a b s t r a c tThe texture and microstructure evolutions of a fine-grained TWIP steel subjected to tensile tests at room temperature were investigated in relation to the mechanical behavior. This steel combines both high ductility and strength owing to the TWIP effect. Also the steel exhibits a high strain hardening rate that evolves according to five stages, which are related to the microstructure and texture evolutions and characteristics. The formation of nano-twins in the initial stage of deformation leads to an increase in strain hardening rate. The development of the pronounced <1 1 1> fiber in the tensile direction sustains mechanical twinning and maintains the strain hardening rate on a high level. The resulting microstructure exhibits several types of twin configurations and sub-boundaries with high misorientations due to intense activities of dislocation glide. The twin volume fraction was estimated to be 9% at the final stage of tensile deformation. The new orientations generated by mechanical twinning do not change considerably the final texture.

We consider the theoretical problems of calculating the physical properties of an aggregate from the constituent crystal properties and the lattice preferred orientation. The notion of a macroscopically homogeneous sample with an internally varing distribution of stress and strain fields is introduced to explain why further efforts have to be made to improve on the physically based Voigt and Reuss bounds. It is shown that the Voigt and Reuss bounds become increasingly separated with inceasing anisotropy, emphasising the need for better methods. The problem of highly anisotropic minerals is illustrated with polycrystals of plagioclase feldspar and biotite. Biotite is used to illustrate the mean velocity, the geometric mean and the self-consistent methods. The self-consistent method, which is generally accepted to give the best estimate, is almost identical to geometric mean recently introduced by Matthies and Humbert (1993) and similar to the arithmetic mean of the Voigt and Reuss bounds (Hill, 1952). The geometric mean has the powerful physical condition that the aggregate mean is equal to the mean of the inverse property (e.g. mean elastic stiffness and compliance). Despite its lack of theoretical justification the Hill average remains a useful estimate.

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The electron backscattered diffraction (EBSD) technique has been used to assess crystallographic features of the residual ␥ phase and the strain-induced /␣Ј martensites in a 304 stainless steel, tensile tested to 10 pct strain at T ϭ Ϫ60 °C. The martensitic transformation rate varies according to the ␥-grain orientation against the applied stress and the ␥-grain size. The ␣Ј-transformation textures as well as the ␥-misorientation spreads observed in specific ␥-grain orientations have been analyzed. Large misorientation spreads are observed in the less-transformed ␥ grains. This reveals an important crystallographic slip activity, even if less strain-induced martensite has been formed. A strong variant selection was detected in the cube-and Goss-oriented ␥ grains for which the transformation is less developed. For the {110}Ͻ1-11Ͼ and copper-oriented ␥ grains, the amount of ␣Ј martensite is significantly higher and the variant selection is less pronounced. This variant selection is then analyzed on at a local scale and is related to the presence of {111} ␥ localized deformation bands on which further /␣Ј martensites have nucleated.g → a¿ g → a¿

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