(a) Brinell hardness test. In this test, a hardened steel ball is pressed slowly by a known force against the surface of the metal to be tested. The diameter of the dent in the surface is then measured, and the Brinell hardness number (bhn) is determined by from standard tables (table 7-3).

(b) Rockwell hardness test. This test is based upon the difference between the depth to which a test point is driven into a metal by a light load and the depth to which it is driven in by a heavy load. The light load is first applied and then, without moving the piece, the heavy load is applied. The hardness number is automatically indicated on a dial. The letter designations on the Rockwell scale, such as B and C, indicate the type of penetrator used and the amount of heavy load (table 7-3). The same light load is always used.

(c) Scleroscope hardness test. This test measures hardness by letting a diamond-tipped hammer fall by its own weight from a fixed height and rebound from the surface; the rebound is measured on a scale. It is used on smooth surfaces where dents are not desired.

(a) Spark testing is not of much use on nonferrous metals such as coppers, aluminums, and nickel-base alloys, since they do not exhibit spark streams of any significance. However, this is one way to separate ferrous and nonferrous metals.

(b) The spark resulting from the test should be directed downward and studied. The color, shape, length, and activity of the sparks relate to characteristics of the material being tested. The spark stream has specific items which can be identified. The straight lines are called carrier lines. They are usually solid and continuous. At the end of the carrier line, they may divide into three short lines, or forks. If the spark stream divides into more lines at the end, it is called a sprig. Sprigs also occur at different places along the carrier line. These are called either star or fan bursts. In some cases, the carrier line will enlarge slightly for a very short length, continue, and perhaps enlarge again for a short length. When these heavier portions occur at the end of the carrier line, they are called spear points or buds. High sulfur creates these thicker spots in carrier lines and the spearheads. Cast irons have extremely short streams, whereas low-carbon steels and most alloy steels have relatively long streams. Steels usually have white to yellow color sparks, while cast irons are reddish to straw yellow. A 0.15 percent carbon steel shows sparks in long streaks with some tendency to burst with a sparkler effect; a carbon tool steel exhibits pronounced bursting; and a steel with 1.00 percent carbon shows brilliant and minute explosions or sparklers. As the carbon content increases, the intensity of bursting increases.

(c) One big advantage of this test is that it can be applied to metal in, all stages, bar stock in racks, machined forgings or finished parts. The spark test is best conducted by holding the steel stationary and touching a high speed portable grinder to the specimen with sufficient pressure to throw a horizontal spark stream about 12.00 in. (30.48 cm) long and at right angles to the line of vision. Wheel pressure against the work is important because increasing pressure will raise the temperature of the spark stream and give the appearance of higher carbon content. The sparks near and around the wheel, the middle of the spark stream, and the reaction of incandescent particles at the end of the spark stream should be observed. Sparks produced by various metals are shown in figure 7-4.

(a) General. Wrought iron is almost pure iron. It is made from pig iron in a puddling furnace and has a carbon content of less than 0.08 percent. Carbon and other elements present in pig iron are taken out, leaving almost pure iron. In the process of manufacture, some slag is mixed with iron to form a fibrous structure in which long stringers of slag, running lengthwise, are mixed with long threads of iron. Because of the presence of slag, wrought iron resists corrosion and oxidation, which cause rusting.

(b) Uses. Wrought iron is used for porch railings, fencing, farm implements, nails, barbed wire, chains, modern household furniture, and decorations.

(c) Capabilities. Wrought iron can be gas and arc welded, machined,plated, and is easily formed.

(d) Limitations. Wrought iron has low hardness and low fatigue strength.

(e) Properties. Wrought iron has Brinell hardness number of 105; tensile strength of 35,000 psi; specific gravity of 7.7; melting point of 2750°F (1510°C); and is ductile and corrosion resistant.

(f) Appearance test. The appearance of wrought iron is the same as that of rolled, low-carbon steel.

(g) Fracture test. Wrought iron has a fibrous structure due to threads of slag. As a result, it can be split in the direction in which the fibers run. The metal is soft and easily cut with a chisel, and is quite ductile. When nicked and bent, it acts like rolled steel. However, the break is very jagged due to its fibrous structure. Wrought iron cannot be hardened.

(h) Spark test. When wrought iron is ground, straw-colored sparks form near the grinding wheel, and change to white, forked sparklers near the end of the stream.

