stainless steel & phospher bronze
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STAINLESS STEEL
Composition :
When an alloy of steel contains more than approximately 10 ½% Chromium it can beclassified as a stainless steel. This is because Chromium has a high affinity for Oxygen
and forms a stable Oxide film on the surface of the steel. This film is resistant to further
chemical or physical change.tainless steels can be di!ided into four ma"or groups# namely $artensitic# erritic#
&ustenitic and 'uplex.
The Martensitic Group
This group contains a minimum of 1(% Chrome and usually a maximum of 1)% *ith
Carbon in the range of 0.0+ to (.0%. 'ue to the high Carbon content of the steel it
responds *ell to heat treatment to gi!e !arious mechanical strengths# such as hardness.
When heat treated this group of steels sho* a useful combination of corrosion resistance
and mechanical properties that ,ualify them for a *ide range of applications. These steelsare all magnetic.
The Ferritic Group
This group contains a minimum of 1-% Chrome and Carbon in the range 0.0+ 0.(%.
The increase in Chromium gi!es increased corrosion resistance at high temperatures.
/o*e!er it can not be heat treated therefore its applications are limited. These steels aremagnetic.
The Austenitic Group
This group contains Chromium in the range 1- (% and ic2el in the range + (0%#
*ith !arious elements added in an effort to achie!e desired properties. When fullyannealed this group exhibits a useful range of mechanical and physical properties. These
steel are normally non magnetic.
Duplex Stainless Steels
This relati!ely ne* group has a balance of Chromium# ic2el# $olybdenum and itrogen to gi!e a near e,ual mix of austenite and ferrite. The result is a high strength#
highly corrosion resistant material. 3ecommended extended use *ithin temperature limitsof 0 to 4500 6C due to embrittlement. They are referred to by 7 numbers# or
manufacturer8s trade names.
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9roperties:
/igh oxidationresistance in air at ambient temperature is normally achie!ed *ith
additions of a minimum of 15% by *eight; chromium# and up to (<% is used for harshen!ironments.=1(> The chromium forms a passi!ation layer of chromium???; oxide Cr (O5;
*hen exposed to oxygen. The layer is too thin to be !isible# and the metal remainslustrous. The layer is imper!ious to *ater and air# protecting the metal beneath. &lso# this
layer ,uic2ly reforms *hen the surface is scratched. This phenomenon is called passi!ation and is seen in other metals# such as aluminium and titanium. Corrosion
resistance can be ad!ersely affected if the component is used in a nonoxygenated
en!ironment# a typical example being under*ater 2eel bolts buried in timber .
When stainless steel parts such as nuts and bolts are forced together# the oxide layer can
be scraped off# causing the parts to *eld together. When disassembled# the *elded
material may be torn and pitted# an effect 2no*n as galling. This destructi!e galling can
be best a!oided by the use of dissimilar materials for the parts forced together# for
example bron@e and stainless steel# or e!en different types of stainless steels martensiticagainst austenitic;# *hen metaltometal *ear is a concern. itronic alloys reduce the
tendency to gall through selecti!e alloying *ith manganese and nitrogen. ?n addition#threaded "oints may be lubricated to pre!ent galling.
&pplications :
tainless steelAs resistance to corrosion and staining# lo* maintenance and familiar lustre
ma2e it an ideal material for many applications. There are o!er 10 grades of stainlesssteel# of *hich fifteen are most commonly used. The alloy is milled into coils# sheets#
plates# bars# *ire# and tubing to be used in coo2*are# cutlery# hard*are# surgical
instruments# ma"or appliances# industrial e,uipment for example# in sugar refineries; andas an automoti!e and aerospace structural alloy and construction material in large buildings. torage tan2s and tan2ers used to transport orange "uice and other food are
often made of stainless steel# because of its corrosion resistance and antibacterial
properties. This also influences its use in commercial 2itchens and food processing plants# as it can be steamcleaned and sterili@ed and does not need paint or other surface
finishes.
tainless steel is used for "e*ellery and *atches *ith 51<B being the type commonly
used for such applications. ?t can be refinished by any "e*eler and *ill not oxidi@e or turn blac2.
ome firearms incorporate stainless steel components as an alternati!e to blued or
par2eri@ed steel. ome handgun models# such as the mith Wesson $odel <0 and the
Colt $1D11 pistol# can be made entirely from stainless steel. This gi!es a highluster finish similar in appearance to nic2el plating. 7nli2e plating# the finish is not sub"ect to
fla2ing# peeling# *earoff from rubbing as *hen repeatedly remo!ed from a holster;# or
rust *hen scratched.
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ome automoti!e manufacturers use stainless steel as decorati!e highlights in their
!ehicles.
PHOSPHER BRONZE
Composition
Phosphor bronze is an alloy of copper *ith 5. to 10% of tin and a significant
phosphorus content of up to 1%. The phosphorus is added as deoxidi@ing agent during
melting
Properties :
These alloys are notable for their toughness# strength# lo* coefficient of friction# and fine
grain. The phosphorus also impro!es the fluidity of the molten metal and thereby
impro!es the castability# and impro!es mechanical properties by cleaning up the grain boundaries.
Uses :
9hosphor bron@e is used for springs# bolts and !arious other items used in situations
*here resistance to fatigue# *ear and chemical corrosion are re,uired e.g.# a ship8s propellers in a marine en!ironment;. The alloy is also used in some dental bridges.
Erades &# C and F G C1000# (100# 0-00 are commonly used nonferrous spring alloys.
The combination of good physical properties# fair electrical conducti!ity and moderate
cost ma2e 9hosphor Hron@e round# s,uare# flat and special shaped *ire desirable formany springs and electrical contacts and a *ide !ariety of *ire forms *here cost of
properties does not prescribe Heryllium copper . =