Redistribution of carbon caused by butterfly defects in bearing steels
Redistribution of carbon caused by butterfly defects in bearing steels
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DOI：
10.1016/j.actamat.2019.10.057
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发表时间：
2020-01-15
期刊：
影响因子：
9.4
通讯作者：
Withers, P. J.
中科院分区：
文献类型：
--
作者：
Curd, M. E.;Burnett, T. L.;Withers, P. J.
蝶形缺陷是由受滚动接触的钢轴承部件表面下的夹杂物引起的。白色腐蚀物质（WEM）微观结构是蝴蝶的一个特征，与碳化物的溶解有关，因此通常认为相对于母体微观结构，在过饱和固溶体中富含碳。本文利用波长色散光谱（WDS）、软x射线发射光谱（SXES）和电子显微镜（EM）对几种蝴蝶进行了研究。与既定的想法相反，在所有被调查的情况下，与蝴蝶相邻的WEM被发现相对于母体材料的碳含量减少了约27%（以计数测量）。此外，碳含量低于基体本身，这表明在形成过程中，溶质碳也从WEM中排出，这可能是由于碳在铁氧体中的溶解度较低。这在AISI 52100和18NiCrMo14-6轴承钢中都观察到了。尽管有这种损耗，纳米压痕发现，两种合金中的WEM比母材的硬度高17%。这也许可以解释在wem -母界面附近观察到的微孔串，它们似乎在蝴蝶裂纹的生长中起作用。结果表明，合金硬度的提高主要是由于显微组织的变化，而不是溶质碳浓度的变化。(C) 2019材料学报Elsevier Ltd.出版。
Butterfly defects initiate from inclusions in the subsurface of steel bearing components subject to rolling contact. The white etching matter (WEM) microstructure is a characteristic of butterflies and is related to the dissolution of carbides and thus generally believed to be enriched with carbon, in supersaturated solid solution, relative to the parent microstructure. Here, several butterflies are investigated using wavelength dispersive spectroscopy (WDS), soft x-ray emission spectroscopy (SXES) and electron microscopy (EM). Contrary to established thinking, in all cases investigated the butterfly-neighbouring WEM was found to be depleted in carbon, relative to parent material, by around 27% (measured in counts). Furthermore, the carbon level was shown to be lower than the matrix itself, suggesting that solute carbon is also expelled from the WEM during its formation, possibly due to the low level of solubility of carbon in ferrite. This was observed in both AISI 52100 and 18NiCrMo14-6 bearing steels. In spite of this depletion, nano-indentation found that WEM in both alloys was similar to 17% harder than the parent material. This may explain the strings of micro-voids observed near the WEM-parent interface, which appear to play a role in the growth of the butterfly cracks. It is suggested that the increased hardness of the WEM is mainly due to microstructural changes, rather than changes in solute carbon concentration. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd.