New Type of Corrosion-Active Nonmetallic Inclusions and their Influence on the Corrosion of 38KHN3МFА Steel

We study the influence of corrosion-active nonmetallic inclusions on the corrosion of 38KhN3MFA steel. A new type of fluorine-containing inclusions of this kind with a size 2–30 μm is discovered. These inclusions are responsible for anomalously rapid damage of drill pipes made of the indicated type of steel. It is difficult to identify them with the help of metallographic analysis. They do not affect the general chemical composition of steel, the characteristics of strength and impact toughness at room and lowered (– 50°С) temperatures. We propose a new approach to the detection of corrosion-active nonmetallic inclusions in steels reduced to the investigation of the fracture surfaces of specimens instead of their microsections. Unlike the existing methods, this approach enables one to determine the chemical composition and correctly reproduces the shape of inclusions.