Volume 01 - Properties and Selection Irons, Steels, and High-Performance Alloys Episode 2 docx

M5003 (c) 517 75 345 50 187-241 3 M5503 (d) 517 75 379 55 187-241 3 M7002 (d) 621 90 483 70 229-269 2 M8501 (d) 724 105 586 85 269-302 1 (a) Minimum in 50 mm (2 in.). (b) Annealed. (c) Air quenched and tempered. (d) Liquid quenched and tempered The different microstructures of malleable irons are determined and controlled by variations in heat treatment and/or composition. Table 3, for example, lists various types of malleable irons used in automotive applications according to heat treatment and microstructure. The range of compositions for a ferritic or pearlitic microstructure is given in Table 1. Table 3 Grades of malleable iron specified according to hardness per ASTM A 602 and SAE J158 See Table 2 for mechanical properties. Grade Specified hardness, HB Heat treatment Microstructure Typical applications M 3210 156 max Annealed Ferritic For low-stress parts requiring good machinability: steering-gear housings, carriers, and mounting brackets M 4504 163-217 Air quenched and tempered Ferrite and tempered pearlite (a) Compressor crankshafts and hubs M 5003 187-241 Air quenched and tempered Ferrite and tempered pearlite (a) For selective hardening: planet carriers, transmission gears, and differential cases M 5503 187-241 Liquid quenched and tempered Tempered martensite For machinability and improved response to induction hardening M 7002 229-269 Liquid quenched and tempered Tempered martensite For high-strength parts: connecting rods and universal- joint yokes M 269-302 Liquid quenched Tempered For high strength plus good wear resistance: certain 8501 and tempered martensite gears (a) May be all tempered martensite for some applications Because the mechanical properties of malleable iron are dominated by matrix microstructure, the mechanical properties may relate quite well to the relative hardness levels of different matrix microstructures.This general effect of microstructure on malleable irons is similar to that of many other steels and irons. The softer ferritic matrix provides maximum ductility with lower strength, while increasing the amount of pearlite increases hardness and strength but decreases ductility. Martensite provides further increases in hardness and strength but with additional decreases in ductility. The mechanical properties of pearlitic and martensitic malleable irons are closely related to hardness, as discussed in "Mechanical Properties" in the section "Pearlitic and Martensitic Malleable Irons" in this article. Therefore, grades of malleable irons are dependably specified by hardness and microstructure in ASTM A 602 and SAE J158 (Table 3). Malleable irons are also classified according to microstructure and minimum tensile properties (Table 4). Table 4 Grades of malleable iron specified according to minimum tensile properties See Table 2 for hardness. Specification No. Class or grade (a) ASTM metric equivalent class (b) Microstructure Typical applications Ferritic 32510 22010 ASTM A 47 (c) , ANSI G48.1, FED QQ-1- 666c 35018 24018 Temper carbon and ferrite General engineering service at normal and elevated temperatures for good machinability and excellent shock resistance ASTM A 338 (d) . . . Temper carbon and ferrite Flanges, pipe fittings, and valve parts for railroad, marine, and other heavy-duty service to 345 °C (650 °F) ASTM A 197, ANSI G49.1 (e) . . . Free of primary graphite Pipe fittings and valve parts for pressure service Pearlitic and martensitic 40010 280M10 45008 310M8 ASTM A 220 (c) , ANSI G48.2, MIL-I-11444B 45006 310M6 Temper carbon in necessary matrix without primary cementite or graphite General engineering service at normal and elevated temperatures. Dimensional tolerance range for castings is stipulated. 