Strength and ductility

METALS AND METAL ALLOYS Plain Carbon and Low-Alloy Steels 

Material/Condition Yield Strength (MPa [fai]) Tensile Strength (MPa Percent Elongatioi 

GRAPHITE, CERAMICS, AND SEMICONDUCTING MATERIALS Aluminum oxide 99.9% pure - 282-551 (41-80)  

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Austempering. Lower bainite is generally as strong as and somewhat more ductile than tempered martensite. Austempering, which is an isothermal heat treatment that results in lower bainite, offers an alternative heat treatment for obtaining optimum strength and ductility if the specimens are sufficiently small. 

Intergranular Corrosion Selec tive corrosion in the grain boundaries of a metal or alloy without appreciable attack on the grains or crystals themselves is called intergranular corrosion. When severe, this attack causes a loss of strength and ductility out of proportion to the amount of metal actually destroyed by corrosion. 

The most important displacive transformation is the one that happens in carbon steels. If you take a piece of 0.8% carbon steel "off the shelf" and measure its mechanical properties you will find, roughly, the values of hardness, tensile strength and ductility given in Table 8.1. But if you test a piece that has been heated to red heat and then quenched into cold water, you will find a dramatic increase in hardness (4 times or more), and a big decrease in ductility (it is practically zero) (Table 8.1). 

High Li excellent creep resistance. Good strength and ductility scarce. 

Environments. Among the environmental factors that can shorten life under thermal fatigue conditions are surface decarburization, oxidation, and carburization. The last can be detrimental because it is likely to reduce both hot strength and ductility at the same time. The usual failure mechanism of heat-resistant alloy fixtures in carburizing furnaces is by thermal fatigue damage, evidenced by a prominent network of deep cracks. 

Also, as might be expected, the use of plasticiser has a similar effect to that of increasing the hydroxyvalerate content. It also has a more marked effect on depressing the glass transition temperature and therefore improves properties such as impact strength and ductility at lower temperatures. 

Figure 3.5. Eflett of temperature on the tensile strength of copper (A) effect of annealing on strength and ductility (B) hardened high-conductivity copper 129. ...

The strength and ductility of brasses are well maintained over a range of 300° to -180°C, and castings are easy to make as well as to machine. Brass behaves similarly to copper in chemical plant environments, with somewhat greater rates of attack. 

Aluminum and its alloys are excellent for low temperatures as well as for cryogenic applications because their tensile strength and ductility are increased at low temperatures. 

For some purposes where the strength and ductility of steel are not prerequisites, other metals or materials may be used to advantage, particularly when the component or article is not a load-bearing one. Some of the non-ferrous metals and plastics materials are extremely useful in this respect, especially the latter with their excellent corrosion-resistant properties and ease of formability. Non-ferrous metals in sheet form are often used as roof covering. In such situations they could well become subject to condensation. Condensation could be the result of thermal pumping or internal conditions. Under conditions in which condensation can occur, copper is not normally attacked, but lead, zinc and aluminium may be attacked and corrode from the inside of the building outwards. 

The characteristic mode of corrosion of some alloys may be the formation as a corrosion product of a redeposited layer of one of the alloy constituents, as in the case of the brasses that dezincify, or of a residue of one of the components, as in the case of the graphitic corrosion of cast iron. Particularly in the case of the dezincified brass, the adherent copper is not likely to be removed with the other corrosion products, and therefore the mass-loss determination will not disclose the total amount of brass that has been corroded. This is especially important because the copper layer has very little strength and ductility and the extent of weakening of the alloy will not be indicated by the mass loss. In these cases, also, the mass-loss determinations must be supplemented by, or replaced by, mechanical tests or metallographic examination, or both, to reveal the true extent of damage by corrosion. Difficulties in obtaining accurate mass losses of heavily graphitised specimens have been reported... 

Low carbon steel (mild steel) is the most commonly used engineering material. It is cheap is available in a wide range of standard forms and sizes and can be easily worked and welded. It has good tensile strength and ductility. 

In the equation above, mass carries the same "weight" as strength and ductility (deflection) in developing impulse capacity. 

TABLE 16.2. Strength and Ductility Data for Electrodeposited Metals and Their Wrought Counterparts... 

Beryllium oxide is a component of precious stones, emerald, aquamarine and topaz. Beryllium is utilized in nuclear reactors to moderate the velocity of slow neutrons. It is hot-pressed to appropriate shapes and sizes that yield high strength and ductility for its applications. 

There were essentially two problems associated with malleable irons. One was that the heat treatment procedures were costly. Secondly, it was imperative that the iron solidify in the metastable state. That requirement made production of heavier, slow-cooled sections impossible since they would likely contain free graphite. However, the higher tensile strengths and ductility of malleable irons were desired in some cases. 

Figure 5.18 Influence of annealing temperature on tensile strength and ductility of a brass alloy. Grain structures during recovery, recrystallization, and grain growth are shown schematically. Reprinted, by permission, from W. Callister, Materials Science and Engineering An Introduction, 5th ed., p. 175. Copyright 2000 by John WUey Sons, Inc.

We turn our attention now to some practical aspects of mechanical property determinations. The important quantities such as modulus, strength, and ductility are typically summarized in graphical form on a stress-strain diagram. The details of how the experiment is performed and how the stress-strain diagram is generated are described for some common types of applied forces below. 

A reasonably close match of thermal expansion of the coating and substrate over a wide temperature range to limit failure caused by residual stresses is desired for coatings. Because temperature gradients cause stress even in a well-matched system, the mechanical properties, strength, and ductility of the coating as well as the interfacial strength must be considered. 

Quality of Tin Plates.—The tests for tin plates are ductility, strength, and color and to possess these, the iron used must be of the best quality, and all the process be conducted with care and skill. The following conditions are inserted in some specifications, and will serve to indicate the strength and ductility of first-class tin plates —... 

Impact Modifiers. Notched impact strength and ductility can be improved with the incorporation of impact modifiers, which also can lower the britde— ductile transition temperature and give much improved low temperature toughness. Impact modifiers are rubbers (often olefin copolymers) that are either modified or contain functional groups to make them more compatible with the nylon matrix. Dispersion of the mbber into small (micrometer size) particles is important in order to obtain effective toughening (29). Impact modifiers can be combined with other additives, such as glass fiber and minerals, in order to obtain a particular balance of stiffness and toughness. 

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