Formation of strain-induced martensite in austempered ductile iron
Formation of strain-induced martensite in austempered ductile iron
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DOI：
10.1007/s10853-007-2258-6
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发表时间：
2008-01-01
影响因子：
4.5
通讯作者：
Rao, P. Prasad
中科院分区：
文献类型：
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作者：
Daber, Srinivasmurthy;Rao, P. Prasad
研究了组织对等温淬火球铁马氏体形成的影响。含1.5重量%的球墨铸铁镍和0.3重量%对钼进行两种类型的等温淬火处理。在第一种方法中，称为常规等温淬火，样品在300、350或400 ℃下等温淬火2小时。在第二次处理中，称为分级等温淬火，样品最初在300 ℃等温淬火10、20、30、45或60 min。随后在400 ℃等温淬火2 h。拉伸试验表明，在应变硬化行为的样品与不同的热处理相当大的变化。在样品进行常规等温淬火的情况下，它被发现，应变硬化指数随等温淬火温度的增加而增加。在样品的情况下进行阶梯式等温淬火，增加应变硬化观察样品进行短期的第一步等温淬火。显微组织的研究表明，应变硬化的增加与应变诱发马氏体的形成有关。在含有较多块状奥氏体的试样中，应变诱发马氏体的形成倾向较大。残余奥氏体以铁素体鞘层间的薄膜形式存在，相对稳定。研究表明，残余奥氏体的形态、尺寸和碳含量是控制其向马氏体转变趋势的重要参数。
The present work has been taken up to study the influence of microstructure on the formation of martensite in austempered ductile iron. Ductile iron containing 1.5 wt.% nickel and 0.3 wt.% molybdenum was subjected to two types of austempering treatments. In the first, called as conventional austempering, the samples were austempered for 2 h at 300, 350 or 400 degrees C. In the second treatment, called as stepped austempering, the samples were initially austempered at 300 degrees C for 10, 20, 30, 45 or 60 min. These were subsequently austempered for 2 h at 400 degrees C. Tensile tests revealed considerable variation in the strain-hardening behaviour of the samples with different heat treatments. In the case of samples subjected to conventional austempering, it was found that strain-hardening exponent increased with increasing austempering temperature. In the case of samples subjected to stepped austempering, increased strain hardening was observed in samples subjected to short periods of first step austempering. Study of the microstructures revealed that increased strain hardening was associated with the formation of strain-induced martensite. There was a greater propensity for the formation of strain-induced martensite in the samples containing more of blocky austenite. Retained austenite in the form of fine films between sheaths of ferrite was relatively more stable. Studies revealed that the morphology, size and carbon content of the retained austenite were important parameters controlling their tendency to transform to martensite.