conjugate slip system Slip system becoming active after the resolved shear stress on a primary slip system decreases below critical value, due to a lattice rotation in the course of plastic deformation. See Schmid’s law. conode See tie line. constitution diagram See phase diagram. constitutional undercooling/supercooling Undercooling of melt due to changes in its equilibrium solidification temperature, T 0 , caused by changes in the solute concentration next to the solid/liquid interface. If the actual melt temperature is lower than T 0 , the melt is constitutionally undercooled, which results in an instability of the planar shape of the interface. This instability leads to the evolution of cellular or dendritic structures, depending on the undercooling and the linear growth rate. constraint Restriction of a process, e.g., of the crystal growth or plastic defor- mation. continuous cooling transformation (CCT) diagram Presentation of the evolu- tion of phase transformations at different cooling rates by lines, in coor- dinates temperature–time, corresponding to the transformation start and its finish. continuous grain growth See normal grain growth. continuous precipitation Phase transformation evolving according to the occurrence and diffusion-controlled growth of new phase precipitates inside the parent phase. continuous recrystallization Process of microstructural alterations on anneal - ing plastically deformed material, which results in a decrease of the overall dislocation density and the formation of strain-free subgrains. A further annealing is accompanied by subgrain growth only, identical to normal grain growth. This can be explained by the exhaustion of the elastic strain energy associated with lattice defects, which might contribute to the for - mation of recrystallization nuclei. Continuous recrystallization is observed in materials of high stacking-fault energy (e.g., in Al alloys), where dislocation rearrangements, leading to the formation of subgrain structure, evolve fast. Precipitation from supersaturated solid solution enhances continuous recrystallization because it retards the evolution of recrystallization nuclei. The latter is a result of the preferential arrange - ment of precipitates at subboundaries (see heterogeneous nucleation), which inhibits their migration (see particle drag). Because of this, an increase of the disorientation angle at the subboundaries, their transfor - mation into high-angle boundaries, and the formation of the recrystalli- zation nuclei are inhibited. Continuous recrystallization is also called recrystallization inþsitu. continuous [x-ray] spectrum See white radiation. controlled rolling Thermo-mechanical treatment of low-alloy steels with <0.1 wt% C, aiming at increasing their toughness and strength by decreasing ferrite grain size (see grain-boundary strengthening), as well as by increasing the volume fraction of dispersed phases (see precipitation strengthening). The main stage of controlled rolling is hot deformation, © 2003 by CRC Press LLC conjugate slip system Slip system becoming active after the resolved shear stress on a primary slip system decreases below critical value, due to a lattice rotation in the course of plastic deformation. See Schmid’s law. conode See tie line. constitution diagram See phase diagram. constitutional undercooling/supercooling Undercooling of melt due to changes in its equilibrium solidification temperature, T 0 , caused by changes in the solute concentration next to the solid/liquid interface. If the actual melt temperature is lower than T 0 , the melt is constitutionally undercooled, which results in an instability of the planar shape of the interface. This instability leads to the evolution of cellular or dendritic structures, depending on the undercooling and the linear growth rate. constraint Restriction of a process, e.g., of the crystal growth or plastic defor- mation. continuous cooling transformation (CCT) diagram Presentation of the evolu- tion of phase transformations at different cooling rates by lines, in coor- dinates temperature–time, corresponding to the transformation start and its finish. continuous grain growth See normal grain growth. continuous precipitation Phase transformation evolving according to the occurrence and diffusion-controlled growth of new phase precipitates inside the parent phase. continuous recrystallization Process of microstructural alterations on anneal - ing plastically deformed material, which results in a decrease of the overall dislocation density and the formation of strain-free subgrains. A further annealing is accompanied by subgrain growth only, identical to normal grain growth. This can be explained by the exhaustion of the elastic strain energy associated with lattice defects, which might contribute to the for - mation of recrystallization nuclei. Continuous recrystallization is observed in materials of high stacking-fault energy (e.g., in Al alloys), where dislocation rearrangements, leading to the formation of subgrain structure, evolve fast. Precipitation from supersaturated solid solution enhances continuous recrystallization because it retards the evolution of recrystallization nuclei. The latter is a result of the preferential arrange - ment of precipitates at subboundaries (see heterogeneous nucleation), which inhibits their migration (see particle drag). Because of this, an increase of the disorientation angle at the subboundaries, their transfor - mation into high-angle boundaries, and the formation of the recrystalli- zation nuclei are inhibited. Continuous recrystallization is also called recrystallization inþsitu. continuous [x-ray] spectrum See white radiation. controlled rolling Thermo-mechanical treatment of low-alloy steels with <0.1 wt% C, aiming at increasing their toughness and strength by decreasing ferrite grain size (see grain-boundary strengthening), as well as by increasing the volume fraction of dispersed phases (see precipitation strengthening). The main stage of controlled rolling is hot deformation, © 2003 by CRC Press LLC D δ-Fe Allotropic form of iron having BCC crystal structure and existing at atmo - spheric pressure at temperatures above A 4 (i.e., > 1400°C) up to the melting point. δ-ferrite Solid solution of alloying elements and/or carbon in δ-Fe. ∆r-value Quantity characterizing planar anisotropy in sheets: ∆ r = (r 0 + r 90 – 2r 45 )/4 where r is the r-value, and the subscripts 0, 45, and 90 denote the angles between the axis of the tension specimen and RD of the sheet. dark-field illumination In optical microscopes, such illumination that flat hor- izontal features of an opaque sample appear dark, whereas all the inclined features appear bright (e.g., in single-phase materials, grains are dark and grain boundaries bright, in contrast to bright-field illumination). This is due to the fact that the inclined features reflect the incident light into an objective, whereas the horizontal features do not. dark-field image High-resolution image produced by a diffracted beam directed along the TEM axis. The contrast in a dark-field image is opposite to that in a bright-field one, e.g., a dislocation line is bright in the former and dark in the latter. Debye–Scherrer method Powder method wherein a needle-like polycrystalline specimen is placed along the axis of a cylindrical camera and a film is placed inside the camera on its wall. A monochromatic and collimated primary x-ray beam is directed onto the specimen along the camera diameter. The specimen can be rotated during the exposition. decomposition In a phase diagram with a miscibility gap, a phase transition in a solid solution, α, which decomposes upon cooling into isomorphous solid solutions, α 1 a nd α 2 ( see Figure D.1). The same term is used to designate certain phase transformations in the solid state, e.g., eutectoid decomposition, decomposition of supersaturated solid solution on aging treatment into precipitates and saturated solid solution, decomposition of cementite on graphitization into austenite and graphite, etc. In the two latter cases, decomposition is connected with the transformation of a metastable phase into more stable ones. © 2003 by CRC Press LLC . result of the preferential arrange - ment of precipitates at subboundaries (see heterogeneous nucleation), which inhibits their migration (see particle drag). Because of this, an increase of the. result of the preferential arrange - ment of precipitates at subboundaries (see heterogeneous nucleation), which inhibits their migration (see particle drag). Because of this, an increase of the. rate. constraint Restriction of a process, e.g., of the crystal growth or plastic defor- mation. continuous cooling transformation (CCT) diagram Presentation of the evolu- tion of phase transformations