|As a welder, you
will use your
expertise to fabricate all types of metal objects, repair metal items, and
resurface worn machinery parts. You must know the two basic types of
metal and be able to provide initial identification. While they primarily work
with the ferrous metals of iron and steel, you also need to be able to identify
and become familiar with the nonferrous metals coming into more use each day.
This course presents an introductory explanation of the basic types of metal and provide initial instruction on using simple tests to establish their identity.
When you have completed this course, you will be able to:
Metals can initially be divided into two general classifications, and Steelworkers work with both: ferrous and nonferrous metals. Ferrous metals are those composed primarily of iron (atomic symbol Fe) and iron alloys. Nonferrous metals are those composed primarily of some element or elements other than iron, although nonferrous metals or alloys sometimes contain a small amount of iron as an alloying element or as an impurity.
Ferrous metals include all forms of iron and iron-base alloys, with small percentages of carbon (steel, for example), and/or other elements added to achieve desirable properties. Wrought iron, cast iron, carbon steels, alloy steels, and tool steels are just a few examples. Ferrous metals are typically magnetic.
Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, deep purple, to rusty red. Iron ore is the raw material used to make pig iron, which is one of the main raw materials used to make steel. Ninety-eight percent of the mined iron ore is used to make steel.
Iron is produced by converting iron ore to pig iron using a blast furnace. Pig iron is the intermediate product of smelting iron ore with coke, usually with limestone as a flux. Pig iron has very high carbon content, typically 3.54.5%, which makes it very brittle and not useful directly as a material except for limited applications.
From pig iron, many other types of iron and steel are produced by the addition or deletion of carbon and alloys. The following briefly presents different types of iron and steel made from iron. Steelworker Advanced will present additional information about their properties.
Of all the different metals and materials that Steelworkers use, steel and steel alloys are by far the most used and therefore the most important to study.
The development of the economical Bessemer process for manufacturing steel revolutionized the American iron industry. Figure 1 shows the container vessel used for the process.
With economical steel 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 and controlled amounts of alloying elements during the molten stage to produce the desired composition.
Figure 1 Example of a Bessemer Converter.
The composition of a particular steel is determined by its application and the specifications developed by the following:
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:
High-strength steels are covered by American Society for Testing and Materials (ASTM) specifications.
Stainless steels are classified by the American Iron and Steel Institute (AISI) and classified into two general series:
Alloy steels derive their properties primarily from the presence of some alloying element other than carbon, but alloy steels always contain traces of other elements as well. One or more of these elements may be added to the steel during the manufacturing process to produce the desired characteristics.
Alloy steels may be produced in structural sections, sheets, plates, and bars for use in the as-rolled condition, and these steels can obtain better physical properties than are possible with hot-rolled carbon steels.
These alloys are used in structures where the strength of material is especially important, for example in bridge members, railroad cars, dump bodies, dozer blades, and crane booms. The following list describes some of the common alloy steels:
Nonferrous metals contain either no iron or only insignificant amounts used as an alloy, and are nonmagnetic. The following list will introduce you to some of the common nonferrous metals that SWs may encounter and/or work with. Additional information about their properties and usage is available in Steelworker Advanced.
When working with lead, take proper precautions! Lead dust, fumes, or vapors are highly poisonous!
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When you are selecting a metal to use in fabrication, to perform a mechanical repair, or even to determine if the metal is wieldable, you must be able to identify its basic type. A number of field identification methods can be used to identify a piece of metal. Some common methods are surface appearance, spark test, chip test, magnet test, and occasionally a hardness test.
Sometimes you can identify a metal simply by its surface appearance. Table 1 indicates the surface colors of some of the more common metals.
Table 1 Surface Appearance of Some Common Metals
|Metal||Color||Color and Structure|
|Unfinished, unbroken surface||Freshly filed surface||Newly fractured surface|
|Aluminum||Light gray||White||White: finely crystalline|
|Brass and Bronze||Reddish-yellow, yellow-green, or brown||Reddish-yellow to yellowish-white||Red to yellow|
|Copper||Reddish-brown to green||Bright copper color||Bright red|
|Iron, Cast-gray||Dull gray||Light silvery gray||Dark gray: crystalline|
|Iron, Cast-white||Dull gray||Silvery white||Silvery white: crystalline|
|Iron, Malleable||Dull gray||Light silvery gray||Dark gray: finely crystalline|
|Iron, Wrought||Light gray||Light silvery gray||Bright gray|
|Lead||White to gray||White||Light gray: crystalline|
|Monel metals||Dark gray||Light gray||Light gray|
|Nickel||Dark gray||Bright silvery white||Off-white|
|Steel, Cast and Steel, Low-carbon||Dark gray||Bright silvery gray||Bright gray|
|Steel, High-carbon||Dark gray||Bright silvery gray||Light gray|
|Steel, Stainless||Dark gray||Bright silvery gray||Medium gray|
As you can see by studying the table, a metals surface appearance can help you identify it, and if you are unsure, you can obtain further information by studying a fresh filing or a fresh fracture. If a surface examination does not provide you with enough information for a positive identification, it should give you enough information to place the metal into a class.
