under production conditions at the Volga Automobile Factory during quality control of temper hardening for PMC and HCSG castings demonstrated its high efficiency, reliability and productivity.Zaporozhe Automobile Factory "Kommunar." Zaporozhe Machine Building Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 10–11, June, 1987.     

High-temperature oxidation of Ti3Al−Nb alloys

Titanium aluminide (Ti₃Al–Nb) has potential for high-temperature applications because of its low density and high-temperature strength. This research is aimed at improving the high-temperature oxidation resistance of a Ti₃Al–Nb alloy by modification of its composition. The oxidation rates of Ti₃Al–Nb alloys were measured from 600 to 900°C in air. The oxide layer was examined by X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. The experimental results reveal that alloys with added Nb tend to form denser oxide layers and that oxidation rate can be reduced by increasing Nb content (up to 11 at.% in this study), which is in good agreement with other investigators. The only exception is a Ti₆₅Al₂₅Nb₁₀ alloy, which shows better oxidation resistance than the commercial Ti₆₅Al₂₄Nb₁₁ alloy. The oxidation resistance of Ti₆₅Al₂₅Nb₁₀ alloy can also be improved slightly by the addition of small amounts of Si or Cr. An increase in the oxidation resistance of Ti₆₅Al₂₅Nb₁₀ alloy containing Y was observed at 900°C but not at 800°C or below. The parabolic oxidation rate equation is adequate to describe the high-temperature oxidation reaction of the Ti₃Al–Nb alloys in the atmosphere.     

Special Features of Formation of Structure and Properties of Low-Carbon Martensitic Steel 12Kh2G2NMFT

The structure and mechanical properties of steel 12Kh2G2NMFT after continuous cooling at a rate of 600 – 0.035 K/sec and after cooling with isothermal holds in a temperature range of 300 – 650°C are investigated. It is shown that a lath martensite structure with a high level of strength and ductility is formed in a wide range of cooling conditions. The decrease in the impact toughness observed under isothermal conditions in a narrow temperature range below M _i (360 – 410°C) is shown to be connected with the processes of tempering of freshly formed isothermal martensite.     

Effect of solidification rate of the structure of alloys of the system Fe-W

Conclusion In alloy Fe-42% W atomized with a cooling rate during solidification within the limits from 5·10³ to 1·10⁵°C/sec with the maximum cooling rate (not less than 10⁵°C/sec) precipitation of -phase (Fe₇W₆) from the liquid melt is suppressed. In granules of alloy obtained with a high solidification rate it is possible to achieve total dissolution of tungsten in solid solution (42%). Subsequent heating causes precipitation of -phase in dispersed form.I. P. Bardin Central Scientific-Research Institute of Ferrous Metallurgy (TsNIIChERMET) Moscow. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 34–36, September, 1990.     

Phase transformations during tempering of quenched Fe−N alloys

Conclusions It was found that tempering processes are similar in quenched steel and nitrided iron — in the first stage of tempering (20–180°) the martensite with nitrogen transforms, with formation of metastable F₁₆N₂ and temper martensite; in the second stage (180–300°) the retained austenite decomposes and the Fe₁₆N₂ Fe₄N transformation occurs; in the third stage (300–550°) the number of lattice defects decreases and the Fe₄N particles coalesce. After quenching and tempering at 500–600° the alloy consists of a ferrite—nitride mixture of the type of temper sorbite in carbon steel.Kiev Polytechnical Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 28–30, March, 1974.     

Reoxidation of chromium with densified Cr2O3 Scales

Preoxidized chromium specimens have been high vacuum annealed at 1200° and 1300°C to produce densified Cr ₂O₃ scales. These specimens have been reoxidized at the same temperatures at 10^–6 atm O₂. The initial reoxidation is linear with time and is concluded to reflect a volume diffusion controlled transport through the densified scale. The corresponding parabolic rate constant (w² = k_pt)is given by k_p=1.4 · 10^–2 exp(–235,000/RT)(gram of O) ²/cm⁴ sec. It is tentatively concluded that outward chromium diffusion predominates in an inner layer of the Cr₂O₃ scales and inward oxygen diffusion in an outer layer. Under the experimental conditions it has not been possible to maintain growth of the Cr₂O₃ scales controlled by volume diffusion. The new oxide layer consists of fine crystallites; the oxide grows at grain boundaries within the scales. This causes sideways growth of the scale, breakdown of the originally densified layer, and an increased rate of reaction.     

