Gray cast iron

Gray cast iron is the most commonly used cast iron and is the least expensive. It is the easiest to cast and machine. The tensile strength of gray cast iron ranges from 155 to 400 N/mm (10 to 26 ton/in. ). The tensile modulus ranges from 70 to 140 kN/mm and the hardness from 130 to 300 DPN. 

Castings are designed to be loaded in compression because the compressive strength of gray iron is about three times that of its tensile strength. 

The recommended maximum design stress in tension is one-quarter the ultimate tensile strength (for cast irons a value up to 185 N/mm (12 tonf/ in. )). The fatigue strength is one-half the tensile strength. Notched 

Gray iron to BS1452 A Tensile strengtii, N/mm-, of casting with section thickness of  

Tabic 3.2. Typical Data Showing llie Effect of Strength on Gray Iron Castings [ 11 

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Gravure process Gray cast iron Gray iron... 

Most cemented-carbide tools are WC-based and have Co as the binder. Other carbide tool materials based on TiC having a Ni—Mo binder were developed primarily for high (>300 500 m/min) speed finish machining of steels and gray cast irons for automotive appHcations. 

M 20 steel, steel castings, austenitic or manga-nese steel, gray cast iron... 

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). 

Fig. 2. Tool wear mechanisms, (a) Crater wear on a cemented carbide tool produced during machining plain carbon steel, (b) Abrasive wear on the flank face of a cemented carbide tool produced during machining gray cast iron, (c) Built-up edge produced during low speed machining of a nickel-based alloy.

The allowable stress to be used for tliis gray-cast-iron material at its upper temperature limit of 232 C (450 F) is the same as diat shown in the 204 C (400 F) column. 

Temperature, op Carbon steel, carbon-molybdenum low-chromium (through 3 Cr Mo) 5Cr Mo through 9 Cr Mo Austenitic stainless steels, 18 Cr, 8 Ni 12 Cr 17 Cr 27 Cr 25 Cr, 20 Ni Monel 67 Ni, 30Cii 3V2 Nickel Aluminum Gray cast iron Bronze Brass 70Cii, 30 Ni Ni-Fe-Cr Ni-Cr-Fe Ductile iron... 

Graphitic Corrosion Graphitic corrosion usually involves gray cast iron in which metalhc iron is converted into corrosion products, leaving a residue of intact graphite mixed with iron-corrosion products and other insoluble constituents of cast iron. 

Gray iron is resistant to concentrated acids (nitric, sulfuric, phosphoric) as well as to some alkahne and caustic solutions. Caustic fusion pots are usually made from gray cast iron with low silicon content cast-iron valves, pumps, and piping are common in sulfuric acid plants. 

Another group of cast-iron alloys are called Ni-Resist, These materials are related to gray cast iron in that they have high carbon contents (3 percent), with fine graphite flakes distributed throughout the structure. Nickel contents range from 13.5 to 36 percent, and some have 6.5 percent Cu. 

Figure 2.19 Gray cast iron elbow showing thread wastage.

Figure 3.32 Large tubercles on gray cast iron pump housing.

Sample Specifications Pearlitic gray cast iron... 

Graphitic corrosion has two distinct features that are useful in distinguishing it from other forms of corrosion. First, it affects an unusually limited number of metals the only metals commonly affected are gray cast iron and nodular cast iron. Second, metal that has experienced graphitic corrosion may retain its original appearance and dimensions. Consequently, graphitic corrosion frequently escapes detection. 

Figure 17.1 Flakes of graphite embedded in a matrix of iron (gray cast iron).

Sampie Specifications 10 in. (25 cm) outside diameter, gray cast iron pipe... 

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