Effect Of Tungsten On The Mirostructure And Properties Of Hypereutectic High Chromium Cast Iron

As an important wear resistant materials,high chromium cast iron has been widely researched and applicated. In this paper,we have produced samples with different tungsten content by designing alloy composition. We have studied microstructure and properties of as-cast specimens. In order to research deeply, primary carbides has been obtained by electrolytic extraction. For further improving the performance of the as-cast sample, we have explored different heat treatment processes of samples. Cast and heat-treated specimens had finally gotten a three-body abrasive wear test, and we have studied the effects of tungsten and heat treatment on the wear resistance of samples.According to theexperimental data, the matrix of hypereuteic high chromium cast iron eutectic are mainly austenite and martensite with higher hardness, while chromium and tungsten carbide is formed. The mainly chromium carbides are M7C3, M23C6, while tungsten carbide are mainly WC1-x, W6C2.54, CW3.The distribution of tungsten is more uniform. With the tungsten addition,though primary carbides of the sample is coarsen, the mechanical properties of the specimen is improved. The research of primary M7C3 carbides shows, with tungsten addition, the average particle diameter of primary carbide increases, and remains a regular hexagon, and the fracture toughness and hardness of primary carbides are improved. The elastic modulus of the primary carbides is 358.593GPa in sample 5.With the quenching temperature increasing, primary carbides is with little change, and the content of eutectic carbides reduce, and more and more fine carbides has been generated in the matrix. The quenching hardness of samples reach a maximum at 1000℃, while impact toughness of samples maximum at 950 ℃, at the same time, the tungsten carbides has been generated in the matrix. After homogenization, the sample average pearlite lamellar spacing is reduced. With the increase of homogenization treatment holding time at 500 ℃, the hardness of the samples reduce after the first increases. When the homogenization treatment holding time is 6 hours at 500℃, the hardness of samples reach the maximum. With the tempering temperature increase, lath martensite refined into a needle in matrix, and the secondary carbide precipitation increase, while its morphology is coarsening, and primary carbides is with little change. And the tempering hardness of samples increase after first decline, and the samples reach the minimum hardness at 420 ℃.The wear weight loss of cast samples show the trends as "M" type, and the wear rate of samples are same with that. With the tungsten content increase, the wear rate of cast samples decrease, which show that tungsten can improve the wear resistance of hypereuteutectic high chromium cats iron. With different tempering temperature after 1050℃ quenching, sample 5, with the maximum tungsten content in all samples, the wear weight loss of samples show the trend as "N" type, the wear rate is the same, and the wear rate reach the minimum when the tempering temperature is 420 ℃.