(i) Torch test. Wrought iron melts quietly without sparking. It has a peculiar slag coating with white lines that are oily or greasy in appearance.

(a) General. Cast iron is a manmade alloy of iron, carbon, and silicon. A portion of the carbon exists as free carbon or graphite. Total carbon content is between 1.7 and 4.5 percent.

(b) Uses. Cast iron is used for water pipes, machine tool castings, transmission housing, engine blocks, pistons, stove castings, etc.

(c) Capabilities. Cast iron may be brazed or bronze welded, gas and arc welded, hardened, or machined.

(d) Limitations. Cast iron must be preheated prior to welding. It cannot be worked cold.

(e) Properties. Cast iron has a Brinell hardness number of 150 to 220 (no alloys) and 300 to 600 (alloyed); tensile strength of 25,000 to 50,000 psi (172,375 to 344,750 kPa) (no alloys) and 50,000 to 100,000 psi (344,750 to 689,500 kPa) (alloyed); specific gravity of 7.6; high compressive strength that is four times its tensile strength; high rigidity; good wear resistance; and fair corrosion resistance.

(f) Gray cast iron. If the molten pig iron is permitted to cool slowly, the chemical compound of iron and carbon breaks up to a certain extent. Much of the carbon separates as tiny flakes of graphite scattered throughout the metal. This graphite-like carbon, as distinguish from combined carbon, causes the gray appearance of the fracture, which characterizes ordinary gray cast iron. Since graphite is an excellent lubricant, and the metal is shot throughout with tiny, flaky cleavages, gray cast iron is easy to machine but cannot withstand a heavy shock. Gray cast iron consists of 90 to 94 percent metallic iron with a mixture of carbon, manganese, phosphorus, sulfur, and silicon. Special high-strength grades of this metal also contain 0.75 to 1.50 percent nickel and 0.25 to 0.50 percent chromium or 0.25 to 1.25 percent molybdenum. Commercial gray iron has 2.50 to 4.50 percent carbon. About 1 percent of the carbon is combined with the iron, while about 2.75 percent remains in the free or graphitic state. In making gray cast iron, the silicon content is usually increased, since this allows the formation of graphitic carbon. The combined carbon (iron carbide), which is a small percentage of the total carbon present in cast iron, is known as cementite. In general, the more free carbon (graphitic carbon) present in cast iron, the lower the combined carbon content and the softer the iron.

(g) White cast iron. When gray cast iron is heated to the molten state, the carbon completely dissolves in the iron, probably combining chemically with it. If this molten metal is cooled quickly, the two elements remain in the combined state, and white cast iron is formed. The carbon in this type of iron measures above 2.5 to 4.5 percent by weight, and is referred to as combined carbon. White cast iron is very hard and brittle, often impossible to machine, and has a silvery white fracture.

(h) Malleable cast iron. Malleable cast iron is made by heating white cast iron from 1400 to 1700°F (760 and 927°C) for abut 150 hours in boxes containing hematite ore or iron scale. This heating causes a part of the combined carbon to change into the free or uncombined state. This free carbon separates in a different way from carbon in gray cast iron and is called temper carbon. It exists in the form of small, rounded particles of carbon which give malleable iron castings the ability to bend before breaking and to withstand shock better than gray cast iron. The castings have properties more like those of pure iron: high strength, ductility, toughness, and ability to resist shock. Malleable cast iron can be welded and brazed. Any welded part should be annealed after welding.

(a) General. A form of iron, steel contains less carbon than cast iron, but considerably more than wrought iron. The carbon content is from 0.03 to 1.7 percent. Basic carbon steels are alloyed with other elements, such as chromium and nickel, to increase certain physical properties of the metal.

(b) Uses. Steel is used to make nails, rivets, gears, structural steel, roles, desks, hoods, fenders, chisels, hammers, etc.

(c) Capabilities. Steel can be machined, welded, and forged, all to varying degrees, depending on the type of steel.

(d) Limitations. Highly alloyed steel is difficult to produce.

(e) Properties. Steel has tensile strength of 45,000 psi (310,275 kPa) for low-carbon steel, 80,000 psi (551,600 kPa) for medium-carbon steel, 99,000 psi (692,605 kPa) for high-carbon steel, and 150,000 psi (1,034,250 kPa) for alloyed steel; and a melting point of 2800° F (1538°C).

