Ladle Steelmaking Ladle Steelmaking Ladle SteelmakingLadle Steelmaking. The increasing need to produce quality products that meet much tighter chemical and physical
specifications has led to major changes in steelmaking practices during the last two decades. These changes have centered
on modifications to liquid steel within the ladle; therefore, this area of technology is known as ladle steelmaking.
To illustrate the critical nature of correct chemistry, aluminum-killed steels for deep-drawing operations require dissolved
aluminum levels that range between 0.03 and 0.04% (Al)Fe. The aluminum precipitates with dissolved nitrogen as
aluminum nitride during subsequent batch-annealing operations. This precipitation controls grain growth and leads to
steel with a fine grain structure and good deep-drawing qualities. Higher or lower levels of dissolved aluminum lead to
poor performance indices (Fig. 7).
Even tighter specifications were required for high-strength low-alloy steels, which were introduced to compensate for
weight reductions (that is, thinner gages) on automobile parts during the energy crises of the 1970s. Specifications called
for dissolved niobium levels of 0.03%, a difficult target without close control of steel deoxidation procedures.
The production of interstitial-free steels for deep drawing (which are described in the article "High-Strength Structural
and High-Strength Low-Alloy Steels" in this Volume) require carbon and nitrogen levels less than 50 ppm and controlled
additions of titanium and/or niobium to scavenge carbon and nitrogen. To meet such stringent demands, secondary
steelmaking processes, focusing on the teeming ladle, have been developed. Of these, the ladle furnace is used for melt
reheating and temperature control. The Ruhrstahl Hereaus (RH) degasser, or tank degasser, is used to reduce dissolved
(C,O,H,N)Fe levels. A third type of ladle station provides strong stir facilities by using argon and porous plugs set in the
base of each teeming ladle, slag rake-off equipment, and wire feeding that allows precise additions of alloying elements,
such as aluminum.
|