HR3C钢运行过热器管的脆化与晶界M23C6相参量演化的关系THE RELATIONSHIP BETWEEN THE EVOLUTION OF PHASE PARAMETERS OF GRAIN BOUNDARY M23C6 AND THE EMBRITTLEMENT OF HR3C SUPER-HEATER TUBES IN SERVICE
研究了HR3C 钢不同运行态过热器管样晶界碳化物 M23C6相参量(面积分数M23C6和等效宽度 W)的变化与脆化的关系. 利用 ASTM E112 规范奥氏体钢晶粒度评级卡片测算出各级别晶粒度(GL)对应的二维图像晶界总周长(Lgb)并拟合出两者的关系Lgb(GL); 利用各管样的扫描电镜二次电子像(SEM-SE 像), 得到了对应的M23C6及 W, 从而建立了 W 与 GL和M23C6的关系(W(GL, M23C6)); 再结合 Charpy 冲击实验, 获得了冲击值(aKV)与 W 的关系(aKV (W)); 此外, 利用纳米压痕仪测定了晶界的弹性模量(Er). 结果表明, 所有管样冲击断口均呈沿晶断裂形貌; 当M23C6一定时, GL越小, W 越大, 其 Er 也越大,对应的 aKV越小, 即晶界脆化倾向越大. 上述方法可以揭示晶界 M23C6 片等效宽度的增大(粗化)导致脆化的实质并可为有关研究及工业应用提供一个便利途径.
The relationship of the evolution of the phase parameters (equivalent width W and area fraction M23C6) of grain boundary M23C6 plates with the embrittlement of HR3C super-heater tube samples in service was studied. Based on the ASTM E112 standard charts, the total length of two dimensional austenite grain boundaries (Lgb) corresponding to each grain size grade (GL) was determined in the observed area of the metallographic images and expressed as Lgb(GL). Making use of the SEM-SE images of the samples, the W and M23C6 were determined. The relationships of W with GL and M23C6 were established as W (GL, M23C6). Combined with the result from a Charpy impact test, the function of the impact value (aKV) as the W was obtained. In addition, the grain boundary elastic modulus (Er) was measured by a nano-hardness test. The result shows that intergranular fracture occurred on all the room temperature impact test specimens taken from the super-heater tubes exposed under the operating conditions. The W was increased with the decrease of GL and the increase of Er at a constant M23C6, causing a corresponding decrease of aKV, and hence promoting the embrittlement of the HR3C super-heater tubes. The related mechanism for the intergranular fracture caused by the increase of the equivalent width W of grain boundary carbides (carbide coarsening) can be explained through the application of the proposed method, which will facilitate the related research and industrial uses in the future.
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