Preliminary Heat Treatment Research Articles

Effects of the size and morphology of cementite particles on the annealing texture in low-carbon aluminium-killed steel.

The processes of cementite dissolution, recrystallization and annealing-texture formation during isothermal annealing have been observed in cold-rolled sheets of a low-carbon aluminium-killed steel in which the effect of the pre-precipitation clusters of aluminium-nitride was eliminated by preliminary heat-treatments. Inhibition of nucleation due to pinning of dislocations by dissolved carbon atoms and inhibition of the growth of recrystallized grains by carbon atoms or by fine cementite particles have been considered as probable effects which decrease the rate of recrystallization. The predictions were, however, found to be inconsistent with the experimental results obtained. It was supposed that different annealing textures were produced through changes in the size and distribution of constrained-deformation regions in the deformed iron matrix. When the cementite particles were coarse and widely spaced, an annealing texture with strong {222} and weak {110} orientations was obtained by rapid heating directly to a high temperature. In a case when the hot band contained fine spheroidal cementite particles, a similar annealing texture could be obtained by two-stage annealing. The presence of pearlite had a deteriorating effect on the development of the favourable texture.

Quantitative treatment of electron micrographs from fracture surfaces of oriented capron monofibres

The step value on the wave relief of the mirror zone, d, has been measured on a series of successive microphotographs from replicas taken from rupture surfaces of oriented capron monofibres and relationships corresponding to the increase in d with an increase in crack length have been obtained. The effect of preliminary heat treatment and rate of extension on the way in which d depends on crack length has been discussed. It is shown that there is a certain minimum displacement of the crack front, which does not depend on the crack speed within the mirror zone and which is therefore related to specific structural formations of the microfibril type. The change in the value of the minimum displacement as a result of annealing correlates with the coarsening of the elements in the internal structure, as is confirmed by X-ray structural analysis.

Kinetics of decomposition of austenite in steel 9Kh2MF

1. The stability of supercooled austenite in the pearlitic region does not depend on the melting procedure; in the intermediate region the stability is highest for the ESR method. 2. The changes observed in the kinetics of the decomposition of supercooled austenite in steel 9Kh2MF melted by different procedures are due to the effect of the melting procedure on the purity of the steel, grain size, and size and distribution of carbide particles. The experimental data obtained on the kinetics of austenite decomposition under isothermal conditions and during continuous cooling can be used for the development of preliminary and final heat treatments for steel 9Kh2MF melted by different procedures.

Effect of preliminary heat treatment on the properties of the nitrided case on aluminum-free structural steels

Preliminary heat treatment affects the properties of the nitrided case on aluminumfree steels containing carbide-forming elements. For annealed and normalized steels with a ferrite-pearlite structure the depth and hardness of the nitrided case are lower than for quenched and tempered steels with a structure of sorbite.

Stationary and non-stationary crystal nucleation rate in a glass of 2Na 2O.CaO.3SiO 2 stoichiometric composition

Studies have been made of the temperature dependences of stationary and non-stationary nucleation rates of the 2Na 2O.CaO.3SiO 2 crystals in the glass of the same composition. A considerable difference has been established between activation energies of crystal nucleation, crystal growth and glass viscosity. Studies have also been made of the influence of preliminary heat treatment (pt) of the glass at temperatures T pt < T on the non-stationary rate of crystal nucleation at T. With decreasing T pt this influence shows up in the appearance of a maximum. The experimental data are interpreted on the basis of notions about subcritical nuclei formed at T pt.

Preliminary heat treatment of castings

The heat treatment proposed for castings of drive wheels made of steel 20KhGSNDML (tempering at 680° for 10 h) completely eliminates casting stresses, reduces the hardness to the lowest possible values, creates a structure favorable for machining, lowers tool costs, and eliminates scrapping as the result of warping.

