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

Işıkgül Aysun, Ahlatci Hayrettin, Esen İsmail, Türen Yunus, Yağız Onur

Archives of Metallurgy and Materials

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2023

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Vol. 68, iss. 3

1191--1204

EN

This 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.

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Microstructure and Tribological Behavior of Cu-2.5Ti Alloy in Two Different Environments

Efe Ceren, Sun Yavuz, Türen Yunus, Ahlatci Hayrettin

Archives of Metallurgy and Materials

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2022

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Vol. 67, iss. 4

1443--1453

EN

In this study, the nominal composition of Cu-2.5Ti alloy was thermally treated to obtain homogenized, aged, and 40% prior cold-rolled+ aged samples. The hardness, wear behavior, and microstructure of samples were investigated. The reciprocating wear tests were performed under four different loads under dry and 3.5%NaCl corrosive environments. The alloy reached its highest hardness value of 8 hours for the aged sample. The hardness value of the sample that was homogenized then cold-rolled by 40% and aged was found higher than the other samples. A decrease in the wear rates in dry conditions was observed in homogenized, aged and cold-rolled and aged samples, respectively. This decrease was more in the corrosive environment. Studies can be advanced by examining the wear behavior at different alloy ratios. The effects of different alloying elements and the ratio of cold-rolled before or after aging can also be investigated for future research.

3

A comparative Study on the Mechanical and Corrosion Properties of the ZM20 and ZM21 Alloys after Casting and Rolling

Gören Halil Ahmet, Ünal Mehmet, Türen Yunus, Ahlatçı Hayrettin, Sun Yavuz

Archives of Metallurgy and Materials

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2022

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Vol. 67, iss. 4

1387--1394

EN

In this study, the effects of grain refinement and production methods on the corrosion, corrosive wear and mechanical properties of the as-cast and as-rolled Mg-2 wt.% Zn (ZM20) and Mg-2 wt.% Zn-0,51 wt.% Mn (ZM21) alloys were examined by using OM, XRD, SEM, hardness and uniaxial tensile test. Additionally, the potentiodynamic polarization, immersion corrosion test and corrosive wear properties of the ZM20 and ZM21 alloys were compared. According to the XRD results, MgZn and MgZn2 phases were found in the alloys and also MnZn3 phase occurred in the ZM21 alloy with the addition of manganese. Both during solidification forming nucleation points with the added manganese and during rolling the broken secondary phase particles distributed into the matrix prevented grain growth and led to the formation of a more refined structure. The tensile test results showed that the strength of the as-cast ZM21 alloys were better than that of the as-cast ZM20 alloys and further improvement in mechanical properties occurred with the rolling of the both alloys. The most superior hardness was found in the as-rolled ZM21 alloy. In the total 400-m reciprocal corrosive wear test in the 3.5% NaCl solution, the lowest mass loss was in the as-rolled ZM21 alloys. In the potentiodynamic corrosion test, the highest corrosion resistance was occurred by the as-cast ZM20 alloy.