摘要
The ductile-to-brittle transition temperature(DBTT)of high strength steels can be optimized by tailoring microstructure and crystallographic orientation characteristics,where the start cooling temperature plays a key role.In this work,X70 steels with different start cooling temperatures were prepared through thermo-mechanical control process.The quasi-polygonal ferrite(QF),granular bainite(GB),bainitic ferrite(BF)and martensite-austenite constituents were formed at the start cooling temperatures of 780℃(C1),740℃(C2)and 700℃(C3).As start cooling temperature decreased,the amount of GB decreased,the microstructure of QF and BF increased.Microstructure characteristics of the three samples,such as high-angle grain boundaries(HAGBs),MA constituents and crystallographic orientation,also varied with the start cooling temperatures.C2 sample had the lowest DBTT value(−86℃)for its highest fraction of HAGBs,highest content of<110>oriented grains and lowest content of<001>oriented grains parallel to TD.The high density of{332}<113>and low density of rotated cube{001}<110>textures also contributed to the best impact toughness of C2 sample.In addition,a modified model was used in this paper to quantitatively predict the approximate DBTT value of steels.
本文采用三种不同开冷温度(780、740和700℃)制备X70管线钢,结合微观组织表征和低温冲击实验,研究了不同开冷温度对管线钢微观组织、晶体学取向和韧脆转变温度的影响,并构建了修正模型来定量预测X70管线钢的韧脆转变温度。研究结果表明:三种实验钢的微观组织均由准多边形铁素体(QF)、粒状贝氏体(GB)和贝氏体铁素体(BF)组成。其中,780℃开冷样品含有19%QF、14%BF和67%GB,740℃开冷样品含有22%QF、55%BF和23%GB,700℃开冷样品含有36%QF、35%BF和29%GB。随着开冷温度的降低,实验钢平均有效晶粒尺寸分别为3.5μm、2.8μm和3.0μm;MA组元平均尺寸分别为1.27μm、1.44μm和1.56μm;<110>取向晶粒含量先升高后降低,<001>取向晶粒含量先降低后升高;{332}<113>织构密度先降低后升高,旋转立方(Rotated cube){001}织构密度逐渐升高。三种实验钢的韧脆转变温度分别为-79℃、-86℃和-82℃,其中740℃开冷样品具有最低韧脆转变温度,低温韧性最优。
基金
Project(2018XK2301) supported by the Change-Zhu-Tan National Independent Innavation Demonstration Zone Special Program,China。
作者简介
Corresponding author:LI Hong-ying,PhD,Professor,E-mail:lhying@csu.edu.cn,ORCID:https://orcid.org/0000-0003-2481-7966。
