Study of the Cleanness of Q345B Seamless Steel under Process of EAF-RH-LF-CC

The purity of Q345B seamless steel have been studied by sampling and analyzing at each station,which had been produced during the EAF-RH-LF-CC technological process.Results show that:(1)total oxygen content of slabs can be controlled around 0.002%; (2)non-metallic inclusions main shape nearly like a circle and consist of oxides and sulfides in the whole routes of steel production.The number of non-metallic inclusions in steel continue to reduce following the process of steel making and there was the largest drop in refining process;(3)the nitrogen content remarkable increased between LF refining process and continue casting process,so the liquid steel should have prevented from secondary oxidated;(4)after the LF refining,the number of non-metallic inclusions in size of 10μm～20μm were larger,which have been compared with the end of RH refining.Therefore the weak agitation by Ar blowing should be protensive after deoxidation under the LF refining;(5)w(FeO + MnO)was so high in the workingslag of RH refining that the slag needs to be deoxidated.