Influence of temperature and the role of chromium on the kinetics of sulfidation of 310 stainless steel

The sulfidation of 310 stainless steel was studied over the temperature range from 910 to 1285° K. By adjusting the ratio of hydrogen to hydrogen sulfide, variations in sulfur potential were obtained. The effect of temperature on sulfidation was determined at three different sulfur potentials: 39 N·m^–2, 1.4×10^–2 N·m^–2, and 1.5×10^–4 N·m^–2. All sulfide scales contained one or two surface layers in addition to a subscale. The second outer layer (OL-II), furthest from the alloy, contained primarily Fe-Ni-S. The first outer layer0 (OL-I), nearest the subscale, contained Fe-Cr-S. The subscale consisted of sulfide inclusions in the metal matrix. Two different phases were observed in OL-II depending on the temperature and sulfur potential. Below 1065°K OL-II is composed of a mixture of monosulfides of iron and nickel (Fe Ni)_1–xS and pentlandite (Fe_4.5Ni_4.5S₈) with the pentlandite phase exsolved as lamellae upon cooling. At temperatures higher than 1065°K only the pentlandite phase was formed, which melted above 1145°K at sulfur potentials greater than 10^–2 N·m^–2, yielding metal-rich iron-nickel-sulfur. Above 1145°K, and at sulfur potentials less than 10^–2 N·m^–2, OL-II ceased to exist (this temperature is termed transition temperature). Below the transition temperature, where OL-II exists, OL-I could be represented by the general composition (Fe, Cr)_1–xS. This phase on cooling transformed into an array of structures differing in FeCr ratio. These substructures, however, were not observed in quenched samples. Above the transition temperature OL-I changed to a chromium-rich sulfide composition and was associated with a sudden decrease in reaction rate. Subscale formation was found to be due to the dissociation of OL-I at the scale-metal interface, and the extent of subscale growth was found to depend on the temperature and the sulfur potential, as well as the composition of OL-I. At a given temperature and sulfur potential the weight-gain data obeyed the parabolic rate law after an initial transient period. The parabolic rate constants obtained at the sulfur potential of 39 N·m^–2 did not show a break when the logarithm of the rate constant was plotted as a function of the inverse of absolute temperature. Sulfidation carried out at a sulfur potential below 2 × 10^–2 N·m^–2, however, did show a break at 1145°K. This break was found to be associated with the changes which had occurred in the FeCr ratio of OL-I. Below the transition temperature the activation energy was found to be approximately 125 kJ · mole^–1. Above the transition temperature the rate of sulfidation decreased with temperature but depended on the FeCr ratio in the ironchromium-sulfide layers of the OL-I. A reaction mechanism consistent with the experimental results has been proposed in which the diffusion of cations through OL-I is the rate-controlling step. Below the transition temperature the diffusion of Fe and Ni through OL-I contributes to the scale formation, whereas above the transition temperature the diffusion of Cr through OL-I controls the scale formation. Existing literature on the Fe-Ni-S system is compared with the present results.     

Influence of original structure and heating rate on the properties of steel after hardening from the intercritical range

Conclusions The original condition and heating rate determine the mechanical properties of the steel after hardening from the intercritical range. The best properties, particularly ductility, _t=1600 MPa, _0.2=1250 MPa, =14%, anda _n=0.9 MJ/m², are obtained after preliminary hardening from 930°C, tempering at 200°C, a second hardening from 800°C (5% ferrite), and tempering at 200°C. Full hardening from 930°C with subsequent tempering at 200°C (without preliminary hardening) makes it possible to obtain _t=1550 MPa, _0.2=1200 MPa, =9%, anda _n=0.9 MJ/m².Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 52–56, May, 1981.