Grain Boundary Effects on Mechanical Properties : Design Approaches in Steel

For Poly-crystalline metals, Grain boundary design plays an important role to achieve desired mechanical properties in the final product form which may be a hot rolled or cold rolled coil. The fundamental mechanical properties are yield and tensile strengths, elongation and formability where grain refinement is particularly attractive mechanism for property design. Grain boundary strengthening provides benefits both in terms of fracture toughness and mechanical behavior at lower temperatures particularly in case of hot rolled high strength structural and line pipe steels. For cold rolled steels, grain boundary effects play a crucial role in critical automotive application steels such as Bake Hardening Index in Bake-hardening Steels. Additionally, deep drawability and formability characteristics are also strongly dependent upon grain size. Mechanical properties in steels are controlled majorly by two techniques - chemical composition and Steel processing parameters. Through first method of chemical composition control, during hot rolling, the control of austenite grain size is accomplished, alongside retardation of phase transformation to lower temperature. In second method, steel manufacturing process parameters i.e. hot rolling and coil cooling parameters, cold reduction, and subsequent heat treatment parameters such as annealing play an important role.