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    Mechanical properties of ultra-high-strength steels at elevated temperatures
    (Taylor & Francis Ltd, 2019) Şen, Nuri; Durucan, Gökhan; Elkoca, Oktay; Uygur, İlyas
    This paper presents an experimental study on the mechanical properties of ultra-high-strength steels at elevated temperatures. Tensile tests were carried out at 300-600 degrees C on Docol 1200M and Docol 1400M steel samples. The results indicate that as the temperature increases Young's Modulus, yield strength (YS) and ultimate tensile strength (UTS) display a decrease. YS/UTS ratios at 300 degrees C are lower than those at room temperature, they make peaks at 400 and 500 degrees C for Docol 1400M and Docol 1200M, respectively, and then decrease again beyond those temperatures. While total elongation continuously increases, uniform elongation slightly decreases with increasing temperature. Present carbides in tempered matrix continue to grow and new carbides are observed at the grain boundaries. Considering all roll forming parameters, 300 degrees C seems the most convenient temperature for warm forming. In this sense, the warm roll forming has a potential for forming complex-shaped parts by reconciling strength with formability.
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    A STUDY ON THE SURFACE ROUGHNESS OF GALVANNEALED LOW CARBON Al-KILLED AND Ti-Nb STABILIZED INTERSTITIAL FREE STEELS
    (Polska Akad Nauk, Polish Acad Sciences, Inst Metall & Mater Sci Pas, 2021) Sen Elkoca, Candan; Ekmekci, Bulent; Elkoca, Oktay
    In this study, the surface roughness of galvannealed low carbon Al-killed and Ti-Nb stabilized interstitial free steels was investigated using the industrial galvannealing process parameters. The iron content of the coatings was also analysed to establish a relationship with the surface roughness and coating composition. The surface roughness displayed an exponential behaviour with increasing of annealing time at each annealing temperature in both steel coatings, which was in an increasing order in the galvannealed low carbon Al-killed steel coating, whereas it was a reverse order in the galvannealed Ti-Nb stabilized interstitial free steel coating. The craters were observed on the galvannealed coatings resulting in high surface roughness. Increasing the iron content of the coatings leads to a reduction in the surface roughness with delta(1k) phase.