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Gandhinagar Institute of Technology
Submitted by: Faculty Guide:Pavan Narkhede Prof. Amit Patel(130120119111)
Academic Year(2015-16)
ACase Study
On
EFFECT OF ALLOYING ELEMENT LIKE NICKEL, CHROMIUM AND
TUNGSTON
Under a subject of
Design of machine Element
B.E. III, Semester – V_B2
(Mechanical Engineering)
Effect of alloying element
1)Nickel :
Nickel is a silver-white transition metal with a
relative atomic mass (12C=12) of 58.69, an atomic number of 28, a melting point of 1,453°C and a density of 8.902 kg/dm3. It is in group VIII on the periodic table. It has a face-centred-cubic (f.c.c.) crystal structure. Nickel is ferromagnetic up to 353°C, its Curie point.
Effect of nickel on stainless steel In stainless steels, nickel has no direct influence on the passive layer but
exerts a beneficial effect, particularly in sulphuric acid environments.
Thanks to nickel austenitic stainless steels, i.e. Fe-Cr-Ni (Mo) alloys, exhibit
a wide range of mechanical properties that are unparalleled by any other
alloy system today. For instance, these alloys exhibit excellent ductility and
toughness, even at high strength levels and these properties are retained
up to cryogenic temperatures.
Nickel promotes the resistance to corrosion of the nickel-based alloys as
compared with the iron-based alloys under conditions where the passive
layers may be absent, or may be destroyed locally or uniformly. For
example, pitting corrosion tends to progress less rapidly in high-nickel
alloys.
In Fe-Ni alloys, their original features can be explained by two major
phenomena. A one is the abnormally low expansion in compositions close
to INVAR (36% Ni) due to a large spontaneous volume magnetrostriction
and exceptionally high electrical permeabilities resulting from the
disappearance of various anisotropies in the vicinity of 80% Ni.
Nickel forms the base of high temperature super alloys because of its ability
to develop an adherent oxide and precipitation hardening phases based on
Ni3Al.
Nickel is a moderate strengthener, and consequently large amounts can be
added to low-alloy steel before strength increases to an undesirable level.
In low-alloy steel, nickel appears to have a greater overall, beneficial effect
on toughness transition temperature than any other substitutional alloying
element.
NICKEL IN MARTENSITIC STAINLESS STEEL
Effect on Microstructure
Nickel is one element that increases the
amount of Cr that can be added and still
form austenite at high temperatures,
necessary to get martensite formation
when quenched.
Effect on Corrosion Properties
Most standard martensitic SS have relatively low Cr content, 11.5-13.5%,
and thus have relatively low general corrosion resistance compared to
austenitic grades with higher Cr content.
Nickel increases the corrosion resistance of the martensitic grades to
both general corrosion and localized corrosion. The higher Cr S43100
has the highest corrosion resistance of any of the standard martensitic
SS.
All the martensitic SS have their best corrosion resistance in the
hardened and tempered condition; corrosion resistance is much poorer
in the annealed condition.
NICKEL IN MARTENSITIC STAINLESS STEEL
Martensitic-ferritic-austenitic grades (triplex)
1.4418 grade is typically 65% martensite, 30% austenite and 5% ferrite in the tempered condition.It is a weldable martensitic SS with corrosion resistance, good strength and good ductility.Major use in small to medium-sized water turbines (Francis, Kaplan), also used in Pulp & Paper industry.
Super-Martensitic grades
Super-martensitic grades were developed specifically for high pressure,
generally sweet gas applications for offshore use.
There are grades with 2.5-6.5% nickel, some containing Mo, some
without.
They are produced as seamless or welded pipe, but they must be welded
on an offshore pipe-laying platform.
A short Post Weld Heat Treatment is usually performed (e.g. a few
minutes at 600 o C).
NICKEL IN PH GRADE STAINLESS STEEL
Role of Nickel in PH Grades
All PH grades contain nickel, which is needed to obtain austenite to
martensite transformation.
Nickel gives higher corrosion resistance (general
corrosion, localized corrosion, stress corrosion
cracking).
Nickel gives improved ductility and notch toughness.
Example of Nickel as critical raw material in technologies for Mitigating the Climate Change and Low Carbon
Economies.
2)Chromium :
Chromium is a silver-grey transition metal with
a relative atomic mass 12(C=12) of 51.996, an
atomic number of 24, and a melting point of
1,875°C and a density of 7.190 kg/dm3. It is in
group VI of the periodic table. Chromium has a
body-centred-cubic (B.Sc.) crystal structure.
The Effect of Chromium in Stainless SteelsThe properties that distinguish stainless steels i.e. Fe-Cr-(Mo) alloys and
Fe-Cr-Ni-(Mo) alloys from other corrosion-resistant materials depend
essentially on chromium. The high degree of reactivity of chromium is
the basis for the effectiveness of chromium as an alloying element in
stainless steels.
The resistance of these metallic alloys to the chemical effects of
corrosive agents is determined by their ability to protect themselves
through the formation of an adherent, insoluble film of reaction
products that shields the metal substrate from uniform and localised
attack.
The protective film called passive layer or passive film. It is a very fine
layer on the surface, of the order of 1.0 to 2.0 nm, which reduces the
corrosion rate to negligible levels and has a structure similar to
chromite.