Effect of low-cycle overloads on the fatigue strength of structural materials

1. Preliminary low-cycle overloading changes the fatigue strength of materials and makes it necessary to correct the linear rule of additive damage. 2. Depending on the type of material, the load, and the total deformation, low-cycle overloading may have either a softening or hardening effect. 3. The effect of preliminary treatment is evident during subsequent fatigue loading as a softening effect if the structural condition of the material corresponds to stage II of the elastoplastic deformation curve, characterized by a destructive component. 4. For cyclically softened material (steel 14Kh2GMR) preliminary low-cycle loading in the range of strain proper (Npre=5 cycles) and in the region of destructive deformation (Npre=80 cycles) lowers the fatigue limit regardless of the strain amplitude (0.2 and 0.5%). 5. The rate of the softening process is determined by the structural condition of the material, which is characterized by the effective yield strength and varies with the preliminary heat treatment, preliminary deformation, and amplitude of deformation in the original half-cycle of loading. 6. In selecting technological operations associated with overloading it is necessary to establish the permissible level of the load (deformation) and the number of preliminary cycles, depending on the type of material, its structural condition, and the operating conditions.

Preliminary heat treatment of high-speed steel R6M5

Preliminary heat treatment of steel R6M5 can be recommended to prepare the structure for final heat treatment, reduce the holding time during final heating to quenching temperature, reduce distortion, and improve the consistency of the cutting properties of tools up to 60 mm in diameter.

Hydrogenation of catalytic carbons obtained by CO disproportionation or CH 4 decomposition on nickel

The hydrogenation of catalytic carbons has been studied in the temperature range of their deposition (300–700°C) by CO disproportionation or by CH 4 decomposition on nickel powders. When obtained under non carbiding conditions, the catalytic carbons are very reactive between 350 and 600°C where uncatalysed carbons are inert. The reactivity does not depend on the temperature of deposition and on preliminary heat treatment, but depends on the degree of gasification. This reactivity is imputed to the quality of the metal carbon interface which allows a good deposition-gasification reversibility. When deposition occurs under carbiding conditions, both deposition and subsequent hydrogenation are poisoned by the carbon formed by thermal decomposition of the carbide.

Catalytic activity of a supported catalyst for ethylene polymerization, obtained by modification of vulcasil with titanium tetrachloride vapour

Titanium-containing surface compounds have been obtained by the interaction of the silanol groups of Vulcasil with TiCl 4 vapour. These substances have been used, in combination with organ-oaluminium and organo-magnesium compounds, for the polymerization of ethylene. The effects upon the catalyst activity of the reaction conditions (temperature, pressure, duration of polymerization), of the titanium amount on the Vulcasil surface and the Al:Ti and Mg:Ti ratios have been studied. The activity of the catalyst system has been shown to increase with increasing pressure up to 11 kg/cm 2 and to attain its optimum value at 60°. Polymerization has been found to end 15–20 min after the introduction of the monomer. The highest yields of polymer are obtained at Mg:Ti and Al:Ti ratios of about 30. The amount of titanium on the Vulcasil surface depends on the conditions of preliminary heat-treatment of the Vulcasil and decreases from 0.63 to 0.30 mg at/g with increasing dehydroxylation temperature. Simultaneously, the yield of polymer varies within a narrow range (89–107 g/l), and the productivity increases from 21 to 35.5 kg polyethylene (PE) per 1 g of Ti. This is especially clearly expressed with the samples obtained by preliminary heat-treatment at 400–700°.

Specific protection from phenocopy induction by heat shock

AbstractMild heat treatments applied to whole animals or cell cultures of Drosophila prior to lethal heat shocks result in increased survival and protection against phenocopy induction. The optimal condition for the preliminary mild heat treatment is that which induces the synthesis of heat‐shock proteins but does not turn off the protein synthesis that is in progress. Recovery of protein synthesis but not RNA synthesis following a drastic heat shock is much enhanced by the pretreatments. The results suggest that the protection for survival and against phenocopy induction is due to storage of messenger RNA.

