In order to improve the toughness and wear resistance of Hypoeutectic, eutectic or hypereutectic high chromium cast iron, scholars at home and abroad have done a lot of research work on carbide refinement and toughness improvement of high chromium cast iron. For example, in view of the fact that cr15mo3 high chromium cast iron contains more expensive molybdenum elements, Han et al. Studied the technology of replacing molybdenum with manganese in high chromium cast iron, developed 13% CR-4% Mn high Cr Mn cast iron, and adopted boron modification treatment. When its mass fraction is in the range of 0.12% – 0.30%, the carbides gradually change into small isolated clusters with the increase of boron content, Carbide refinement is ideal. After adding rare earth composite modification, the impact toughness can reach 6-7j / cm2. In addition, by adding strong carbide forming elements, graphitization elements, or elements with strong adsorption and purification ability to form a composite modifier in high complex cast iron, the as cast eutectic carbides change into ball shape + worm shape + strip shape and are evenly distributed. After heat treatment, the morphology and distribution of carbides are more ideal. When the hardness reaches 57-60hrc, the impact toughness is stable at 12.8-14.7j/cm2. Russian scholars carried out compound modification on high chromium cast iron through vanadium, titanium, aluminum, niobium and magnesium, which significantly refined the solidification structure and improved the morphology and distribution of carbides. When the hardness of cast iron is 55-65hrc, the impact toughness of cast iron is as high as 25.1-33j/cm2.
Wu Xiaojun et al. Studied the effect of titanium modification on the morphology of primary carbides of 4% C and 20% Cr hypereutectic high chromium cast iron. Theoretical calculation showed that in the solution of hypereutectic high chromium cast iron, Ti atom and C atom would react to form tic nucleus. The test results show that when an appropriate amount of Ti is added to hypereutectic Gaoming cast iron, the primary carbides are significantly refined with the increase of Ti content. The reason for carbide refinement is that adding hypereutectic high chromium cast iron solution will combine with C in molten iron to form a large number of TiC particles with crystal orientation relationship with M7C3 carbide. This particle can be used as the crystal core of primary phase carbide. With the increase of the number of nucleation cores, the primary phase carbide structure is refined.
The above shows that the modification principle of high chromium cast iron is mainly to add strong carbide metal to increase the crystallization core and add active elements such as rare earth, potassium, sodium and calcium to purify the liquid steel, enrich the grain boundary and inhibit the biased growth of carbide. Because the carbon content of hypereutectic high chromium cast iron exceeds the eutectic point, the primary phase carbide is the focus of modification, that is, to find the low-cost primary phase carbide crystallization core and the component supercooling element to narrow the carbide crystallization temperature range.