In the steel casting or hot working process, due to certain factors (such as non-metallic inclusions, gases, incorrect process selection or operation, etc.). Defects within or on the surface of seamless steel pipe will seriously affect the quality of the material or product and sometimes lead to the material or product being scrapped.
Porosity, bubbles, shrinkage crater residue, non-metallic inclusions, segregation, white spots, cracks and various abnormal fracture defects in cold drawn seamless steel pipes can be found through macroscopic inspection . There are two macro inspection methods: acid leach inspection and fracture inspection. Common macroscopic defects revealed by acid leaching are briefly described below:
1. Isolation
Cause of formation: During casting and solidification, certain elements are added due to selective crystallization and diffusion, resulting in non-uniform chemical composition. According to different distribution positions, it can be divided into ingot type, center segregation and point segregation.
Macroscopic characteristics: In acid leach samples, when segregated into corrosive materials or gas inclusions, the color is darker, the shape is irregular, slightly concave, the bottom is flat, and there are many dense microporous spots. If the resisted element is added, it will be a light-colored, irregular-shaped, and relatively smooth microbump.
2. loose
Cause of formation: During the solidification process, steel cannot be welded during hot working due to the final solidification contraction of the low-melting material and the release of gas to create voids. According to their distribution, they can be divided into two categories: central loose and general loose.
Macroscopic characteristics: On the lateral surface of hot acid leaching, the pores are irregular polygons and pits with narrow bottoms, usually at the separation point. In severe cases, there is a tendency to connect in a spongy form.
