Steel, Cast Steel
Steel a form of iron, contains less carbon than cast iron, but considerably more than wrought iron. The carbon content is from 0.03 to 1.7 percent.
Steel is used to make nails, rivets, gears, structural steel, roles, desks, hoods, fenders, chisels, hammers, etc.
Steel can be machined, welded, and forged, all to varying degrees, depending on the type.
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)
Low-carbon Steels (carbon content up to 0.30 percent
Low carbon steels are 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.
The appearance depends upon the method of preparation rather than upon composition. Cast steel has a relatively rough, dark-gray surface, except where it has been machined. Rolled steel has fine surface lines running in one direction. Forged steel is usually recognizable by its shape, hammer marks, or fins.
When low-carbon steels are fractured, the color is bright crystalline gray. It is tough to chip or nick.
Sparks are in long yellow-orange streaks, brighter than cast iron, that show some tendency to burst into white, forked sparklers.
Sparks are produced when melted, and the metal hardens almost instantly.
Medium-carbon Steels (carbon content ranging from 0.30 to 0.50 percent)
Medium-carbon steels 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.
High-carbon Steels (carbon content ranging from 0.50 to 0.90 percent)
High-carbon steels are 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. It is difficult to weld because of the hardening effect of heat at the welded joint.
High-Carbon Appearance test
The unfinished surface of high-carbon steel is dark gray and similar to other steel. It is more expensive, and is usually worked to produce a smooth surface finish.
High-Carbon Fracture test
High-carbon steels usually produces a very fine-grained fracture, whiter than low-carbon steel. Tool steel is harder and more brittle than plate steel or other low-carbon material. High-carbon steel can be hardened by heating to a good red and quenching in water.
High-Carbon Spark test
High-carbon steel gives off a large volume of bright yellow-orange sparks.
High-Carbon Torch test
Molten high-carbon steel is brighter than low carbon steel, and the melting surface has a porous appearance. It sparks more freely than low-carbon (mild) steels, and the sparks are whiter.
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.
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.
Cast Appearance test
The surface of cast steel is brighter than cast or malleable iron and sometimes contains small, bubble-like depressions.
Cast 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.
Cast 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:
Cast Torch test
When melted, cast steel sparks and hardens quickly.
Forgings may be of carbon or alloy steels. Alloy steel forgings are harder and more brittle than low carbon steels.
Forgings Appearance test
The surface of 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.
Forgings 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.
Forgings Spark test
The sparks given off are long, yellow-orange streamers and are typical steel sparks. Sparks from high-carbon steels (machinery and tool steel) are much brighter than those from low-carbon steels.
Forgings Torch test
Forgings spark when melted, and the sparks increase in number and brightness as the carbon content becomes greater.
High speed tool steels. A spark test with these metals will impart a few long; forked sparks which are red near the wheel, and straw-colored near the end of the spark stream.
Special steel. Plate steel is used in the manufacture of built-up welded structures such as gun carriages. In using nickel plate steel, it has been found that commercial grades of low-alloy structural steel of not over 0.25 percent carbon, and several containing no nickel at all, are better suited to welding than those with a maximum carbon content of 0.30 percent. Armorplate, a low carbon alloy, is an example of this kind of plate. Such plate is normally used in the “as rolled” condition. Electric arc welding with a covered electrode may require preheating of the metal, followed by a proper stress-relieving heat treatment (post heating), to produce a structure in which the welded joint has properties equal to those of the plate metal.