The description and general impression of casting defects of various cast steel joints are as follows:
(1) The four cast steel joints showed the same casting defect characteristics, that is, cracks were found in R zone. These four joints are cast steel joints of gymnasium, and they are all bifurcation joints. The crack trend is consistent with the intersecting line, and there are cracks at almost every intersecting line. After high-temperature melting, it is found that the crack has a certain depth and spreads downward. Some cracks again after repair welding, and the casting defects of incomplete fusion of core support are particularly common.
(2) The four cast steels showed the same casting defect characteristics, that is, there were pores at the nozzle. There are small and dense casting defects as well as single casting defects. There are three pore defects at the four nozzles, one on the surface and the other on the inside. It may be because the nozzle is far away from the exhaust hole, and the air hole is difficult to be discharged through the exhaust hole. It may also be because the nozzle is the end of cast steel joint, which dissipates heat quickly and is prone to water vapor condensation.
(3) The 10 cast steel joints found that the core brace was not fused, and some cast steel joints did not even have a core brace fused. The cast steel joint brace is generally clearly visible. The unmelted core brace and the unmelted internal cooling iron are not allowed to have casting defects in ISO standards and ASTM standards, because the unmelted brace is equivalent to the local loss of cast steel joint, which will also cause corrosion penetration. Generally, the cast steel plant will dig out 100% for repair welding.
The flaw detection results show that the qualitative and quantitative of ultrasonic flaw detection for cast steel joint defects depend on empirical judgment, which is very subjective. The nature of many casting defects can not be accurately inferred. Of course, the influence of these random casting defects on the mechanical properties of cast steel joints can not be determined. At the same time, the nature, size and orientation of casting defects also have an impact on the amplitude of echo, and the near-field area of acoustic wave may also become a blind area. Therefore, it is difficult to accurately measure the size of casting defects by equivalent method. More detailed methods need to be used for detection, combined with other technologies such as CT, and destructive test can also be used when necessary.