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.