Abstract Microstructural changes after long-term creep were investigated in low-alloy Cr–Mo steels, focusing on the precipitation-free zone (PFZ) around the grain boundary. The grip and gauge portions of creep-ruptured samples obtained through the NIMS Creep Data Sheet Project were observed by SEM. The PFZ was clearly observed around the grain boundary after long-term creep in 1Cr-0.5Mo (JIS STBA22) and 1.25Cr-0.5Mo–Si (JIS STBA23) steels. Large precipitates were formed on the grain boundaries near where the PFZ was observed. The width of the PFZ increased with increasing creep time at 550 °C–650 °C. The increase in width was remarkable at higher temperatures. The clear relationship between the PFZ width and the Larson-Miller parameter (LMP) has already been reported for 2.25Cr–1Mo steel. This relationship provides a method for predicting the metal temperatures of serviced components in power plants. A good relationship between the PFZ width and the LMP was confirmed for 1Cr-0.5Mo and 1.25Cr-0.5Mo–Si steels. However, the relationship was not consistent with that for 2.25Cr–1Mo steel. The increase in the PFZ width was faster in 1.25Cr-0.5Mo–Si steel than in 1Cr-0.5Mo steel.

中文翻译：

---

低合金钢长期蠕变后晶界周围的显微组织变化

摘要 研究了低合金 Cr-Mo 钢长期蠕变后的显微组织变化，重点是晶界周围的无析出区 (PFZ)。通过 SEM 观察通过 NIMS 蠕变数据表项目获得的蠕变破裂样品的抓地力和规格部分。在 1Cr-0.5Mo (JIS STBA22) 和 1.25Cr-0.5Mo-Si (JIS STBA23) 钢长期蠕变后，在晶界周围可以清楚地观察到 PFZ。在观察到 PFZ 的地方附近的晶界上形成了大的沉淀物。PFZ 的宽度随着蠕变时间在 550 °C–650 °C 的增加而增加。在较高温度下宽度的增加是显着的。对于 2.25Cr-1Mo 钢，PFZ 宽度与 Larson-Miller 参数 (LMP) 之间的明确关系已有报道。这种关系提供了一种预测发电厂维修部件的金属温度的方法。对于 1Cr-0.5Mo 和 1.25Cr-0.5Mo-Si 钢，PFZ 宽度和 LMP 之间有良好的关系。然而，这种关系与 2.25Cr-1Mo 钢的关系不一致。PFZ 宽度的增加在 1.25Cr-0.5Mo-Si 钢中比在 1Cr-0.5Mo 钢中更快。