Continuous Casting Process Banded Pipeline Steel

The banded structure is the main factor of affecting the steel products intrinsic quality. It destroyed the steel' s continuity and has bad influence to the performance. Therefore, analysis and studies must be strengthened to the banded structure originates, the distribution shape in the pipeline steel , as well as some parameters during the pipeline steel rolling process and continuous casting , and the corresponding preventing measures should be made. In this topic during the entire production process of X52 and X60 pipeline steel, by different test method and analysis methods, to the changes and performance behaviors of the banded structure' s shape and rank in the steels from different continuous casting and rolling have been analysed and the researched. This topic has a important guiding and practicalsignificance to develop the pipeline steel in Jinan steel and Iron Group.In order to study the influences of Mo to the banded structure, at the first time the Molybdenum has been added to the steel. After researching we find although the banded structures are still heavy, but looked from the picture to be much lighter (The strip numbers increase while the band width reduces). The organization gets thinner and more homogeneous, 12 levels of crystal grains appeared and the mixed crystal organization reduces greatly. The banded structure gets improved. The non-metallic inclusions rank and the ferrite crystal grain size has all up to the standard requirements. The specification is the crystal grain size in 14mm plate is much more homogeneous than in 18mm .In order to study the influence of the light press measure and the speed of drawing to banded structure in the pipeline steel different speed and lightly presses measures have been used.The experimental result indicated there has practical significance through light press technologyto reduce or the elimination center segregation. Adopt the technologies or not the carbon segregation degree is difference. Under higher pull-speed and bigger light press quantity the carbon segregation degree is lower , on the contrary the carbon segregation degree is larger. Increasing the speed in the continuous casting to a proper degree is benefit to the improvement of microstructure structure in the pipeline steel .Tn order to study influencerule of the final temperature and cooling-speed after rolling to the pipeline steel banded structure, different temperatures and the speeds has been used . Comparing with the experimental result we find that the final temperature influences to banded structure by changing relative crystal grain size 8 d . The test result indicats when 6 d is below - o. 4 the final temperature is lower, band structure decreases;When 5 d is over -0. 4, the final temperature is higher the band structure decreases;The banded structure density in steel plate increases while the cooling speed reduces. When the cooling speed gets to a definite value (critical cooling-rate)the banded structure vanishes.