添加N對(duì)Inconel690合金組織和晶界微區(qū)成分影響

添加N對(duì)Inconel690合金組織和晶界微區(qū)成分影響EFFECTS OF NITROGEN ADDITION ON CARBIDE PRECIPITATION AND GRAIN BOUNDARY MICROCHEMISTRY UPON THERMAL TREATMENT OF INCONEL690

Incone1 690合金是一種含Cr約30%的奧氏體鎳基耐蝕合金，具有優(yōu)異的耐晶間腐蝕開裂性能，被認(rèn)為是理想的核電站蒸汽發(fā)生器傳熱管材料。本文采用SEM和TEM研究了4種不同N含量的Inconel 690合金經(jīng)1080?C、10min固溶及TT處理后的顯微組織演變和晶界微區(qū)元素分布，同時(shí)測(cè)量了合金的層錯(cuò)幾率和晶間腐蝕速率。結(jié)果表明，相同熱處理后，不同N含量Inconel 690合金的晶界M23C6碳化物析出形貌和晶界Cr貧化存在明顯差異。隨N含量增加，碳化物數(shù)量減少，晶界碳化物由連續(xù)分布轉(zhuǎn)變?yōu)榘脒B續(xù)分布，繼而轉(zhuǎn)變?yōu)殡x散分布。隨N含量增加，Inconel 690合金層錯(cuò)幾率先增加，在N含量為100?10-6時(shí)達(dá)到最大值，隨后層錯(cuò)幾率降低。此外，N的加入緩解了晶界Cr貧化，提高了合金抗晶間腐蝕能力；但過高N含量導(dǎo)致較多氮化物夾雜。綜合考慮，N含量在100?10-6較為適宜。

ABSTRACT Inconel alloy 690 is an austenitic nickel-based corrosion resistant alloy with about 30% Cr content, which is considered as the most ideal steam generator tubing materials in nuclear power plants because of its superior resistance to intergranular attack (IGA). However, the existence of impurities and the addition of minor alloying elements cause significant difference of carbide morphology, microstructure and chromium depletion of Inconel alloy 690. Here microstructure and grain boundary chemistry of Inconel alloy 690 with four different nitrogen contents have been investigated by SEM, TEM. Stacking fault probability(SFP) and intergranular attack (IGA) with respect to the microstructure was tested and analyzed. The results indicated that thermal treatment (TT) at 715?C following solution annealing (SA) at 1080?C caused a wide range of intergranular carbide morphology with the associated chromium depletion in the vicinity of grain boundaries. With the nitrogen increasing, the characters of the carbides ranged from thin continuous bands along boundaries to coarse discrete particles. Stacking fault probability was increased with the nitrogen content increasing, and the value reached the peak at 100?10-6 of nitrogen content, then it dropped. The corrosion tests showed that moderate nitrogen content alloy performed favorable intergranular attack correlated with the presence of a semi-continuous grain boundary carbide and chromium depletion was mitigated. The consequent nitrides were appeared in high nitrogen alloy. So, about 100?10-6 contents of nitrogen in alloy 690 is suitable by synthesis considering of carbides, nitrides and chromium depletion.

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