Research On Production Process Of L245³90 Series H₂S Corrosion Resistant Pipeline Steel

Based on the analysis of the effect and harm of each element in steel,combined with the characteristics of 2250mm production line in Baotou Steel Rare Earth Steel Plant,according to the standard GB/T9711 and API5L oil and gas pipeline requirements and user technical conditions.In order to meet the market demand of hot rolled coils for H2S corrosion resistant pipelines at home and abroad,chemical composition design and hot rolling process were developed independently with the application representatives of brand L245MS?BMS?,L360MS?X52MS?and L390MS?X56MS?.The comprehensive properties of the products were systematically analyzed by means of dual smelting process,vacuum calcium treatment technology and TMCP hot-mechanical rolling process.The design and development is based on 2250mm advanced hot rolling control capability,low cost design concept,reasonable design of controlled rolling and controlled cooling process,in order to develop and ultimately produce hot rolling pipeline steel strip with excellent strength,toughness and H₂S corrosion resistance.Through the research,the composition design and control technology of different grades and specifications of steel products are optimized reasonably.In LF-RH process,the content of gas and inclusions in steel is significantly reduced.By optimizing the design of refining slag system,the ability of slag desulfurization and inclusion adsorption in refining process is improved.The smelting process of ultra-low sulphur steel is developed,which can continuously produce molten steel with S content less than0.0020%.Nitrogen increment in continuous casting process can be controlled within 4 ppm and H content can be controlled within 2.0 ppm,thus avoiding the occurrence of single phase MnS inclusions in steel.The total amount of all kinds of inclusions is less than 2.0,which indicates that L245³90 series pipeline steel with H₂S corrosion resistance has high cleanliness.From the analysis of the crystal structure of the finished product,it can be seen that the structure of the finished product is composed of GB+FB+a small amount of M/A island structure,and has a certain proportion of acicular ferrite.Compared with polygonal ferrite,fine acicular ferrite has a large number of dislocations.When impacted,dislocations are intertwined and pinned with carbides,which effectively prevents cracks from propagating by dislocation movement.Fine acicular ferrite shows good dynamic tear resistance.The results show that the mechanical properties of L245-390 series pipeline steel with H2S corrosion resistance can meet the requirements of the design target range by smelting ultra-low sulphur and high purity steel with the design scheme of low carbon and high manganese+Nb and Ti micro-alloys.At the same time,the HIC and SCC test results are all qualified,and the crack length rate and crack rate are all qualified.The crack sensitivity rate and crack thickness rate are both 0%.Compared with other steel mills,the crack area rate CAR also meets the user's requirements,which fully reflects the ultra-low S.The control of high purity steel plays an important role in improving the anti-H₂S corrosion ability of steel.