High-speed Heating Research Articles

High-Speed Frictional Heating of an Elastic Medium With a Near-Surface Horizontal Line Crack

This paper studies the effect of high-speed frictional heating over the surface of an elastic material, which has a near surface horizontal line crack. The frictional heating is represented by a high-speed moving heat source, since the mechanical loading effect is much smaller than the thermal effect in the resulting stress field. Finite difference methods are employed to compute the temperature field and the displacement field, taking into consideration the characteristic singularity at the crack tip. The temperature field solutions are first computed, using the method of heat balance. The thermo-mechanical solutions follow with particular interest in the vicinity of the line crack as represented by the stress intensity factors at the crack tip. It was found that both the open mode and the shear mode occur, as a result of the excitation of the moving thermal load. The paper also presents effects on the stress intensity factors from varying the thermal and the mechanical properties of the medium, and the location of the line crack from the wear surface. The depth at which the maximum thermal stress occurs is an exponential function of the Peclet number, as in the cases when there is no defect in the wear material and when there is a near surface cavity. Albeit, the “critical depth” reduces with increasing Peclet number and severity of the defect.

Study of the chemical composition of the surface of high-speed steel specimens with a coating based on titanium nitride after the action of heat

1. With long-term heating in a vacuum of specimens of high-speed steel R18 with a coating based on titanium nitride applied by means of ion plasma technology diffusion processes of mass transfer are realized in the coating-substrate system. 2. With short-term high-speed heating two regions are observed in the coating: an outer region enriched with oxygen and impoverished in nitrogen and carbon, and an inner region with the opposite ratio of elements. Oxygen enters from the surrounding atmosphere and carbon enters from the substrate material. 3. Additional short-term heating makes it possible to control processes of forming the compound TiNxOyCz of prescribed composition which makes it possible to improve the operating properties of tools and to optimize the technology for treating materials.

Correlation of grain-structure parameters with the properties of thermally strengthened titanium alloys VT6 and VT23

1. The original grain size of two-phase titanium alloys VT6 and VT23 after high-speed heating, quenching, and aging has almost no effect on the ultimate breaking strength of these alloys, but it changes their ductility characteristics to a significant degree. 2. The dependence of mechanical properties for thermally strengthened alloys VT6 and VT23 on original β-grain size may be described by empirical equations which are the well-known Petch-Hall expression only under conditions of constancy for values of ductility characteristics (δ and ϕ).

Structure, texture, and properties of alloy VT20 after deformation and annealing by different schedules

1. Cold rolling of alloy specimens leads to formation of a two-component texture which with deformation at the level of about 30% approaches the baseline. This creates a region of critical reduction (27–40%) were material failure is possible. This region may be passed by repeated rolling with small (approximately 2.5%) reductions per pass. With further deformation (50% or more) a texture of the deviation type forms which makes it possible to achieve (80–90%) reductions. 2. In order to obtain good structural, textural, and mechanical characteristics it is recommended that vacuum annealing in the furance or high-speed heating above the phase recrystallization temperature with cooling in air is carried out after cold rolling. Subsequent short-term annealing in the furnace at 800°C with air cooling was a favorable stabilizing effect on alloy structure.

Kinetic diagrams for austenitizing high-strength cast iron

1. Kinetics for α→γ-transformation are governed by the silicon content in HC, redistribution of silicon between austenite and ferrite, and cast iron heating rate. This dependence expands the transformation range and causes formation of austenite which is inhomogeneous with respect to carbon and silicon concentration. 2. A dependence has been established for the temperature for the start and finish of austenite formation on silicon content in HC and its heating rate. The kinetic diagram plotted makes it possible to select a schedule for high-speed heating of castings for hardening with a given silicon content.

Numerical study of thermal fields in high-speed electrical heating of powdered materials

Three calculation methods are considered for analyzing the temperature fields excited by an electrical current passing through a powdered medium.

Finite-difference solution of the optimization problem in high-speed heating of a body of simple shape by internal heat sources

A method is proposed for construction of optimal fast-response control of body heating under constraints on the control (internal heat sources) and the temperature field or stress-strain parameters.

