Note Chp 4 material science 281 uitm em110

MEC 281 MATERIALS SCIENCE

CHAPTER 4

FERROUS AND NON-FERROUS METALS

Rasdi bin DeramanFakulti Kejuruteraan Mekanikal

UiTM Pulau Pinang

5.1 TYPES OF METAL ALLOYS

Low Alloy steels are usually considered to be those containing a total of less than 5% of such added constituents.

Ferrous alloys include steels and cast irons.

Metal alloys are often grouped into two classes –ferrous and nonferrous.

Generally, carbon is the most important commercial steel alloy. Increasing carbon content increases hardness and strength and improves hardenability. But carbon also increases brittleness and reduces weldability because of its tendency to form martensite. This means carbon content can be both a blessing and a curse when it comes to commercial steel.

The ferrous alloys are classified based on the percentage of carbon present in the ferrous. Mostly the contain of carbon in steel is less than 2 %. Mean while the carbon contain in cast iron is about 2 to 4.3%.

When the contain of carbon in steel is less than 0.76%, it is called hypoeutectoid steel. While the contain of carbon in range 0.76 to 2 % which is called hypereutectoid steel.

5.2 CLASSIFICATION OF FERROUS ALLOYS

• Steels are iron carbon alloys that may contain carbon less than 2.0 percent.

• Steel is considered to be carbon steel when no/ minimum content is specified for chromium, cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect; when the specified minimum for copper : not exceed 0.40% manganese : not exceed 1.65% silicon : not exceed 0.60%

•The microstructures of steels are normally ferrite and relatively soft and weak but good ductility and toughness.

5.3 STEELS

5.3.1 PLAIN CARBON STEELS

Although called plane carbon actually the iron with less than 1% Carbon alloy contains a small amount of manganese, phosphorus, sulfur, and silicon.

Its strength is primarily a function of its carbon content, increasing with carbon amount. The ductility of plain carbon steels decreases as the carbon content increases.

Some disadvantages of plain carbon steel are as follow:+ The hardenability is low.+ The physical properties (Loss of strength and embrittlement) are decreased by both high and low temperatures+ Subject to corrosion in most environments Plain carbon steels are divided into three groups:+ Low carbon steels + Medium carbon steels + High carbon steels

5.3.2 Low Carbon SteelsHas less than 0.3% Carbon and are unresponsive to heat treatments intended to form martensite. Usually a microstructures consist of ferrite and pearlite, and the material is generally used as it comes from the cold work processes.

Advantages:• Posses good formability• Posses good weldability: best of all metals : Note: As a percentage of carbon increases there is a tendency for the metal to harden and crack.• Lowest cost and should be considered first• Rated at 55-60% machinability (soft and drags which builds up heat on the tool.

Typical Uses:• 0.1- 0.2%: Automobile panels, rivets, nails, wire, and pipelines • 0.2 - 0.3%: concrete reinforcing bars, structural shapes (I-beams, angle irons, machine parts, and sheet steels (tin cans).

Low Carbon Steel combine with 10% of other alloying elements such as Copper, Vanadium, Nickel, and Molybdenum produced High Strength Low Alloy (HSLA) steels and possess higher strength than plain low carbon steels. They are ductile, formable, and machinable.

The HSLA steels are more resistant to corrosion environment and they have replaced in many applications where structure strength is critical (e.g., bridges, towers, support columns in high-rise buildings, and pressure vessels).

The Cranes can be made taller because of HSLA steel

5.3.3 Medium Carbon Steel Have between 0.3 to 0.8% Carbon.Special Advantages:• Machinability is 60-70%; therefore cut slightly better than low carbon steels. Both hot and cold rolled steels machine better when annealed. Less machinable than high carbon steel since that is very hard steel. • Good toughness and ductility. • Extremely popular and have numerous applications.• Fair formability• Responds to heat treatment but is often used in the natural condition.

Typical Uses:• 0.3-0.4 : lead screws, gears, spindles, shafts, and machine parts.• 0.4-0.5: crankshafts, gears, axles, and heat-treated machine parts.• 0.6-0.7: called “low carbon tool steel” and is used where a keen edge is not necessary, but where shock strength is wanted e.g. set screws, and screwdrivers.• 0.7-0.8: tough and hard steel. Anvil faces, band saws, hammers, wrenches, cable wire, etc.

