Improving internal quality of slab---center segregation1. Steel composition controlDuring the solidification of molten steel, due to the non-uniformity of the

Improving internal quality of slab---center segregation

1. Steel composition control

During the solidification of molten steel, due to the non-uniformity of the chemical composition of the cast slab formed by the selective crystallization, the carbon, sulfur, and phosphorus content in the center of the cast slab is significantly higher than other parts of the edge. Therefore, reducing the content of easily segregated elements in steel is the primary consideration for improving the center segregation of cast slabs. Jiu Steel has optimized the carbon content of current steel grades from 0.17%-0.21% to 0.14%-0.18%, and by strengthening the control of converter slagging and temperature system, the phosphorus content has been controlled below 0.025% , Through the LF furnace deep desulfurization treatment, the sulfur content is controlled below 0.015%. The reduction of carbon, sulfur, and phosphorus content in steel reduces the degree of component segregation.

2. Optimization of electromagnetic stirring process

The nine steel slabs are equipped with electromagnetic stirring in the second cold zone. The original installation position is the last roller of the second stage. The current is 250-280A. During the production process, the equiaxed crystal ratio of the slab is about 30%, and the center segregation is C1.0 The proportion of and above reaches 20%. It can be seen that under the original process parameters, the effect of electromagnetic stirring metallurgy is not good. In view of this situation, the steelmaking plant has made an attempt to optimize the current, and the current production test is carried out in the following order: 280A→300A→320A→350A→380A→400A→450A, and take a low-magnification sample for comparison. The results show that the internal quality of the cast slab improves to a certain extent when the current increases. When the current reaches 400A and then increases, the effect is not obvious and when the current is large, not only the negative segregation is obvious, but the damage of the electromagnetic coil will also be accelerated. In the case that the effect of increasing the current is not ideal, then the organization is organized to change the position of the electromagnetic stirring roller, that is, the electromagnetic stirring roller is moved down from the end of the second stage to the end of the third stage. The results show that when the electromagnetic stirring roller is installed at the end of the third stage and the current is 320A, the equiaxed crystal ratio of the cast slab can reach more than 45%, and the center segregation basically does not exceed the C0.5 level, and the metallurgical effect is good.