The purpose of this study is to modify the solidification structure of chromium white cast iron by pressure casting. The effect of solidification pressure on the solidification structure of the alloy was studied, especially on the morphology and distribution of carbides. Secondly, the effect of solidification pressure on the phase composition of chromium white cast iron, including the phase composition of carbide and matrix, was studied to reveal the phase transformation mechanism under pressure. Finally, the effect of solidification pressure on the mechanical properties of chromium white cast iron and the strengthening mechanism are studied, and how to use the reasonable size of pressure casting to get better economic benefits and performance ratio is obtained.
(1) The variation of solidification structure morphology of chromium white cast iron with solidification pressure was studied
The effects of solidification pressure on the morphology transformation of primary phase and eutectic phase, as well as their size and distribution, such as eutectic structure content and eutectic spacing, were studied. At the same time, the microstructure of different sampling positions was compared to study the effect of position effect on Solidification Microstructure of chromium white cast iron under pressure.
(2) The effect of solidification pressure on eutectic growth mechanism of chromium white cast iron was studied
The effect of pressure on the eutectic growth mode of chromium white cast iron was studied. The formation mechanism of eutectic structure under high pressure was analyzed from the thermodynamics and kinetics of solid-liquid phase transformation, and the essence of solidification behavior of different phases of eutectic structure under pressure was revealed.
(3) The effect of solidification pressure on the morphology and distribution of carbides in chromium white cast iron was studied
The morphology, size, distribution and crystal growth of primary carbides and eutectic carbides under different pressures are compared, that is, the diffusion of atoms in the liquid phase to the crystal surface makes the solid-liquid interface face the liquid. The transformation of facet growth mode of carbides during solidification under pressure was studied.
(4) The phase transformation law of solidification structure of chromium white cast iron under Solidification pressure was studied
Through the analysis of XRD diffraction pattern, the phase types of solidification structure of alloy 1 and alloy 2 under different pressure conditions were obtained. The change of the type and content of different phases and the generation of new phases in the alloy were compared under different pressures. The type and transformation of carbides are mainly studied, and the stability of different types of carbides is obtained by first principle calculation to further explain the mechanism of phase transformation.
(5) The effect of solidification pressure on the mechanical properties of chromium white cast iron was studied
The hardness, impact toughness and impact wear properties of the samples were tested to comprehensively evaluate the mechanical properties of the samples, and then the effect of solidification pressure on the mechanical properties of the alloy was obtained. Combined with the results of mechanical experiments and the microstructure and phase composition of solidification structure under pressure, the strengthening mechanism of the alloy under pressure was analyzed and summarized, and then the experimental process parameters of pressure casting were optimized.