After the test, the macro fracture characteristics of the cylinder samples cast in each package were first checked. It was found that the fracture characteristics of the 1st to 3rd, 5th and 6th packages were similar to those of, and the macro fracture characteristics of the other secondary cylinder samples were vermicular graphite iron. Therefore, the mechanical properties, metallography and composition of the 4th, 7th, 8th and 9th packages were selectively tested. All the test results are shown in Table , and the metallographic photos are shown in the figure.
|Rm/MPa||540 530||475 486||461 522||361 376|
|R0.2/MPa||415 418||332 336||448 448||— —|
|A/%||2.7 1.1||1.3 1.6||0.4 1.4||— 0.6|
|Hardness HB||228 229||239 237||238 234||207 214|
(1) As shown in the figure, with a certain amount of sulfur, the vermicularization rate of vermicular graphite cast iron increases with the decrease of the addition amount of vermicular graphite cast iron. When the addition amount of vermicularizing agent is 0.54% (the ninth package), the vermicularization rate is too high (95%), and there is a tendency to appear flake graphite (Fig. d); With the increase of the amount of vermicular graphite cast iron, when the amount of vermicular agent is 0.62%, the vermicular rate reaches 85%, and the vermicular effect of vermicular graphite cast iron is good (see Fig. a). The national standard GB/T26655-2011 clearly states that vermicular graphite should have at least 80% vermicular graphite on its two-dimensional polishing plane, so it can be concluded that when the sulfur content is about 0.03%, the reasonable adding range of vermicular graphite agent for vermicular graphite cast iron should be 0.55%~0.65%.
(2) The effect of Sn can be seen as 10 times of Cu, and the pearlite content and hardness of the lowest package of Cu and Sn (the fourth and seventh packages) are still high. The test results show that the comprehensive content of Cu and Sn (Cu+10Sn) should also be reduced, that is, lower than 0.94%.