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PROPERTIES, IDENTIFICATION, AND HEAT TREATMENT OF …

TC 9-524 Chapter 2 PROPERTIES, IDENTIFICATION, ANDHEAT TREATMENT OF METALSGENERALPURPOSEThis chapter contains basic information pertaining toproperties and identification of metal and heat -treatingprocedures used for metals. For more specific information onmetal and heat -treating techniques, refer to TM CLASSIFICATIONAll metals may be classified as ferrous or nonferrous. Aferrous metal has iron as its main element. A metal is stillconsidered ferrous even if it contains less than 50 percent iron,as long as it contains more iron than any other one metal.

The temper designation is separated from the basic four-digit identification number by a dash; for ex-ample, 2024-T6. In this case there is an aluminum alloy, 2024, with a T6 temper (solution heat treated and then artificially aged). Figure 2-11 shows the numerals 2 through 10 that have been assigned in the AA system to indicate specific sequences

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Transcription of PROPERTIES, IDENTIFICATION, AND HEAT TREATMENT OF …

1 TC 9-524 Chapter 2 PROPERTIES, IDENTIFICATION, ANDHEAT TREATMENT OF METALSGENERALPURPOSEThis chapter contains basic information pertaining toproperties and identification of metal and heat -treatingprocedures used for metals. For more specific information onmetal and heat -treating techniques, refer to TM CLASSIFICATIONAll metals may be classified as ferrous or nonferrous. Aferrous metal has iron as its main element. A metal is stillconsidered ferrous even if it contains less than 50 percent iron,as long as it contains more iron than any other one metal.

2 Ametal is nonferrous if it contains less iron than any metals include cast iron, steel, and the various steelalloys, The only difference between iron and steel is the carboncontent. Cast iron contains more than 2-percent carbon, whilesteel contains less than 2 percent. An alloy is a substancecomposed of two or more elements. Therefore, all steels arean alloy of iron and carbon, but the term alloy steel normally refers to a steel that also contains one or more otherelements. For example, if the main alloying element istungsten, the steel is a tungsten steel or tungsten alloy.

3 Ifthere is no alloying material, it is a carbon steel. NonferrousNonferrous metals include a great many metals that are usedmainly for metal plating or as alloying elements, such as tin,zinc, silver, and gold. However, this chapter will focus onlyon the metals used in the manufacture of parts, such asaluminum, magnesium, titanium, nickel, copper, and 9-524 GENERALPROPERTIES OF METALSThe internal reactions of a metalknown as mechanical properties. Theto external forces aremechanical propertiesare directly related to each other.

4 A change in one propertyusually causes a change in one or more additional example, if the hardness of a metal is increased, thebrittleness usually increases and the toughness usuallydecreases. Following is a brief explanation of the mechanicalproperties and how they relate to each STRENGTHT ensile strength is the ability of a metal to resist being pulledapart by opposing forces acting in a straight line (Figure 2-1).It is expressed as the number of pounds of force required topull apart a bar of the material 1 inch wide and 1 inch STRENGTHS hear strength is the ability of a metalfractured by opposing forces not acting into resist beinga straight line(Figure 2-2).

5 Shear strength can be controlled by varying thehardness of the 9-524 COMPRESSIVE STRENGTHC ompressive strength is the ability of a metal to withstandpressures acting on a given plane (Figure 2-3).ELASTICITYE lasticity is the ability of metal to return to its original sizeand shape after being stretched or pulled out of shape (Figure2-4).DUCTILITYD uctility is the ability of a metal to be drawn or stretchedpermanently without rupture or fracture (Figure 2-5). Metalsthat lack ductility will crack or break before is the ability of a metal to be hammered,rolled, or pressed into various shapes without rupture orfracture (Figure 2-6).

6 2-3TC 9-524 TOUGHNESST oughness is the ability of a metal to resist fracture plusthe ability to resist failure after the damage has begun. Atough metal can withstand considerable stress, slowly orsuddenly applied, and will deform before is the ability of a metal to resist penetration andwear by another metal or material. It takes a combination ofhardness and toughness to withstand heavy pounding. Thehardness of a metal limits the ease with which it can bemachined, since toughness decreases as hardness hardness of a metal can usually be controlled by AND WELDABILITYM achinability and weldability are the ease or difficultywith which a material can be machined or RESISTANCEC orrosion resistance is the resistance to eating or wearingaway by air, moisture.

7 Or other AND ELECTRICAL CONDUCTIVITYHeat and electrical conductivity is the ease with which ametal conducts or transfers heat or is the tendency of a material to fracture orbreak with little or no deformation, bending, or is usually not a desirable mechanical , the harder the metal, the more brittle it OF METALSGENERALPart of the metalworker s skill lies in the ability to identifyvarious metal products brought to the shop. The metalworkermust be able to identify the metal so the proper work methodscan be applied.

8 For Army equipment, drawings should beavailable. They must be examined in order to determine themetal to be used and its heat TREATMENT (if required). If nodrawing is available, knowledge of what the parts are going todo will serve as a guide to the type of metal to OF METALSS imple tests can be made in the shop to identify the ability to judge metals can be developed onlythrough personal experience, practice these tests with knownmetals until familiar with the reactions of each metal to eachtype of TestThis test includes such things as the color and appearanceof machined as well as unmachined TestSome metals can be quickly identified by looking at thesurface of the broken part or by studying the chips producedwith a hammer and TestThis is a simple identification test used to observe thecolor, spacing, and quantity of sparks produced by grinding.

9 Itis a fast and convenient method of sorting mixed steels withknown spark characteristics. This test is best conducted byholding the steel stationary and touching a high-speed portablegrinder to the steel with sufficient pressure to throw a sparkstream about 12 inches long. The characteristics of sparksgenerated by a spark grinding test are shown in Figure spark patterns provide general information about thetype of steel, cast iron, or alloy steel. In all cases, it is best touse standard samples of metal when comparing their sparkswith that of the test 9-5242-5TC 9-524 THE ROCKWELL HARDNESS NUMBER ISDETERMINED BY THE DEPTH OF THEIMPRESSION WHILE THE BRINELL HARDNESSNUMBER IS DETERMINED BY THE AREA OF THEIMPRESSIONFile TestOne simple way to check for hardness in a piece of metal isto file a small portion of it.

10 If it is soft enough to be machinedwith regular tooling, the file will cut it. If it is too hard tomachine, the file will not cut it. This method will indicatewhether the material being tested is softer or harder than thefile, but it will not tell exactly how soft or hard it is. The filecan also be used to determine the harder of two pieces ofmetal; the file will cut the softer metal faster and easier. Thefile method should only be used in situations when the exacthardness is not required.


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