Mn-Si-Cr系中碳钢在过冷奥氏体状态下变形时的显微组织演变

将Mn-Si-Cr系中碳钢在过冷奥氏体状态下进行低速率变形, 变形促进先共析铁素体转变, 但未见层状珠光体形成. 铁素体在奥氏体晶界和晶内形核, 以近似等轴状长大、交联, 并分割奥氏体, 形成富碳奥氏体区. 随着变形量的增大, 铁素体可在富碳奥氏体区内部继续形核长大并交联, 导致富碳奥氏体区不断被分割且碳浓度升高, 当碳浓度足够高时, 一次析出球状碳化物可在富碳奥氏体区边界处形成, 尺寸为0.5-1 μm; 变形过程中铁素体的动态回复和再结晶导致碳原子从Cottrell气团中逸出, 在铁素体内部形成几十纳米的二次析出球状碳化物.

MICROSTRUCTURAL EVOLUTION OF Mn-Si-Cr MEDIUM CARBON STEEL DEFORMED UNDER UNDERCOOLED AUSTENITE STATE

An appropriate deformation with low strain rate was applied to a Mn-Si-Cr medium carbon steel at undercooled austenite state. The deformation promotes the formation of pro--eutectoid ferrite, but no lamellar pearlite was observed during deformation. The ferrites nucleate at the grain boundary of austenite and inside the austenite grains, grow in nearly equiaxial shape, and finally divide austenite and connect with one another, leading to the formation of carbon-rich austenite zones. With the increase of strain, ferrites can continue to nucleate inside carbon-rich austenite zones, grow and connect so that the carbon-rich austenite zones are divided continuously and their carbon concentration becomes higher. When the carbon concentration is enough high, the prime spheroidized carbides with 0.5-1 μm in diameter begin to precipitate at the edge of carbon-rich austenite zones. The dynamic recovery and recrystallization of ferrite during deformation process make carbon atoms escape from the Cottrell atmosphere, resulting in precipitation of the secondary spheroidized carbides with size of several decade nanometers within ferrite grains.