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采用OM、TEM和EDS分析技术,研究了1000 MPa级Nb-Ti微合金化超高强度钢在不同加热温度下保温不同时间时奥氏体晶粒粗化行为与微合金元素碳氮化物溶解行为。结果表明,铸坯中存在尺寸与形状明显不同的3类析出物:尺寸大于1μm的方形Ti N粒子;尺寸在500 nm以下的球形、椭球形或方形Nb、Ti复合析出物;少量方形或椭球形Ti S或Ti(C,S)析出物。随着温度的升高,原始奥氏体晶粒尺寸呈现出单调增大的趋势,当加热温度超过1200℃时奥氏体晶粒发生快速长大,而析出物数量不断减少、尺寸逐渐增大、Ti/Nb原子比逐渐升高,EDS显示均为Ti、Nb复合析出。随着保温时间的延长,原始奥氏体平均晶粒尺寸呈抛物线规律长大,小尺寸的球形、椭球形的析出物逐渐溶解,大尺寸方形析出物数量逐渐增加且棱角变得模糊。综合考虑加热温度和保温时间对Nb、Ti微合金元素的固溶行为和奥氏体晶粒粗化行为的影响,1000 MPa级Nb-Ti微合金化超高强度钢的加热温度和保温时间分别为1250℃和80 min较合适。
The austenite grain coarsening behavior and microalloying carbonitride dissolution behavior of 1000 MPa grade Nb-Ti microalloying superalloy at different heating temperatures were studied by OM, TEM and EDS analysis. . The results show that there are three types of precipitates with different sizes and shapes in the slab: square Ti N particles larger than 1μm; spheroidal, ellipsoidal or square Nb, Ti composite precipitates with size less than 500 nm; a small amount of square or ellipsoid Spherical Ti S or Ti (C, S) precipitates. With the increase of temperature, the grain size of the original austenite increases monotonically. When the heating temperature exceeds 1200 ℃, the austenite grains grow rapidly, while the amount of precipitates decreases and the size increases , Ti / Nb atomic ratio gradually increased, EDS showed Ti, Nb composite precipitation. As the holding time prolongs, the average grain size of the original austenite grows parabolically. The small spherical and ellipsoidal precipitates gradually dissolve, and the size of the large size square precipitates gradually increases and the corners become blurred. Considering the influence of heating temperature and holding time on the solution behavior of Nb and Ti microalloying elements and the austenite grain coarsening behavior, the heating temperature and holding time of 1000 MPa grade Nb-Ti microalloying superalloy respectively For 1250 ℃ and 80 min more appropriate.