HR3C鋼運行過熱器管的脆化與晶界M23C6相參量演化的關系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 鋼不同運行態過熱器管樣晶界碳化物 M23C6相參量(面積分數M23C6和等效寬度 W)的變化與脆化的關系. 利用 ASTM E112 規范奧氏體鋼晶粒度評級卡片測算出各級別晶粒度(GL)對應的二維圖像晶界總周長(Lgb)并擬合出兩者的關系Lgb(GL); 利用各管樣的掃描電鏡二次電子像(SEM-SE 像), 得到了對應的?M23C6及 W, 從而建立了 W 與 GL和M23C6的關系(W(GL, M23C6)); 再結合 Charpy 沖擊實驗, 獲得了沖擊值(aKV)與 W 的關系(aKV (W)); 此外, 利用納米壓痕儀測定了晶界的彈性模量(Er). 結果表明, 所有管樣沖擊斷口均呈沿晶斷裂形貌; 當?M23C6一定時, GL越小, W 越大, 其 Er 也越大,對應的 aKV越小, 即晶界脆化傾向越大. 上述方法可以揭示晶界 M23C6 片等效寬度的增大(粗化)導致脆化的實質并可為有關研究及工業應用提供一個便利途徑.
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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