Effect of Inclusions on X70 Pipeline Steel

The performance of X70 pipeline steel mainly depends on its chemical composition and structure. Inclusions in X70 pipeline steel mainly exist in the form of non-metallic compounds, such as oxides, sulfides, nitrides, etc., which can cause uneven microstructure of X70 pipeline steel. Their geometric shape, chemical composition and physical factors not only deteriorate the cold and hot processing performance and some physical and chemical indicators of X70 pipeline steel, but also reduce the mechanical properties and fatigue properties of X70 pipeline steel.

When considering the influence of inclusions on the properties of X70 pipeline steel, attention should be paid to the number, particle size, shape and distribution of inclusions, the connection ability between different inclusions and X70 pipeline steel matrix, the plasticity and elastic coefficient of inclusions, and factors such as thermal expansion coefficient, melting point, hardness, etc. When the inclusion particles are relatively large, the yield degree of X70 pipeline steel will be significantly reduced, and the tensile strength of X70 pipeline steel will be reduced at the same time. When the number of inclusions increases, it will reduce the elongation of X70 pipeline steel.

Generally, inclusions have little effect on the longitudinal extension of X70 pipeline steel, but have a significant effect on the transverse extension. The transverse section reduction rate of X70 pipeline steel decreases significantly with the increase of the total amount of inclusions and the number of banded inclusions, and the banded inclusions are mostly sulfides.