The bainitic transformation of the steels with different mass fractions of N, ~0.002% and 0.021%, was observed in situ by using high-temperature metalloscope. Micrometer- and nanometer-sized aluminum nitride (AlN) particles were found in the steel with 0.021% N. Grain boundaries, the interior of the grains, and AlN particles were used as initial nucleation sites of bainitic ferrite, and bainitic ferrite subunits served as new nucleation sites to induce secondary nucleation. The lengthening rate of bainitic ferrite varied at different nucleation sites, which was controlled by the repeated nucleation and growth of bainitic subunits. The AlN particles not only provided several nucleation sites, but also increased the autocatalytic effect on the transformation, further shortening the incubation period, promoting the bainitic transformation, and refining the bainitic microstructure.

在原位观察到不同质量分数的N分别为〜0.002％和0.021％的钢的贝氏体转变通过使用高温金属镜。在氮含量为0.021％的钢中发现了微米和纳米尺寸的氮化铝（AlN）颗粒。晶界，晶粒内部和AlN颗粒用作贝氏体铁素体的初始成核位点，贝氏体铁素体亚基用作新的成核位点，以诱导二次成核。贝氏体铁素体的伸长率在不同的成核位置变化，这由贝氏体亚基的重复成核和生长控制。AlN颗粒不仅提供了几个成核位点，而且增加了对转化的自催化作用，进一步缩短了潜伏期，促进了贝氏体的转化，并细化了贝氏体的微观结构。