Continuous casting of thin slabs

In traditional continuous casting for flat products, slab thickness ranges from 130 to 300 mm.

More recent techniques make it possible to continuously cast flat semi-finished products of thinner thickness. The following classification can be provisionally proposed:

• thin slabs: thickness 35 to 80 mm ;

• strips: thickness 20 to 35 mm ;

• thin strips: thickness 1.5 to 20 mm ;

• very thin strips: thickness less than 1.5 mm.

The main focus of this article is on the casting of thin slabs (35 to 80 mm), where considerable progress has been made in recent years, leading to the emergence of specific technologies that are now part of the industrial domain. The casting of strips (20 to 35 mm) is also covered, but to a lesser extent, where progress has been slower. On the other hand, thin and very thin strips call for quite different techniques, not covered here.

It should be noted that all continuous casting technologies leading to thin semi-finished products, and therefore closer to the final product, are called NNSCC (Near Net Shape Continuous Casting).

To obtain finished product coil weights in line with current commercial practice (20 to 28 t), thin slabs necessarily have a long length (40 to 50 m). Such slabs are difficult to handle, store and heat. That's why we plan to roll them in-line (direct rolling), after heating and homogenization.

A hot-rolled strip production plant therefore consists of three separate parts, arranged in line: the thin-slab continuous-casting machine, the furnace and the rolling mill.

This article is mainly devoted to continuous casting, with a brief mention of the furnace and rolling mill.

The main advantage of thin slabs is that they are much thinner, making continuous casting simpler and the rolling mill much smaller. In addition, in-line rolling, imposed by the slab length, is a source of appreciable advantages. The result is :

• lower investments in continuous casting and rolling mills, paving the way for competitive mini-factories for flat products;

• a lower cost price, mainly due to lower energy consumption, greater automation, reduced manpower, lower maintenance costs, a shorter production cycle, the absence of intermediate stocks, and lower overheads.

It is assumed that traditional continuous casting is well known (see, in this treatise, articles Continuous casting of steel: general information, physical and metallurgical data, etc.)....