Manufacturing Processes Chapter 6

What is an alloy?

An alloy is a metal comprised of two or more elements, at least one of which is metallic.

What important alloy is formed from lead and tin?

Solder.

Besides high carbon content, what other alloying element is characteristic of the cast irons?

Silicon.

Which of the following metals is noted for its good electrical conductivity (one best answer): (a) copper, (b) gold, (c) iron, (d) nickel, or (e) tungsten?

(a).

Which one of the following elements is the most important alloying ingredient in steel: (a) carbon, (b) chromium, (c) nickel, (d) molybdenum, or (e) vanadium?

(a).

Which one of the metallic elements is the most abundant on the earth: (a) aluminum, (b) copper, (c) iron, (d) magnesium, or (e) silicon?

(a).

The strength and hardness of steel increases as carbon content (a) increases or (b) decreases?

(a).

Solid solution alloying is the principal strengthening mechanism in high-strength low-alloy (HSLA) steels: (a) true or (b) false?

(a).

(a) Name the four principal noble metals. (b) Why are they called noble metals?

(a) The principal noble metals are copper, gold, platinum, and silver. (b) Nobel metals are so-named because they are chemically inactive.

Which of the following alloying elements are most commonly associated with stainless steel (two best answers): (a) chromium, (b) manganese, (c) molybdenum, (d) nickel, and (e) tungsten?

(a) and (d).

Traditional brass is an alloy of which of the following metallic elements (two correct answers): (a) aluminum, (b) copper, (c) gold, (d) tin, and (e) zinc?

(b) and (e).

From which of the following ores is aluminum derived: (a) alumina, (b) bauxite, (c) cementite, (d) hematite, or (e) scheelite?

(b).

Plain carbon steels are designated in the AISI code system by which of the following: (a) 01XX, (b) 10XX, (c) 11XX, (d) 12XX, or (e) 30XX?

(b).

Which of the following is the most important cast iron commercially: (a) ductile cast iron, (b) gray cast iron, (c) malleable iron, or (d) white cast iron?

(b).

Which one of the following metals has the lowest density: (a) aluminum, (b) magnesium, (c) tin, or (d) titanium.?

(b).

Which of the following properties or characteristics are inconsistent with the metals (two correct answers): (a) good thermal conductivity, (b) high strength, (c) high electrical resistivity, (d) high stiffness, and (e) ionic bonding?

(c) and (e).

A steel with 1.0% carbon is known as which one of the following: (a) eutectoid, (b) hypoeutectoid, (c) hypereutectoid, or (d) wrought iron?

(c).

Which of the following metals has the highest density: (a) gold, (b) lead, (c) platinum, (d) silver, or (e) tungsten?

(c).

The predominant phase in the iron-carbon alloy system for a composition with 99% Fe at room temperature is which one of the following: (a) austenite, (b) cementite, (c) delta, (d) ferrite, or (e) gamma?

(d).

Which one of the following metals has the lowest melting point: (a) aluminum, (b) lead, (c) magnesium, (d) tin, or (e) zinc?

(d).

Which one of the following is not a common alloying ingredient in steel: (a) chromium, (b) manganese, (c) nickel, (d) vanadium, (e) zinc?

(e).

What is a solid solution in the context of alloys?

A solid solution is an alloy in which one of the metallic elements is dissolved in another to form a single phase.

Distinguish between a substitutional solid solution and an interstitial solid solution

A substitutional solid solution is where the atoms of the dissolved element replace atoms of the solution element in the lattice structure of the metal. An interstitial solid solution is where the dissolved atoms are small and fit into the vacant spaces (the interstices) in the lattice structure of the solvent metal.

What are some of the mechanisms by which the alloying elements other than carbon strengthen steel?

All of the alloying elements other than C strengthen the steel by solid solution alloying. Cr, Mn, Mo, and Ni increase hardenability during heat treatment. Cr and Mo improve hot hardness. Several of the alloying elements (Cr, Mo, V) form hard carbides with C, which increases wear resistance. Vanadium inhibits grain growth during heat treatment which improves strength and toughness.

