Comparative Study on Austenite Decomposition and Cu Precipitation During Continuous Cooling Transformation
Comparative Study on Austenite Decomposition and Cu Precipitation During Continuous Cooling Transformation
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连续冷却转变过程中奥氏体分解与Cu析出的对比研究
DOI：
10.1007/s11661-012-1383-2
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发表时间：
2013-01-01
影响因子：
2.8
通讯作者：
Zhao, Shi-Jin
中科院分区：
文献类型：
--
作者：
Liu, Qing-Dong;Zhao, Shi-Jin
奥氏体连续冷却过程中Cu析出的性质是含Cu高强度低合金钢形变热处理的关键问题。采用透射电镜、光学显微镜、透射电镜和原子探针等手段，对0.1和10 K/s两种典型冷却速率下Cu的析出行为和组织演变进行了对比研究。在0.1 K/s的冷却速率下开发的显微组织包含多边形铁素体、针状铁素体、贝氏体、马氏体和残余奥氏体的各种微观成分，这归因于未转变的奥氏体的不同浓度，从而改变奥氏体分解动力学。Cu的析出仅与多边形铁素体相变相关联，通过相间析出机制进行。在针状铁素体、残余奥氏体和马氏体中未检测到Cu沉淀。在10 K/s的冷却速率下，显微组织由针状铁素体占主导地位，针状铁素体分散有C-Ni沉淀物，这些沉淀物被认为是在残余奥氏体上形成的。由于高温和过饱和奥氏体伴随针状铁素体转变，Cu析出通常发生在时效过程中。不同冷却速率下Cu析出的性质在很大程度上取决于原始未转变奥氏体中溶质的初始成分或富集程度以及相关的相变机制，从而导致Cu析出的尺寸、形貌和成分的差异。
The nature of Cu precipitation during continuous cooling of austenite is an essential issue in thermomechanical processing of Cu-bearing high-strength low-alloyed steel. The Cu precipitation behaviors and microstructural evolution are comparatively studied at two representative cooling rates of 0.1 and 10 K/s using dilatometry, optical microscopy, transmission electron microscope, and atom probe tomography. The microstructure developed at the cooling rate of 0.1 K/s contains a variety of microconstituents of polygonal ferrite, acicular ferrite, bainite, martensite, and retained austenite, which is attributed to the varying concentrations of untransformed austenite and consequently changing austenite decomposition kinetics. The Cu precipitation occurs only in association with polygonal ferrite transformation by interphase precipitation mechanism. No Cu precipitates are detected in acicular ferrite, retained austenite, and martensite. At the cooling rate of 10 K/s, the microstructure is dominated by acicular ferrite dispersed with the C-Ni precipitates that are assumed to be formed on the retained austenite. The Cu precipitation generally occurs from aging because of the high temperature and supersaturated austenite in association with acicular ferrite transformation. The nature of Cu precipitation in different cooling rates greatly depends on the initial composition or the extent of solute enrichment in the prior untransformed austenite and the associated phase transformation mechanisms, resulting in the differences in sizes, morphology, and compositions of Cu precipitation.