Mechanism of carburization defects
The mechanism of carburizing defect is the diffusion of carbon into soft moving molten steel and solidified casting. During the filling process of LFC, the solid pattern is decomposed into gas increase, liquid increase and solid increase under the action of high temperature of molten steel, and a dynamic gap is formed at the soft moving front of molten steel. However, the solid carburization is adsorbed on the surface of the coating wall casting, resulting in the surface carburization defect of the casting. In addition, when the vapor of styrene and benzene is discharged from the mold under negative pressure, it will condense in the coating and surrounding dry sand. The organic liquid substance adsorbed on the coating layer will continue to decompose during the solidification of molten steel and cooling process of casting, which will also cause carburization defects of steel castings.
Research status of carburization defects at home and abroad
After years of research, the mechanism of carburization has been basically known and recognized. However, how to fundamentally solve the problem of carbon increase has been a worldwide problem. As early as the 1990s, the British Steel Casting Research and industry trade association proposed a process called replica ceramic shell process (soft called replica CS). The process takes the foam pattern of lost foam casting as a prototype, combines with the shell making technology of investment casting to form a thick sand shell on the model surface, then takes off the foam pattern and roasts the shell, then fills in the sand, and after the vibration is compact, the casting is casted under negative pressure, so as to solve the problem of increasing the carbon content of the steel castings. Some universities and research institutions in China have carried out research on this technology and successfully produced stainless steel ball valve castings. However, this process is only suitable for small steel castings, with low efficiency, high cost and poor operability, so it is difficult to adapt to industrial mass production, so it has not been widely applied in domestic EPC enterprises.
Wang Zhongke, Huang naiyu, Luo Jirong, ye Shengping, etc. of the older generation of scientific research workers in China, such as Wang Zhongke, Huang naiyu, Luo Jirong, ye Shengping, etc In 1997, the research on the mechanism of carbon defect and the effect of carburizing defects on the increase and performance of castings were carried out. It was pointed out that the influence of carbon addition defects on casting quality should be reduced from the selection of foam pattern, the reasonable casting process and the permeability of coating.
