Microstructural Transformation and Precipitation of an Ultra-high Strength Steel under Continuous Cooling
来源期刊：Journal Of Wuhan University Of Technology Materials Science Edition2016年第2期
论文作者：陈永利 ZHAO Yang ZHOU Xuejiao HUANG Jianguo
文章页码：387 - 392
摘 要：We investigated phase transition and precipitation of ultra-high strength steel（UHSS）in a new "short process" with controlled rolling and controlled cooling.Thermalexpansion test combined with metallographic observation was used to research the continuous cooling transformation（CCT）curve.Moreover,the microstructuraltransformation and precipitation law was revealed by morphologicalobservation and alloying elements by electron probe micro-analyzer（EPMA）.Transmission electron microscopy（TEM）was utilized to analyze the composition and grain orientation of microstructure.The study showed that the measured criticaltransformation temperatures of Ac1 and Ac3 were 746 and 868 ℃,respectively.The CCT curve indicated that the undercooled austenite was transformed into proeutectoid ferrite and bainite with HV 520 in a broad range of cooling rate 0.1-1 ℃·s-1.When subjected to a cooling rate of 1 ℃·s-1,the undercooled austenite was divided into small-sized blocks by formed martensite.With further increase of cooling rate,micro-hardness increased dramatically,the microstructure of specimen was mainly lathe bainite（LB）,granular bainite（GB）,lath martensite（LM）and residualaustenite.By diffraction test analysis,it was identified that there was K-S orientation relationship between martensite and austenite for {110}α//{111}γ,{111}α//{101}γ.EPMA clearly showed that carbon diffused adequately due to staying for a long time at high temperature with a lower cooling rate of 2 ℃·s-1.Phase transition drive force was lower and the residualaustenite existed in the block form of Martensite austenite island（M-A）.With the increase of cooling rate to 10 ℃·s-1,the block residualaustenite reduced,the carbon content of residualaustenite increased and α phase around the residualaustenite formed into a low carbon bainite form.
陈永利1,2，ZHAO Yang3，ZHOU Xuejiao2，HUANG Jianguo1,4
1. State Key laboratory of Rolling and Automation,Northeastern University2. School of Metallurgical and Materials Engineering,Chongqing University of Science and Technology3. School of Materials Science and Engineering,Northeastern University4. Manufacture Department of Benxi Steel Plate Co.LTD
摘 要：We investigated phase transition and precipitation of ultra-high strength steel（UHSS）in a new "short process" with controlled rolling and controlled cooling.Thermalexpansion test combined with metallographic observation was used to research the continuous cooling transformation（CCT）curve.Moreover,the microstructuraltransformation and precipitation law was revealed by morphologicalobservation and alloying elements by electron probe micro-analyzer（EPMA）.Transmission electron microscopy（TEM）was utilized to analyze the composition and grain orientation of microstructure.The study showed that the measured criticaltransformation temperatures of Ac1 and Ac3 were 746 and 868 ℃,respectively.The CCT curve indicated that the undercooled austenite was transformed into proeutectoid ferrite and bainite with HV 520 in a broad range of cooling rate 0.1-1 ℃·s-1.When subjected to a cooling rate of 1 ℃·s-1,the undercooled austenite was divided into small-sized blocks by formed martensite.With further increase of cooling rate,micro-hardness increased dramatically,the microstructure of specimen was mainly lathe bainite（LB）,granular bainite（GB）,lath martensite（LM）and residualaustenite.By diffraction test analysis,it was identified that there was K-S orientation relationship between martensite and austenite for {110}α//{111}γ,{111}α//{101}γ.EPMA clearly showed that carbon diffused adequately due to staying for a long time at high temperature with a lower cooling rate of 2 ℃·s-1.Phase transition drive force was lower and the residualaustenite existed in the block form of Martensite austenite island（M-A）.With the increase of cooling rate to 10 ℃·s-1,the block residualaustenite reduced,the carbon content of residualaustenite increased and α phase around the residualaustenite formed into a low carbon bainite form.
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