1. Chemical composition detection

Arl3460 direct reading spectrometer is used for chemical composition detection, and the chemical composition detection results are shown in Table 1.

Serial number	C	Si	Mn	Cu	P	S	Mg
1	3.78	2.76	0.30	0.17	0.028	0.011	0.044
2	3.74	2.74	0.29	0.15	0.033	0.010	0.040
3	3.79	2.81	0.28	0.16	0.028	0.010	0.043
4	3.80	2.79	0.30	0.16	0.030	0.010	0.050

2. Metallographic examination

According to gb/t 9441-2009 metallographic examination of nodular cast iron, the metallographic specimen of the body is prepared and tested. The wall thickness of the metallographic structure test part of the body is 20 mm, the test part is shown in Figure 1, and the metallographic structure test result is shown in Figure 2. It can be seen that the spheroidization rate is more than 90%, the matrix structure is 75% ferrite +25% pearlite, and there is no cementite.

3. Mechanical property test

Figure 3 shows the mechanical property testing position, and the processing size of the body test bar is shown in Figure 4. Use electronic universal testing machine and Brinell hardness tester to test the mechanical properties and hardness respectively, and the test results are shown in Table 2.

Sample No.	Tensile strength /MPa	Yield strength /Mpa	Elongation /%	Hardness /HB
1	476	336	15.6	180
2	479	331	13.3	178
3	485	327	13.3	168
4	472	331	18.6	164
5	462	321	20	188
6	479	334	17	172

4. Internal quality inspection

The internal quality of nodular cast iron automobile brake caliper castings was tested by X-ray flaw detection and sectioning dye detection. The test results are shown in Fig. 5 and Fig. 6. According to the flaw detection results and coloring results, no shrinkage defects were found inside the nodular cast iron automobile brake caliper castings.

After early development and optimization, the utilization rate of molten iron in this process layout is 61.6%, which is 19% higher than the conventional layout. The mechanical properties, internal quality and appearance quality of nodular cast iron automobile brake caliper castings meet the requirements. Now nodular cast iron automobile brake caliper castings have entered the stage of mass production, and the production process is stable. The scrap rates of \1~\6 nodular cast iron automobile brake caliper castings are 2.0%, 2.1%, 2.3%, 1.6%, 1.5% and 1.9% respectively, and the overall scrap rate is 1.9%.