Effects of Cold-Manufacturing Processes on Mechanical Properties of Galvaspan G450 Cold-Formed Steel Channel Sections

Cold-formed steel in the construction industry has become widely popular owing to its advantages, such as high strength to mass ratio and easy installation. This has led to the necessity of understanding the effects of the cold-working processes on cold-formed steel members. The manufacturing process of cold-formed steels starts with cold-reducing hot-rolled steel sheet under a series of rollers until a pre-defined thickness is achieved. The process is followed by a cold-forming step to create cold-formed sections with desired shapes at ambient temperature. The plastic deformation associated with the cold-reduction and cold-forming process results in strain hardening of the material, which affects its mechanical properties. It has been customary, from a structural point of view, to only look at the mechanical property changes after processing without looking at the changes in the microstructure of the material. However, it is useful to approach the problem by using both mechanical and microstructural methods to have a better understanding of the structural behaviour of cold-formed members. This combined approach has been used in this project to investigate the behaviour of a high strength cold-formed steel GALVASPAN G450 fabricated by BlueScope Steel and Lysaght. This thesis presents both microstructural and mechanical investigations realised on the flat and corner regions of different C-shaped cold-formed sections and describes the effects of the processing method on the resulting microstructure and properties. The methods in this research include Vickers microhardness testing, tensile testing, sectioning method for measuring residual stresses, optical microscopy, scanning electron microscopy and electron backscatter diffraction. Understanding the microstructural changes will provide insight into the structural behaviour of these members