According to the experimental results of the first two sections, the carburization defects will lead to the excessive chemical composition and unqualified mechanical properties of the steel castings, and the unqualified rate of the sampling positions C and D is the highest. In order to further study the effect of carburizing defects on the gold addition, the optical gold enrichment microscope was used to observe the gold addition of the main body of the test piece.
The steel castings produced by EPS and stmma were sampled at the D position of the casting body, corroded by 4% nitric acid alcohol solution, and detected by gold enrichment. The results are shown in Fig. 1 and Fig. 2.
From the comparison between figure 1 and Figure 2, it can be seen that since zgs10crnicu is a hypoeutectoid steel, all the additions of Jinzeng group are ferrite + pearlite. However, when EPS is used to produce steel castings, the increase ratio of carbon content is far greater than that of steel castings produced by stmma, so the increase of pearlite group in EPS steel castings is more than that in stmma steel castings. In addition, it can be seen from Figure 1 that the distribution of EPS carburizing defects is very uneven, pearlite group distribution is irregular, some areas are agglomerated and there are sharp corners at the edge of grain boundary, which seriously affects the uniformity of casting performance, which is the main cause of mechanical properties disqualification; it can be seen from Fig. 2 that stmma is used The distribution of ferrite and pearlite is uniform, and the grain boundary is clear and smooth, which is beneficial to improve the mechanical properties of steel castings.