50005 340M5 60004 410M4 70003 480M3 80002 560M2 90001 620M1 (a) The first three digits of the grade designation indicate the minimum yield strength (× 100 psi), and the last two digits indicate minimum elongation (%). (b) ASTM specifications designated by footnote (c) provide a metric equivalent class where the first three digits indicate minimum yield strength in MPa. (c) Specifications with a suffix "M" utilize the metric equivalent class designation. (d) Zinc-coated malleable iron specified per ASTM A 47. (e) Cupola ferritic malleable iron Table 2 summarizes some of the mechanical properties of the malleable irons listed in Tables 3 and 4. Additional information on the properties and heat treatment of ferritic, pearlitic, and martensitic malleable irons is provided in the following sections. Ferritic Malleable Iron The microstructure of ferritic malleable iron is shown in Fig. 2. A satisfactory structure consists of temper carbon in a matrix of ferrite. There should be no flake graphite and essentially no combined carbon in ferritic malleable iron. Because ferritic malleable iron consists of only ferrite and temper carbon, the properties of ferritic malleable castings depend on the quantity, size, shape, and distribution of temper carbon and on the composition of the ferrite. Fig. 2 Structure of annealed ferritic malleable iron showing temper carbon in ferrite. 100× Heat Treatment. Ferritic malleable iron requires a two-stage annealing cycle. The first stage converts primary carbides to temper carbon, and the second stage converts the carbon dissolved in austenite at the first-stage annealing temperature to temper carbon and ferrite. After first-stage annealing, the castings are cooled as rapidly as practical to 740 to 760 °C (1360 to 1400 °F) in preparation for second-stage annealing. The fast cooling step requires 1 to 6 h, depending on the equipment used. Castings are then cooled slowly at a rate of about 3 to 10 °C (5 to 20 °F) per hour. During cooling, the carbon dissolved in the austenite is converted to graphite and deposited on the existing particles of temper carbon. This results in a fully ferritic matrix. Composites. Fully annealed ferritic malleable iron castings contain 2.00 to 2.70% graphite carbon by weight, which is equivalent to about 6 to 8% by volume. Because the graphite carbon contributes nothing to the strength of the castings, those with the lesser amount of graphite are somewhat stronger and more ductile than those containing the greater amount (assuming equal size and distribution of graphite particles). Elements such as silicon and manganese in solid solution in the ferritic matrix contribute to the strength and reduce the elongation of the ferrite. Therefore, by varying base metal composition, slightly different strength levels can be obtained in a fully annealed ferritic product. The mechanical properties that are most important for design purposes are tensile strength, yield strength, modulus of elasticity, fatigue strength, and impact strength. Hardness can be considered an approximate indicator that the ferritizing anneal was complete. The hardness of ferritic malleable iron almost always ranges from 110 to 156 HB and is influenced by the total carbon and silicon contents. The tensile properties of ferritic malleable iron are usually measured on unmachined test bars. These properties are listed in Table 2. The fatigue limit of unnotched ferritic malleable iron is about 50 or 60% of the tensile strength (see the two unnotched plots in Fig. 3). Figure 3 also plots the fatigue properties with notched specimens. Notch radius generally has little effect on fatigue strength, but fatigue strength decreases with increasing notch depth (Fig. 4). Fig. 3 Fatigue properties of two ferritic malleable irons (25 mm, or 1 in., diam bars) from bending fatigue tests on notched and unnotched specimens. The unnotched fatigue limit is about 200 MPa (29 ksi) for the iron with a 342 MPa (50 ksi) tensile strength and about 185 MPa (27 