Benefit of Continuous Casting

 

Prior to the development of continuous casting, ingots provided the only starting material in wrought‑steel products. The typical sequence of operations from the steelmaking furnace to the rolling mills was:

 

1)       Tapping liquid steel from a steelmaking furnace into a ladle.

2)       Transferring ladle to pouring platform and teeming liquid steel into ingot molds.

3)       Transferring filled molds to stripping area for ingot removal.

4)       Transferring and charging ingots into soaking pits and heating to rolling temperature.

5)       Removal of heated ingots from soaking pits and transfer of them to primary mill for rolling into semifinished shapes.

6)       Transferring semi‑finished shapes to subsequent rolling mills.

 

Using continuous casting, the following much shorter sequence of operations is required:

 

1)       Tapping liquid steel from a steelmaking furnace into a ladle.

2)       Transferring the ladle to a casting platform and continuously casting liquid steel into semifinished shapes.

3)       Transferring the semi‑finished shapes to rolling milts.

 

The benefits derived from the shorter sequence of operations provided the main impetus for the adoption of continuously casting:

 

a)       increased yield;

b)       improved product quality;

c)       energy savings;

d)       less pollution;

e)       and reduced costs.

 

Yield ‑ Increased yield from liquid steel in the ladle to the semi‑finished rolled shape results from a reduction in scrap generation in three areas: the primary rolling mill; the pouring operation; and ingot heating. The major contribution to the improved yield is the absence of crop losses corresponding to the ingot top and bottom location when an ingot is rolled in the primary mill. Reduction in yield losses associated with the pouring operation includes "short" ingots, ingot butts and general pit scrap. Scaling losses associated with ingot heating in the soaking pit are also avoided.

 

Quality ‑ Metallurgical quality improvements include less variability in chemical composition and solidification characteristics. In addition to improved segregation characteristics of carbon, sulfur and alloying elements across the section of a continuously cast shape, there is also less variability along the length of the cast shape. (In casting a heat into ingots there are a multitude of individual ingots each with their associated vertical segregation and structural variability, whereas a continuous cast strand is not only as one ingot but also an ingot which has less variability in a vertical direction.) In modern continuous casting, the surface quality of the cast shape is superior to that of a semi‑finished rolled shape with respect to surface defects such as seams and scabs, and, consequently, conditioning requirements and yield losses are minimized. A majority of continuously cast steels can be further processed without any conditioning. Thus, an improved, more uniform finished product can be obtained with fewer internal and surface defects.

 

Energy ‑ Energy savings are achieved with continuous casting because of the elimination of the energy consuming steps in the ingot process. These include fuel consumption in soaking pits and the electric power requirements for operating the primary rolling mills. Energy is also indirectly saved through the increased yield which requires the production of less raw steel for a comparable quantity of semi‑finished product. In addition to these savings, a practice in which hot continuously cast shapes are charged directly into a heating furnace in the finishing mills is receiving attention. Thus the sensible heat of the cast product is conserved.

 

Pollution ‑ Continuous casting reduces pollution through the elimination of ingot‑processing facilities such as soaking pits.

 

Costs ‑ Both capital and operating costs are reduced with the installation of continuous casting in comparison with ingot processing. Capital assets savings are attributable to the elimination of the additional equipment required for ingot processing. Operating cost savings are primarily the result f lower manpower requirements and higher yields.

 

 

Reference:

[1] The making, Shaping and Treating of Steel, 1985, US Steel.

[2] The making, Shaping and Treating of Steel, 2002, AISE Steel Foundation.