低温回火马氏体取向关系的电子背散射衍射研究

Orientation relationship of low temperature tempered Martensite investigated by electron back scattered diffraction

为了研究马氏体的相变特征,利用电子背散射衍射(EBSD)技术并结合金相显微镜和显微硬度计分析低温回火的20MnCr5渗碳齿轮钢的性能和组织。根据马氏体相变理论中的K-S和N-W取向关系分别计算得到马氏体{110}α极射赤面投影图。利用EBSD技术对20MnCr5齿轮钢心部选定的区域进行扫描,分析区域中马氏体的取向分布特征。研究结果表明:马氏体取向整体呈随机分布,但在局部区域呈有规律分布。整个扫描区域的取向差主要分布在5°以下和45°以上。为反映马氏体局部区域取向分布的规律,选定一个原奥氏体晶粒,并做出区域中所有马氏体{110}α晶面的极射赤面投影图,得到极点有规律分布的极图。通过对{110}α极图分别使用K-S和N-W关系拟合,确定所选区域的马氏体的取向关系以N-W关系为主,实际极点离散分布在理论极点周围;使用协同形变机理解释实际取向分布与理论分布的偏差是由马氏体相变导致周围组织复杂的畸变引起。

Microhardness tester,optical microscope and electron back scattered diffraction technique were used to examine the property and microstructure of a low temperature tempered 20MnCr5 carburized gear.{110}α polar figure of Martensite was calculated according to the K-S and N-W orientation relationship.Orientation distribution of Martensite at the center of the gear was examined by electron back scattered diffraction technique.{110}α polar figure of Martensite in a selected prior austenite grain was plotted.The orientation distributes randomly in the whole scanned area,but distributes regularly in local area.The misorientation of the scanned area distributes mainly below 5° and above 45°.In order to characterize the orientation distribution law in local areas,stereographic projection of Martensite {110}α in a selected prior austenite area was plotted.The orientation relationship in the selected prior austenite is determined to be mainly N-W orientation by fitting the polar figure.Discrepancy between practical and theoretical orientation distribution is interpreted by cooperative strain mechanism.