Chapter 1 △T J=K where AT/AX is the thermal gradient (i. e, temperature change) per unit thickness X and K is the thermal conductivity. The thermal conductivity is expressed as Btu ft/hr ft F in English units and as kcal m/s m K in the netric system. These values are used when calculating the heat transfer through a metal wall. Thermal Expansion Coefficient The thermal expansion coefficient represents a change in dimension per unit temperature change. Values are usually given as in /in.F or cm/cmC. Ther- mal expansion can be expressed as change in either volume, area, or length, with the last being the most frequently used. Thermal expansion data are usually reported to three significant figures and can be measured accurately by a number of means Charpy and Izod impact tests determine the amount of energy absorbed in deforming and fracturing a standard specimen by impact loading with a hamme The Charpy V-notch test is more commonly used for metals in this country, while the Izod impact test is used for plastics and metals in Europe A schematic of the impact testing machine is shown in Figure 1. 4 with the Charpy specimen shown above the machine e specimen is placed on the anvil and the pendulum hammer is released from its starting position, impacting the specimen and thereby caus- ng a fast fracture to take place. The fracture may be of either a brittle or ductile nature or a combination of both. a pointer attached to the hammer will show on a calibrated scale the foot-pounds of energy absorbed. A brittle material will absorb very little energy and the pointer will point to the right part of the scale near the zero mark. A reading below 25 ft-lb for steels is considered unacceptable and would not be used at the temperature of the bresee sail re le failure as the service temperature decreases. Body-centered steels, such as ferritic steels, tend to become embrittled as the operating temperature decreases. The impact tests can detect the transition temperature Defining the transition temperature poses somewhat of a problem since the transition in behavior is not sharp. Several proposals for defining the MARCEL DEKKER. INC 270 Madison Avenue. New York. New York 10016
8 Chapter 1 T J=K X where T/X is the thermal gradient (i.e., temperature change) per unit thickness X and K is the thermal conductivity. The thermal conductivity is expressed as Btu ft/hr ft2 F in English units and as kcal m/s m2 K in the metric system. These values are used when calculating the heat transfer through a metal wall. I. Thermal Expansion Coefficient The thermal expansion coefficient represents a change in dimension per unit temperature change. Values are usually given as in./in.F or cm/cmC. Thermal expansion can be expressed as change in either volume, area, or length, with the last being the most frequently used. Thermal expansion data are usually reported to three significant figures and can be measured accurately by a number of means. J. Impact Charpy and Izod impact tests determine the amount of energy absorbed in deforming and fracturing a standard specimen by impact loading with a hammer. The Charpy V-notch test is more commonly used for metals in this country, while the Izod impact test is used for plastics and metals in Europe. A schematic of the impact testing machine is shown in Figure 1.4 with the Charpy specimen shown above the machine. The specimen is placed on the anvil and the pendulum hammer is released from its starting position, impacting the specimen and thereby causing a fast fracture to take place. The fracture may be of either a brittle or ductile nature or a combination of both. A pointer attached to the hammer will show on a calibrated scale the foot-pounds of energy absorbed. A brittle material will absorb very little energy and the pointer will point to the right part of the scale near the zero mark. A reading below 25 ft-lb for steels is considered unacceptable and would not be used at the temperature of the test. These tests provide data to compare the relative ability of materials to resist brittle failure as the service temperature decreases. Body-centered steels, such as ferritic steels, tend to become embrittled as the operating temperature decreases. The impact tests can detect the transition temperature. Defining the transition temperature poses somewhat of a problem since the transition in behavior is not sharp. Several proposals for defining the
Physical and Mechanical Properties Scale Pointer End of swing Specimen FIGURE 1. 4 Schematic diagram of Charpy impact testing apparatus transition temperature have been made. Measures have be en proposed or used which define the temperature as that at which 1. An arbitrarily chosen energy level of, say, 30 ft-lb occurs 2. The impact energy is the average of the impact energy at high temperature and the impact energy at low temperature 3. The fracture surface contains a certain percentage of cleavage (brittle) and fibrous(ductile) appearance, approximately 50: 50 4. Some arbitrarily predetermined amount of strain occurs in the lat eral direction in the vicinity of the notch These tests are an indication of a metals toughness or ability to resist crack propagation. The impact test indicates at what temperature it is safe to use the particular material being tested. It does not provide data that can be used for design purposes. MARCEL DEKKER. INC 270 Madison Avenue. New York. New York 10016
Physical and Mechanical Properties 9 FIGURE 1.4 Schematic diagram of Charpy impact testing apparatus. transition temperature have been made. Measures have been proposed or used which define the temperature as that at which 1. An arbitrarily chosen energy level of, say, 30 ft-lb occurs. 2. The impact energy is the average of the impact energy at high temperature and the impact energy at low temperature. 3. The fracture surface contains a certain percentage of cleavage (brittle) and fibrous (ductile) appearance, approximately 50:50. 4. Some arbitrarily predetermined amount of strain occurs in the lateral direction in the vicinity of the notch. These tests are an indication of a metal’s toughness or ability to resist crack propagation. The impact test indicates at what temperature it is safe to use the particular material being tested. It does not provide data that can be used for design purposes
MARCEL DEKKER. INC 270 Madison Avenue. New York. New York 10016
