Materials Science Forum Vols. 558-559

Abstract: Effects of the crystallographic misorientation across boundaries between recrystallising grains and the neighbouring deformed matrices are discussed and exemplified by recrystallisation investigations of fcc metals. Classic misorientation observations are reviewed in the introduction, whereas the main parts of the paper focuses on two special boundary migration phenomena observed by in-situ recrystallisation experiments; namely protrusions and facets.

Abstract: The drawing textures of aluminum, copper, gold, silver, and Cu-7.3% Al bronze wires are approximated by major <111>+minor <100>, except silver wire, which can have the <100> texture at extremely high reductions. The <111> component in the drawing textures of aluminum, copper, gold, and silver transform to the <100> component after recrystallization. On the other hand, the <111> deformation texture of the Cu-7.3% Al bronze wire, which has very low stackingfault- energy, remains unchanged after recrystallization. The <100> + <111> recrystallization textures change to the <111> texture after abnormal grain growth. The Brass component {110}<112> in rolling textures of high stacking-fault-energy metals such as aluminum, copper, Cu- 16% Mn, and Cu-1% P changes to the Goss orientation {110}<001> after recrystallization. However, the Brass orientation in rolling textures of low stacking-fault-energy fcc metals such as brass and silver appears to change to an orientation approximated by the {236}<385> orientation after annealing. The texture changes are discussed based on the strain-energy-release-maximization model for medium to high stacking-fault-energy metals and on grain growth for low stacking-fault energy metals.

Abstract: This paper showed an example of the phenomena that a strong deformed texture does not change after the annealing process in steels. An Fe – 22%Cr – 3%Ni ferritic stainless steel was processed by bar rolling/swaging to a total strain of 4.4 at an ambient temperature, and its annealing behaviour was studied in a temperature range of 400 ~ 700oC. The deformed sample showed a grain size of 200nm, a fraction of high-angle boundary (HAB) of about 0.6, and a strong fiber texture of <110>{uvw}. This texture showed very little change after annealing which was characterised by the development of continuous recrystallization involving recovery processes and followed by a normal grain growth. On the other hand, by annealing a sample that was deformed to total strain of 2.0 containing rather fine grains (270nm) but without a large enough fraction of HAB (0.3), a discontinuous recrystallization took place, and its deformed texture changed considerably.

Abstract: The effects of alloying elements and impurities on the microstructure and properties of metals and alloys are important. Understanding of these effects may help to control and produce products with desired properties at lower cost. In the present work the effects of Al, Si and Mn on the recrystallization behavior, hardness and microstructural changes of an Fe- containing brass during annealing were studied. The results show that alloying elements strongly affect recrystallization kinetics and resulted finer microstructures. Hardness variations during annealing are consistent with microstructural observations and the presence of alloying elements. All elements slow down recrystallization progress and increase resulted hardness values. The resulted microstructures in the presence of alloying elements are much finer than that of plain 70B brass. It was concluded that the present alloying elements affect the recrystallization behavior of 70B brass in a similar manner. Their mechanism of interactions is solute drag effect and their effects sum up when they present together.

Abstract: Several studies have shown that recrystallization of cold rolled martensite results in low carbon steels with very fine microstructures. Correspondingly, these materials exhibit promising combinations of strength and elongation. Most of the work on this processing route has focused on low carbon steels (0.1-0.2wt% carbon) where the interstitial content may play an important role in the microstructure refinement. In this note we describe experiments performed on a low interstitial stainless steel containing 0.02wt%C. It has been possible to achieve materials with high strengths (UTS > 1 GPa) and significant uniform elongation (> 8%), however, the microstructures associated with these properties are very different from those previously reported for low carbon steels.

Abstract: 15%Cr ferritic stainless steel was machined in rectangular samples and then processed by multiple forging to a total cumulative strain of 7.2 at an ambient temperature. The large strain deformation resulted in almost equiaxed submicrocrystalline structure with a mean grain/subgrain size of 230 nm and about 2.2×1014 m-2 dislocation density in grain/subgrain interiors. The annealing at a relatively low temperature of 500oC did not lead to any discontinuous recrystallizations. The grain/subgrain size and the interior dislocation density slightly changed to 240 nm and 2.1×1014 m-2, respectively, after annealing for 30 min, while the Vickers hardness decreased from 3140 MPa in the as-processed state to 2900 MPa. This annealing softening was attributed to remarkable release (by 50%) of internal stresses, which are associated with a non-equilibrium character of strain-induced grain/subgrain boundaries.

Abstract: High-purity niobium single crystals were deformed by equal-channel angular extrusion (ECAE) at room temperature to an equivalent Von Mises strain of about 1.15. Deformed samples were annealed in vacuum from 500 to 800oC for 1 hour to investigate their microstructure evolution. The microstructure of deformed and annealed samples was characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and Vickers microhardness testing. The deformed structure after one ECAE pass is rather inhomogenous and consists of parallel sets of coarse shear bands whose spacing varies from one region to another in the cylindrical billet. the microstructure within the shear bands consists of elongated subgrains with sizes below 3 μm and lamellar boundaries. The remaining non-sheared regions display a coarser subgrain structure. Recrystallization is virtually absent in samples annealed at 500oC for 1 hour. Nucleation begins mostly within shear bands. The new grains with sizes ranging from 10 to 50 μm are arranged in clusters rather than being homogenously distributed. The recrystallized volume fraction also varies from one region to another indicating an inhomogenous distribution of stored energy. At 700oC, recrystallization is complete after annealing for 1 hour resulting in a structure with a mean grain size of about 100 μm.

Abstract: The recrystallization behavior of 71% cold rolled aluminum alloy 3103 was investigated by measuring the crystallographic texture and the grain microstructure during heat treatment at 288°C, 310°C and 330°C in a magnetic field of 17 T. The results revealed that the application of a magnetic field substantially enhances recrystallization kinetics.

Abstract: The recrystallization behaviour of a cold rolled austenitic Fe-Mn steel is studied to explain the fine grained final microstructure. Thorough investigation of the kinetics, the microstructure and the texture evolution during recrystallization showed that the fast recrystallization kinetics is responsible for the final microstructure, while an oriented nucleation mechanism determines the texture evolution. The reason for the fast recrystallization kinetics is the low amount of recovery prior to recrystallization, resulting in a high driving force for the latter.