Heat Treatment

Motivation

Approx. 15 components

- How do we select the best material for each component?

- How are each of these manufactured?

Stapler (~HK$ 5)

Car: ~ 15,000 parts;Boeing 747 plane: ~6 million partsIntel core 2 duo processor: 65 nm feature size, 291 million transistors

Properties of materials

Mechanical properties of materialsStrength, Toughness, Hardness, Ductility,Elasticity, Fatigue and Creep

Chemical propertiesOxidation, Corrosion, Flammability, Toxicity, …

Physical propertiesDensity, Specific heat, Melting and boiling point,Thermal expansion and conductivity,Electrical and magnetic properties

Steels are heat treated for one of the following reasons:

Materials

Nanomaterials, shape-memory alloys, superconductors, …

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

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, scratching"

(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

QUENCHING

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.

HARDNESS TESTINGROCKWELL TESTMeasures the difference in penetration between a

minor and major loadMinor load 10 KgMajor load 60(a), 100 (B), 150 ( c) kgA= Diamond, B= 1/16 in. ball, C= diamond

Rockwell scale runs to 130 bur only useful in range 20 -100

HARDENINGSURFACE HARDENINGl. Carburizing or Case HardeningSteel 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

FLAME HARDENING:

Heating by oxyacetylene flame to above critical temperature; heated part immediately quenched by water spray; produces hard surface with ductile backing.