ksi) for the iron with a 293 MPa (42.5 ksi) tensile strength. Source: Ref 5 Fig. 4 Effects of notch radius and notch depth on the fatigue strength of ferritic malleable iron The modulus of elasticity in tension is about 170 GPa (25 × 10 6 psi). The modulus in compression ranges from 150 to 170 GPa (22 × 10 6 to 25 × 10 6 psi); in torsion, from 65 to 75 GPa (9.5 × 10 6 to 11 × 10 6 psi). Fracture Toughness. Because brittle fractures are most likely to occur at high strain rates, at low temperatures, and with a high restraint on metal deformation, notch tests such as the Charpy V-notch test are conducted over a range of test temperatures to establish the toughness behavior and the temperature range of transition from ductile to a brittle fracture. Figure 5 illustrates the behavior of ferritic malleable iron and several types of pearlitic malleable iron in the Charpy V-notch test. This shows that ferritic malleable iron has a higher upper shelf energy and a lower transition temperature to a brittle fracture than pearlitic malleable iron. Additional information on the fracture toughness of malleable irons is available in the section "Pearlitic and Martensitic Malleable Iron" in this article. Fig. 5 Charpy V-notch transition curves for ferritic and pearlitic malleable irons. Source: Ref 1 Elevated-Temperature Properties. Short-term, high-temperature tensile properties typically show no significant change to 370 °C (700 °F). The short-term tensile properties of two ferritic malleable irons are shown in Fig. 6. Sustained-load stress-rupture data from 425 to 650 °C (800 to 1200 °F) are given in Fig. 7. Fig. 6 Short-term high-temperature tensile properties of two ferritic malleable irons. (a) Tensile strength. (b) Elongation. Source: Ref 5 Composition, % Group Grade C Si Mn P S Cr A-1 35018 2.21 1.14 0.35 0.161 0.081 . . . B-1 32510 2.50 1.32 0.43 0.024 0.159 0.029 E-1 35018 2.16 1.17 0.38 0.137 0.095 0.017 Fig. 7 Stress- rupture plot for various grades of ferritic malleable iron. The solid lines are curves determined by the method of least squares from the exis ting data and are least squares fit to the data. The dashed lines define the 90% symmetrical tolerance interval. The lower dashed curve defines time and load for 95% survivors, and the upper dashed curve is the boundary for 5% survivors. Normal distribution is assumed. Source: Ref 6 The corrosion resistance of ferritic malleable iron is increased by the addition of copper, usually about 1%, in certain applications, for example, conveyor buckets, bridge castings, pipe fittings, railroad switch stands, and freight-car hardware. One important use for copper-bearing ferritic malleable iron is chain links. Ferritic malleable iron can be galvanized to provide added protection. The effects of copper on the corrosion resistance of ferrous alloys are documented in Corrosion, Volume 13 of ASM Handbook, formerly 9th Edition Metals Handbook. Welding and Brazing. Welding of ferritic malleable iron almost always produces brittle white iron in the weld zone and the portion of the heat-affected zone immediately adjacent to the weld zone. During welding, temper carbon is dissolved, and upon cooling it is reprecipitated as carbide rather than graphite. In some cases, welding with a cast iron electrode may produce a brittle gray iron weld zone. The loss of ductility due to welding may not be serious in some applications. However, welding is usually not recommended unless the castings are subsequently annealed to convert the carbide to temper carbon and ferrite. Ferritic malleable iron can be fusion welded to steel without subsequent annealing if a completely decarburized zone as deep as the normal heat- affected zone is produced at the faying surface of the malleable iron part before welding. Silver brazing and tin- lead soldering can be satisfactorily used. Pearlitic and Martensitic Malleable Iron Pearlitic and