Over 0.8% Carbon and less than 1.4% Carbon are the hardest, strongest, and yet least ductile of the carbon steels.

Disadvantages:

• Toughness and formability and hardenability are quite low.• Not recommended for welding.• Usually joined by brazing with low temperature silver alloy making it possible to repair or fabricate tool-steel parts without affecting their heat treated condition.

Advantages:

• Hardness is high• Wear resistance is high• Fair formability• Quench cracking is often a problem with severe quenching

5.3.4 High Carbon Steels

Typical Uses:

• 0.8-0.9% C: punches for metal, rock drills, shear blades, cold chisels, rivet sets, and many hand tools.• 0.9-1.0% C: used for hardness and high tensile strength, springs, cutting tools, press tools, and striking dies.• 1.0-1.15% C: drills, taps, milling cutters, knives.• 1.1-1.2% C : cold cutting dies, wood working tools.• 1.2-1.3% C : files, reamers, knives, tools for cutting wood and brass.• 1.3-1.4% C : used where a keen cutting edge is necessary, razors, saws, and where wear resistance is important.

5.3.5 Stainless Steels

Stainless steels are at least 12 percent chromium and many

have high nickel contents. The three basic types of stainless

are Austenitic, Ferritic and Martensitic.

• Martensitic stainless steels make up the cutlery grades. They have the least amount of chromium, offer high hardenability, and when welding require to prevent cracking in the heat-affected zone (HAZ).

• Ferritic stainless steels have 12 to 27 percent chromium with small amounts of austenite-forming alloys.

• Austenitic stainless steels offer excellent weldability, but austenite isn’t stable at room temperature. The most important austenite stabilizer is nickel, and others include carbon, manganese, and nitrogen.

Classification of stainless steel

There are various types of Tool Steel for gauges, tools, instruments and wear surfaces. Some typical applications include shear knives, slitter knives, punches, blanking and drawing dies, rolls, mandrels, pins, chisels, cams, spindles, and moulds for die casting

5.3.6 Tool Steels

These are high carbon steel alloys that have been designed to provide wear resistance and toughness combined with high strength.Tool steels typically have excess carbides (carbon alloys) which make them hard and wear-resistant. Most tool steels are used in a heat-treated state, generally hardened and tempered.

5.4 CAST IRONS

The wide spectrum of properties of cast iron is controlled by three main factors: (1) the chemical composition of the iron;(2) the rate of cooling of the casting in the mould (which part on the section thicknesses in the casting);(3) the type of graphite formed (if any). Cast irons may often be used in place of steel at considerable cost savings. The design and production advantages of cast iron include:- low tooling and production cost- ready availability- good machinability without burring- readily cast into complex shapes- high inherent damping - excellent wear resistance and high hardness (particularly white irons)

5.4.1 Gray Cast Irons

• The composition of Carbon and Silicon contents of gray cast irons vary between 2.5 to 4.0% and 1.0 to 3.0% respectively.

• The microstructures of gray cast irons are consist of graphite flakes and normally surrounded by an alpha ferrite or pearlite matrix.

• The formation of graphite occurs because of the cooling rate is too slow where the austenite in unstable position and brake down to give graphite microstructure.

• This cast iron is known as a gray iron because of the gray appearance of its freshly fracture.

• The mechanical characteristic of Gray cast Irons are as follows: - Less hard and brittle - Very weak in tension due to the pointed and sharp end of graphite flakes, where the failure of component initiated at this point. - Good during compression which graphite acts as a cushion or sponge that could absorb the compression energy. - Low shrinkage in mould due to formation of graphite flakes. - Good dry bearing qualities due to graphite.

Park Bench Sprockets

Manhole Covers with Frames

GREY CAST IRON PRODUCTS

Gas Burners

THE MICRISTRUCTURE OF GREY CAST IRON

5.4.2 White Cast Irons

• The composition of Carbon and Silicon contents for white cast irons are in range between 2.5 to 4.0% and less than 1.0% respectively.

