T91钢550℃时效初期析出相演变行为研究

Study on Evolution of Precipitates in T91 Steel over Initial Period of Aging at 550 ℃

采用Thermal-Calc软件、金相显微镜、透射电子显微镜和显微硬度仪等试验设备,研究了T91钢经1 050℃固溶处理及550℃时效不同时间后显微组织及力学性能的变化。结果表明,时效初期,随着时效时间的延长,析出相的尺寸增大且数量增多,马氏体发生回复,亚晶界合并粗化,导致T91钢的硬度下降;时效后的T91钢,其析出相尺寸细小、种类较多。MX型析出相主要在晶界和基体内析出,随着时效时间的延长其尺寸变化不大;M_2X型析出相呈针状,属于亚稳相,主要在时效早期析出;M_(23)C_6碳化物呈"包夹"式结构,富Fe、Cr、V、Ti等元素,随着时效时间的延长其尺寸增大,中间贫Cr、Fe元素区域缩小,形状逐渐由椭圆形变成圆形。

Microstructure and mechanical properties of T91steel after solution treatment at1050℃for0.5h and aging at550℃for different times were studied by Thermal-Calc software,optical microscopy(OM),transmission electron microscope(TEM)and Vickers hardness tester.The results showed that the size and amount of precipitates increased with the aging time increasing at the early aging stage,the hardness of T91steel decreased due to the martensite recovery as well as the combining and coarsening of subgrain boundaries.Furthermore,the precipitated phases in T91steel was fine and varied after aging.The MX-type precipitates were mainly precipitated at grain boundaries and matrix,their size changed little with aging time increasing.The needle-like M2X-type precipitates as a metastable phase mainly precipitated at the early aging stage.Moreover,the M23C6carbides with a"double band冶structure were rich in Fe,Cr,V and Ti,etc.With the increase of aging time,the size of M23C6carbides increased,and its middle area depleted in Cr and Fe reduced,exhibited a shape that changed gradually from elliptical to circular.