Principle of the shift of the temperature of the instrumental onset of the austenite transformation in steels during high-speed and laser heating

It is shown that the shift of the temperature of the onset of the austenitic transformation in steels during high-speed heating can be interpreted as a time delay of the α→γ transformation relative to the rate of change of temperature. During heating of steels with laser radiation pulses the temperature shift may be considerable and this restricts the range of temperatures in which steels can be hardened without melting and can reduce the hardening efficiency. The calculated and experimental temperatures agree satisfactorily.

Resins and asphaltenes in sintering petroleum coke

One of the directions in utilization of sintering coke breeze that may be effective is its addition to a coal or coal briquet charge to coke ovens in place of sintering and weakly sintering coals in coal-tar chemical production. For their investigation they took commercial samples of petroleum coke breeze (0-25 mm) obtained from different types of raw material: (1) a semitar (medium straight-run resid) produced from mixed Perm' and West Siberian crudes by the Industrial Association Permnefteorgsintez; (2) a blend of vacuum resid and tar from cracking atmospheric resid (1:1), from the Krasnovodsk refinery; (3) a blend of cracked tars from processing vacuum resid and thermal gasoil (1:1.5), from the Novo-Ufa refinery. The dependence of the yield of resins and asphaltenes in thermal breakdown of coke as a function of the calcination temperature and the coke size distribution was investigated with continuous heating (2-4/sup 0/C/min) and isothermal (high-speed) heating.

Sintering of compacts from iron-base powders under conditions of high-speed heating by high frequency current

The sintering of iron-base P/M materials under conditions of short-time electric heating by HFCs proceeds rapidly, and enables results to be obtained in 3–5 min which require periods of 1.5–2 h in sintering by conventional techniques. This opens up many possibilities for the development of effective high-speed methods of manufacture of parts in P/M materials.

Electron beam heating in amorphous semiconductor beam memory

The high-speed electron beam heating and the subsequent cooling processes in an amorphous semiconductor target of a beam memory have been studied by computer simulation. Such a memory would utilize the amorphous and the crystalline phases of chalcogenide thin films as the binary states of the memory. For an electron source of 1-µ radius, the results suggest that a storage target, consisting of a chalcogenide thin film whose thickness is twice the electron penetration range on a good heat sinking substrate, is the optimum target configuration. Possible high-speed memory operating characteristics with present long-life high-brightness electron guns are described.

Operation of a sectional furnace for high-speed heating of tubes before sizing and reducing

Operation of a sectional furnace for high-speed heating of tubes before sizing and reducing

Sectional furnace for high-speed heating of tubes

Sectional furnace for high-speed heating of tubes

Mechanism by which cold-hardened iron softens during high-speed heating

1. Removal of the distortions in the crystal structure and the microrecrystallization processes develop independently of one another. Under our experimental conditions (a high heating rate), recrystallized iron inherited most of the hardening effect and distortions introduced by preliminary cold-hardening. 2. The sequence in recovery and recrystallization observed when cold-hardened metal is heated is governed by kinetic factors and is a function of temperature. The sequence in completion of these processes is reversed in the experimental conditions; this indicates that recovery and microrecrystallization are different in nature and independent.

Structural changes in steel when subjected to compressed gas stream at high temperature

1. The structural changes in the surface layers of steel 45 when subjected to the single action of a compressed gas stream at high temperature are determined by the chemical and thermal action of the gas medium. The diffusion of the carbon and nitrogen from the gas medium extends to a depth of 10 microns and causes formation of nitrogencarbon austenite. 2. High temperatures and high pressures cause secondary-quenching and high-speed tempering structures in the surface layer of the steel, which can be brought to light metallographically in the form of a poorly-etched white layer and an increased etchability zone. The thickness of the white layer decreases as the temper temperature of the initial structure of the steel is increased. The over-all depth of the structural changes is 300 microns. 3. The phase composition of the white layer is determined by the distribution of temperatures over the supercritical range during high-speed heating. The structure of the high-speed high temper under conditions of external pressure differs from the structure of ordinary high tempering in its submicrostructure andα-phase crystal lattice parameter, as well as in the degree of dispersion of the carbide phase.

High-speed heating of swaging dies prior to quenching

High-speed heating of swaging dies prior to quenching

Sectional furnaces for high-speed heating of metal

Sectional furnaces for high-speed heating of metal