Why Do Gray Iron Castings Appear To Be Too Hard?

First of all, the chemical composition in the molten metal is inappropriate, and the content of carbon and silicon is low. The content of silicon and carbon shall be strictly controlled in the production of gray iron castings. Generally, the carbon content shall be controlled between 2.9-3.5% and the silicon content shall be controlled between 1.5-2.4%. If the content of these two elements is too low, it will cause the finished products of gray castings to be too hard.

Second, the carbon element is not fully absorbed. When the gray cast iron manufacturer proportions the amount of metal raw materials, if the added carbon is not fully absorbed or the fluidity of the carburizing agent is poor, the undercooling degree of molten iron will be high or the cooling temperature will be uneven, which will cause the finished gray cast iron castings to be too hard.

Finally, the reason for the mold. If the mold has defects, it will lead to poor fluidity of molten iron and uneven cooling speed; If the air permeability of the mold is poor, there is no way for the water vapor to overflow, so that the cooling speed of some parts is too fast and the hardness of the casting is increased; Too long pouring time will also lead to the failure of inoculant, the burning loss of carbon in molten iron and the increase of hardness due to low silicon carbon content.