(f) Low-carbon steel (carbon content up to 0.30 percent. This steel is soft and ductile, and can be rolled, punched, sheared, and worked when either hot or cold. It is easily machined and can readily be welded by all methods. It does not harden to any great amount; however, it can easily be case hardened.

(g) Medium-carbon steel (carbon content ranging from 0.30 to 0.50 percent). This steel may be heat-treated after fabrication. It is used for general machining and forging of parts that require surface hardness and strength. It is made in bar form in the cold-rolled or the normalized and annealed condition. During welding, the weld zone will become hardened if cooled rapidly and must be stress-relieved after welding.

(h) High-carbon steel (carbon content ranging from 0.50 to 0.90 percent). This steel is used for the manufacture of drills, taps, dies, springs, and other machine tools and hand tools that are heat treated after fabrication to develop the hard structure necessary to withstand high shear stress and wear. It is manufactured in bar, sheet, and wire forms, and in the annealed or normalized condition in order to be suitable for machining before heat treatment. This steel is difficult to weld because of the hardening effect of heat at the welded joint.

(i) High carbon tool steel. Tool steel (carbon content ranging from 0.90 to 1.55 percent) is used in the manufacture of chisels, shear blades, cutters, large taps, wood-turning tools, blacksmith’s tools, razors, and similar parts where high hardness is required to maintain a sharp cutting edge. It is difficult to weld due to the high carbon content. A spark test shows a moderately large volume of white sparks having many fine, repeating bursts.

(a) General. Welding is difficult on steel castings containing over 0.30 percent carbon and 0.20 percent silicon. Alloy steel castings containing nickel, molybdenum, or both of these metals, are easily welded if the carbon content is low. Those containing chromium or vanadium are more difficult to weld. Since manganese steel is nearly always used in the form of castings, it is also considered with cast steel. Its high resistance to wear is its most valuable property.

(b) Appearance test. The surface of cast steel is brighter than cast or malleable iron and sometimes contains small, bubble-like depressions.

(c) Fracture test. The color of a fracture in cast steel is bright crystalline gray. This steel is tough and does not break short. Steel castings are tougher than malleable iron, and chips made with a chisel curl up more. Manganese steel, however, is so tough that is cannot be cut with a chisel nor can it be machined.

(d) Spark test. The sparks created from cast steel are much brighter than those from cast iron. Manganese steel gives off marks that explode, throwing off brilliant sparklers at right angles to the original-path of the spark:

(e) Torch test. When melted, cast steel sparks and hardens quickly.

(a) General. Steel forgings may be of carbon or alloy steels. Alloy steel forgings are harder and more brittle than low carbon steels.

(b) Appearance test. The surface of steel forgings is smooth. Where the surface of drop forgings has not been finished, there will be evidence of the fin that results from the metal squeezing out between the two forging dies. This fin is removed by the trimming dies, but enough of the sheared surface remains for identification. All forgings are covered with reddish brown or black scale, unless they have been purposely cleaned.

(c) Fracture test. The color of a fracture in a steel forging varies from bright crystalline to silky gray. Chips are tough; and when a sample is nicked, it is harder to break than cast steel and has a finer grain. Forgings may be of low-or high-carbon steel or of alloy steel. Tool steel is harder and more brittle than plate steel or other low-carbon material. The fracture is usually whiter and finer grained. Tool steel can be hardened by heating to a good red and then quenching in water. Low-carbon steel, wrought iron, and steel castings cannot be usefully hardened.

(d) Spark test. The sparks given off are long, yellow-orange streamers and are typical steel sparks. Sparks from high-carbon steel (machinery and tool steel) are much brighter than those from low-carbon steel.

(e) Torch test. Steel forgings spark when melted, and the sparks increase in number and brightness as the carbon content becomes greater.

(a) General. Alloy steel is frequently recognizable by its use. There are many varieties of alloy steel used in the manufacture of Army equipment. They have greater strength and durability than carbon steel, and a given strength is secured with less material weight. Manganese steel is a special alloy steel that is always used in the cast condition (see cast steel, above).

Nickel, chromium, vanadium, tungsten, molybdenum, and silicon are the most common elements used in alloy steel.

(b) Appearance test. Alloy steel appear the same as drop-forged steel.

(c) Fracture test. Alloy steel is usually very close grained; at times the fracture appears velvety.

