Heat Treatment 1 ex 5

Stapler (~HK$ 5)
Approx. 15 components
- How do we select the best material for each component?
- How are each of these manufactured?
Car: ~ 15,000 parts;
Boeing 747 plane: ~6 million parts
Intel core 2 duo processor: 65 nm feature size, 291 million transistors
Properties of materials
Steels are heat treated for one of the following reasons:
Mechanical properties of materials
Strength, Toughness, Hardness, Ductility,
Elasticity, Fatigue and Creep
Physical properties
Density, Specific heat, Melting and boiling point,
Thermal expansion and conductivity,
Electrical and magnetic properties
Chemical properties
Oxidation, Corrosion, Flammability, Toxicity, …
Ferrous metals: carbon-, alloy-, stainless-, tool-and-die steels
Non-ferrous metals: aluminum, magnesium, copper, nickel,
titanium, super alloys, refractory metals,
beryllium, zirconium, low-melting alloys,
gold, silver, platinum, …
Plastics: thermoplastics (acrylic, nylon, polyethylene, ABS,…)
thermosets (epoxies, Polymides, Phenolics, …)
elastomers (rubbers, silicones, polyurethanes, …)
Ceramics, Glasses, Graphite, Diamond, Cubic Boron Nitride
Composites: reinforced plastics, metal-, ceramic matrix composites
Nanomaterials, shape-memory alloys, superconductors, …
 Heat Treatment
 is the controlled heating and cooling of metals to alter their
physical and mechanical properties without changing the
product shape.
 Heat Treatment
 is often associated with increasing the strength of material,
but it can also be used to alter certain manufacturability
objectives such as improve machining, improve formability,
restore ductility.
Heat Treatment
 A: Definition
 "Hardening is the process of heating a piece of steel to a
temperature within or above its critical range and than
cooling it rapidly"
 (Begeman, M.L. - Manufacturing processes - 1977)
 B: Definition
 "Hardening is that property of a material that enables it to
resist plastic deformation, penetration, indentation,
 (Lindberg, R. A. - Material & Manufacturing Technology 1968)
 Hardening:
 Hardening of steel is done to increase the strenth and wear
properties. One of the pre- requisites for hardening is sufficient
carbon and alloy content
 Softening:
 Softening is done to reduce strength or hardness, remove residual
stresses, improve tough-ness, restore ductility, refine grain size or
change the electromagnetic properties of the steel.
 Material Modification:
 Heat treatment is used to modify properties of materials in
addition to hardening and softening. These processes modify the
behavior of the steels in a beneficial manner to maximize service
life, e.g., stress relieving
 Tempering
 Tempering is a process done subsequent to quench hardening.
Quench-hardened parts are often too brittle. This brittleness is
removed by tempering.
 Tempering results in a desired combination of:
 Hardness, Ductility, Toughness, Strength, structural stability
 Cooling alloy fast enough to retain a supersaturated
solid solution of alloying constituents without
introducing adverse metallurgical or mechanical
conditions; water is most common quenching media
(immersion or spray); other media include air blasts,
soap solutions, ind hot oil.
 Measures the difference in penetration between a minor and
major load
 Minor load 10 Kg
 Major load 60(a), 100 (B), 150 ( c) kg
 A= Diamond, B= 1/16 in. ball, C= diamond
 Rockwell scale runs to 130 bur only useful in range 20 -100
 l. Carburizing or Case Hardening
 Steel is heated in contact with some carbonaceous material
in solid, liquid, or gas form; the steel absorbs carbon, which
is gradually diffused into the interior of the part.
 Pack carburizing
 (.030 to .160 thick); it employs packing parts in charcoal
or coke.
 Gas carburizing
 (.005 to .030 thick); it employs hydrocarbon fuels.
 Liquid carburizing
 (up to .250 thick); it employs a cyanide salt bath
Heating by oxyacetylene flame to above critical temperature;
heated part immediately quenched by water spray; produces
hard surface with ductile backing.

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