Investigation of Mechanical Properties of Accelerated Cooled and Self-Tempered H-Type Structural Sections

Abstract

InvestIgatIon of MechanIcal ProPertIes of accelerated cooled and self-teMPered h-tyPe structural sectIonsthis study investigates mechanical properties of accelerated cooled and self-tempered (Ac-st) H-type s275Jr quality steel sections in HEA120 and HEB120 sizes. the cooling process is conducted with a specially manufactured system that sprays a coolant consisting of a water + compressed air mixture on the section surfaces. cooling times were applied as 10 and 30 seconds using 4 and 12 bar compressed air + water at an average constant pressure of 5 bar and a constant flow rate of 0.08 kg/s. In the HEA120 sections, the highest cooling rate was obtained with 83°c/s in the web region under the cooling time of 30 s and the air pressure cooling condition of 12 bar. At the cooling rate up to 6°c/s, the microstructure is transformed to acicular ferrite and polygonal ferrite phase from Ferrite+Pearlite. But upper bainite phase was formed at a cooling rate of 30°c/s, and a small amount of martensite and lower bainite microstructures were observed at a cooling rate of 60°c/s and above. the hardness in the untreated sections, in the range of 106-120 HB, was increased to 195 HB at a cooling rate of 83 c/s in the web region of the HEA120 section. For a cooling rate of 23°c/s, the maximum compressive residual stresses of -352 MPa are measured in the crotch region of the HEB120. And for a cooling rate of 6°c/s, the maximum tensile residual stresses of 442 MPa were determined in the flange region of the HEA120 section.