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Creep behaviour, creep damage and precipitation in the austenitic cast steel HK30 at 750 °C

机译：在750°C时，奥氏体铸钢HK30中的蠕变行为，蠕变损伤和降水

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The austenitic cast steel HK30, used in exhaust manifolds of heavy-duty truck engines, was studied with respect to creep, creep damage, oxidation and precipitation at 750 °C in air. Even though creep clearly affects the lifetime of the manifolds, there are very few studies available on the topic. The results of the present study provide a basis for materials selection as well as creep data input to component lifetime simulations. In the present study, five specimens were subjected to constant loads resulting in creep rupture times between 1 and 94 days. The minimum creep rate follows Norton's creep law with a Norton parameter (n) of 8.9 and the logarithmic creep rupture time increases linearly with reduced stress. At low stresses secondary creep is predominant observing oxide intrusions from the specimen surface, precipitation of sigma and G-phases, creep cavitation at grain boundaries and weak dislocation networks. At high stresses direct transitions from primary to tertiary creep are observed as well as stronger dislocation networks, but no oxide intrusions, no precipitation, or cavitation are observed. The material has grains of cm size and intergranular fracture is predominant at all stress levels. The segregation of elements during solidification was studied by Scheil/Gulliver simulations and precipitations of sigma and G-phases in the last solidified regions were predicted using Thermo-Calc.
机译：用于在空气中的蠕变，蠕变损伤，氧化，沉淀，在空气中的蠕变，蠕变损伤，氧化和沉淀，研究了用于重型卡车发动机的排气歧管的奥氏体铸钢HK30。尽管蠕变清楚地影响了歧管的寿命，但在该主题上有很少的研究。本研究的结果为材料选择提供了基础，以及对组件寿命模拟的蠕变数据输入。在本研究中，对5个标本进行恒定载荷，导致1至94天之间的蠕变破裂时间。最小蠕变率跟随Norton的蠕变定律，Norton参数（N）为8.9，对数蠕变破裂时间随着应力减小而线性增加。在低应力下，二次蠕变是从样本表面，σ和G阶段沉淀的主要观察氧化物入侵，在晶界和弱错位网络处蠕变空化。在高应力下，观察到初级蠕变的直接转变以及较强的位错网络，但没有观察到氧化物入侵，无沉淀或空化。该材料具有Cm尺寸的晶粒，并且骨间骨折在所有应激水平都是主要的。通过Scheil / Gulliver模拟研究了凝固过程中的元素的分离，并且使用热量计算预测了最后一个固化区域中的Sigma和G阶段的沉淀。

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