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.