Study On Internal Metallurgical Quality Control Of Heavy Slab In Baosteel

Thick plate products are widely used in large-caliber conveyor pipes,boilers,pressure vessels,offshore platforms and various naval vessels.Because of the harsh service conditions,it is not only required that these kinds of steel have high strength,high toughness,and weldability,but also requires very high quality of its core.Internal metallurgical quality,such as slab center segregation,UT quality,are the key factors affecting the core quality of high quality thick slabs.Therefore,it is of great significance to carry out relevant technical research on improving the internal metallurgical quality of thick slabs.In view of the actual production of Baosteel 2300mm thick slab caster,the influence of molten steel composition,continuous casting process parameters and dynamic soft reduction technology at the solidification end on the internal metallurgical quality of thick slab are studied.The technical measures to ensure the internal metallurgical quality of slab are put forward.The main contents and results are as follows:(1)Reducing tundish superheat is conducive to improving center segregation.For some high carbon steels and other special steels,it is necessary to reduce superheat in order to control center segregation.Low sulfur and phosphorus design is conducive to improving center segregation.For some steels with higher requirements,0.010%phosphorus and 0.0010%sulfur are conducive to improving center segregation.(2)Soft reduction can significantly improve the center segregation quality of slab.The soft reduction model needs to calculate the solidification end accurately to ensure that the reduction position is in the paste zone and there is enough reduction.Good roll gap accuracy is conducive to improving the center segregation quality.The center segregation rating of articulated sector section is between 1.8 and 2.0 of Mandarin Standard.The center segregation quality of the flexible rod sector section is better,and the mandarin standard is between 1.5 and 1.8.(3)Superheat has obvious influence on the UT quality,the lower the degree of superheat,the higher the rate of incompatibility of flaw detection.Ensuring proper high degree of superheat is helpful to improve the quality of flaw detection.Generally,the control of superheat in steel tundish of flaw detection quality is not less than 20℃,but high degree of superheat has adverse effect on central segregation.(4)The hydrogen before RH of double treatment is 1.13 ppm higher than that of single treatment,but the RH end hydrogen of double treatment steel is 0.11 ppm lower than that of single treatment,and enough high vacuum time of RH can ensure that the end hydrogen is low even if the hydrogen before treatment is high.Prolong baking time of Tuudish,reduce the moisture content of covering flux,and reduce hydrogen increase in continuous casting.It is helpful to reduce hydrogen-induced incompatibility by reducing the cold bed detention time and slow cooling.