(d) Spark test. Alloy steel produces characteristic sparks both in color and shape. Some of the more common alloys used in steel and their effects on the spark stream are as follows:

(a) General. Aluminum is a lightweight, soft, low strength metal which can easily be cast, forged, machined, formed, and welded. It is suitable only in low temperature applications, except when alloyed with specific elements. Commercial aluminum alloys are classified into two groups, wrought alloys and cast alloys. The wrought alloy group includes those alloys which are designed for mill products whose final physical forms are obtained by working the metal mechanically. The casting alloy group includes those alloys whose final shapes are obtained by allowing the molten metal to solidify in a mold.

(b) Uses. Aluminum is used as a deoxidizer and alloying agent in the manufacture of steel. Castings, pistons, torque converter pump housings, aircraft structures, kitchen utensils, railways cars, and transmission lines are made of aluminum.

(c) Capabilities. Aluminum can be cast, forged, machined, formed, and welded.

(d) Limitations. Direct metal contact of aluminum with copper and copper alloys should be avoided. Aluminum should be used in low-temperature applications.

(e) Properties. Pure aluminum has a Brinell hardness number of 17 to 27; tensile strength of 6000 to 16,000 psi (41,370 to 110,320 kPa); specific gravity of 2.7; and a melting point of 1220°F (660°C). Aluminum alloys have a Brinell hardness number of 100 to 130, and tensile strength of 30,000 to 75,000 psi (206,850 to 517,125 kPa). Generally, aluminum and aluminum alloys have excellent heat conductivity; high electrical conductivity (60 percent that of copper, volume for volume; high strength/weight ratio at room temperature; and unfairly corrosion resistant.

(f) Appearance test. Aluminum is light gray to silver in color, very bright when polished, dull when oxidized, and light in weight. Rolled and sheet aluminum materials are usually pure metal. Castings are alloys of aluminum with other metals, usually zinc, copper, silicon, and sometimes iron and magnesium. Wrought aluminum alloys may contain chromium, silicon, magnesium, or manganese. Aluminum strongly resembles magnesium in appearance. Aluminum is distinguished from magnesium by the application of a drop of silver nitrate solution on each surface. The silver nitrate will not react with the aluminum, but leaves a black deposit of silver on the magnesium.

(g) Fracture test. A fracture in rolled aluminum sections shows a smooth, bright structure. A fracture in an aluminum casting shins a bright crystalline structure.

(h) Spark test. No sparks are given off from aluminum.

(i) Torch test. Aluminum does not turn red before melting. It holds its shape until almost molten, then collapses (hot shorts) suddenly. A heavy film of white oxide forms instantly on the molten surface.

(a) General. Chromium is an alloying agent used in steel, cast iron, and nonferrous alloys of nickel, copper, aluminum, and cobalt. It is hard, brittle, corrosion resistant, can be welded, machined, forged, and is widely used in electroplating. Chromium is not resistant to hydrochloric acid and cannot be used in its pure state because of its difficulty to work.

(b) Uses. Chromium is one of the most widely used alloys. It is used as an alloying agent in steel and cast iron (0.25 to 0.35 percent) and in nonferrous alloys of nickel, copper, aluminum, and cobalt. It is also used in electroplating for appearance and wear, in powder metallurgy, and to make mirrors and stainless steel.

(c) Capabilities. Chromium alloys can be welded, machined, and forged. Chromium is never used in its pure state.

(d) Limitations. Chromium is not resistant to hydrochloric acid, and cannot be used in the pure state because of its brittleness and difficulty to work.

(e) Properties (pure). Chromium has a specific gravity of 7.19; a melting point of 3300°F (1816°C); Brinell hardness number of 110 to 170; is resistant to acids other than hydrochloric; and is wear, heat, and corrosion resistant.

(a) General. Cobalt is a hard, white metal similar to nickel in appearance, but has a slightly bluish cast.

(b) Uses. Cobalt is mainly used as an alloying element in permanent and soft magnetic materials, high-speed tool bits and cutters, high-temperature, creep-resisting alloys, and cemented carbide tools, bits, and cutters. It is also used in making insoluble paint pigmnts and blue ceramic glazes. In the metallic form, cobalt does not have many uses. However, when combined with other elements, it is used for hard facing materials.

(c) Capabilities. Cobalt can be welded, machined (limited), and cold-drawn.

