Application of Fractional Gas Analysis to Control the Production of 22GYu Steel

The production of 22GYu steel, which is used in the manufacture of pipes for transporting oil and natural gas over long distances under high pressure, is studied. The heat logs of 22GYu steel are statistically analyzed, metal samples are taken at various stages of steelmaking, and the changes in the nitrogen and oxygen contents in the metal samples are analyzed by fractional gas analysis (FGA). The metal samples are analyzed using a JEOL JSX ISP 100 EPMA electronic microanalyzer equipped with energy dispersive (EDS) and wave dispersive (WDS) spectrometers. The nitrogen content in the metal is found to increase mainly during casting of the metal from an electric arc furnace (EAF) into a ladle furnace (LF) at the EAF–LF process stage. The following three main types of oxide NMIs in the metal have been identified using the results of electron-probe microanalysis (EPMA) of nonmetallic inclusions (NMIs) and processing of FGA evalograms (gas evolution curves) with the OxSeP Pro software package. The oxygen content determined by FGA in various types of oxide NMIs after recalculation corresponds to the volume fraction of oxides of this type in the metal. At the beginning of processing steel in LF, the metal has a high content of NMIs such as silicates, aluminates, and spinels, and the main type of NMIs is represented by aluminates. During LF steel processing, the content of NMIs decreases as a result of their transition to a slag. The dissolved nitrogen content in the metal samples taken from LF is ~82 ppm. The metal samples taken from a continuous casting machine (CCM) have an increased NMI content, which can be due to secondary oxidation of steel during casting. To determine the main types of inclusions in the metal and to confirm the FGA results, we study the metal samples taken from the LF, CCM, and a slab by EPMA on a JEOL JSX ISP 100 scanning electron microscope. Metal sample 2 taken from LF is found to be characterized by a large number of NMIs, which are represented by aluminates, aluminocalcium spinels, and sulfides. Other samples taken along the process chain exhibit a decrease in the NMI contamination of polished sections, and globular inclusions based on the CaO–Al 2 O 3 –SiO 2 system become predominant. Inclusions of the corundum type (Al 2 O 3 ) are detected much more rarely. A small amount of inclusions based on calcium oxide is detected. Metallographic studies of the metal generally confirm the FGA results. The contamination of the metal with NMIs