For the lost foam casting process, the carbon-increasing defect of steel castings is a difficult problem. Carburization means that the carbon content in steel castings will be higher than expected after casting. The carbon content is mainly derived from the carbon element produced when the foam pattern is vaporized.
The carbon increase phenomenon of lost foam steel castings has the following characteristics:
1) The lower the original carbon content of molten steel, the greater the degree of carbon increase and the deeper the carbon layer.
2) The degree of carbon increase in steel castings will vary in different parts of the casting. The carbon increase at the end of the filling and the highest part of the casting is significantly greater than that of other parts. In addition, the amount of carbon added to steel castings with different wall thicknesses is also different.
3) Due to the uneven carbon increase range, the mechanical properties of steel castings fluctuate greatly. Compared with investment casting, the elongation of lost foam castings is significantly reduced, but the surface hardness is significantly increased. These phenomena increase the difficulty of the machining of the castings, and at the same time reduce the welding performance of the castings.
How to prevent the carburization defects of lost foam casting steel parts?
1) Use the copolymer foam pattern, or reduce the density of the foam pattern.
2) Use a top pouring system or place more risers to increase the discharge of foam-like decomposition products and absorb the molten metal from the carbon-increasing front.
3) Use coarse sand and paint that can absorb the decomposition products of foam.