In addition to the color of the metal, distinctive marks left from manufacturing also help in determining the identity of the metal.
Inspecting the surface texture by feel may also provide another clue to its identity.
When visual clues from surface appearance, filings, fractures, manufacturing marks, or textural clues from the feel of the surfaces do not give enough information to allow positive identification, other tests become necessary.
Some are complicated and require equipment Seabees do not usually have. However, the following are a few additional simple tests, which are reliable when done by a skilled person: spark test, chip test, magnetic tests, hardness test.
You perform the spark test by holding a sample of the unidentified material against an abrasive wheel and visually inspecting the spark stream. This test is fast, economical, convenient, easily accomplished, and requires no special equipment. As you become a more experienced Steelworker, you will be able to identify the sample metals with considerable accuracy. You can use this test to identify scrap-salvaged metal, which is particularly important when you are selecting material for cast iron or cast steel heat treatment. When you hold a piece of iron or steel (ferrous metals) in contact with a high-speed abrasive wheel, small particles of the metal are torn loose so rapidly that they become red-hot. These small particles of metal fly away from the wheel, and glow as they follow a trajectory path called the carrier line, which is easily followed with the eye, especially when observed against a dark background. The sparks (or lack of sparks) given off can help you identify the metal. Features you should look for include:
Refer to Figure 2 through Figure 8 for illustrations of the various terms used in referring to the basic spark forms produced during spark testing.
Figure 2 Example of spark testing term: STREAM.
Figure 3 Example of spark testing term: SHAFT.
Figure 4 Example of spark testing term: FORK.
Figure 5 Example of spark testing term: SPRIGS.
Figure 6 Example of spark testing term: DASHES.
Figure 7 Example of spark testing term: APPENDAGES.
Steels that have the same carbon content but include different alloying elements are difficult to identify; the alloys have an effect on the carrier lines, the bursts themselves, or the forms of the characteristic bursts in the spark picture.
The alloying element may slow or accelerate the carbon spark, or make the carrier line lighter or darker in color. For example:
You can perform spark testing with either a portable or a stationary grinder, but in either case, the outer rim speed of the wheel should be not less than 4,500 feet per minute with a clean, very hard, rather coarse abrasive wheel. Each point is necessary to produce a true spark.
When you conduct a spark test, hold the metal on the abrasive wheel in a position that will allow the carrier line to cross your line of vision. By trial and error, you will soon find what pressure you need in order to get a stream of the proper length without reducing the speed of the grinder. In addition to reducing the grinders speed, excessive pressure against the wheel can increase the temperature of the spark stream, which in turn increases the temperature of the burst and gives the appearance of a higher carbon content than actually is present.
Use the following technique when making the test:
An abrasive wheel on a grinder traveling at high speed requires respect, and you need to review some of the safety precautions associated with this tool (Figure 9).
Figure 9 Example of a grinders OSHA-designated safety points.
Vibration can cause the wheel to shatter, and when an abrasive wheel shatters, it can be disastrous for personnel standing in line with the wheel.
Grinding wheels require frequent reconditioning.
Dressing is the term you use to describe the cleaning of the working face of an abrasive wheel. Proper dressing breaks away dull abrasive grains, smoothes the surface, and removes grooves. The wheel dresser shown in Figure 10 is used for dressing grinding wheels on bench and pedestal grinders.
Figure 10 Typical wheel dresser.
Refer now to Figure 11 through Figure 16 for examples of spark testing results for specific identified material.
Figure 11 Example of low-carbon and cast steel spark stream.
| High-carbon steel
Figure 12 Example of high-carbon spark stream.
|Gray cast iron
Figure 13 Example of gray cast iron spark stream.
Because of their similar spark pictures, you must use some other method to distinguish monel from nickel.
Figure 14 Example of monel and nickel spark streams.
Figure 15 Example of stainless steel spark stream.
Figure 16 Example of wrought iron spark stream.
One way to become proficient in identifying ferrous metals by spark testing is to practice by testing yourself in the blind. Gather an assortment of known metals for testing. Make individual samples so similar that size and shape will not reveal their identities. Number each sample and prepare a master list of correct names with corresponding numbers.
Then, without looking at the number on the sample, spark test it and call out its name to someone assigned to check your identification against the names and numbers on the list. Repeating this self-testing practice will give you some of the experience you need to become proficient in identifying individual samples.
Another simple field test you can use to identify an unknown piece of metal is the chip test. You perform the chip test by removing a small amount of material from the test piece with a sharp, cold chisel. The material you remove can vary from small, broken fragments to a continuous strip. The chip may have smooth, sharp edges, may be coarse-grained or fine-grained, or may have saw-like edges.
The size of the chip is important in identifying the metal, as well as the ease with which you can accomplish the chipping. Refer to Table 2 for information to help you identify various metals by the chip test.
