Austempered spheroidal graphite cast iron (ADI) is a cast material which accompanies a well balanced combination of superior tensile strength and good ductility. Therefore, its application to the structural components subjected to high strength is increasing recently and is expected to expand more in future. However, the authors recognized that ADI has a characteristic that exposure to water or covering its surface with some kinds of adhesive agents leads to considerable reduction of its tensile properties. This embrittlement behavior and its preventing methods are investigated from several points of view. In this paper, the authors studied about the embrittlement behavior of the fracture toughness characteristics of ADI caused by exposure to water. An ADI sample whose tensile strength and elongation are some 1100 MPa and some 11 % respectively was applied to fracture toughness testing at room temperature following to JSME-S001 (Standard method of test for elastic-plastic fracture toughness J1c) using compact tension (CT) specimens of 15 mm in thickness. In case of a dry CT specimen without any history of exposure to water, the Load (P) vs. Load line displacement (LLD) trace exhibited a relatively ductile fracture state whereby a rapid fracture occurred after decreasing the load somewhat upon passing the maximum load (Pmax) point. However, in case of a wet CT specimen which was tested soon after having been exposed to tap water for an hour, the P vs. LLD trace exhibited a extremely brittle state and a rapid fracture occurred at a point where the P and LLD values are less than half of those of a dry CT specimen. The fracture toughness value at the Pmax point (J(Pmax)) became less than 15% of that of a dry specimen. Fracture toughness testing was carried out with several CT specimens that had been exposed to water for various length of time between 5 minutes and 20 days, and all these exhibited a similarly remarkable embrittlement behavior in fracture toughness characteristics, and length of exposure time to water was recognized to have little influence on the embrittlement behavior. However, in case of a CT specimen which was dried well by slight healing after having been exposed to water for a long lime, its fracture toughness characteristics showed to have recovered its original toughness similar to those of a virgin dry CT specimen. This embrittlement behavior of fracture toughness in ADI caused by exposure to water is considered to result from the hydrogen that is produced by chemical reaction between water and the matrix of the crack tip area during plastic deformation.
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机译：奥氏体球墨铸铁（ADI）是一种铸造材料，具有出色的抗拉强度和良好的延展性的良好平衡。因此，其在经受高强度的结构部件中的应用近来正在增加，并且有望在将来进一步扩展。但是，作者认识到ADI具有的特征是，暴露于水或用某种粘合剂覆盖其表面会导致其拉伸性能大大降低。从多个角度研究了这种脆化行为及其预防方法。本文研究了暴露于水引起的ADI断裂韧性特征的脆化行为。遵循JSME-S001（弹塑性断裂韧性测试标准方法J1c），使用紧密张力（CT），将拉伸强度和伸长率分别约为1100 MPa和11％的ADI样品用于室温断裂韧性测试。厚度为15毫米的样品。如果是干燥的CT样品，没有任何暴露于水的历史记录，则载荷（P）与载荷线位移（LLD）的关系曲线显示出相对易延展的断裂状态，从而在经过最大载荷后稍微降低载荷后会发生快速断裂（Pmax）点。但是，如果湿CT样品在暴露于自来水一小时后不久就进行了测试，则P vs. LLD迹线显示出极脆的状态，并且在P和LLD值达到不到干CT样本的一半。在Pmax点的断裂韧性值（J（Pmax））小于干燥样品的15％。断裂韧性测试是通过将几个在5分钟至20天的不同时间暴露于水的CT试样进行的，所有这些试样的断裂韧性特征均表现出类似的显着的脆化行为，并且与水接触的时间为公认对脆性行为影响很小。但是，如果将CT试样暴露于长石灰中后通过轻微的愈合可以很好地干燥，则其断裂韧度特性将恢复其原始韧度，与原始的干燥CT试样相似。认为由于暴露于水而导致的ADI断裂韧性的这种脆化行为是由于塑性变形过程中水与裂纹尖端区域的基体之间发生化学反应而产生的氢引起的。
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