hardness. A malleable cast iron is produced through a prolonged annealing process.

INGOT IRON. - Ingot iron is a commercially pure iron (99.85% iron) that is easily formed and possesses good ductility and corrosion resistance. The chemical analysis and properties of this iron and the lowest carbon steel are practically the same. The lowest carbon steel, known as dead-soft, has about 0.06% more carbon than ingot iron. In iron the carbon content is considered an impurity and in steel it is considered an alloying element. The primary use for ingot iron is for galvanized and enameled sheet.

Steel

Of all the different metals and materials that we use in our trade, steel is by far the most important. When steel was developed, it revolutionized the American iron industry. With it came skyscrapers, stronger and longer bridges, and railroad tracks that did not collapse. Steel is manufactured from pig iron by decreasing the amount of carbon and other impurities and adding specific amounts of alloying elements.

Do not confuse steel with the two general classes of iron: cast iron (greater than 2% carbon) and pure iron (less than 0.15% carbon). In steel manufacturing, controlled amounts of alloying elements are added during the molten stage to produce the desired composition. The composition of a steel is determined by its application and the specifications that were developed by the following: American Society for Testing and Materials (ASTM), the American Society of Mechanical Engineers (ASME), the Society of Automotive Engineers (SAE), and the American Iron and Steel Institute (AISI).

Carbon steel is a term applied to a broad range of steel that falls between the commercially pure ingot iron and the cast irons. This range of carbon steel may be classified into four groups:

Low-Carbon Steel . . . . . . . . 0.05% to 0.30% carbon

Medium-Carbon Steel . . . . . . 0.30% to 0.45% carbon

High-Carbon Steel . . . . . . . . 0.45% to 0.75% carbon

Very High-Carbon Steel . . . . . 0.75% to 1.70% carbon

LOW-CARBON STEEL. - Steel in this classification is tough and ductile, easily machined, formed, and welded. It does not respond to any form of heat treating, except case hardening.

MEDIUM-CARBON STEEL. - These steels are strong and hard but cannot be welded or worked as easily as the low-carbon steels. They are used for crane hooks, axles, shafts, setscrews, and so on.

HIGH-CARBON STEEL/VERY HIGH-CARBON STEEL. - Steel in these classes respond well to heat treatment and can be welded. When welding, special electrodes must be used along with preheating and stress-relieving procedures to prevent cracks in the weld areas. These steels are used for dies, cutting tools, mill tools, railroad car wheels, chisels, knives, and so on.

LOW-ALLOY, HIGH-STRENGTH, TEMPERED STRUCTURAL STEEL. - A special low- carbon steel, containing specific small amounts of alloying elements, that is quenched and tempered to get a yield strength of greater than 50,000 psi and tensile strengths of 70,000 to 120,000 psi. Structural members made from these high-strength steels may have smaller cross-sectional areas than common structural steels and still have equal or greater strength. Additionally, these steels are normally more corrosion- and abrasion- resistant. High-strength steels are covered by ASTM specifications.

NOTE: This type of steel is much tougher than low-carbon steels. Shearing machines for this type of steel must have twice the capacity than that required for low-carbon steels.

STAINLESS STEEL. - This type of steel is classified by the American Iron and Steel Institute (AISI) into two general series named the 200-300 series and 400 series. Each series includes several types of steel with different characteristics.

The 200-300 series of stainless steel is known as AUSTENITIC. This type of steel is very tough and ductile in the as-welded condition; therefore, it is ideal for welding and requires no annealing under normal atmospheric conditions. The most well-known types of steel in this series are the 302 and 304. They are commonly called 18-8 because they are composed of 18% chromium and 8% nickel. The chromium nickel steels are the most widely used and are normally nonmagnetic.

The 400 series of steel is subdivided according to their crystalline structure into two general groups. One group is known as FERRITIC CHROMIUM and the other group as MARTENSITIC CHROMIUM.

Ferritic Chromium.-This type of steel contains 12% to 27% chromium and 0.08% to 0.20% carbon. These alloys are the straight chromium grades of stainless steel since they contain no nickel. They are nonhardenable by heat treatment and are normally used in the annealed or soft condition. Ferritic steels are magnetic