Table 2 Metal Identification by Chip Test
|Aluminum and Aluminum Alloys||Smooth with saw tooth edges. A chip can be cut as a continuous strip.|
|Brass and Bronze||Smooth with saw tooth edges. These metals are easily cut, but chips are more brittle than chips of copper. Continuous strip is not easily cut.|
|Copper||Smooth with saw tooth edges where cut. Metal is easily cut as a continuous strip.|
|Iron, Cast-white||Small brittle fragments. Chipped surfaces are not smooth.|
|Iron, Cast-gray||About 1/8 inch in length. Metal is not easily chipped; therefore, chips break off and prevent smooth cut.|
|Iron, Malleable||Vary from 1/4 to 3/8 inch in length (larger than chips from cast iron). Metal is tough and hard to chip.|
|Iron, Wrought||Smooth edges. Metal is easily cut or chipped, and a chip can be made as a continuous strip.|
|Lead||Any shape may be obtained because the metal is so soft that it can be cut with a knife.|
|Monel||Smooth edges. Continuous strips can be cut. Metal chips easily.|
|Nickel||Smooth edges. Continuous strips can be cut. Metal chips easily.|
|Steel, Cast and Steel, Low-carbon||Smooth edges. Metal is easily cut or chipped, and a chip can be taken off as a continuous strip.|
|Steel, High-carbon||Show a fine-grain structure. Edges of chips are lighter in color than chips of low-carbon steel. Metal is hard, but can be chipped in a continuous strip.|
A magnet test is another method you can use to aid in a metals general identification. Remember: ferrous metals are iron-based alloys and normally magnetic; nonferrous metals are nonmagnetic. This test is not 100 percent accurate because some stainless steels are nonmagnetic, but it can aid in the first differentiation of most metals. When dealing with stainless steel, there is no substitute for experience.
Hardness is the property of a material to resist permanent indentation. One simple way to check for hardness in a piece of metal is to file a small portion of it. If it is soft enough to be machined with regular tooling, the file will cut it. If it is too hard to machine, the file will not cut it. This method will indicate whether the material being tested is softer or harder than the file, but it will not tell exactly how soft or hard it is.
The file can also be used to determine the harder of two pieces of metal; the file will cut the softer metal faster and easier. The file method should be used only in situations when the exact hardness is not required. This test has the added advantage of needing very little in the way of time, equipment, and experience.
Because there are several methods of measuring exact hardness, the hardness of a material is always specified in terms of the particular test used to measure this property. Rockwell, Vickers, or Brinell are some of the methods of testing.
Of these tests, Rockwell is the one most frequently used, and requires a Rockwell hardness testing machine. The basic principle used in the Rockwell test is that a hard material can penetrate a softer one, and the amount of penetration is measured and compared to a scale.
For ferrous metals, usually harder than nonferrous metals, a diamond tip is used for depth penetration measurement and the hardness is indicated by a Rockwell C number. On nonferrous metals, which are softer, a metal ball is used for surface indentation measurement and the hardness is indicated by a Rockwell B number.
Consider lead and steel for an idea of the property of hardness. Lead can be scratched with a pointed wooden stick, but steel cannot because it is harder than lead.
You can get a more complete explanation of the various methods used to determine the hardness of a material from commercial books or books located in your base library.
This handbook has introduced you to the basics of the different types of metals and the simple field and shop methods you can use to identify them. From here, you can begin to build on your experiences to become a seasoned steelworker considered a resident expert on metals.
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1. What term is used to describe the equivalent of the Steelworker rating in civilian construction?
2. A material must be primarily composed of _____ to be considered a ferrous metal.
3. Ferrous metals are typically _____.
4. Which type of iron is one of the main raw materials used to make steel?
5. What characteristic of pig iron limits its use?
6. What material do Steelworkers use the most?
7. Cast iron is any iron containing greater than _____ alloy.
8. What process is used to produce malleability in cast iron?
9. What group of steel is best suited for the manufacture of crane hooks and axles?
10. What groups specifications cover high-strength steels?
11. What groups specifications cover stainless steels?
12. What stainless steel is normally nonmagnetic?
13. What common alloy steel is used to make high-quality hand tools?
14. Which of the following metals is nonferrous?
15. What combination of elements in proper proportion make bronze?
16. What action does the letter T signify when used in conjunction with a numbering system that classifies different aluminum alloys?
17. What manufacturing marks can you look for when a metals color does not provide positive identification?
18. When applying the spark test to a metal, you notice the spark stream has white shafts and forks only. What does this condition indicate about the metal under test?
19. What metal produces a spark stream about 25 inches long with small and repeating sparklers of small volume that are initially red in color?
20. Which of the following metals produces the shortest length spark stream?
21. You perform the chip test by removing a small amount of material from the test piece with a _____.
22. You can depend on a magnetic test for 100% accuracy to determine a ferrous metal.
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