Preliminary heat treatment of forgings

1. An investigation of the kinetics of hydrogen precipitation from large steel forgings with use of the theory of heat transfer showed that the hydrogen concentration in the center of large forgings changes negligibly after annealing. 2. Redistribution of hydrogen between the metal and voids has a large effect on the formation of shattercracks. Hydrogen is found in the solid solution in the process of annealing with isothermal holding and at higher temperatures. At low temperatures, especially at room temperature, almost all the hydrogen is in equilibrium in voids. 3. During isothermal holding the hydrogen diffuses to the surface of voids. During supercooling and in the process of final cooling it precipitates in voids, molecular hydrogen is formed, and the steel becomes resistant to formation of shattercracks.

Effect of vacuum heating on the corrosion resistance of Al-4.5Zn-2Mg

Preliminary heat treatment in vacuum of Al-Zn-Mg alloys improves the stress corrosion resistance. One of the probable reasons for this effect is the impoverishment of the surface layer in magnesium and zinc.

Effect of preliminary heat treatment on phase transformations and properties of steel Kh15N5D2T (VNS-2)

Preliminary heat treatment has a substantial effect on the kinetics of the α→γ transformation, the amount of retained austenite, the grain size, and the work of crack propagation in steel Kh15N2D2T after final heat treatment.

Preliminary heat treatment of industrial ceramic articles in a fluidized bed layer

Preliminary heat treatment of industrial ceramic articles in a fluidized bed layer

Effect of preliminary heat treatment, cold deformation, and electric heating on the mechanical properties of steel 30KhGSA

Effect of preliminary heat treatment, cold deformation, and electric heating on the mechanical properties of steel 30KhGSA

Selecting the composition and structure of steel for cold working dies

1. For dies operating at low impact loads it is expedient to use steel 6Kh3FS. The working life of dies increases considerably in this case. 2. Steel 6Kh3FS should be heat treated as follows: oil quenched from 950–970°, tempered at 200–220° (HRC 56–57,an=3 kgf-m/cm2), austempered at 220–240° for 45 min, and tempered at 160–180° (HRC 55–57,an=4.5 kgf-m/cm3). 3. The working life can be increased considerably by preliminary heat treatment ensuring the necessary surface finish after turning.

Low-temperature diffusion of lithium in CdTe

The diffusion of lithium at 300°C has been studied in CdTe samples in which the native defect concentration was fixed by preliminary heat treatments in Cd and Te vapors. It has been found that at low temperatures lithium diffuses in two forms characterized by two different diffusion mechanisms. The high-concentration, slowly diffusing form depends on the cadmium vacancy concentration (via the nature of heat treatment) whereas the low-concentration, fast-diffusing form is independent of it. The experimental results were analyzed in terms of Kucher's phenomenological theory. This theory supposes the simultaneous diffusion of the diffusing species in two different forms with exchange interaction between them. Whereas the rapid form is likely to be interstitial lithium, the slowly diffusing one is lithium interacting with cadmium vacancies, probably in a nonsimple configuration.

Effect of hot deformation conditions and preliminary heat treatment on the properties of tungsten-molybdenum high-speed steels

1. The initial rolling temperature (1000\2-1200\dg) and preliminary heat treatment have a large effect on the consistency of the properties of tungsten-molybdenum steels. An initial rolling temperature of 1000° ensures consistent properties of all 20 heats investigated after annealing and tempering. Initial rolling temperatures of 1100–1200° increase the susceptibility of tungsten-molybdenum steels to grain growth during quenching. Steels rolled at 1000–1200° and not subjected to preliminary softening heat treatment have a tendency to grain growth, unevenness of grain size, and brittleness of the fracture (with rolling at 1200°). 2. Initial rolling temperatures from 1000 to 1200\dg have no essential effect on the red hardness after tempering and annealing. Among the heats tested, the red hardness of 30% tended to decrease when the initial rolling temperature was raised to 1200\dg after tempering and after annealing.

Paramagnetic centers in gamma-irradiated magnesium oxide

1. The authors have studied the formation of electron and hole paramagnetic centers in gamma-irradiated magnesium hydroxide and oxide with various degrees of dehydration. 2. Rise in the temperature of preliminary heat treatment of the magnesium oxide causes an increase in the radiation-chemical yield of FS+ centers and a decrease in that of Vsu− centers. 3. The thermal stability of paramagnetic centers in magnesium oxide increases as the hydroxyl group content decreases.