中文摘要：

基于T91钢传统的“正火＋回火”热处理制度，在Therma-Calc软件热力学计算的辅助下，通过在正火与回火热处理间引入850℃等温处理，设计了2种新的热处理制度．研究了3种不同热处理制度下T91钢中析出相的尺寸及分布规律．与传统“正火＋回火”处理制度相比，新设计的热处理制度使得钢中M23C6碳化物的尺寸由350nm降至250nm左右，并使MX碳氮化物的数密度有所增加．通过Thermal—Calc模拟计算，M23C6碳化物析出相变的驱动力随着C含量的降低而增加．利用经典晶界形核理论并结合Thermal—Calc计算结果，定量描述了M23C6碳化物形核率与C含量的关系，较好地解释了M23C6碳化物的细化原因．

英文摘要：

T91 steel is one representative of （9%-12%）Cr （mass fraction） ferritic heat-resistant steel, in which MX carbonitrides and M23C6 carbides are two major strengthened precipitates for long-term creep under high temperature. This work attempted to control the precipitation of MX carbonitrides and M23C6 carbides by applying new heat treatment procedures. With the assist of Thermal-Calc software calculation, two new heat treatment procedures have been designed for T91 steel based on its traditional normalized-tempered treatment, in which an isothermal treatment at 850 E was introduced between normalized treatment and tempered treatment. The mean size of M2366 carbides decreased from 350 nm to 250 nm and the number density of MX carbonitrides increased due to the new heat treatment procedures. The calculated results of Thermal-Calc software showed that the nucleation rate of M23C6 carbides at 750 ℃ increased with the decrease of carbon content in the matrix, which might be the major reason why the mean size of M23C6 carbides decreased.