Control of Shape, Content and Chemical Composition of Non-metallic Inclusions in API-X42 Pipeline Steel and the Influences of Them on the Mechanical and Corrosion Properties of Steel

In recent years many different ways have been investigated by steel producers to increase ductility, formability and corrosion resistance of steel. More important ways are steels with very low amounts of inclusion, small size inclusions and modified inclusions. In this study, experiments have been performed on the API-X42 pipe line steel produced by the electric arc furnace in Mobarakeh Steel Co. After the preparation of the melt in the electric arc furnace, it is taped in a 200-ton ladle and ladle treatment was performed in a ladle furnace (LF) in the steelmaking shop. In this study the effect of calcium compound addition on the shape, content and chemical composition of non-metallic inclusions were investigated by Scanning Electron Microscopy (SEM) and chemical Energy analysis Dispersive System (EDS) that the optimum conditions for adding compound for inclusions control were also determined. It should be considered, presence of inclusions in steel can have worse effects on corrosion properties and strength of hydrogen damage in H2S included environment. Therefore, displacement of glycerin was used to measure the amount of diffusible hydrogen. Immersed test is sour media was performed on NACE standard and similar media with added thiosulphate ions. The results show that adding the 300 grams calcium powder per ton of molten steel cause to generate of spherical inclusions and therefore, the suitable conditions will be prepared for flotation and removing of them in the ladle by changing the chemical composition. The results also show the reducing and spherical inclusions lead to reducing diffusible hydrogen and corrosion rate.

Keywords:

Shape control and modified inclusions , Calcium treatment , Hydrogen damage , Immersed corrosion