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    INVESTIGATION OF THE FLOW BEHAVIOUR OF MARTENSITIC STEELAT ELEVATED TEMPERATURES VIA UNIAxIAL TENSILE TESTS
    (Polska Akad Nauk, Polish Acad Sciences, Inst Metall & Mater Sci Pas, 2025) Sen, N.; Civek, T.; Elkoca, O.; Cevik, E. c
    In recent years, advanced high strength steels have been the main choice of automobile manufacturers due to their excellent strengths and decent formability. In this study, the forming behaviour of a martensitic steel (MART 1200) at elevated temperatures, where higher formability and an acceptable strength can be achieved, has been investigated. For this purpose, tensile test experiments have been conducted at room temperature, 175 degrees C, 275 degrees C, 375 degrees C and 475 degrees C in two different strain rates (0.005 s-1, 0.05 s-1). The flow behaviour, elongation capacity, strain rate sensitivity, strain hardening and strain hardening rate of MART1200 have been investigated and fracture surfaces and microstructures have been examined by scanning electron microscope. It has been shown that the strain rate sensitivity of MART1200 increases significantly after 275 degrees C and, for the higher strain rate, a significant improvement up to 80% in the elongation capacity has been achieved in return for a 19% strength reduction at 375 degrees C.
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    Tensile deformation behavior of dual-phase steels at elevated temperatures
    (Redakcia Kovove Materialy, 2020) Sen, N.
    In this study, two distinct grades of commercial steel, DP600 and DP800, were thermo-mechanically tested relevant to mechanical behavior at five temperatures and two elongation rates. Some fundamental structural properties were also determined, including work (strain) hardening, strain rate sensitivity, and optimum ranges of forming temperatures. For both high-quality steels, tensile strength and flow stress noticeably decreased as work temperature increased. The maximum work hardening ratio for both strain rates was exhibited at 350 degrees C for DP600 and at 300 degrees C for DP800. Deformation velocity effects for the DP600 occurred at 500 degrees C, whereas they manifested at 400 and 500 degrees C for DP800. In the warm deep drawing tests, the optimum forming temperature for DP600 was 400 degrees C, while it was 450 degrees C for DP800, taking into account the deformation velocity of both steels. It was concluded that a controllable and feasible manufacturing alternative is possible using local warm forming.