Hot Working Parameters Research Articles

Hot-working characteristics of Zircaloy-2 in the temperature range of 650–950°C

The hot-working characteristics of Zircaloy-2 have been studied in the temperature range of 650 to 950°C and in the strain-rate range of 10−3 to 102 s−1 using power dissipation maps which describe the variation of the efficiency of power dissipation, η = 2m /(m + 1) where m is the strain-rate sensitivity of flow stress. The individual domains exhibited by the map have been interpreted and validated by detailed metallographic investigations. Dynamic recrystallization occurs in the temperature range of 730 to 830°C and in the strain-rate range of 10−2 to 2 s−1. The peak efficiency occurs at 800°C and 0.1 s−1 which may be considered as the optimum hot-working parameters in the α-phase field of Zircaloy-2. Superplastic behaviour, characterized by a high efficiency of power dissipation is observed at temperatures greater than 860°C and at strain rates lower than 10−2 s−1. When deformed at 650°C and 10−3 s−1, the primary restoration mechanism is dynamic recovery, while at rates higher than 2s−1, the material exhibits microstructural instabilities in the form of localized shear bands.

α<SUB>2</SUB>+γ型Ti-Al系金属間化合物のα域加工によるラメラ粒の微細化

Hot working in the high temperature single α phase region have been employed to achieve a fine equiaxed lamellar grain structure in an α2+γ type Ti-Al intermetallic compound, which is expected to be the optimum microstructure for balancing the mechanical properties, such as room temperature ductility, fracture toughness and high temperature strength. Effects of hot working parameters, such as temperature, reduction and strain rates, and the subsequent cooling rate on the microstructures were systematically examined in the Ti-40 mol%Al alloy. The microstructures were characterized by the hardness measurement, X-ray diffractometry, optical microscopy and TEM.It was clearly demonstrated that the refinement of fully lamellar grain structure is possible with the above method. It was revealed that the critical cooling rate for the formation of γ phase exists at 0.2 K/s when the alloy was deformed by 60% with 10−2s−1 at 1473 K. Parameters of hot working also strongly influence the lamellar grain size. Lower temperature, higher reduction and higher strain rates respectively promotes the refinement of lamellar grain size and an optimum combination of the working parameters produced the grain size of 100 μm. Furthermore, an isothermal process for the precipitation of γ phase after quenching into the α2+γ region achieved the grain size of 70 μm. The formation of γ phase in the α phase during continuous cooling and the role of hot working in the α phase on the eventual lamellar grain structures were discussed.

Processing map for hot working of alpha-zirconium

The hot deformation characteristics of alpha-zirconium in the temperature range of 650 °C to 850 °C and in the strain-rate range of 10-3 to 102 s-1 are studied with the help of a power dissipation map developed on the basis of the Dynamic Materials Model.[7,8,9] The processing map describes the variation of the efficiency of power dissipation (η =2m/m + 1) calculated on the basis of the strain-rate sensitivity parameter (m), which partitions power dissipation between thermal and microstructural means. The processing map reveals a domain of dynamic recrystallization in the range of 730 °C to 850 °C and 10−2 to 1−1 with its peak efficiency of 40 pct at 800 °C and 0.1 s-1 which may be considered as optimum hot-working parameters. The characteristics of dynamic recrystallization are similar to those of static recrystallization regarding the sigmoidal variation of grain size (or hardness) with temperature, although the dynamic recrystallization temperature is much higher. When deformed at 650 °C and 10-3 s-1 texture-induced dynamic recovery occurred, while at strain rates higher than 1 s-1, alpha-zirconium exhibits microstructural instabilities in the form of localized shear bands which are to be avoided in processing.

Basic study for plastic deformation of rapidly quenched Nd-Fe-Co-Ga-B magnets at elevated temperature

In order to optimize hot-working conditions of rapidly quenched Nd-Fe-Co-Ga-B magnets, the behavior of plastic deformation at elevated temperatures has been studied. Compressive and tensile tests were performed with various hot-working parameters. From compression tests, a strain-rate sensitivity factor and a strain hardening factor at 700 degrees C of 0.4 and 0.3, respectively, were obtained. From tensile tests, the tensile strength and elongation at 700 degrees C were determined to be 1.0 approximately 1.8 kgf/mm/sup 2/ and 6 approximately 12%, respectively. Based on these data, computer simulation of the die upsetting process was performed by rigid plastic FEM (finite-element method) calculation. It was found that, to suppress the occurrence of peripheral cracks and improve magnetic properties, low strain rates are necessary. Computer calculation of the stress distribution can explain the mechanism of peripheral crack initiation in the die upsetting process.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A study of the hot-working behavior of SiC−Al alloy composites and their matrix alloys by hot torsion testing

The hot-working behavior of two metal matrix composites (7090+20 vol pct SiC whiskers and 6061+20 vol pct SiC whiskers) and their powder metallurgy matrix alloys (7090 and 6061) was studied by hot torsion testing. Flow stress (σ0) and strain-to-failure (ef) data were generated at deformation temperatures and strain rates corresponding to the potential range for commercially hot-working these alloys. Based on the hot torsion data, hot-working parameters were recommended where (σ0) was low and (ef) was high. Strain rate sensitivities and activation energies of deformation were computed for the alloys.

Influence of hot-working parameters on earing behaviour of Al–2Mg sheet

Abstract Experiments have been conducted to investigate the effect of hot-working parameters on the earing quality of sheet at each stage of fabrication. It is shown that a linear relationship exists between hot-work induced subgrain size and percentage earing for material which has been (i) hot rolled, (ii) hot rolled and cold rolled, (iii) hot rolled and annealed, (iv) hot rolled, annealed, and cold rolled, and (v) hot rolled, annealed, cold rolled, and annealed. It is argued that the relationship is indirect and arises because the mechanisms which determine the subgrain size also govern the development of texture. Further, it is shown that annealing after hot working produces a recrystallized grain size which bears a linear relationship to the subgrain size produced by hot working alone. Finally, tests involving different heating rates during the annealing cycle have shown that the earing quality is affected by this parameter.