The conditions for ferrite and pearlite banding in strip and plate made of structural steels were investigated. Factors found to influence the formation of banded structures were the cooling rate during the γ/α‐transformation, the former austenite grain size, and the work‐hardened condition of the former austenite. Analyses with the aid of an electron beam microprobe made it possible to demonstrate that the carbon‐rich bands correspond locally with banded manganese enrichments, yet that they do not form before the course of the γ/α‐transformation as a result of secondary segregation. It was possible to explain the mechanism of action of the influencing factors on the basis of this model.
Subsequent to the completion of an extensive investigation on the behaviour of thermal expansion of iron -primarily in the range of the two stages of phase transformation of the first order (1) -the intention of the present work is to apply the method of dilatometric analysis to a study of the stages of phase transformation of the second order. As has been shown by Williams (2) as well a s Esser and Eusterbrock (3) with nickelor iron respectively a slight anomaly at the Curie temperature is discernible in the course of the linear thermal expansion coefficient. An interpretation of this effect can be based, according to Dehlinger (4), on the assumption that a variation of volume magnetostriction due to the decrease of the magnetization gives a contribution to the thermal change in volume at temperatures near the Curie point. This leads to a method for the determination of magnetostriction uM, defined as the relative change in volume, taking place during the isothermal transition from the non-ferromagnetic into the ferromagnetic state (5, 6).According to C a r r (6) aM is given by where T is the absolute temperature and fi of thermal expansion at constant field H and constant magnetization M respectively.
The effect of thermomechanical treatment on the γ – α‐transformation in steel has been reviewed. It has been shown that the thermo‐mechanically conditioned austenite significantly influences the kinetics of transformation due to the differences in the formation of product phases. An enhanced nucleation during the diffusion controlled transformation, as a result of austenite grain refinement and/or austenite strengthening, leads to a substantial refinement of the microstructure (ferrite grains, pearlite nodules). The deformation substructure of austenite may strongly affect the shear mechanism of the diffusionless transformation, which leads to finely fragmented martensite crystals. Such differences in the transformation characteristics result in different formation temperatures of transformation products and so to the changes in CCT diagrams.
Steel sheets frequently exhibit pronounced textures influencing the product properties by causing anisotropies. In the present paper a survey is given of the typical textures in steel sheets in the final and also in the intermediate stages of the manufacturing process. In order to quantify and characterize textures the method of ODF is used, which also allows a simple representation of the main texture features by plotting the pole density along texture fibres. For hot‐rolled strip the textures of mild unalloyed and high‐strength microalloyed steels are considered for different finish‐rolling temperatures including rolling in the γ/α dual phase region. Besides the textures in the middle‐section the surface textures are also dealt with. The cold‐rolling texture is investigated with regard to the influence of hot‐band texture and grain size for unalloyed mild deep‐drawing grades and IF‐steels. The recrystallization texture of different deep‐drawing qualities is presented together with results of the influence of N‐fixation on the texture determined r‐values.
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