Macrostructure inspection of internal crack in 42CrMo4 gear hub blank

The instrument model used for ultrasonic flaw detection is cts-1002 digital ultrasonic flaw detector. As the diameter of steel is Φ 400 mm, according to the standard requirements, the probe is 2.5P Φ 20 straight probe, the coupling agent is oil, the initial sensitivity is fbh2.0 mm, and the scanning speed is adjusted according to the depth of 1:4.

According to the flaw detection situation, two defects were located respectively, and two transverse macro samples were obtained by sawing. After grinding and corrosion inspection, it was found that there were many internal cracks and three small holes with a length of about 2-15 mm which were not welded on the cross-section of the sample. The defects were located in the 1 / 2 radius circle of the center, and the other parts were dense. The macrostructure is shown in Fig.