Effect of composition of nodular cast iron on shrinkage and porosity

After shot peening and grinding, ut test was carried out on the surface of the test block after sanding, and the volume and distribution of shrinkage and porosity of each test block were recorded. In order to fully ensure the reliability of the experimental results, the test block was dissected by mechanical processing method to verify the accuracy of the recorded ut detection defects. According to the recorded defect volume, the shrinkage and porosity tendency of test blocks with different components were analyzed.

(1) Detection range: shrinkage cavity and porosity within the thickness range of test block.

(2) Detection method: ultrasonic flaw detection.

(3) Relevant parameters of ultrasonic flaw detection:

Testing instrument: hg-d106c ultrasonic flaw detector.

Detection sensitivity: Φ 6fbh + 36dB.

Execution and result judgment standard: technical conditions for ultrasonic flaw detection of ductile iron castings (EN 12680-3).

(4) Record method: defect record chart, record the distribution of shrinkage cavity and porosity shown by UT inspection, and calculate the defect volume.

Through ut detection, the test blocks of scheme e3-1, e3-2, e3-3, e3-4 and e3-5 are in good condition, with no defect clutter and good bottom wave feedback; the upper surface of test block e3-6 has clutter display, with bottom wave, and the defect depth is about 10-40mm; for scheme e3-7, e3-8, e3-9, there are clutter display on the upper and lower surfaces, without bottom wave feedback, the defect depth is about The depth of defects in the lower part of pouring position is about 20-100 mm. Among them, e3-7 and e3-8 have the most serious defects. There is an area of about 70mm × 70mm without bottom wave at the thickness of 400mm, and it can be judged from the defect wave shape that it is a serious shrinkage porosity defect.

The defect position of two test blocks was dissected by mechanical processing. The anatomical section is shown in Fig. 1 and Fig. 2. By measuring the size of shrinkage cavity defect on anatomical section, the calculation results of shrinkage cavity and porosity defect volume are basically consistent with UT detection results, which fully proves the reliability of UT detection results.

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