martensitic-pearlitic malleable irons can be produced with a wide variety of mechanical properties, depending on heat treatment, alloying, and melting practices. The lower-strength pearlitic malleable irons are often produced by air cooling the casting after the first-stage anneal, while the higher-strength (pearlitic- martensitic) malleable irons are made by liquid quenching after the first-stage anneal. These two methods are discussed in the sections "Heat Treatment for Pearlitic Malleable Irons" and "Heat Treatment for Pearlitic- Martensitic Malleable Irons" in this article. Given suitable heat treatment facilities, air cooling or liquid quenching after the first-stage anneal is generally the most economical heat treatment for producing pearlitic or martensitic-pearlitic malleable irons, respectively. Otherwise, ferritic iron produced from two-stage annealing is reheated to the austenite temperature and then quenched. This method is discussed in the section "Rehardened-and-Tempered Malleable Iron" in this article. Finally, the lower-strength pearlitic malleable irons can also be produced by alloying and a two-stage annealing process. The last method involves alloying during the melting process so that the carbides dissolved in the austenite do not decompose during cooling from the first-stage annealing temperature. Heat Treatment for Pearlitic Malleable Irons. In the production of pearlitic malleable iron, the first-stage anneal is identical to that used for ferritic malleable iron. After this, however, the process changes. Some foundries then slowly cool the castings to about 870 °C (1600 °F). During cooling, the combined carbon content of the austenite is reduced to about 0.75%, and the castings are then air cooled. Air cooling is accelerated by an air blast to avoid the formation of ferrite envelopes around the temper carbon particles (bull's- eye structure) and to produce a fine pearlitic matrix (Fig. 8). The castings are then tempered to specification, or they are reheated to reaustenitize at about 870 °C (1600 °F), oil quenched, and tempered to specification. Large foundries usually eliminate the reaustenitizing step and quench the castings in oil directly from the first-stage annealing furnace after stabilizing the temperature at 845 to 870 °C (1550 to 1600 °F). Fig. 8 Structure of air- cooled pearlitic malleable iron. (a) Slowly air cooled. 400×. (b) Cooled in an air blast. 400× The rate of cooling after first-stage annealing is important in the formation of a uniform pearlitic matrix in the air-cooled casting, because slow rates permit partial decomposition of carbon in the immediate vicinity of the temper carbon nodules, which results in the formation of films of ferrite around the temper carbon (bull's-eye structure). When the extent of these films becomes excessive, a carbon gradient is developed in the matrix. Air cooling is usually done at a rate not less than about 80 °C (150 °F) per minute. Air-quenched malleable iron castings have hardnesses ranging from 269 to 321 HB, depending on casting size and cooling rate. Such castings can be tempered immediately after air cooling to obtain pearlitic malleable iron with a hardness of 241 HB or less. Heat Treatment for Pearlitic-Martensitic Malleable Irons. High-strength malleable iron castings of uniformly high quality are usually produced by liquid quenching and tempering. The most economical procedure is direct quenching after first-stage annealing. In this procedure, the castings are cooled in the furnace to the quenching temperature of 845 to 870 °C (1550 to 1600 °F) and held for 15 to 30 min to homogenize the matrix. The castings are then quenched in agitated oil to develop a matrix microstructure of martensite having a hardness of 415 to 601 HB. Finally, the castings are tempered at an appropriate temperature between 590 and 725 °C (1100 and 1340 °F) to develop the specified