Full DRX Research Articles

Hot deformation and processing maps of Inconel 690 superalloy

The hot deformation behavior of Inconel 690 has been investigated by means of hot compression tests in the temperature range of 950–1200 °C and strain rate range of 0.001–10 s −1. The results show that the maximum stress decreases with decreasing strain rate and increasing temperature, and the activation energy is about 380.215 kJ/mol. Processing maps developed on the basis of experimental data and using the principles of the dynamic materials model exhibited two domains. The first domain occurs in the temperature range of 970–1120 °C and strain rate range of 0.03–3.3 s −1, with a peak efficiency of power dissipation of 0.39. The second domain occurs in the temperature range of 1150–1200 °C and strain rate range of 0.003–0.1 s −1, with a peak efficiency of power dissipation of about 0.37. Microstructural observations revealed that the full dynamic recrystallization (DRX) occurred in these two domains. In the first domain, the undissolved carbides assisted in nucleating DRX and restricted the coarsening of the full DRX grains and the refined grains were obtained. A small regime of flow instability was noticed at low temperature and high strain rate.

Dynamic Recrystallization Behaviour in Cu-Sn-P Alloy for High Strength Copper Tube

Dynamic recrystallization (DRX) behaviour in a newly developed Cu-Sn-P alloy for heat exchangers and tubes was systematically investigated. For this purpose, Cu-Sn-P alloys with different content of Sn were deformed in compression at temperatures between 1073 K and 1213 K and at various strain rates from 2 x 10-4 s-1 to 2 x 10-1 s-1. The onset of DRX was more advanced with increasing temperature and with decreasing strain rate. Full DRX was not achieved at the testing conditions of lower temperature and higher strain rate even after straining to ε = 1.0. This tendency was more significant in the alloy with higher Sn content. With increasing Sn content, the flow stress and the obtained grains size became higher and finer, respectively. These experimental results indicate the important role of Sn for strengthening and microstructual control.

Dynamic recrystallization microstructures under hot working conditions

The characteristics of high temperature flow curves and evolution of new grain structures under conditions of dynamic recrystallization (DRX) are reviewed, together with the associated development of dislocation substructures. It is shown that the type of DRX taking place depends on the relative grain size D o/D s, where and D o and D s are the initial and stable dynamic grain sizes, and also on the nature of dispersion particles. These can be attributed to that dynamic nucleation occurs mainly at or near existing grain boundaries, and dynamic growth is controlled by not only the temperature corrected strain rate Z, but also dispersion particles. The work softening accompanied with DRX results from a change in the substructural nature from homogeneous. The dislocation substructures under full DRX are classified into the three categories: (i) DRX nuclei, (ii) growing DRX grains containing a dislocation density gradient, and (iii) large DRX grains with fairly homogeneous substructure. Finally, the metadynamic or post-dynamic restoration processes taking place in the DRX matrices are reviewed. The static softening-annealing time curve observed after DRX consists of three distinct stages with the respective inflection plateaus, followed by incomplete softening (stage 1,2 and 3). The rate of grain growth at stage 3 is much lower than that of normal grain growth. These can be caused by the stable existence of growing DRX grains having many-sided irregular shapes as well as high density dislocations.

Kinetics of Recovery and Recrystallization in Dynamically Recrystallized Austenite

The static softening processes taking place after dynamic recovery (DRV) and dynamic recrystallization (DRX) were studied by means of interrupted tensile tests for a 0.4%C-1.5%Mn steel at a temperature-compensated strain rate Z. The softening curves associated with a DRV matrix (ε=0.1) consist of two stages followed by complete softening, in which (i) classical recovery and (ii) classical recrystallization take place in sequence. In contrast, the softening curves in a full DRX structure (ε=0.26) consist of three distinct stages with the respective inflection plateaus, followed by incomplete softening. The controlling mechanisms operating in each stage are mainly (i) metadynamic recrystallization, (ii) metadynamic recovery and classical recrystallization, and (iii) grain growth. Both the activation energy and the Avrami exponent in stage 2 for a DRX matrix is clearly smaller than those for static recrystallization. It is concluded that all stages of softening after DRX can be strongly affected by the existence of growing DRX grains, which have no potential for classical nucleation, and also by the role of metadynamic recovery taking place within them.

Dislocation substructures developed during dynamic recrystallisation in polycrystalline nickel

AbstractThe dislocation substructures developed during dynamic recrystallisation (DRX) were studied by means of tensile tests and metallographic observations on polycrystalline nickel. The average cell size in the homogeneous substructures decreased rapidly with straining to about half the peak strain, whereupon DRX nuclei began to form. The average cell size then approached a constant value for increasing strain. Full DRX substructures were distributed heterogeneously throughout all areas, and were classifiable into three categories: (i) DRX nuclei, (ii) growing DRX grains containing a dislocation density gradient, and (iii) large DRX grains with a fairly homogeneous substructure. The average cell size in region (iii) could be expressed as a function of either the peak flow stress or the DRX grain size. The relationship between these microstructures and flow behaviour under DRX are discussed in detail.MST/1285

炭素鋼における動的再結晶オーステナイトの静的軟化

The static softening processes taking place after dynamic recovery (DRV) and dynamic recrystallization (DRX) were studied by means of interrupted tensile tests for a 0.4%C-1.5%Mn steel at a temperature-compensated strain rate Z. The softening curves associated with DRV matrices (ε=0.1) consist of two stages followed by complete softening, in which (i) classical recovery and (ii) classical recrystallization take place in sequence. By contrast, the softening curves in a full DRX structure (ε=0.26) consist of three distinct stages with each inflection plateau, followed by incomplete softening. These can be controlled mainly by (i) metadynamic recrystallization, (ii) metadynamic recovery and classical recrystallization, and (iii) grain growth. The activation energy for the softening in stage 2 nearly equals that for dynamic recrystaIlization, which is clearly smaller than that for static recrystallization. It is concluded that all stages of softening after DRX can be strongly affected by the existence of growing DRX grains having no potentiality for classical nucleation and the role of metadynamic recovery taking place within them.

Recovery and recrystallization of polycrystalline nickel after hot working

The static softening processes taking place after the hot working of polycrystalline pure nickel were studied by means of interrupted tensile tests and microhardness measurements as well as metallographic observations. The samples were deformed at 1050 K (0.61 T m ) and at 2 × 10 −3 s −1 to four levels of prestrain between 0.04 and 0.28. The effect of dynamically recovered (DR) and dynamically recrystallized (DRX) structures on the subsequent progress of static softening was analysed. The softening processes taking place in a DR matrix are classical recovery and classical recrystallization, and full softening can be achieved when the prior strain exceeds the critical strain required for static nucleation. By contrast, four separate softening mechanisms can be distinguished in a full DRX structure: classical static recovery and recrystallization, and metadynamic or post-dynamic recovery and recrystallization. Static softening after DRX proceeds very rapidly because of the operation of metadynamic recrystallization, which does not involve an incubation time. It cannot go to completion, however, because of the presence of metadynamically recovered grains, which are quite stable at high temperatures. Metadynamic recrystallization consists of the continued growth of DRX nuclei after deformation. Metadynamic recovery takes place in growing DRX grains containing a dislocation density gradient; the low density regions of these grains are below the critical strain level and thus have no potential for static nucleation. As a result of these inhomogeneous dislocation substructures, softening does not go to completion in DRX grains.