Firstly, the mechanism and manifestation of carburization defects in steel castings are described, and then the experimental methods and main masters of the research on Carburization defects of steel castings for bridge bearings are planned, and the detection and verification are carried out through the tests, and the following conclusions are drawn:
(1) The distribution of carburizing defects is: the farther away from the gate, the longer the soft moving distance of molten steel in the mold, the more serious the carburization; the more serious the carburization is at the position with the same distance from the gate and the later the solidification time.
(2) When EPS is used to produce low carbon steel castings, the surface and volume carburization are 0.1% ~ 0.3% and 0.01% ~ 0.04% respectively; when using stmma to produce low carbon steel castings, the surface and volume carburization are less than 0.1% and 0.015%, respectively. This shows that the surface carburization of steel castings is more serious than that of volume carburization.
(3) Volume carburizing can improve the tensile strength and yield strength of steel castings, and slightly reduce the reduction of area and elongation after fracture, but it has a great impact on the impact toughness, which is the main reason for the unqualified mechanical properties of steel castings.
(4) From the analysis of Jinzeng group, it is found that the uneven distribution of pearlite and the sharp angle of grain boundary in the steel castings produced by EPS are the main reasons for the unqualified impact toughness of castings; the pearlite and ferrite of steel castings produced by stmma are evenly distributed and the grain boundaries are smooth, which is conducive to guarantee the mechanical properties of the castings.
(5) the higher the carbon content of the foam material is, the more serious the carburizing tendency of the steel castings is, and the lower the qualified rate of the products is. In order to ensure the chemical composition and mechanical properties of steel castings, stmma copolymer is recommended in production.