对不同轧后开冷温度下试验钢的金相组织观察见图4.4。从图中可以看出试验钢的组织随着开冷温度的升高发生了明显的变化。在650℃～680℃的开冷温度范围内，微观组织为少量针状铁素体+粒状贝氏体和晶界处分布的M-A岛组成。随着开冷温度的升高，组织中的复相组织逐渐转变成以板条马氏体/贝氏体为主的单一结构，少量的M-A岛分布在贝氏体基体中。

The observation of the metallographic structure of the test steel at different open-cooling temperatures after rolling is shown in Figure 4.4. It can be seen from the figure that the structure of the test steel changes significantly with the increase of the cooling temperature. In the open-cooling temperature range of 650°C to 680°C, the microstructure is composed of a small amount of acicular ferrite + granular bainite and M-A islands distributed at the grain boundary. With the increase of the open cooling temperature, the complex structure in the structure gradually transforms into a single structure dominated by lath martensite/bainite, and a small amount of M-A islands are distributed in the bainite matrix.