Chemical composition detection of CN7M investment casting

As shown in the table, the composition after furnace of CN7M scrapped products of ZHY Casting 3 heats randomly selected.

Number	C	Si	Mn	P	S	Cr	Ni	Mo	Cu	Al	Sn	As	Pb	Sb	Fe
1	0.024 2	0.86	0.88	0.016 9	0.001 1	19.47	28.03	2.17	3.33	0.018 1	0.057 6	0.002 1	0.001 8	＜0.002	Bal.
2	0.031 3	0.79	0.91	0.017 7	0.001 2	19.68	28.16	2.15	3.29	0.015 6	0.051 3	0.001 9	0.001 7	＜0.002	Bal.
3	0.028 3	0.83	0.90	0.017 2	0.001 1	19.71	28.22	2.15	3.27	0.016 7	0.055 3	0.001 9	0.001 8	＜0.002	Bal.

It can be seen from the test results of chemical composition that the mass fraction of Sn element in scrapped products reaches 0.05%~0.06%. In the production of steel castings, as harmful residual elements, the total content of Pb and Sn is usually controlled below 0.01%, and the content of Sn in cracked products has far exceeded 0.01%, which is the key factor leading to product cracking. The reason for the high content of Sn element is that unqualified purchased bars were used in the melting process, and the Sn element in the bars was about 0.06%. During the incoming inspection, the harmful effect of low melting point Sn element on the casting was ignored.