Phase Transformation and Carbide Precipitation of Functional Gradient Semi-solid 9Cr18 Steel
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The unique phase transformation and carbide evolution in 9Cr18 steel were investigated during semi-solid forming and subsequent heat treatment. The functional gradient thixoforging 9Cr18 component was divided into inner area and edge area. Microstructure evolution was different at each area. After semi-solid cooling, the solid particles in the inner area were retained as meta-austenite. During annealing, M23C6 carbide began to precipitate when temperature reached 700 °C. Martensite transformation occurred when temperature reached 800 °C. The occurrence of M23C6 carbide and martensite structure would be harmful to the mechanical properties of inner area. In the edge area, the liquid underwent eutectic transformation to form bar-shape M7C3 carbide and secondary austenite after semi-solid cooling. The width of bar-shape carbide would decrease during annealing. By controlling the carbide evolution, we could tailor the functional gradient material with required property.
KeywordsSemi-solid forming Solid/liquid phase Annealing Carbide precipitation
The research was supported by the National Natural Science Foundation of China (No. 51175036) and the authors are also grateful to the support from the China Scholarship Council (CSC) (Grant No. 201606460014).
- M. Rosso, I. Peter, Int. J. Micro. Mater. Prop. 8, 113 (2013)Google Scholar