mechanical properties. The final microstructure consists of tempered martensite plus temper carbon, as shown in Fig. 9. In heavy sections, higher-temperature transformation products such as fine pearlite are usually present. Fig. 9 Structure of oil-quenched and tempered martensitic malleable iron. (a) 163 HB. 500×. (b) 179 HB. 500×. (c) 207 HB. 500×. (d) 229 HB. 500× Some foundries produce high-strength malleable iron by an alternative procedure in which the castings are forced-air cooled after first-stage annealing, retaining about 0.75% C as pearlite. The castings are then reheated at 840 to 870 °C (1545 to 1600 °F) for 15 to 30 min, followed by quenching and tempering as above for the direct-quench process. Rehardened-and-tempered malleable iron can also be produced from fully annealed ferritic malleable iron with a slight variation in the heat treatment used for arrested-annealed (air-quenched) malleable. The matrix of fully annealed ferritic malleable iron is essentially carbon free, but can be recarburized by heating at 840 to 870 °C (1545 to 1600 °F) for 1 h. In general, the combined carbon content of the matrix produced by this procedure is slightly lower than that of arrested-annealed pearlitic malleable iron, and the final tempering temperatures required for the development of specific hardnesses are lower. Rehardened malleable iron made from ferritic malleable may not be capable of meeting certain specifications. Tempering times of 2 h or more after either air cooling or liquid quenching are needed for uniformity. In general, the control of final hardness of the castings is precise, with process limitations approximately the same as those encountered in the heat treatment of medium- or high-carbon steels. This is particularly true when specifications require hardnesses of 241 to 321 HB where control limits of ±0.2 mm Brinell diameter can be maintained with ease. At lower hardnesses, a wider process control limit is required because of certain unique characteristics of the pearlitic malleable iron microstructure. The mechanical properties of pearlitic and martensitic malleable iron vary in a substantially linear relationship with Brinell hardness (Fig. 10 and 11). In the low-hardness ranges, below about 207 HB, the properties of air-quenched and tempered pearlitic malleable are essentially the same as those of oil-quenched tempered martensitic malleable. This is because attaining the low hardnesses requires considerable coarsening of the matrix carbides and partial second-stage graphitization. Either an air-quenched pearlitic structure or an oil-quenched martensitic structure can be coarsened and decarburized to meet this hardness requirement. Fig. 10 Relationships of tensile properties to Brinell h ardness for pearlitic malleable irons from two foundries. The mechanical properties of these irons vary in a substantially linear relationship with Brinell hardness, and in the low-hardness ranges (below about 207 HB), the properties of air-quenched and te mpered material are essentially the same as those produced by oil quenching and tempering. [...]... Martensitic nickel-chromium iron 2. 5-3 .7 1.3 0.30 0.15 0.8 2. 7-5 .0 1. 1-4 .0 1.0 M, A Martensitic nickel, high-chromium iron 2. 5-3 .6 1.3 0.10 0.15 1. 0 -2 .2 5-7 7-1 1 1.0 M, A Martensitic chromium-molybdenum iron 2. 0-3 .6 0. 5-1 .5 0.10 0.06 1.0 1.5 1 1 -2 3 0. 5-3 .5 1 .2 M, A High-chromium iron 2. 3-3 .0 0. 5-1 .5 0.10 0.06 1.0 1.5 2 3 -2 8 1.5 1 .2 M High-silicon iron(f) 0. 4-1 .1 1.5 0.15 0.15 1 4-1 7 5.0 1.0 0.5 F High-chromium... Nickel-chromium-silicon iron(j) 1. 8 -2 .6 0. 4-1 .0 0.10 0.10 5. 0-6 .0 1 3-4 3 1. 8-5 .5 1.0 10.0 A High-aluminum iron 1. 3 -2 .0 0. 4-1 .0 0.15 0.15 1. 3-6 .0 2 0 -2 5 Al F Medium-silicon ductile iron 2. 8-3 .8 0. 2- 0 .6 0.08 0. 12 2. 5-6 .0 1.5 2. 0 F Nickel-chromium ductile iron(h) 3.0 0. 7 -2 .4 0.08 0. 