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通过Thermo-Calc热力学软件计算、光学显微镜、扫描电镜及透射电镜对0Cr19Mn21Ni2N奥氏体不锈钢在800℃等温时效过程中碳化物、氮化物的析出机制进行了研究。结果表明:第二相碳化物、氮化物析出的成分、种类、分布随局部C元素贫化而发生变化。在800℃等温时效过程中,当时效时间为10~60 min时,晶界上较高浓度的C元素偏析、较大的晶格错配能和畸变能为M_(23)C_6首先在晶界位置形核并形成连续析出颗粒提供充足的热力学和动力学条件;随着时效时间进一步延长,由于碳化物M_(23)C_6的较多析出导致该析出区域C元素逐渐贫化,M_(23)C_6析出的热力学和动力学条件逐渐受到抑制,氮化物Cr_2N开始在晶界析出的M_(23)C_6碳化物附近形核。随后,片层状Cr_2N逐渐在相邻晶粒内长大,其生长方向与奥氏体晶格取向具有固定的位向关系。
The mechanism of precipitation of carbides and nitrides in 0Cr19Mn21Ni2N austenitic stainless steel during isothermal aging at 800 ℃ was studied by means of Thermo-Calc thermodynamic software, optical microscopy, scanning electron microscopy and transmission electron microscopy. The results show that the composition, type and distribution of the second phase carbides and nitrides change with the depletion of local C elements. In the isothermal aging at 800 ℃, when the aging time is 10 ~ 60 min, the higher concentration of C element on the grain boundary segregates, and the larger lattice mismatch energy and distortion energy are M_ (23) C_6, The nucleation and formation of continuous precipitates provide sufficient conditions of thermodynamics and kinetics. With the further aging time, the element C of the precipitation area is gradually depleted due to the more precipitation of M_ (23) C_6, The thermodynamic and kinetic conditions for the precipitation of C_6 were gradually suppressed. The nitride Cr_2N began to nucleate near the M_ (23) C_6 carbides precipitated at grain boundaries. Subsequently, lamellar Cr_2N gradually grew up in adjacent grains and its growth direction had a fixed orientation relationship with the austenite lattice orientation.