Identify some of the properties for which aluminum is noted?

Aluminum is noted for its low density, high electrical and thermal conductivity, formability, good corrosion resistance due to the formation of a tough oxide film on its surface, and ability to be alloyed and strengthened to achieve good strength-to-weight ratios.

What is an intermediate phase in the context of alloys?

An intermediate phase is an alloy formed when the solubility limit of the base metal in the mixture is exceeded and a new phase, such as a metallic compound (e.g., Fe3C) or intermetallic compound (e.g., Mg2Pb) is formed.

What is the predominant alloying element in all of the stainless steels?

Chromium.

What are the two major groups of metals? Define them.

Ferrous metals, which are based on iron; and nonferrous, which includes all others.

Why is austenitic stainless steel called by that name?

It is called austenitic because this alloy exists in its austenitic phase at room temperature. The reason is that nickel has the effect of enlarging the austenitic temperature range to include room temperature.

What is the most important engineering property of copper that determines most of its applications?

Its high electrical conductivity (low resistivity).

What are some of the noteworthy properties of magnesium?

Magnesium is noted for its very low density (lightest of the structural metals), propensity to oxidize (which can cause problems in processing), and low strength; however, it can be alloyed and strengthened by methods similar to those used for aluminum alloys to achieve respectable strength-to-weight ratios.

The copper-nickel system is a simple alloy system, as indicated by its phase diagram. Why is it so simple?

The Cu-Ni alloy system is simple because it is a solid solution alloy throughout its entire composition range.

What is the range of carbon percentages which defines an iron-carbon alloy as a steel?

The carbon content ranges from 0.02% to 2.11%.

What is the range of carbon percentages which defines an iron-carbon alloy as cast iron?

The carbon content ranges from 2.11% to about 5%.

Identify some of the common alloying elements other than carbon in low alloy steels.

The common alloying elements in low alloy steel are Cr, Mn, Mo, Ni, and V.

What elements are traditionally alloyed with copper to form (a) bronze and (b) brass?

The elements are (a) tin and (b) zinc, respectivley.

What are some of the important applications of nickel?

The important applications of Ni are (1) as an alloying ingredient in steel, e.g., stainless steel; (2) for plating of steel to resist corrosion; and (3) to form nickel-based alloys noted for high-temperature performance and corrosion resistance.

Identify some of the important applications of zinc.

The important applications of Zn are (1) die castings - zinc is an easy metal to cast; (2) as a coating in galvanized steel; (3) as an alloying element with copper to form brass.

What is so special about the superalloys? What distinguishes them from other alloys?

The superalloys are generally distinguished by their strength and resistance to corrosion and oxidation at elevated temperatures.

What are the three basic methods by which metals can be strengthened?

The three basic methods are (1) alloying to form solid solutions and two-phase structures which are stronger than the elemental metals; (2) cold working, in which the strain-hardened metal is stronger and harder than the unstrained metal; and (3) heat treatment - most of the commercial heat treatments are designed to increase the strength of the metal.

The superalloys divide into three basic groups, according to the base metal used in the alloy. Name the three groups.

The three groups are (1) iron-based alloys, (2) nickel-based alloys, and (3) cobalt-based alloys.

What are the noteworthy properties of titanium?

Titanium is noted for its high strength-to-weight ratio, corrosion resistance (due to the formation of a thin but tough oxide film), and high temperature strength.

What are some of the general properties that distinguish metals from ceramics and polymers?

Typical metallic properties include: high strength and stiffness, good electrical and thermal conductivity, and higher density than ceramics or polymers.

(a) Name the important refractory metals. (b) What does the term refractory mean?

a) The refractory metals include columbium (Cb), molybdenum (Mo), tantalum (Ta), and tungsten (W). Mo and W are the most important. (b) Refractory means the capability to withstand high temperature service.