(d) Limitations. Cobalt must be machined with cemented carbide cutters. Welding high carbon cobalt steel often causes cracking.

(e) Properties. Pure cobalt has a tensile strength of 34,000 psi (234,430 kPa); Brinell hardness number of 125; specific gravity of 8.9; and a melting point of 2720°F (1493°C). Cobalt alloy (Stellite 21) has a tensile strength of 101,000 psi (696,395 kPa) and is heat and corrosion resistant.

(a) General. Copper is a reddish metal, is very ductile and malleable, and has high electrical and heat conductivity. It is used as a major element in hundreds of alloys. Commercially pure copper is not suitable for welding. Though it is very soft, it is very difficult to machine due to its high ductility. Beryllium copper contains from 1.50 to 2.75 percent beryllium. It is ductile when soft, but loses ductility and gains tensile strength when hardened. Nickel copper contains either 10, 20, or 30 percent nickel. Nickel alloys have moderately high to high tensile strength, which increases with the nickel content. They are moderately hard, quite tough, and ductile. They are very resistant to the erosive and corrosive effects of high velocity sea water, stress corrosion, and corrosion fatigue. Nickel is added to copper zinc alloys (brasses) to lighten their color; the resultant alloys are called nickel silver. These alloys are of two general types, one type containing 65 percent or more copper and nickel combined, the other containing 55 to 60 percent copper and nickel combined. The first type can be cold worked by such operations as deep drawing, stamping, and spinning. The second type is much harder end is not processed by any of the cold working methods. Gas welding is the preferred process for joining copper and copper alloys.

(b) Uses. The principal use of commercially pure copper is in the electrical industry where it is made into wire or other such conductors. It is also used in the manufacture of nonferrous alloys such as brass, bronze, and Monel metal. Typical copper products are sheet roofing, cartridge cases, bushings, wire, bearings, and statues.

(c) Capababilities. Copper can be forged, cast, and cold worked. It can also be welded, but its machinability is only fair. Copper alloys can be welded.

(d) Limitations. Electrolytic tough pitch copper cannot be welded satisfactorily. Pure copper is not suitable for welding and is difficult to machine due to its ductility.

(e) Properties. Pure copper is nonmagnetic; has a Brinell hardness number of 60 to 110; a tensile strength of 32,000 to 60,000 psi (220,640 to 413,700 kPa); specific gravity of 8.9; melting point of 1980°F (1082°C); and is corrosion resistant. Copper alloys have a tensile strength of 50,000 to 90,000 psi (344,750 to 620,550 kPa) and a Brinell hardness number of 100 to 185.

(f) Appearance test. Copper is red in color when polished, and oxidizes to various shades of green.

(g) Fracture test. Copper presents a smooth surface when fractured, which is free from crystalline appearance.

(h) Spark test. Copper gives off no sparks.

(i) Torch test. Because copper conducts heat rapidly, a larger flame is required to produce fusion of copper than is needed for the same size piece of steel. Copper melts suddenly and solidifies instantly. Copper alloy, containing small amounts of other metals, melts more easily and solidifies more slowly than pure copper.

(j) Brass and bronze. Brass, an alloy of copper and zinc (60 to 68 percent copper and 32 to 40 percent zinc), has a low melting point and high heat conductivity. There are several types of brass, such as naval, red, admiralty, yellow, and commercial. All differ in copper and zinc content; may be alloyed with other elements such as lead, tin, manganese, or iron; have good machinability; and can be welded. Bronze is an alloy of copper and tin and may contain lead, zinc, nickel, manganese, or phosphorus. It has high strength, is rust or corrosion resistant, has good machinability, and can be welded.

(k) Aluminum bronze.

(a) General. Lead is a heavy, soft, malleable metal with low melting point, low tensile strength, and low creep strength. It is resistant to corrosion from ordering atmosphere, moisture, and water, and is effective against many acids. Lead is well suited for cold working and casting. The low melting point of lead makes the correct welding rod selection very important.

(b) Uses. Lead is used mainly in the manufacture of electrical equipment such as lead-coated power and telephone cables, and storage batteries. It is also used in building construction in both pipe and sheet form, and in solder. Zinc alloys are used in the manufacture of lead weights, bearings, gaskets, seals, bullets, and shot. Many types of chemical compounds are produced from lead; among these are lead carbonate (paint pigment) and tetraethyl lead (antiknock gasoline). Lead is also used for X-ray protection (radiation shields). Lead has more fields of application than any other metal.

(c) Capabilities. Lead can be cast, cold worked, welded, and machined. It is corrosion, atmosphere, moisture, and water resistant, and is resistant to many acids.

(d) Limitations. Lead has low strength with heavy weight. Lead dust and fumes are very poisonous.

(e) Properties. Pure lead has tensile strength of 2500 to 3000 psi (17,237.5 to 20,685 kPa); specific gravity of 11.3; and a melting point of 620°F (327°C). Alloy lead B32-467 has tensile strength of 5800 psi (39,991 kPa). Generally, lead has low electrical conductivity; is self-lubricating; is malleable; and is corrosion resistant.

(a) General. Magnesium is an extremely light metal, is white in color, has a low melting point, excellent machinability, and is weldable. Welding by either the arc or gas process requires the use of a gaseous shield. Magnesium is moderately resistant to atmospheric exposure, many chemicals such as alkalies, chromic and hydrofluoric acids, hydrocarbons, and most alcohols, phenols, esters, and oils. It is nonmagnetic. Galvanic corrosion is an important factor in any assembly with magnesium.

(b) Uses. Magnesium is used as a deoxidizer for brass, bronze, nickel, and silver. Because of its light weight, it is used in many weight-saving applications, particularly in the aircraft industry. It is also used in the manufacture and use of fireworks for railroad flares and signals, and for military purposes. Magnesium castings are used for engine housings, blowers, hose pieces, landing wheels, and certain parts of the fuselage of aircraft. Magnesium alloy materials are used in sewing machines, typewriters, and textile machines.

(c) Capabilities. Magnesium can be forged, cast, welded, and machined.

(d) Limitations. Magnesium in fine chip form will ignite at low temperatures (800 to 1200°F (427 to 649°C)). The flame can be mothered with suitable materials such as carbon dioxide (CO₂), foam, and sand.

(e) Properties. Pure magnesium has tensile strength of 12,000 psi (82,740 kPa) (cast) and tensile strength of 37,000 psi (255,115 kPa) (rolled); Brinell hardness number of 30 (cast) and 50 (rolled); specific gravity of 1.7; and a melting point of 1202°F (650°C). Magnesium alloy has Brinell hardness number of 72 (hard) and 50 (forged); and tensile strength of 42,000 psi (289,590 kPa) (hard) and 32,000 psi (220,640 kPa) (forged).

(f) Appearance test. Magnesium resembles aluminum in appearance. The polished surface is silver-white, but quickly oxidizes to a grayish film. Like aluminum, it is highly corrosion resistant and has a good strength-to-weight ratio, but is lighter in weight than aluminum. It has a very low kindling point and is not very weldable, except when it is alloyed with manganese and aluminum. Magnesium is distinguished from aluminum by the use of a silver nitrate solution. The solution does not react with aluminum, but leaves a black deposit of silver on magnesium. Magnesium is produced in large quantities from sea water. It has excellent machinability, but special care must be used when machining because of its low kindling point.

(g) Fracture test. Magnesium has a rough surface with a fine grain structure.

(h) Spark test. No sparks are given off.

(i) Torch test. Magnesium oxidizes rapidly when heated in open air, producing an oxide film which is insoluble in the liquid metal. A fire may result when magnesium is heated in the open atmosphere. As a safety precaution, magnesium should be melted in an atmosphere of inert gas.

(a) General. Pure manganese has a relatively high tensile strength, but is very brittle. Manganese is used as an alloying agent in steel to deoxidize and desulfurize the metal. In metals other than steel, percentages of 1 to 15 percent manganese will increase the toughness and the hardenability of the metal involved.

(b) Uses. Manganese is used mainly as an alloying agent in making steel to increase tensile strength. It is also added during the steel-making process to remove sulfur as a slag. Austenitic manganese steels are used for railroad track work, power shovel buckets, and rock crushers. Medium-carbon manganese steels are used to make car axles and gears.

(c) Capabilities. Manganese can be welded, machined, and cold-worked.

(d) Limitations. Austenitic manganese steels are best machined with cemented carbide, cobalt, and high-speed steel cutters.

(e) Properties. Pure manganese has tensile strength of 72,000 psi (496,440 kPa) (quenched) Brinell hardness number of 330; specific gravity of 7.43: a melting point of 2270°F (1243°C); and is brittle. Manganese alloy has a tensile strength of 110,000 psi (758,450 kPa). Generally, manganese is highly polishable and brittle.

(a) General. Pure molybdenum has a high tensile strength and is very resistant to heat. It is principally used as an alloying agent in steel to increase strength, hardenability, and resistance to heat.

(b) Uses. Molybdenum is used mainly as an alloy. Heating elements, switches, contacts, thermocouplers, welding electrodes, and cathode ray tubes are made of molybdenum.

(c) Capabilities. Molybdenum can be swaged, rolled, drawn, or machined.

(d) Limitations. Molybdenum can only be welded by atomic hydrogen arc, or butt welded by resistance heating in vacuum. It is attacked by nitric acid, hot sulfuric acid, and hot hydrochloric acid.

(e) Properties. Pure molybdenum has a tensile strength of 100,000 psi (689,500 kPa) (sheet) and 30,000 Psi (206,850 kPa) (wire); Brinell hardness number of 160 to 185; specific gravity of 10.2; meting point of 4800°F (2649°C); retains hardness and strength at high temperatures; and is corrosion resistant.

(a) General. Nickel is a hard, malleable, ductile metal. As an alloy, it will increase ductility, has no effect on grain size, lowers the critical point for heat treatment, aids fatigue strength, and increases impact values in low temperature operations. Both nickel and nickel alloys are machinable and are readily welded by gas and arc methods.

(b) Uses. Nickel is used in making alloys of both ferrous and nonferrous metal. Chemical and food processing equipment, electrical resistance heating elements, ornamental trim, and parts that must withstand elevated temperatures are all produced from nickel-containing metal. Alloyed with chromium, it is used in the making of stainless steel.

(c) Capabilities. Nickel alloys are readily welded by either the gas or arc methods. Nickel alloys can be machined, forged, cast, and easily formed.

(d) Limitations. Nickel oxidizes very slowly in the presence of moisture or corrosive gases.

(e) Properties. Pure nickel has tensile strength of 46,000 psi (317,170 kPa); Brinell hardness number 220; specific gravity of 8.9; and melting point of 2650°F (1454°C). Nickel alloys have Brinell hardness number of 140 to 230. Monel-forged nickel has tensile strength of 100,000 psi (689,500 kPa), and high strength and toughness at high temperatures.

(f) Appearance. Pure nickel has a grayish white color.

(g) Fracture. The fracture surface of nickel is smooth and fine grained.

(h) Spark test. In a spark test, nickel produces a very small amount of short, orange streaks which are generally wavy.

(i) Monel metal. Monel metal is a nickel alloy of silver-white color containing about 67.00 percent nickel, 29.00 to 80.00 percent copper, 1.40 percent iron, 1.00 percent manganese, 0.10 percent silicon, and 0.15 percent carbon. In appearance, it resembles untarnished nickel. After use, or after contact with chemical solutions, the silver-white color takes on a yellow tinge, and some of the luster is lost. It has a very high resistance to corrosion and can be welded.

(a) General. Tin is a very soft, malleable, somewhat ductile, corrosion resistant metal having low tensile strength and high crystalline structure. It is used in coating metals to prevent corrosion.

(b) Uses. The major application of tin is in coating steel. It serves as the best container for preserving perishable focal. Tin, in the form of foil, is often used in wrapping food products. A second major use of tin is as an alloying element. Tin is alloyed with copper to produce tin brass and bronze, with lead to produce solder, and with antimony and lead to form babbitt.

(c) Capabilities. Tin can be die cast, cold worked (extruded), machined, and soldered.

(d) Limitations. Tin is not weldable.

(e) Properties. Pure tin has tensile strength of 2800 psi (19,306 kPa); specific gravity of 7.29; melting point of 450°F (232°C); and is corrosion resistant. Babbitt alloy tin has tensile strength of 10,000 psi (68,950 kPa) and Brinell hardness number of 30.

(f) Appearance. Tin is silvery white in color.

(g) Fracture test. The fracture surface of tin is silvery white and fairly smooth.

(h) Spark test. Tin gives off no sparks in a spark test.

(i) Torch test. Tin melts at 450°F (232°C), and will boil under the torch.

(a) General. Titanium is a very soft, silvery white, medium-strength metal having very good corrosion resistance. It has a high strength to weight ratio, and its tensile strength increases as the temperature decreases. Titanium has low impact and creep strengths, as well as seizing tendencies, at temperatures above 800°F (427°C).

