ABSTRACT It is not clear whether the growth behavior of creep cracks is the same in the type IV cracking area as in other areas. We investigated the creep rupture strength by a uniaxial creep test, using specimens simulated the welding thermal cycle at different peak temperatures. The creep rupture strength was high when the austenite transformation didn’t occur during the thermal cycle, with a rupture time exceeding 10,000 h. In this case, the creep cracks propagated along grain boundaries with repeated oxide formation and fracture. By contrast, the strength was low when the austenite transformation occurred during the thermal cycle, with a rupture time shorter than 1000 h. In this case, the creep cracks were formed by the interlinking of voids from prior austenite grain boundaries, then propagated until fracture. Therefore, the peak temperature of the thermal cycle is a crucial determinant of the growth behavior of creep cracks.

中文翻译：

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改性9Cr-1Mo钢模拟热影响区蠕变裂纹扩展行为

摘要 IV 型裂纹区蠕变裂纹的扩展行为是否与其他区相同尚不清楚。我们通过单轴蠕变试验研究了蠕变断裂强度，使用试样模拟了不同峰值温度下的焊接热循环。热循环过程中未发生奥氏体转变时蠕变断裂强度较高，断裂时间超过10,000 h。在这种情况下，蠕变裂纹沿晶界传播，重复氧化物形成和断裂。相比之下，热循环过程中发生奥氏体转变时强度较低，断裂时间小于 1000 小时。在这种情况下，蠕变裂纹是由原始奥氏体晶界的空隙相互连接形成的，然后扩展直至断裂。所以，