Cast iron graphite

The selective corrosion of cast iron (graphitization), the preferential corrosion of the steel welding (grooving corrosion), sensitization and knife line attack of welded stainless steels are typical examples of corrosion influenced by metallurgical parameters. 

Groszek, A.J., Preferential Adsorption of Compounds with Long Methylene Chains on Cast Iron, Graphite, Boron Nitride and Molybdenum Disulfide, ASLE Trans., 9, 67, (1996). 

Cast iron corrodes because of the exposure of graphite content of cast iron (graphitic corrosion), which is cathodic to both low alloy and mild steels. The trim of a valve must be cathodic to the valve body to avoid pitting attack. Thus in aggressive media valve bodies of steel are preferred to cast iron bodies. Steel bolts and nuts coupled to underground mild steel pipes or a weld rod used for steel plates on the hull of a ship should always be of a low nickel, low chromium steel, or from a similar composition to that of the steel pipe (8). 

Impressed-current CP uses an outside power supply such as a rectifier to control the voltage between the pipe and an anode (cast iron, graphite, platinum clad, mixed metal oxide) in such a manner that the pipe becomes the cathode in the circuit and corrosion is mitigated. 

Fig. 6.42. Two-phase microstructure of grey cast iron. Graphite grains are embedded in the hght ferritic phase...

Dies typically cast iron, graphite or refractory material. 

However, since the current flow is not dependent on the favorable potential difference between the electrode and the structure to be protected, more noble materials can be selected for the anode. These materials include high-silicon cast iron, graphite and even more noble materials such as platinized titanium or platinized niobium. These metals corrode or are consumed very slowly, less than 1 lb. per amp year. 

One production line of a paper mill consists according the size and the quality of the produced paper sometimes from more than 50 steam drums to dry and flatten the produced paper. These drums (cylinders with flat bottoms, see figure 1) will be used with a steam pressure up to 500 kPa (5 bar) and additionally with a rotation speed up 1200 m.min the material is mainly grey cast iron (with lamellar graphite). The diameters can reach up to 2.2 m and the cylindrical lengths up to 10 m. For the specific flattening drums the cyhndrical diameters can be up to 5 m and more. 

Alloys with other useful properties can be obtained by using yttrium as an additive. The metal can be used as a deoxidizer for vanadium and other nonferrous metals. The metal has a low cross section for nuclear capture. 90Y, one of the isotopes of yttrium, exists in equilibrium with its parent 90Sr, a product of nuclear explosions. Yttrium has been considered for use as a nodulizer for producing nodular cast iron, in which the graphite forms compact nodules instead of the usual flakes. Such iron has increased ductility. 

In general, siUca has proved to be a good material of constmetion for the burner. Cast iron, steel, or graphite was sometimes used. Gaseous HCl produced by this method is very pure and can be used to manufacture pure hydrochloric acid by the adiabatic absorption process (33) or falling film absorption process (34). 

An ahoy of titanium containing 40—50% Ti and 45—50% Si is used as an additive in cast iron to shorten the graphite flakes. The effect is to provide a smooth casting surface. The resulting casting is then used to produce glass botde molds. 

In metallurgical practice, sodium uses include preparation of powdered metals removal of antimony, tin, and sulfur from lead modification of the stmcture of siHcon—aluminum alloys appHcation of diffusion alloy coatings to substrate metals (162,163) cleaning and desulfurizing alloy steels via NaH (164) nodularization of graphite in cast iron deoxidation of molten metals heat treatment and the coating of steel using aluminum or zinc. 

A second, more recently developed use for strontium metal is as an inoculant in ductile iron castings. Inoculants provide nuclei upon which graphite forms during the sohdification of cast iron, thus preventing the formation of white cast iron. Elkem Metals Company has commercialized a range of fine-sized foundry inoculants for iron castings. These inoculants, called superseed, are ferrosiUcon alloys containing 50 or 75% Si, 0.8% Sr. Most of the balance is iron. 

Tellurium also improves the properties of electrical steels by aiding in the magnetic anisotropy, malleable cast iron (77), and spheroidal (graphitic) cast irons (see also Metal surface TiiEATiffiNTs). 

Antimony may be added to copper-base alloys such as naval brass. Admiralty Metal, and leaded Muntz metal in amounts of 0.02—0.10% to prevent dezincification. Additions of antimony to ductile iron in an amount of 50 ppm, preferably with some cerium, can make the graphite fliUy nodular to the center of thick castings and when added to gray cast iron in the amount of 0.05%, antimony acts as a powerflil carbide stabilizer with an improvement in both the wear resistance and thermal cycling properties (26) (see Carbides). 

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