Heat Treatment 1 ex

awfulhihatUrban and Civil

Nov 15, 2013 (3 years and 6 months ago)

94 views



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 parts

Intel core 2 duo processor: 65 nm feature size, 291 million transistors

Properties of materials


Mechanical properties of materials


Strength, Toughness, Hardness, Ductility,


Elasticity, Fatigue and Creep

Chemical properties


Oxidation, Corrosion, Flammability, Toxicity, …

Physical properties


Density, 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 TESTING


ROCKWELL TEST


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


HARDENING


SURFACE
HARDENING


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


FLAME
HARDENING:


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