Abstract
Laser annealing experiments are performed on cold rolled IF steel whereby highly localized microstructure and property modification are achieved. The microstructure is seen to develop by strongly heterogeneous recrystallization to provide steep gradients, across the submillimeter scale, of grain size and crystallographic texture. Hardness mapping by microindentation is used to reveal the corresponding gradients in macroscopic properties. A 2D level set model of the microstructure development is established as a tool to further optimize the method and to investigate, for example, the development of grain size variations due to the strong and transient thermal gradient. Particular focus is given to the evolution of the beneficial γ-fiber texture during laser annealing. The simulations indicate that the influence of selective growth based on anisotropic grain boundary properties only has a minor effect on texture evolution compared to heterogeneous stored energy, temperature variations, and nucleation conditions. It is also shown that although the α-fiber has an initial frequency advantage, the higher probability of γ-nucleation, in combination with a higher stored energy driving force in this fiber, promotes a stronger presence of the γ-fiber as also observed in experiments.
Highlights
WITH few exceptions, the present use of laser annealing is related to modification of the structure and properties of thin films
One example related to local modification of a thin Ni-Ti shape memory alloy strip with 0.5 mm thickness is given in Reference 5 and surface laser annealing of stainless steel is studied in References 6 and 7
This is an indication of the small spatial variation in temperature in this particular representative volume element (RVE), located directly α-fiber γ-fiber h
Summary
WITH few exceptions, the present use of laser annealing is related to modification of the structure and properties of thin films. Even less attention is given to the possibility of using laser annealing on larger samples of rolled sheet metal in order to manufacture functionally graded materials through local modifications of the microstructure, which is not achievable by standard annealing methods This kind of applications are in focus of the present study. It is shown that local microstructural modifications through recrystallization and grain growth can be achieved and related macroscopic properties such as ductility and hardness can be modified in confined regions of the material This makes laser annealing a promising method for manufacturing of functionally graded materials. Modeling of rolling and recrystallization textures in IF steel—considering oriented growth relative to oriented nucleation—is performed using a statistical model in References 11 and 23 Such an approach provides little information on the microstructure morphology or on the influence of any thermal gradient conditions.
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