12 1.7 5-5 .5 1 8-3 6 1.7 5-3 .5 1.0 A Corrosion-resistant irons Heat-resistant gray irons Heat-resistant ductile irons Heat-resistant white... iron 1. 2- 4 .0 0. 3-1 .5 0.15 0.15 0. 5-3 .0 5.0 1 2- 3 5 4.0 3.0 M, A Nickel-chromium gray iron(g) 3.0 0. 5-1 .5 0.08 0. 12 1. 0 -2 .8 13. 5-3 6 1. 5-6 .0 1.0 7.5 A Nickel-chromium ductile iron(h) 3.0 0. 7-4 .5 0.08 0. 12 1. 0-3 .0 1 8-3 6 1. 0-5 .5 1.0 A Medium-silicon iron(i) 1. 6 -2 .5 0. 4-0 .8 0.30 0.10 4. 0-7 .0 F Nickel-chromium iron(g) 1. 8-3 .0 0. 4-1 .5 0.15 0.15 1. 0 -2 .75 13. 5-3 6 1. 8-6 .0 1.0 7.5 A Nickel-chromium-silicon... Group C -2 2.65 1.35 0.41 0.15 0 .018 0.0 020 B Group W-1 2. 45 1.38 0.41 0. 12 0.04 0.0 32 Pearlitic (low carbon-high phosphorus) Pearlitic (high carbon-low phosphorus) Alloyed pearlitic (low carbon-high phosphorus) Group E-3 2. 21 1.13 0.88 0.110 0. 122 0. 021 0.47Mo,1.03Cu Group L-1 2. 16 1.18 0. 72 0. 120 0. 128 0.34Mo,0.83 Ni Group L -2 2.16 1.18 0.80 0. 123 0. 128 0.40Mo,0. 62 Ni Group L-3 2. 32 1.14 0. 82 0.117... for 25 mm (1 in.) wide compact-tension specimens Table 5 Fracture toughness of malleable irons Test temperature Yield strength KIc °C Malleable iron grade °F MPa ksi MPa 24 75 23 0 33 44 40 -1 9 -3 24 0 35 42 38 m ksi Ferritic M 321 0 in -5 9 -7 4 25 0 36 44 40 24 75 360 52 55 50 -1 9 -2 380 55 48 44 -5 7 -7 0 390 57 30 27 24 75 410 60 45 41 -1 9 -3 440 64 52 47 -5 8 -7 3 455 66 30 27 24 75 520 75 54 49 -1 9 -3 550... standard martensitic white cast irons Certain specific compositions of alloys II-B, II-C, II-D, and II-E are covered by U.S Patent 3,410,6 82 Class Type Designation Composition, wt % (a) TC(b) Mn P S Si Cr Ni Mo Cu I A Ni-Cr-HC 3. 0-3 .6 1.3 0.30 0.15 0.8 1. 4-4 .0 3. 3-5 .0 1.0 I B Ni-Cr-LC 2. 5-3 .0 1.3 0.30 0.15 0.8 1. 4-4 .0 3. 3-5 .0 1.0 I C Ni-Cr-GB 2. 9-3 .7 1.3 0.30 0.15 0.8 1. 1-1 .5 2. 7-4 .0 1.0 I D Ni-Hi... types of alloys used in specific kinds of applications Table 1 Ranges of alloy content for various types of alloy cast irons Description Composition, wt %(a) TC(b) Mn P Matrix structure, as-cast(c) S Si Ni Cr Mo Cu Abrasion-resistant white irons Low-carbon white iron(d) 2. 2- 2 .8 0. 2- 0 .6 0.15 0.15 1. 0-1 .6 1.5 1.0 0.5 (e) CP High-carbon, low-silicon white iron 2. 8-3 .6 0. 3 -2 .0 0.30 0.15 0. 3-1 .0 2. 5 3.0... gray and ductile irons are dealt with in the articles "Gray Iron" and "Ductile Iron" in this Volume This article discusses abrasion-resistant chilled and white irons, high-alloy corrosion-resistant irons, and medium-alloy and high-alloy heat-resistant gray and ductile irons Table 1 lists approximate ranges of alloy content for various types of alloy cast irons covered in this article Individual alloys. .. °F) for 6 h and then slow cooled to 700 °C ( 129 0 °F) before reheating Sustained-load stress-rupture data for eight grades of pearlitic malleable iron are shown in Fig 14 Results of high-temperature Charpy V-notch tests showing the effect of hardness on impact energy are given in Fig 15 Material Composition, % C Si Mn S P Cr Others Group E -2 2 .27 1.15 0.89 0.098 0.135 0 .019 Group G -2 2 .29 1 .01 0.75 0.086... 1. 4-4 .0 3. 3-5 .0 1.0 I B Ni-Cr-LC 2. 5-3 .0 1.3 0.30 0.15 0.8 1. 4-4 .0 3. 3-5 .0 1.0 I C Ni-Cr-GB 2. 9-3 .7 1.3 0.30 0.15 0.8 1. 1-1 .5 2. 7-4 .0 1.0 I D Ni-Hi Cr 2. 5-3 .6 1.3 0.10 0.15 1. 0 -2 .2 7-1 1 5-7 1.0 II A 12% Cr 2. 4 -2 .8 0. 5-1 .5 0.10 0.06 1.0 1 1-1 4 0.5 0. 5-1 .0 1 .2 . Ferritic 24 75 23 0 33 44 40 M 321 0 -1 9 -3 24 0 35 42 38 -5 9 -7 4 25 0 36 44 40 Pearlitic 24 75 360 52 55 50 -1 9 -2 380 55 48 44 M4504 (normalized) -5 7 -7 0 390 57 30 27 24 75 410. 517 75 345 50 18 7 -2 41 3 M5503 (d) 517 75 379 55 18 7 -2 41 3 M70 02 (d) 621 90 483 70 22 9 -2 69 2 M8 501 (d) 724 105 586 85 26 9-3 02 1 (a) Minimum in 50 mm (2 in.). (b) Annealed 410 60 45 41 -1 9 -3 440 64 52 47 M5503 (quenched and tempered) -5 8 -7 3 455 66 30 27 24 75 520 75 54 49 -1 9 -3 550 80 38 35 M70 02 (quenched and tempered) -5 8 -7 2 570 83 40 36 Source: