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The ferrous metals are iron and its various alloys, such as cast iron, malleable cast iron, wrought iron, and steel. There are many others. The best way of forming parts of irregular shape from the ferrous metals is by making a pattern and pouring molten metal into a mold. These are known as castings.

Cast Iron. Cast iron is iron containing so much carbon or its equivalent that it is not usefully malleable at any temperature. The amount of carbon varies from 2.2 to 4.3 per cent, depending on the amount of silicon, sulfur, phosphorus, and manganese also present.

There are two grades of cast iron: gray cast iron, in which the carbon is segregated from the iron in the form of graphite; and white cast iron, which has carbon and iron combined. Another grade is often mentioned, mottled cast iron, which is a mixture of the gray and white. Cast iron is made by combining pig iron and scrap iron and pouring the molten metal into sand molds of the desired shape, where it is allowed to cool. Then, it is cleaned and made ready for use.

Cast-iron castings are generaly large, bulky, and very brittle. They cannot be hammered to any great extent without breaking. They cannot be forged, but can be cemented together by brazing or welding. The brazing process consists of heating the broken parts to a welding heat and applying a brazing compound. Welding is the process of fusing two pieces by heating them with an oxyacetylene-gas flame and applying the proper rod.

Malleable Cast Iron. Malleable iron is annealed white cast iron in which the carbon has been separated from the iron without forming flakes or graphite, as in gray cast iron. It will bend to a limited extent without breaking.

The process of making malleable cast iron consists of melting the white pig iron, with scrap, in the furnace and pouring it rapidly into sand molds while very hot. After cooling, the castings are cleaned and made ready for annealing. The annealing pots are usually of cast iron. The castings are packed in these pots along with iron scale (iron oxide), which acts as a decarburizer and causes much of the brittle quality to disappear. The annealing pots containing the castings and iron scale are placed in an oven and the temperature raised to a cherry-red heat, about 1450°F., and held there for from 3 to 5 days, depending on the size of the castings and the amount of decarbonizing desired. Then the furnace is allowed to cool slowly for a few days before the castings are removed and cleaned. Malleable cast iron is used extensively in building farm machinery and for various kinds of hardware.

Chilled Cast Iron. Chilled cast iron is cast iron poured into molds that have a part of the mold made of metal instead of sand. This metal causes the molten iron that comes in contact with it to cool more rapidly than the balance of the casting, thus forming a hard surface. The metal portion of the mold must be heated to a temperature of about 350°F. before pouring, to prevent explosions when the hot metal strikes the cold. Chilled-cast-iron moldboards for plow bottoms show that the iron fibers are brought perpendicular to the surface in the areas where the metal is chilled.

Ductile Cast Iron. This is a new metal for farm-equipment parts. Patents were granted on the process of producing ductile cast iron in 1949. This is a high-grade iron, produced by the ladle addition of magnesium alloy to molten iron prepared to produce gray cast iron. The magnesium acts as a desulfurizer, and when added in controlled amounts it produces spheroidal carbon instead of flake carbon (graphite).

Ductile cast iron has many applications in farm equipment, such as sprockets, gears, chilled plowshares, mower guards, parts for hay-baler knotter mechanism, and tail-wheel mounting brackets for plows.

Ductile cast iron can be welded similarly to gray cast iron. It requires, however, a special reverse-polarity arc rod designated as Ni-rod 55. This rod deposits a bead with 8 per cent elongation and with tensile properties of over 60,000 pounds per square inch.

Cast Steel. Cast steel is a steel that is cast. It can be made in varying degrees of hardness and is more durable than the best grade of cast iron. It is used mostly in gearing. Not much of it is found in agricultural machinery.

Wrought Iron. Wrought iron is nearly pure iron, with some slag, and is used in forge work as it is readily welded and easy to work. Wrought iron has very little carbon in it, ranging from 0.05 to 0.10 of 1 per cent. It is expensive, however, and a mild steel is used to a considerable extent in place of it. The commercial form is obtained by rolling the hot iron into bars or plates from which nails, bolts, nuts, wire, chains, and many other products are made.

Kinds of Steel. Steel is a variety of iron classed between cast iron and wrought iron, very tough, and, when tempered, hard and elastic. The hardness of steel is determined principally by its carbon content but is influenced by the percentages of manganese, phosphorus, and sulfur it also contains. The composition of the various grades of carbon, manganese, nickel, molybdenum, chromium, chromium-vanadium, and tungsten steel is identified by a numbering system as follows:

TABLE 2–1. CARBON CONTENT AND NUMBER OF DIFFERENT KINDS OF STEEL

The last two digits in the number indicate the hardness of the steel. Steels with small amounts of carbon are used in making items that are easily cut and shaped. High-carbon steel is used in making tools, thread dies, ball and roller bearings and items that will cut the low-carbon steels. Strength is closely related to the carbon content and the degree of hardness. Copper-bearing steels and the various alloys have numbers ranging above non-copper-bearing steels.

Color schemes are used as marks of identification for various kinds of steel when stored in warehouses.

Steel Alloys. A steel alloy is a mixture of two or more metals. The mixture is composed largely of steel with small amounts of one or more alloy metals. The more common alloy elements used in steel are boron, manganese, nickel, vanadium, tungsten, and chromium.

Boron Steel. This contains a small amount of boron. The boron acts to increase the hardening ability of the steel, that is, its ability to harden deeply when heat-treated by quenching and tempering. It is used for axle shafts, wheel spindles, sterring-knuckle arms, cap screws, and studs.

Manganese Steel. This usually contains 11 to 14 per cent manganese and from 0.8 to 1.5 per cent carbon and has properties of extreme hardness and ductility. It is usually cast for the desired shape and finished by grinding. It is used in feed grinders and machine parts subject to severe wear.

Nickel Steel. Steel containing from 2 to 5 per cent nickel and from 0.10 to 0.50 per cent carbon is strong, tough, and ductile. Nickel steels are used in making parts that are subjected to repeated shocks and stresses.

Vanadium Steel. When less than 0.20 per cent vanadium is added to steel, the resulting alloy is given additional tensile strength and elasticity comparable to the low- and medium-carbon steels with a corresponding loss of ductility.

Chrome-Vanadium Steels. These contain about 0.5 to 1.5 per cent chromium, 0.15 to 0.30 per cent vanadium, and 0.15 to 1.10 per cent carbon. These steels are used extensively in making machinery castings, forgings, springs, shafting, gears, and pins.

Tungsten Steel. Steels containing from 3 to 18 per cent tungsten and from 0.2 to 1.5 per cent carbon are used for dies and high-speed cutting tools.

Molybdenum Steel. This steel has properties similar to tungsten steel.

Chrome Steel. Chrome steels usually contain from 0.50 to 2.0 per cent chromium and from 0.10 to 1.50 per cent carbon. Chromium steels are used in making high-grade balls, rollers, and races for ball and roller bearings. Chrome steels containing from 14 to 18 per cent chromium produce a variety of stainless steel.

Chrome-Nickel Steel. The average chrome-nickel steel contains about 0.30 to 2.0 per cent chromium, from 1.0 to 4.0 per cent nickel, and from 0.10 to 0.60 per cent carbon. Heat-treatment increases its tensile strength, elasticity, and endurance limits. It is tough and ductile. Chrome-nickel steel is used in making gears, forgings, crankshafts, connecting rods, and machine parts.

When chrome-nickel steel contains from 16 to 19 per cent chromium, 7 to 10 per cent nickel, and less than 0.15 per cent carbon, it is generally called stainless steel. The commonly called 18–8 stainless falls in this group.

Tool Steel. The term tool steel is used in designating a high-carbon steel that is used for making tools. It has the property of becoming extremely hard by quenching from a temperature of 1400 to 1800°F. It can then be treated to obtain any degree of hardness by heating at lower temperatures.

Soft-center Steel. Soft-center steel consists of three layers of steel, as shown in Fig. 2–1. Two layers of hard steel are placed on each side and welded to an inner layer of soft steel. In this manner, a hard surface is obtained, without brittleness. Soft-center steel is used in the making of plow bottoms. Filing a slight notch in the edge of the metal will reveal the three layers.

Clad steels or bimetal steels are made by permanently bonding a layer of nickel, inconel, or monel metal to a heavier base layer of steel by hot rolling. The cladding layer may range in thickness from 3/16 inch up, with the cladding amounting to about 10 to 20 per cent of the total plate thickness.

Shapes of Steel. Steel that is formed into angles, channels, Tee bars I beams, Z bars, U bars, and hollow squares, as shown in Fig. 2–2, is known as structural steel. Solid bars are furnished in many shapes, such as round, half-round, oval, half-oval, square, hexagon, and flat-rectangle strips. Various sizes of round and square tubing are available. Many special parts are formed from flat-rolled carbon steel and stainless sheets and plates. A few of these shapes are shown in Fig. 2–3.

FIG. 2–1. Different types of soft-center steel.

FIG. 2–2. Types of structural steel.

Hardening of Finished Steels. In many cases where long-life service is desired, extremely hard steels cannot be forged and machined to the required shape and finish. Under these conditions a softer steel is shaped and finished, then given a hardening treatment. The most common hardening processes are casehardening and hardening by heat-treatment.

Casehardening. This is a process of hardening a ferrous alloy so that the surface layer or case is made substantially harder than the interior or core (Fig. 2–4). Casehardening can be done by several processes, such as carburizing and quenching, carbonitriding, nitriding, cyaniding, induction hardening, and flame hardening.

Carburizing is a process in which steel is packed in charred peach pits or charcoal and heated at about 1600°F. for a long enough period to give the desired depth of hardness. It is then removed, quenched, and tempered to give the desired hardness.

Nitriding is a process of casehardening by placing the finished heat-treated steel in an airtight box and heating to 1000°F. as ammonia gas is injected into the chamber.

FIG. 2–3. Sheet metal can be pressed into many different shapes.

Carbonitriding is a process of hardening steel by the addition of a carbon-rich gas, as well as ammonia.

Cyaniding is a process where the steel is dipped into a molten bath of potassium cyanide for a short time. Some carbon and nitrogen are absorbed by the steel, which results in the hardening of a thin surface layer.

Induction hardening is accomplished by the use of a high-frequency alternating electric current for a short period. A current is induced on the surface of the steel, which causes localized heating. After heating, the surface is flooded with water to quench and harden it.

FIG. 2–4. Casehardened steel.

Flame hardening is a process in which an oxyacetylene torch is used to heat the surface quickly to a temperature above the critical temperature, after which the surface is quenched with water.

Hardening by Heat-treatment. Heat-treatment is a term used to describe the application of heating and cooling processes to steel, through a range of temperatures, to improve the structure and produce desirable characteristics. Such treatments include annealing, hardening, tempering, and casehardening.

Plow beams, plow disks, and disk-harrow blades are examples of parts of agricultural machines that are heat-treated in order to make more serviceable implements.

Hard Facing or Surfacing. The application of a hard surface, or face, by welding is not to be confused with the hardening of finished surfaces. Hard facing, or surfacing by welding, is the addition of a hard metal over the base metal by applying a welding-rod deposit to provide a final surface that is harder than the original surface.

Hard facings are applied to parts for wear resistance, heat resistance, corrosion resistance, or combinations of the three. Most hard facing is done to prevent wear. In hard-facing parts, it is essential that the correct hardening material be selected to suit the base metal.

There are possibly hundreds of different hard-facing alloys available, and these are manufactured in three forms: as welding rods, as insert shapes, and in powdered forms. There are many types of welding rods. The rods used with the oxyacetylene torch are not coated. They are heated and dipped into a special flux. Electric rods usually have a flux coating.

Inserts and filler bars are welded on surfaces where extra-heavy hard facing is required.

Hard-facing powders are spread over the base metal, which is heated to the melting point to embed the powders firmly.