TY - CONF A1 - Rehmer, Birgit A1 - Skrotzki, Birgit A1 - Kühn, Hans-Joachim T1 - Thermo-mechanical fatigue of heat resistant austenitic cast iron EN-GJSA-NiSiCr35-5-2 (Ni-Resist D-5S) N2 - Austenitic cast iron was primarily used as material for pumps and mountings due to their excellent corrosion resistance. Certain grades, especially those with spherical graphite morphology, offer also a good high temperature strength and a high scaling resistance, which opened new fields of application e.g. for casing part of gas turbines, exhaust manifolds and turbo chargers. For such applications, a high ductility and creep resistance is beneficial, as exhibited by the studied alloy EN-GJSA-XNiSiCr35-5-2. Its high Ni-content produces the austenitic matrix, while Cr increases strength, hardness and scaling resistance. The alloy is standardized according to DIN EN 13835 with respect to chemical composition and mechanical properties (strength, elongation at fracture, Young's modulus, hardness and impact energy) at room temperature. However, data on mechanical properties at high temperature were rarely published in the open literature. In a recently completed research project, we comprehensively characterized the alloy EN-GJSA-XNiSiCr35-5-2 in terms of its temperature dependent mechanical behavior concerning strength and to isothermal as well as non-isothermal fatigue behavior. The results were used to calibrate a material and lifetime model. TMF tests were carried out with a constant minimum temperature (Tmin = 400 °C) and varying maximum temperatures (Tmax = 700 °C, 800 °C, 900 °C) with hold times of 180 s at Tmax and two phase angles (in-phase (IP), 180° out-of-phase (OP)). The investigated alloy showed a strongly deviating TMF behavior as compared to ferritic SiMo alloys investigated in a previous project: the austenitic material exhibits a comparable strength under OP- and IP-TMF loading, while the ferritic alloys showed a distinct higher strength under IP- than under OP-TMF load. At Tmax = 700 °C and 900 °C, the lifetime of Ni-Resist in IP-tests is slightly longer than that of OP-tests, while it is vice versa at Tmax = 800 °C. The IP-tests at Tmax = 900 °C show a comparable lifetime as OP-tests at Tmax = 700 °C and 800 °C, which was unexpected for such a high testing temperature. When plotting the stress range versus N it becomes clear that the behavior at Tmax = 900 °C is different from the other investigated temperatures: at 700 °C and 800 °C the stress-curve exhibits a range of stabilized stress for both phase angles. This is also true for the OP-tests at Tmax = 900 °C. However, all IP-tests at Tmax = 900 °C show a continuous cyclic softening from the beginning on. The stiffness of the test pieces decrease continuously with increasing number of cycles and their surfaces show numerous cracks. Complementary metallographic investigations showed that beside classical fatigue damage with cracks initiated at the surface, intergranular creep damage was found in the volume of the test pieces. Pores and cracks are formed at grain boundaries perpendicular to the applied load. This is also a distinct difference to the SiMo alloys. T2 - 3rd International Workshop on Thermo-mechanical Fatigue CY - Berlin, Germany DA - 27.04.2016 KW - cast iron. fatigue KW - cyclic softening PY - 2016 AN - OPUS4-35912 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rehmer, Birgit A1 - Beckmann, Jörg T1 - Mechanical Behavior Especially at Very High Temperatures (Invited) T2 - 29th International Conference on Advanced Ceramics and Composites T2 - 29th International Conference on Advanced Ceramics and Composites CY - Cocoa Beach, FL, USA DA - 2005-01-23 PY - 2005 AN - OPUS4-7134 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -