Rimmed steels

Fluoridation of potable water suppHes for the prevention of dental caries is one of the principal uses for sodium fluoride (see Water, municipal WATER treatment). Use rate for this appHcation is on the order of 0.7 to 1.0 mg/L of water as fluoride or 1.5 to 2.2 mg/L as NaF (2). NaF is also appHed topically to teeth as a 2% solution (see Dentifrices). Other uses are as a flux for deoxidiziag (degassiag) rimmed steel (qv), and ia the resmelting of aluminum. NaF is also used ia the manufacture of vitreous enamels, ia pickling stainless steel, ia wood preservation compounds, caseia glues, ia the manufacture of coated papers, ia heat-treating salts, and as a component of laundry sours. 

Low-carbon plate and sheet are made in three qualities fully killed with silicon and aluminum, semikiUed (or balanced), and rimmed steel. Fully killed steels are used for pressure vessels. Most general-purpose structural mild steels are semikiUed steels. Rimming steels have minimum amounts of deoxidation and are used mainly as thin sheet for consumer applications. 

These steels account for over 90% of all steel production, There are numerous varieties, depending upon carbon content and method of production. In one classification, there are killed steels, semikilled steels, rimmed steels, and capped steels, These are described in considerable detail under Iron Metals, Alloys, and Steels. 

Deoxidation Practice. As far as deoxidation is concerned, carbon steel may be divided into three categories rimming steel, killed and semikilled steel. 

Rimming steel is often used for furnace-welded pipe. The low carbon skin of skelp rolledout from a rimmed ingot is particularly good for pressure welding and the finished pipe has good corrosion resistance on both inside and outside surfaces. Seamless pipe made from rimming steel is, however, only acceptable for non-corrosive service. 

Germany DIN 1626 Blatt 3 DIN 17100 St 34-2 KUIed or rimming steel any process Double-side fusion weld or any type of pressure weld (including butt weld). Not required... 

Rimming steel is not acceptable for seamless or fusion welded pipe. 

Figure 10.24 Cross-sections of hot-dip zinc coatings a) on rimming steel (a similar coating is obtained on Al-kiUed steel) and b) on Si-kUled steel [10.40],...

Table 2 lists n values for several materials [1]. Typically, the n values for most metals vary between 0.1 and 0.5. The n values of aluminum alloy sheets decrease sharply with an increase in the tensile strain and are lower than those of steel sheets. The n value of commercial HSLA steels decreases with increasing strength and its low n value makes it less formable than mild steel [38]. There are different strain hardening behaviors for mild steels and high-strength steels. The strain distribution ability of steels increases with the increase in overall n value. The peak n value at a low strain level increases the strain distribution ability of the steel. Aging of rimmed steels causes the n value to decrease with time. Additionally, excessive temper rolling beyond that required to eliminate YPE (Cv) will also reduce the n value. 

A drawback with rimmed steel is the tendency to central segregations... 

Figure 8.25 Rimmed steel ingot, cast without a preceding killing of the steel.

Rimmed steel products are rarely available nowadays. Because of the tendency to form central segregations (concentration differencies) in this type of ingot, and due to the dominance of continuous casting, killed steel is used instead. 

Fig. 9.6 Cross section of a rimmed steel ingot showing carbon monoxide blowholes...

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