Isikgul, A.Ahlatci, H.Esen, I.Turen, Y.Yagiz, O.2024-09-292024-09-2920231733-34902300-1909https://doi.org/10.24425/amm.2023.145493https://hdl.handle.net/20.500.14619/7133This 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 degrees 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 degrees 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 degrees C/s, and a small amount of martensite and lower bainite microstructures were observed at a cooling rate of 60 degrees 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 degrees 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 degrees C/s, the maximum tensile residual stresses of 442 MPa were determined in the flange region of the HEA120 section.eninfo:eu-repo/semantics/openAccessH-Type SectionsAccelerated Cooling and Self-Tempering (AC-ST)Construction SteelCooling RateArticle10.24425/amm.2023.1454932-s2.0-8517288369612043Q4119168WOS:001106664500043Q4