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采用光学显微镜、扫描电镜和透射电镜研究了20Cr2Ni4、45CrNi、30CrMnSi钢中(1200℃进行固体渗碳20 h后淬火)蝶状马氏体的几种形貌。根据马氏体晶体学和相变力矩原理,提出了蝶状马氏体的形成机理,并用它对蝶状马氏体的特性进行了合理的解释;同时发现蝶状马氏体只发生在马氏体比容大、迁移激活能高而导致形核和核长大困难的合金里。当形核困难时,尤其是在压力场下,“伴生核”相变的形核功和核长大功较低,比“普通核”相变更容易发生。核长大功高的合金,当粗大的马氏体片因过高的应变能而停止长大时,可以通过两种方式继续相变:1)在粗马氏体片一侧,沿另一个惯习面长出分支;2)发生“伴生核”相变,在残留的奥氏体中形成蝶状马氏体。
Several morphologies of butterfly martensite in 20Cr2Ni4, 45CrNi and 30CrMnSi steels were investigated by optical microscope, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) after tempered at 1200 ℃ for 20 h. Based on the theory of martensitic crystallography and phase transformation torque, the formation mechanism of butterfly martensite is proposed, and its characteristics of butterfly martensite are reasonably explained. It is also found that the butterfly martensite only occurs in horse Larger than the specific volume of the body, migration and activation can lead to high nucleation and nuclear growth difficulties in the alloy. When the nucleation is difficult, especially under the pressure field, the nucleation and nuclear long service of “concomitant nucleus ” phase transition are lower than those of “common nuclear ” phase transition. When a large martensite sheet ceases to grow due to excessive strain energy, the phase transformation can continue in two ways: 1) along the coarse martensite sheet, along another 2) Occurrence of “concomitant nucleus” phase transformation, forming butterfly martensite in the retained austenite.