Characteristics of the resistance to brittle fracture of the elements of light steel thin-walled structures determined on samples with a sharp notch groove

The structure and mechanical properties of 350 steel (GOST R 52246) are studied under tensile and impact bending in the zones of bend of galvanized light-gage steel structure elements. Batch sheet samples consisting of two and three samples with a V-shaped notch were used for profiles 1.5 and 2.0 mm thick, respectively. It is shown that a visco-brittle transition occurs in the temperature range of 20 – 90°C in galvanized samples subjected to plastic deformation. The critical temperature of brittleness T₃₄ of steel 350 decreases with a decrease in the thickness of rolled products from 3.0 to 1.5 mm due to a decrease in the rigidity of the stress-strain state under tension. At the same time, the size of ferrite grains in the studied ferrite-pearlite steels (1.17 – 0.22 C; 0.11 – 0.14 Si; 0.49 – 0.54 wt.% Mn) changes slightly and amounts to 8.0 – 8.9 μm. A crystalline fracture surface oriented perpendicular to the axis of the sample is formed in the zones of bending of 3-mm light-gage steel structure elements in the region of the critical temperature of brittleness in the central zones of the fracture. In the samples 2 and 1.5 mm thick, the fracture surface is formed by two shear planes oriented at an angle of 45° to the sample axis at the base of which the colonies of facets of trans-crystallite cleavage are located. Galvanized steel 350 profiles (GOST R 52246) with a ferrite grain size 8.8 – 8.9 μm can be used in light steel thin-walled (1.5 – 3.0 mm) structures in the operation temperature range of up to – 65°C.

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