For passivation to occur and remain stable, the Fe-Cr alloy must have a
minimum chromium content of about 11% by weight, above which
passivity can occur and below which it is impossible.
The corrosion resistance of Fe-Cr alloys tends to improve as the
chromium content is increased, and definite changes happen at about
11% Cr, and again around 17% Cr.
USES OF CHROMIUM :
Chrome Metal Chrome metal consists of nearly 100% chromium. Impurities include Fe, Al, and Si.There are two ways of producing chromium metal, the aluminothermy process chrome oxide and the electrolytic process using ferrochromium or chromic acid. Chromium metal standard grades range from 99% to 99.4%. Higher grades are available as 99.6% Cr and degassed quality with 99.8% Cr and low gas.Chrome metal is mainly used in the production of specialty alloys, nickel and cobalt -based alloys (super alloys) where low iron is required. Due to their unique high temperature and corrosion resistance properties, these high performance alloys are used in the most critical environments, such as aeronautic, oil & gas production, land based turbines, petrochemical and chemical processing.In addition, chromium metal powder is used in the production of welding electrodes and cored wires, aluminium briquettes and master alloys.
SPECIAL STEELSChrome brings amazing properties to the metals with which it is alloyed. Add it to carbon steel in sufficient quantities and the steel miraculously becomes “stainless” – in other words, corrosion resistant, mechanically strong, and heat resistant, hard wearing, shiny and glamorous. Stainless steel, which accounts for some 66% of the use of chrome today, is found everywhere in modern life, from nuclear reactors to exhaust pipes, architecture, kitchenware and a host of other applications.The corrosion resistance and shiny appearance of stainless steel come from an extremely thin, continuous chromium-oxide film which
spontaneously forms on the surface of the steel, in the presence of air. This film renders the surface inert to chemical reaction, thus protecting steel from corrosive attack. Should the surface be damaged or scratched, this “passive” layer instantly re-forms. Thanks to chrome, stainless steel literally self-heals. In fact, chrome is the one and only magic ingredient making stainless steel “stainless”, whatever the grade.Speciality steels produced for applications such as tools, injection moulds, camshafts, dies, bearings and mill rollers also derive the high mechanical strength, hardness and heat-resistance required from their chrome content.Certain exceptionally demanding applications require an alloy known as chrome metal, which, is almost pure chrome (99%). Chrome metal provides the solidity and resistance to wear and high temperatures required for critical applications in the aircraft, gas, petrochemical and nuclear sectors.Chrome is also used in alloyed cast irons, to bestow hardness and resistance to abrasion and impact. These alloys are used for applications such as pumps, valves, pipes, rolls and wear plates.
OTHER USES OF CHROMEChromium and health
Chromium is a metallic element which exists primarily in the mineral,
chromite. This mineral is the main constituent of chrome ore and the
only commercial source of chromium. After processing, chromium
occurs in several forms, also called oxidation states...
Chromium in cement
World-wide, there is an annual production of some 1.5 billion tonnes of
cement - the concrete of our modern global infrastructure, from roads
to houses, from dams to water treatment systems, from schools to
hospitals...
Chromium and leather
Making leather from the skins of animals, reptiles and fish is one of
society's oldest industries. Most leather is made from the hides of
animals reared for their meat and hence tanning converts what would
otherwise be waste products from the food industry into valuable retail
products...
3)TUNGSTON :
Tungsten is known chiefly for its strong tendency to form extremely hardand stable_carbides. This property, in fact, is the basis for the most important use of tungsten insteels: as a constituent of high speed and other tool steels. About 30% of all tungsten_produced is used in this fashion. Carbide cutting tools account for onehalf of the totaltungsten market; alloy steels, superalloys, lamp filaments and miscellaneous applications make up the remainder.The economic history of tungsten has been one of the most erratic of all
steel alloying_constituents. Prices have risen and fallen abruptly in irregular cycles throughout the_years. Adequate supply has been an occasional problem, despite massive government_and private stockpile accumulation.It has been estimated that China holds over 50% of world tungsten reserves, followedby Canada and the U.S. Bolivia, Peru, Thailand and Korea also have important_reserves. The Chinese and, more recently, the Russians have taken over.
Effect of Tungsten AlloyTungsten is a refractory metal with a high melting point and a very high density. It can be used in a pure form but it becomes more useful as an engineering material when alloyed with small quantities of other elements to form a group of products sometimes_referred to as Tungsten Heavy Metal Alloys (WHAs). These alloys usually contain 9097% tungsten and initial forming requires a_proce
ss of pressing and sintering. Wrought shapes can then be produced however nearfinalshape sintering is more common.Most of the major applications for tungsten alloys are based on its very high density where it is used to control or distribute weight in_some way. Tungsten is up to 65% denser than lead and 130% denser than steel. Radiation shielding is a second common application area. Tungsten alloys generally have high strength and good creep resistance however at low temperatures ductility is poor making it unsuitable for some applications. Corrosion resistance and magnetic properties canal so be factors in alloy selection.
Tungsten can be used in a granular form to provide balance weight when used as simple ballast. However, more advanced applications form an actual component out of a suitable tungsten alloy making it a functioning part of a final assembly. Examples of this are found in aerospace (wing balances), defence(missile fin balance) and motorsport. Other application areas include computer disk balances, ordnance (kinetic energy_penetration), marine balancing components and gyroscope components.