Study on Microstructure and properties of ht350 high strength gray cast iron

The following contents are mainly studied: the influence rules and mechanisms of different inoculation treatments on the microstructure, mechanical properties and turning properties of high-strength gray cast iron, and the influence rules and mechanisms of different modifier addition and alloy element Mo on the microstructure, mechanical properties and thermal fatigue resistance of high-strength gray cast iron. The following conclusions are drawn:

1.By studying the effects of different inoculation treatments on the microstructure and properties of gray cast iron, it is concluded that the graphite structure of the sample inoculated with Si Zr Mn inoculant is uniform and fine, the pearlite sheet spacing is small, the primary austenite network frame structure is the most complex, the tensile strength and matrix microhardness are the highest, the mechanical properties are the best, but the cutting performance is poor. In terms of improving mechanical properties, the inoculation effects of the four inoculants from low to high are: silicon zirconium aluminum inoculant → 75 ferrosilicon → silicon zirconium inoculant → silicon zirconium manganese inoculant. In terms of improving cutting performance, the inoculation effects of the four inoculants from poor to good are: silicon zirconium inoculant → silicon zirconium manganese inoculant → silicon zirconium aluminum inoculant → 75 ferrosilicon.

2.The modification first changed the growth process of primary austenite, not only increased the number of primary austenite, but also developed the primary austenite in a spatial network, limited the space of Eutectic Transformation of gray cast iron, reduced the size and increased the number of eutectic clusters. The primary austenite with complex network frame structure in the molten liquid will also block the growing graphite crystal. When the graphite crystal grows into contact with the austenite dendrite, it will bend and bifurcate. Therefore, the graphite will be more curved and fine. The more modifier is added, the more complex the framework structure of primary austenite network, the more eutectic clusters, the finer and curved graphite, and the smaller the lamellar spacing of matrix pearlite. Therefore, the higher the mechanical properties of gray cast iron. After modification, the thermal fatigue property of gray cast iron is improved, and the more modifier is added, the better the thermal fatigue property is.

3.Due to the addition of alloy element Mo, the spatial network framework structure of primary austenite will be more obvious, the number of primary austenite will be increased, the eutectic group in gray cast iron will be refined, the growth of graphite will become fine and curved, and the layer thickness of matrix pearlite will be reduced. Therefore, the addition of 0.25% Mo will increase the tensile strength and matrix microhardness of gray cast iron. Moreover, the addition of alloy element Mo can improve the thermal fatigue properties of gray cast iron.

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