A company used the wet casting method to produce a certain type of automobile shell castings, which are made of GX40CrNiSi25-20 (German standard is 1.4848, national standard is 2520 stainless steel). The casting defect rate in the production process is as high as 20%. In order to reduce the scrap rate of castings and improve the qualification rate of product production, it is urgent to analyze the types of casting defects of shells, analyze the causes of defects, and formulate corresponding solutions. In order to analyze and judge the defects of shell castings, scanning electron microscope was used to observe the morphology of the shell casting defect samples, and energy spectrometer was used to measure the defect components.
(1) The casting defects were observed by scanning electron microscope and analyzed by energy spectrometer. The types of casting defects were well determined and the causes of defects were analyzed.
(2) Through analysis, the three casting defects of shell casting are sand hole, oxidation slag inclusion and sand hole+oxidation slag inclusion composite defects.
(3) In the process of shell casting, measures such as optimizing the gating system, thoroughly removing the free sand particles in the mold cavity, improving the sand mold strength, setting ceramic filters in the gating system, and controlling the oxidation of molten steel are conducive to preventing the occurrence of casting defects such as sand holes and oxidation slag inclusion.