Abstract: The effect of quenching cooling method on the mechanical properties of 20Cr1Mo1VTiB steel bar after overall heat treatment was studied through microstructure test methods such as mechanical property test， scanning electron microscope （SEM）， transmission electron microscope （TEM）， and electron backscattered diffraction （EBSD） . The results show that when quenching water cooling after austenitizing treatment 1 h at 1 040 °C， good strength and low-temperature impact toughness can be obtained. When quenching water cooling， the strength does not change much， but the low-temperature toughness decreases sharply. When the quenching cooling rate continues to decrease， the low temperature impact toughness performance continues to deteriorate. After austenitizing treatment， the cooling method changes from water cooling→ oil cooling→ air cooling → furnace cooling， the transformation process of the matrix structure is slatted bainite→ granular bainite + slatted bainite→ granular bainite →α ferrite. When tempering at 700°C， the precipitated phase of the slatted bainite is finely dispersed， and M₃C carbides with a certain orientation and continuous distribution are precipitated from the granular bainite M/A island. The slower the quenching cooling rate， the larger the M₃C phase size and the higher the degree of aggregation along the edge of the M/A island. The deterioration of impact toughness performance caused by the decrease of quenching cooling rate from water cooling to oil cooling is mainly caused by three factors， which are the widening of bainite slats， the decrease of the proportion of grain boundaries at large angles， and the continuous distribution of M₃C carbides in the M/A fraction of the granular bainite tissue. The continuous distribution of M₃C carbides providing a low-energy channel for crack growth is the main reason for the rapid decline of low-temperature impact toughness.

Key words: High Temperature Bolting Steel, Quenching Cooling Method, Low-temperature Impact Toughness, Granular Bainite, M₃C Carbides

摘要： 通过力学性能测试，扫描电子显微镜（SEM）、透射电子显微镜（TEM）、电子背散射衍射（EBSD）等微观组织测试方法，研究了淬火冷却方式对20Cr1Mo1VTiB钢棒材整体热处理后力学性能的影响。结果表明，1 040 ℃奥氏体化处理1 h后，采用水冷淬火能够获得较好的强度与低温冲击韧性匹配，采用油冷淬火强度变化不大，低温冲击韧性急剧下降，进一步降低冷却速度，低温冲击韧性持续恶化。奥氏体化处理后，冷却方式由水冷→油冷→空冷→炉冷，基体组织的转变过程为板条状贝氏体→粒状贝氏体+板条状贝氏体→粒状贝氏体→α铁素体。700 ℃回火后，板条贝氏体中析出相细小弥散，粒状贝氏体M/A岛中析出具有一定取向连续分布的M₃C碳化物。奥氏体化处理后冷速越慢，M₃C相尺寸越大，沿M/A岛边缘聚集程度越高。淬火冷却速度由水冷降至油冷，导致的低温冲击韧性恶化主要由三个因素引起，分别为贝氏体板条宽化、大角度晶界比例下降、粒状贝氏体组织中M/A分解析出连续分布的M₃C碳化物。M₃C碳化物连续分布，为裂纹扩展提供了低能通道，是导致低温冲击韧性快速下降的主要原因。

关键词: 高温螺栓钢, 淬火冷却方式, 低温冲击韧性, 粒状贝氏体, M₃C碳化物