Through the observation of metallographic photos, the spheroidization level of a1-a8 and B1-B4 and the size level of nodular graphite ball of nodular cast iron are evaluated. The results are shown in Table 1 and table 2.
| Number | A1 | A2 | A3 | A4 | A5 | A6 | A7 | A8 | B1 | B2 | B3 | B4 |
| Spheroidization level | Grade 1 | Grade 2 | Grade 2 | Grade 2 | Grade 1 | Grade 1 | Grade 2 | Grade 2 | Grade 2 | Grade 1 | Grade 2 | Grade 2 |
| Graphite size | Grade 5 | Grade 5 | Grade 6 | Grade 5-6 | Grade 6 | Grade 6 | Grade 7 | Grade 7-8 | Grade 7-8 | Grade 8 | Grade 7-8 | Grade 8 |
The results show that the spheroidizing rates of a1-a6 are more than 90% and the spheroidizing grades of nodular cast iron are both grade 1 and grade 2. The overall spheroidizing effect is ideal. The graphite size grade of nodular cast iron is mainly Grade 5-6, and the grade of A7 and A8 is higher, which is grade 7-8. The spheroidization grade of B1-B4 is mainly grade 2, and the graphite size grade of nodular cast iron increases, mainly grade 7-8 The graphite ball is very small.
| Number | A1 | A2 | A3 | A4 | A5 | A6 | A7 | A8 | B1 | B2 | B3 | B4 |
| Spheroidization level | Grade 2 | Grade 2 | Grade 2 | Grade 2 | Grade 2 | Grade 2 | Grade 2 | Grade 2 | Grade 2 | Grade 1 | Grade 2 | Grade 2 |
| Graphite size | Grade 5 | Grade 5 | Grade 5 | Grade 5 | Grade 5 | Grade 5 | Grade 6 | Grade 5 | Grade 7 | Grade 8 | Grade 7-8 | Grade 7 |
The heat treatment of nodular cast iron has a slight effect on the spheroidization grade and graphite size grade. The spheroidization of grade 1 in a1-a8 is reduced to grade 2, and the graphite size of grade 6 is reduced to grade 5. There was no significant change in the spheroidization grade and graphite size grade of B1-B4. On the whole, the heat treatment of nodular cast iron has little effect on the morphology of graphite balls, and there is no serious segregation or increase in the metal phase. It can be seen that the heat treatment of nodular cast iron mainly affects the matrix, but has little effect on the graphite ball.
The figure lists the metallographic photos of graphite balls of A6, a7 and B2 as cast and as heat treated nodular cast iron. Through comparison, it is found that the spheroidization effect of as cast and heat treated state is the best in all samples, with spheroidization level of 1 and size level of 8, as shown in Figure E. Its characteristics are: the spheroidization rate of graphite is high, and the spheroidization rate is more than 90%. Graphite balls have high roundness, small diameter, large quantity and uniform distribution. After heat treatment, the difference between nodular cast iron and as cast iron is not obvious. The main reason for this phenomenon is that the graphite ball is refined after adding tin.