Qizhi CHEN
,
Xingfang WU
,
Liuyng WEI and Jun KE (T.Ke)(Dept. of Materials Physics
,
University of Science and Technology Beijing
,
Beijing 100083
,
China)
材料科学技术（英文）
The effect of austenite ageing on martensite transformation in an iron and nickel alloy was studied. Attention was paid to the variation of dislocation configurations in austenite before martensite transformation. The clusters or precipitates produced during austenite ageing and the alteration of dislocation configurations affect together the consequent martensite transformation.Dispersed fine clusters and precipitates cripple nucleus role of special dislocation configurations and drop M. Coarse precipitates make Ms rise again. Densely piled up dislocations in nuclei lead to rise of Ms. All the changes in austenite are of benefit to small martensite plates.
关键词:
Zhengfei HU
,
Xingfang WU
,
Chunxu WANG
材料科学技术（英文）
The secondary hardening reaction is accompanied with precipitation of fine carbides in high CoNi ultrahigh strength steel. The crystal structure of the precipitating carbides is unambiguously determined by microbeam diffraction in transmission electron microscopy. It is identified that the needle-shaped carbides are M2C with a hexagonal structure. The concentration of substitutional alloying elements in the carbides quantified by energy dispersive X-ray spectroscopy (EDS) also supports the result above. The spatial structure of M2C is identical with 3 type. Metal atoms are in a close packed hexagonal structure, the carbon atoms partly distribute with random in the octahedral interstices and the filling probability is less than 1/2. Particular attention was paid to the relationship of needleshaped carbides/ferrite matrix at secondary hardening peak tempered at 482℃ for 5 h. Observation by high resolution transmission electron microscopy (HRTEM) confirms that carbides with black-white contrast are fully coherent with ferrite and have individual crystal structure, and the coarsened carbides with moir fringe are partially coherent with matrix. The orientation relationship between M2C and ferrite matrix is directly observed and identified with the well established P-S relationship [001]α //[ ]c.
关键词:
Ultrahigh strength steel
,
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,
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