(b) Uses. Titanium is a metal of the tin group which occurs naturally as titanium oxide or in other oxide forms. The free element is separated by heating the oxide with aluminum or by the electrolysis of the solution in calcium chloride. Its most important compound is titanium dioxide, which is used widely in welding electrode coatings. It is used as a stabilizer in stainless steel so that carbon will not be separated during the welding operation. It is also used as an additive in alloying aluminum, copper, magnesium, steel, and nickel; making powder for fireworks; and in the manufacture of turbine blades, aircraft firewalls, engine nacelles, frame assemblies, ammunition tracks, and mortar base plates.

(c) Capabilities. Titanium can be machined at low speeds and fast feeds; formal; spot-and seam-welded, and fusion welded using inert gas.

(d) Limitations. Titanium has low impact strength, and low creep strength at high temperatures (above 800°F (427°C)). It can only be cast into simple shapes, and it cannot be welded by any gas welding process because of its high attraction for oxygen. Oxidation causes this metal to become quite brittle. The inert gas welding process is recommended to reduce contamination of the weld metal.

(e) Properties. Pure titanium has a tensile strength of 100,000 psi; Brinell hardness number of 200; specific gravity of 4.5; melting point of 3300°F (1851°C); and good corrosion resistance. Alloy titanium has a Brinell hardness number of 340; tensile strength of 150,000 psi; and a high strength/weight ratio (twice that of aluminum alloy at 400°F (204°C)).

(f) Appearance test. Titanium is a soft, shiny, silvery-white metal burns in air and is the only element that burns in nitrogen. Titanium alloys look like steel, and can be distinguished from steel by a copper sulfate solution. The solution will not react with titanium, but will leave a coating of copper on steel.

(g) Spark test. The sparks given off are large, brilliant white, and of medium length.

(a) General. Tungsten is a hard, heavy, nonmagnetic metal which will melt at approximately 6150°F (3400°C).

(b) Uses. Tungsten is used in making light bulb filaments, phonograph needles, and as an alloying agent in production of high-speed steel, armorplate, and projectiles. It is also used as an alloying agent in nonconsumable welding electrodes, armor plate, die and tool steels, and hard metal carbide cutting tools.

(c) Capabilities. Tungsten can be cold and hot drawn.

(d) Limitations. Tungsten is hard to machine, requires high temperatures for melting, and is produced by powered metallurgy (sintering process).

(e) Properties. Tungsten has a melting point of 6170 ± 35°F (3410 ± 19°C); is ductile; has tensile strength of 105,000 psi (723,975 kPa); a specific gravity of 19.32; thermal conductivity of 0.397; a Brinell hardness number of 38; and is a dull white color.

(f) Appearance. Tungsten is steel gray in color.

(g) Spark test. Tungsten produces a very small volume of short, straight, orange streaks in a spark test.

(a) General. Zinc is a medium low strength metal having a very low melting point. Ito is easy to machine, but coarse grain zinc should be heated to approximately 180°F (82°C) to avoid cleavage of crystals. Zinc can be soldered or welded if it is properly cleaned and the heat input closely controlled.

(b) Uses.

(c) Capabilities. Zinc can be cast, cold worked (extruded), machined, and welded.

(d) Limitations. Do not use zinc die castings in continuous contact with steam.

(e) Properties. Zinc has a tensile strength of 12,000 psi (82,740 kPa) (cast) and 27,000 psi (186,165 kPa) (rolled); a specific gravity of 7.1; a melting point of 790°F (421°C); is corrosion resistant; and is brittle at 220°F (104°C).

(f) Appearance. Both zinc and zinc alloys are blue-white in color when polished, and oxidize to gray.

(g) Fracture test. Zinc fractures appear somewhat granular.

(h) Spark test. Zinc and zinc alloys give off no sparks in a spark test.

(i) Zinc die castings.

(a) General. These are usually made with alloys of aluminum, lead, magnesium, or tin. Except for those made of lead and tin, they are generally light in weight and white in color.

(b) Appearance. The surface is much smoother than that produced by castings made in sand.

(c) Fracture test. Fractured surface is white and somewhat granular.

(d) Spark test. No sparks given off in a spark test.

(e) Torch test. Melting points are low, and the metal boils under the torch.

Authorization Letter