Chapter 5
5-2. What types of properties can be altered through heat treatment?
Strength, toughness, machinability, wear resistance, and corrosion resistance
5-77. For what type of products or product mixers might a batch furnace be preferred to a continuous furnace?
Batch furnaces, where the workpiece remains stationary throughout its treatment, are preferred for large parts or small lots of a particular part or grade of steel.
6-41. What is the role of chip-breakers in free-machining steels?
Chip breakers help reduce the length of contact between the chip and cutting tool, thereby reducing associated friction and heat, as well as required power and wear on the cutting tool. They also reduce the likelihood of chip entanglement in the machine and make chip removal much faster.
6-73. What is the dominant mechanical property of white cast iron?
The dominant mechanical property of white cast iron is its extreme hardness, brittleness, and high abrasion resistance.
7-26. Why do aluminum and aluminum alloys present special problems when welding?
Pure aluminum is very reactive and forms a tight, adherent oxide coating on the surface as soon as it is exposed to air. This oxide coating causes difficulty when welding. To produce consistent quality resistance welds, it is usually necessary to remove the tenacious oxide immediately before welding. For fusion welding, special fluxes or protective inert gas atmospheres must be used to prevent material oxidation.
5-7. What are some possible objectives of annealing operations?
Some possible objectives of annealing operations are to reduce strength or hardness, remove residual stresses, improve machinability, improve toughness, restore ductility, refine grain size, reduce segregation, stabilize dimensions, and alter the electrical or magnetic properties of the material.
6-1. Why might it be important to know the prior processing history of an engineering material?
The final properties of metals are clearly affected by their past processing history. The particular details of the smelting and refining process control the resulting purity and type and nature of any influential contaminants. The solidification process imparts structural features that may be transmitted to the final product. Preliminary operations such as the rolling of sheet of plate often impart directional variations to properties, and their impact should be considered during subsequent processing and use.
6-45. What are some of the coating materials that have been applied to precoated steel sheet?
The entire spectrum of dipped and plated metals (including aluminum, zinc, and chromium), vinyls, paints, primers, and other polymers or organics
7-3. In what ways might the nonferrous metals offer attractive ease of fabrication?
Nonferrous metals often possess certain properties or combinations of properties that are not available in the ferrous metals, such as:
1. Resistance to corrosion
2. Ease of fabrication
3. High electrical and thermal conductivity
4. Light weight
5. Strength at elevated temperatures
6. Color
Nearly all of the nonferrous alloys possess at least two of these listed qualities, and some possess nearly all.
7-43. What are some of the attractive characteristics of the zinc die-casting alloys?
For the purpose of die-casting alloys, zinc offers low cost, a low melting point, and the attractive property of not adversely affecting steel dies when in molten metal contact.
5-18. What are the six major mechanisms that can be used to increase the strength of a metal?
1. Solid-solution strengthening
2. Strain hardening
3. Grain-size refinement
4. Precipitation hardening
5. Dispersion strengthening
6. Phase transformations
6-2. What is a ferrous material?
An iron-based metal or alloy
6-50. What feature is responsible for the observed corrosion resistance of stainless steels?
A thin, chromium-oxide based layer that is tough, adherent, transparent, and self-healing when oxygen is present
7-9. What is the primary use of commercially pure copper?
Electrical applications
7-65. What are some of the medical applications of engineering materials?
A number of materials have been used or adapted for medical applications, including joint replacements, medical implants, and medical devices.
5-48. What is hardenability? How does it differ from hardness?
- Hardenability (depth/volumetric property) is the depth of hardening (martensite formation) achieved after quenching.
- Hardness (surface-level property) is a measure of a material’s resistance to penetration or deformation.
6-4. Why is the recycling of steel so attractive compared to the manufacture of new steel from virgin ore?
All steel is recyclable and this recycling does not involve any loss in material quality. Because steel is magnetic, it is easily separated and recovered from demolished buildings, junked automobiles, and discarded appliances. The overall recycling rate for steel is nearly 90%. Two-thirds of all new steel is produced from old steel, and each ton of recycled steel saves over 4000lbs of raw materials and about 75% of the energy required to make new steel.
6-61. What is a tool steel?
Tool steels are high-carbon, high-strength, ferrous alloys that have been modified by alloy additions to provide a desired balance of strength, toughness, and wear resistance when properly heat-treated.
7-13. Why might the term bronze be potentially confusing when used in reference to a copper-based alloy?
8-1. Discuss the terms "plastics" and "polymers". In what sense are they interchangeable, and in what sense are they not?
Plastics, from a technical viewpoint, refers to engineered materials characterized by large molecules that are built up by the joining of smaller molecules.
Polymers are when a number of basic units (monomers) link to form a large molecule in which there is a repeated unit.
All plastics are polymers and both involve long chains of repeating monomer units. Polymers can be natural. Plastics are generally defined as man-made. Plastics are an engineered subset of polymers.
5-54. Why is an oil quench less likely to produce quench cracks than water or brine?
Oil quenches provide slower cooling rates than water or brine, which reduces the amount of quench induced distortion and the likelihood of quench cracking.
6-18. Why should plain-carbon steels be given first consideration for applications requiring steel?
Compared to other engineering materials, the plain carbon steels offer high strength and high stiffness, coupled with reasonable toughness. They are also the lowest-cost steel material.
6-71. What are some of the attractive engineering properties of gray cast iron?
Gray cast iron is readily available, cheap, and offers excellent compressive strength, excellent machinability, good resistance to adhesive wear and galling, and outstanding sound and vibration dampening characteristics. It also has high thermal conductivity, low rate of thermal expansion, good stiffness, resistance to thermal fatigue, 100% recyclability, and good corrosion resistance.
7-23. What features might limit the mechanical uses and applications of aluminum and aluminum alloys?
A serious weakness of aluminum from an engineering viewpoint is its relatively low modulus of elasticity, which is also about 1/3 that of steel. In addition, aluminum alloys rapidly lose their strength and dimensions change by creep when temperature is increased.
8-18. What are the four most common thermoplastic polymers?
1. Polyethylene
2. Polypropylene
3. Polystyrene
4. Polyvinylchloride