Kinetics and mechanism of thermal aging embrittlement of duplex stainless steels-猫眼课题宝

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1987-06

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H. Chung;O. Chopra

采用扫描电子显微镜（SEM）、透射电子显微镜（TEM）、小角中子散射（SANS）和原子探针场离子显微镜（APONS）等技术研究了八次实验炉熔炼的长期时效铸造双相不锈钢试样和一个商用沸水堆实际构件的显微组织特征。三个沉淀相，即，富铬。阿尔法帽。和富Ni和Si的G相，gamma../ sub 2/奥氏体，已被确定在铁素体基体的老化试样。对于CF-8级材料，在大于或等于450/sup 0/C的温度下老化时，在镁橄榄石-铁素体边界以及铁素体基体中发现了M/sub 23/C/sub 6/碳化物。结果表明，Si、C和Mo含量是影响G相析出动力学的重要因素。透射电镜和X射线衍射分析表明，400/sup 0/C以下时效脆化主要与Fe、Cr在铁素体中的偏聚有关。对于长期老化，例如，在350至400/sup 0/C下储存6至8年，大片状。阿尔法帽。通过从由亚稳分解产生的结构成核和生长而形成。Cr含量似乎在促进板状组织中起重要作用。阿尔法帽。（高铬含量）或抑制铬的氧化。阿尔法帽。赞成... gamma../ sub 2/沉淀（低Cr）。近似TTT图的spinodal，.阿尔法帽。“，G，.. gamma../ sub 2/和铁氧体内M/sub 23/C/sub 6/已被构造用于250至450/sup 0/C时效。还讨论了与550/sup 0/C再退火和随后的韧性恢复相关联的显微组织修改。结果表明，韧性恢复主要与铁素体富铬区的溶解有关。«少

Microstructural characteristics of long-term-aged cast duplex stainless steel specimens from eight laboratory heats and an actual component from a commercial boiling water reactor have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), small angle neutron scattering (SANS), and atom probe field ion microscopy (APFIM) techniques. Three precipitate phases, i.e., Cr-rich ..cap alpha..' and the Ni- and Si-rich G phase, and ..gamma../sub 2/ austenite, have been identified in the ferrite matrix of the aged specimens. For CF-8 grade materials, M/sub 23/C/sub 6/ carbides were identified on the austenite-ferrite boundaries as well as in the ferrite matrix for aging at greater than or equal to 450/sup 0/C. It has been shown that Si, C, and Mo contents are important factors that influence the kinetics of the G-phase precipitation. However, TEM and APFIM analyses indicate that the embrittlement for less than or equal to400/sup 0/C aging is primarily associated with Fe and Cr segregation in ferrite by spinodal decomposition. For extended aging, e.g., 6 to 8 years at 350 to 400/sup 0/C, large platelike ..cap alpha..' formed by nucleation and growth from the structure produced by the spinodal decomposition. The Cr content appears to play an important role either tomore » promote the platelike ..cap alpha..' (high Cr content) or to suppress the ..cap alpha..' in favor of ..gamma../sub 2/ precipitation (low Cr). Approximate TTT diagrams for the spinodal, ..cap alpha..', G, ..gamma../sub 2/, and the in-ferrite M/sub 23/C/sub 6/ have been constructed for 250 to 450/sup 0/C aging. Microstructural modifications associated with a 550/sup 0/C reannealing and a subsequent toughness restoration are also discussed. It is shown that the toughness restoration is associated primarily with the dissolution of the Cr-rich region in ferrite.« less

Kinetics and mechanism of thermal aging embrittlement of duplex stainless steels

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