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The present work focuses the effect of the precipitate's shape on the hardness of V–4Cr–4Ti alloy. It is found that there are numerous lath-like Ti-rich precipitates occurring in the samples subjected to different heat treatment. The habit plane of these precipitates is the {200} plane of the matrix. The distribution density of the precipitates is closely related to heating temperatures and times. The hardness valley of the samples occurs at the heating temperatures corresponding to the high distribution density of precipitates. The abnormal hardening effect can be interpreted by a model, in term of which lath-like precipitates with high distribution density result in single gliding of dislocations and reduced work-hardening.

The V–4Cr–4Ti alloy which contains the pre-precipitates has been subjected to implantation of high energy ions at room temperature. It was found that the Ti-rich precipitates occur at grain boundaries while the far finer precipitates form within the grains. The ion implantation also results in variation of appearance of the pre-precipitates in the samples. These results indicate that diffusion in the samples is obviously enhanced by ion implantation-induced vacancies. The vacancies will disappear at the grain boundaries and the precipitates/matrix interfaces, which will transfer vanadium atoms prior out of the boundaries or the interfaces due to Kirkendall effect. In this way, the Ti-rich precipitates will form at the boundaries. Meanwhile, the pre-precipitates will change their shape.

Microstructures of casting samples of Fe–9%Cr steel and samples subjected to different heat treatments were investigated to determine their formation and evolution mechanism. The results show that there is no macroscopic segregation in the casting Fe–9%Cr steel. During cooling from solidification temperature to room temperature, δ-ferrite → austenite transformation is obviously influenced by cooling rate, while subsequent transformation of austenite does not obviously depend on the cooling rate. In the casting samples, a great number of precipitates distribute inside martensitic laths while there are almost no precipitates inside δ-ferrite. When the casting samples were reheated to and isothermally held at 800 °C, the original precipitates and the lath boundaries disappeared gradually. Meanwhile, new precipitates nucleate and grow at the prior lath boundaries.