2 Corrosion of metallic materials A wide variety of metals and alloys is available; these include a family of ferrous alloys and alloys of nonferrous materials as well as numerous"pure metals. Over the years these materials have been produced as needs arose in industry for materials to handle specific corrodents and/or to operate at As may be expected, no one material is completely corrosion resistant, although some come close. However, as the overall corrosion resistance improves, material cost increases. Because of this, the most corrosion-resis tant material is not always selected for the application. Compromises must be made. This can be done effectively by making judicious decisions Although other forms of attack must be considered in special circum- stances, uniform attack is one form most common confronting the user of metals and alloys. The rate of uniform attack is reported in various units. In the United States it is generally reported in inches penetration per year(ipy) and milligrams per square decimeter per day (mdd). Multiply the ipy value by 1000 to convert from ipy to mpy (i.e,0.I in. X 1000=100 mpy) Conversion of ipy to mdd or vice versa requires knowledge of the metal density. Conversion factors are given in Table 2.1. The subject of uniform corrosion will be discussed later Corrosion is the destructive attack of a metal by a chemical or elec- trochemical reaction. Deterioration by physical causes is not called corro. sion,but is described as erosion, galling, or wear. In some instances corro- sion may accompany physical deterioration and is described by such terms as erosion corrosion corrosive wear. or fretting corrosion MARCEL DEKKER. INC 270 Madison Avenue. New York. New York 10016
11 2 Corrosion of Metallic Materials A wide variety of metals and alloys is available; these include a family of ferrous alloys and alloys of nonferrous materials as well as numerous ‘‘pure’’ metals. Over the years these materials have been produced as needs arose in industry for materials to handle specific corrodents and/or to operate at elevated temperatures in the presence of corrodents. As may be expected, no one material is completely corrosion resistant, although some come close. However, as the overall corrosion resistance improves, material cost increases. Because of this, the most corrosion-resistant material is not always selected for the application. Compromises must be made. This can be done effectively by making judicious decisions. Although other forms of attack must be considered in special circumstances, uniform attack is one form most common confronting the user of metals and alloys. The rate of uniform attack is reported in various units. In the United States it is generally reported in inches penetration per year (ipy) and milligrams per square decimeter per day (mdd). Multiply the ipy value by 1000 to convert from ipy to mpy (i.e., 0.1 in. 1000 = 100 mpy). Conversion of ipy to mdd or vice versa requires knowledge of the metal density. Conversion factors are given in Table 2.1. The subject of uniform corrosion will be discussed later. Corrosion is the destructive attack of a metal by a chemical or electrochemical reaction. Deterioration by physical causes is not called corrosion, but is described as erosion, galling, or wear. In some instances corrosion may accompany physical deterioration and is described by such terms as erosion corrosion, corrosive wear, or fretting corrosion
12 Chapter 2 TABLE 2.1 Conversion Factors from Inches per Year(ipy) to milligrams per Square Decimeter per day(mdd) 0.00144 (g/cc) (×10-3) 696× density 890 Brass(red) 8.75 0.164 6100 8.47 0.170 6020 Columbium 5850 8.92 0.161 6210 Copper-nickel(70/30 895 0.161 6210 7.8 Duriron 11.35 0.826 10 Nickel 8.89 0.162 6180 Si ver 7300 Tantalum 16.6 0.0868 729 0.198 5070 Zinc 7.14 0.202 4970 0.223 Note: Multiply ipy by(696 x density) to obtain mdd. Multiply mdd by (0.00144/density to obtain ipy. Direct chemical corrosion is limited to unusual conditions involving highly aggressive environments or high temperature or both. Examples are metals in contact with strong acids or alkalies Electrochemical reaction is the result of electrical energy passing from a negative area to a positive area through an electrolyte medium. with iron surface itself, covered by porous rust(iron oxides), and positive electrodes are areas exposed to oxygen. The positive and negative electrode areas in- terchange and shift from place to place as the corrosion reaction proceeds The term Rusting applies to the corrosion of iron-based alloys with the formation of corrosion products consisting largely of hydrous ferric oxide Nonferrous metals and alloys corrode, but do not rust. All structural metals corrode to some extent in material environments Bronzes, brasses, stainless steels, zinc, and aluminum corrode so slowly MARCEL DEKKER. INC 270 Madison Avenue. New York. New York 10016
12 Chapter 2 TABLE 2.1 Conversion Factors from Inches per Year (ipy) to Milligrams per Square Decimeter per day (mdd) Metal Density (g/cc) 0.00144 density ( 103 ) 696 density Aluminum 2.72 0.529 1890 Brass (red) 8.75 0.164 6100 Brass (yellow) 8.47 0.170 5880 Cadmium 8.65 0.167 6020 Columbium 8.4 0.171 5850 Copper 8.92 0.161 6210 Copper-nickel (70/30) 8.95 0.161 6210 Iron 7.87 0.183 5480 Duriron 7.0 0.205 4870 Lead (chemical) 11.35 0.127 7900 Magnesium 1.74 0.826 1210 Nickel 8.89 0.162 6180 Monel 8.84 0.163 6140 Silver 10.50 0.137 7300 Tantalum 16.6 0.0868 11550 Titanium 4.54 0.317 3160 Tin 7.29 0.198 5070 Zinc 7.14 0.202 4970 Zirconium 6.45 0.223 4490 Note: Multiply ipy by (696 density) to obtain mdd. Multiply mdd by (0.00144/density) to obtain ipy. Direct chemical corrosion is limited to unusual conditions involving highly aggressive environments or high temperature or both. Examples are metals in contact with strong acids or alkalies. Electrochemical reaction is the result of electrical energy passing from a negative area to a positive area through an electrolyte medium. With iron or steel in aerated water, the negative electrodes are portions of the iron surface itself, covered by porous rust (iron oxides), and positive electrodes are areas exposed to oxygen. The positive and negative electrode areas interchange and shift from place to place as the corrosion reaction proceeds. The term Rusting applies to the corrosion of iron-based alloys with the formation of corrosion products consisting largely of hydrous ferric oxides. Nonferrous metals and alloys corrode, but do not rust. All structural metals corrode to some extent in material environments. Bronzes, brasses, stainless steels, zinc, and aluminum corrode so slowly