在HR3C钢化学成分的基础上调整铌元素的质量分数分别为0.5%，0.8%和1.1%，熔炼得到3种成分钢锭，再进行热轧、1 200℃均匀化退火和固溶处理、750℃不同时间（0~2 000 h）时效处理，研究了铌含量对试验钢显微组织、晶粒尺寸和硬度的影响。结果表明：增加铌含量将提高固溶态试验钢中未溶MX相的含量，减小晶粒尺寸；在750℃时效过程中，增加铌含量会促进σ相在晶界和晶内的析出和粗化，提高硬度；在时效2 000 h时铌含量对晶界析出相的尺寸和分布影响不大，但对晶内析出相的尺寸和形态有所影响，铌质量分数1.1%试验钢中晶内析出相的数量相对较少且呈条状。

On the basis of the chemical composition of HR3C steel, the mass fractions of niobium element were adjusted to 0.5%, 0.8% and 1.1%, respectively. The ingot samples with the three components were obtained by melting, and then subjected to hot rolling, homogenization annealing at 1 200℃, solid solution at 1 200℃, and aging at 750℃ for different times (0-2 000 h). The effects of niobium content on the microstructure, grain size and hardness of the test steel were studied. The results show that increasing the niobium content could increase the content of undissolved MX phase in the solid solution test steel and reduce the grain size. During aging at 750℃, increasing the niobium content could promote the precipitation and coarsening of σ phase at grain boundaries and inside grains, and improve the hardness. When aging for 2 000 h, the niobium content had little effect on the size and distribution of grain boundary precipitates, but had some influence on the size and shape of intragranular precipitates; the test steel containing 1.1wt% niobium had a relatively small number of strip-like intragranular precipitates.