Influence of austenitizing temperature on fracture toughness of a low manganese austempered ductile iron (ADI) with ferritic as cast structure
Influence of austenitizing temperature on fracture toughness of a low manganese austempered ductile iron (ADI) with ferritic as cast structure
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DOI：
10.1016/s0921-5093(99)00120-3
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发表时间：
1999-08
期刊：
影响因子：
6.4
通讯作者：
S. Putatunda;Pavan K. Gadicherla
中科院分区：
文献类型：
--
作者：
S. Putatunda;Pavan K. Gadicherla
研究了奥氏体化温度对非合金化低锰铸铁和铸（固化）铁素体组织的组织和力学性能的影响。研究了奥氏体化温度对材料断裂韧性的影响。致密拉伸试样和圆筒形拉伸试样是由不含任何合金元素（如镍、钼或铜）、锰含量极低、铸态（凝固）铁素体结构的球墨铸铁制备的。然后在871°C（1600°F）至982°C（1800°F）的几个温度下进行奥氏体化，然后在302°C（575°F）的恒定等温下进行2小时的固定时间。通过光学显微镜和x射线衍射表征了微观结构。测定了这些材料的拉伸性能和平面应变断裂韧性，并与显微组织进行了对比。在扫描电子显微镜下观察断口表面以确定断裂模式。研究结果表明，982℃以上的奥氏体化温度对材料的断裂韧性有不利影响。随着奥氏体化温度的升高，奥氏体体积分数和碳含量均增加。该材料的应变硬化指数随奥氏体碳含量（x γ - c γ）1/2的增加而增大，其中x γ为奥氏体体积分数，c γ为奥氏体碳含量。在铁素体中，屈服强度与位错运动平均自由径d之间存在Hall-Petch型关系。建立了ADI的断裂韧性模型。目前的试验结果与模型吻合较好。
An investigation was carried out to examine the influence of austenitizing temperature on the resultant microstructure and mechanical properties of an unalloyed and low manganese ADI and with an as cast (solidified) ferritic structure. The investigation also examined the influence of austenitizing temperature on the fracture toughness of this material. Compact tension and round cylindrical tensile specimens were prepared from a nodular cast iron without any alloying elements (e.g. nickel, molybdenum or copper) and with very low manganese content and with an as cast (solidified) ferritic structure. These were then austenitized at several temperatures ranging from 871°C (1600°F) to 982°C (1800°F) and then austempered at a constant austempering temperature of 302°C (575°F) for a fixed time period of 2 h. Microstructure was characterized through optical microscopy and X-ray diffraction. Tensile properties and plane strain fracture toughness of all these materials were determined and correlated with the microstructure. Fracture surfaces were examined under scanning electron microscope to determine the fracture mode. The results of this investigation indicate that the austenitizing temperature above 982°C (1800°F) has a detrimental effect on the fracture toughness of this material. Both volume fraction of austenite and its carbon content increased with austenitizing temperature. The strain hardening exponent of this material was found to increase with increase in the austenitic carbon content i.e. (XγCγ)1/2where Xγis the volume fraction of austenite and Cγis the carbon content of austenite. A Hall–Petch type relationship was found to exist between yield strength and mean free path of dislocation motion, d in ferrite. A model for fracture toughness of ADI has been developed. Present test results indicate good agreement with the model.