Carbides Evolution in 12Cr Martensitic Heat-resistant Steel with Life Depletion for Long-term Service

Zheng-fei HU,Da-hai HE,Fan MO

钢铁研究学报(英文版) ›› 2015, Vol. 22 ›› Issue (3) : 250-255.

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钢铁研究学报(英文版) ›› 2015, Vol. 22 ›› Issue (3) : 250-255.
Material

Carbides Evolution in 12Cr Martensitic Heat-resistant Steel with Life Depletion for Long-term Service

  • Zheng-fei HU,Da-hai HE,Fan MO
作者信息 +

Carbides Evolution in 12Cr Martensitic Heat-resistant Steel with Life Depletion for Long-term Service

  • Zheng-fei HU,Da-hai HE,Fan MO
Author information +
文章历史 +

摘要

Evaluating the residual life of exposed components in power industry is a very important procedure in routine examination. The microstructures of a series of X20CrMoV12.1 martensitic superheater tube samples in a boiler in different service periods were investigated extensively to extract a quantitative relationship. During long-term service from start to rupture, hardness decreased monotonically with life depletion, and the decrease of hardness in prior austenite grain boundary was steeper than that in the matrix. Microstructure observation showed obvious damage characteristics, including carbide coarsening and martensite decomposing, and the martensite structure decomposed completely in rupture state. The morphology, distribution and composition of the main precipitates M23C6 varied distinctly. The aspect ratio of coarsened carbides along grain boundary increased several fold with respect to their original size. The composition of coarsened M23C6 carbide shows the most regular trend of Cr enrichment and the statistical result of Cr enrichment in M23C6 shows a linear correlation between the ratio of Cr to Fe and service time to the power of 3/2, which may be considered as an index of material degradation due to long-term service exposure.

Abstract

Evaluating the residual life of exposed components in power industry is a very important procedure in routine examination. The microstructures of a series of X20CrMoV12.1 martensitic superheater tube samples in a boiler in different service periods were investigated extensively to extract a quantitative relationship. During long-term service from start to rupture, hardness decreased monotonically with life depletion, and the decrease of hardness in prior austenite grain boundary was steeper than that in the matrix. Microstructure observation showed obvious damage characteristics, including carbide coarsening and martensite decomposing, and the martensite structure decomposed completely in rupture state. The morphology, distribution and composition of the main precipitates M23C6 varied distinctly. The aspect ratio of coarsened carbides along grain boundary increased several fold with respect to their original size. The composition of coarsened M23C6 carbide shows the most regular trend of Cr enrichment and the statistical result of Cr enrichment in M23C6 shows a linear correlation between the ratio of Cr to Fe and service time to the power of 3/2, which may be considered as an index of material degradation due to long-term service exposure.

关键词

12%Cr Martensitic heat-resistant steel / carbide / microstructure / creep damage / compositions enrichment

Key words

12%Cr Martensitic heat-resistant steel / carbide / microstructure / creep damage / compositions enrichment

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胡正飞, 何大海, 莫凡. Carbides Evolution in 12Cr Martensitic Heat-resistant Steel with Life Depletion for Long-term Service[J]. 钢铁研究学报(英文版), 2015, 22(3): 250-255
HU Zheng-Fei, HE Tai-Hai, WU Fan. Carbides Evolution in 12Cr Martensitic Heat-resistant Steel with Life Depletion for Long-term Service[J]. Journal of Iron and Steel Research International, 2015, 22(3): 250-255

参考文献

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National Natural Science Foundation of China

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