• With a rapid cooling rate most of the carbon in the cast irons consist of pearlite and cementite (Fe3C).

• The mechanical characteristic of White cast Irons are as follows: - Relatively very hard, brittle and not weldable compared to gray cast iron, since it is obtained from rapid cooling process. - When it’s annealed, it becomes malleable cast iron.

THE MICRISTRUCTURE OF WHITE CAST IRON

• A fracture surface of these alloy has a white appearance and it is called white cast iron.

• Typical Uses: Necessitate a very hard and wear resistance surface such as rollers in rolling mills, railroads wheel.

5.4.3 Ductile (Nodular) Cast Irons

THE MICRISTRUCTURE OF DUCTILE CAST IRON

• Typical Uses: Valves, pump bodies, gears crankshafts, and other machine components.

• Ductile cast iron, which is sometimes called nodular or spheroidal graphite cast iron. It gets this name because its carbon is in the shape of small spheres, not flakes.

• Magnesium or cerium is added to the iron before casting occurs. The effect of these material is to prevent the formation of graphite flakes during the slow cooling of the iron.

• The structures of the cast irons is mainly pearlite with nodules of graphite.

• A heat treatment process can be applied to a pearlite nodular iron to give a microstructure of graphite nodules in ferrite. The ferrite structure is more ductile but has less tensile strength than the pearlite form. It’s also weldable.

TEE pipe

5.4.4 Malleable Cast Irons• Malleable cast iron is produced by the heat treatment of

white cast irons. • Heating white iron at temperatures 800 c to 900 c for 50

hours in a neutral atmosphere (to prevent oxidation) causes a decomposition of the cementite, forming graphite in the form of clusters/ rossettes surrounded by a ferrite or pearlite matrix depending on cooling rate.

• The mechanical characteristic of malleable cast iron is similar to nodular cast iron and give higher strength and more ductility and malleability. The silicon content is low.

THE MICRISTRUCTURE OF MALLEABLE

CAST IRON

MALLEABLE CASTIRON PRODUCTS

CLAMPS

The term non-ferrous alloys are used for those alloys which

do not have iron as the base element. Generally, the non-

ferrous alloys commonly used in engineering application are

Aluminium alloys, Copper alloys, Magnesium alloys, Titanium alloys etc.

The advantages of Ferrous alloys over non-ferrous alloys are as follows: a) Generally greater strengths.b) Generally greater stiffness, i.e. larger values of Young’s Modules.c) Better for welding.

NONFERROUS ALLOYS

The advantages of Non-ferrous alloys over ferrous alloys are

as follows:

a)  Good resistance to corrosion without special processes having to be carried out.

b)  Most non-ferrous alloys have a much lower density and hence lighter weight components can be produced.

c) Casting is often easies because of the lower melting points.

d) Cold working processes are often easier because of the greater ductility.

e) Higher thermal and electrical conductivities.f) More decorative colours.

Non-ferrous metals can be improved the mech. properties by using solution treatment, ageing & precipitation hardening, as shown in figure below.

Aluminium

Properties:• Low density (2.7 g/cm3)• Very good corrosion resistance in common environments (due to protective oxide layer, can be improved by anodising)• Ductile (FCC crystal structure)• High electrical and thermal conductivity• High strength to weight ratio • BUT, low melting point: 660°C (e.g. melting point of iron is 1535°C).

restricts use at high temperatures.

Applications:• Aerospace & air travel: structural

components of planes, fuel tanks in spacecraft

• Building and construction: panels, roofs, window frames…

• Packaging: beverage cans, foil…• Transport: bikes, car engine parts, bus

bodies…• Electrical: e.g. overhead cables

Classification of Aluminium• Generally Aluminium alloys can be divided into two groups:

# Heat Treatable Alloys

# Non- Heat Treatable Alloys

• Wrought alloys are designed specifically for fabrication by hot and cold forming processes, such as rolling, forging and extrusion.

• Casting alloys (or foundry alloys) are exclusively used for the fabrication of cast parts and have favourable characteristics for this process. They exhibit high fluidity in the liquid state and good resistance to hot cracking during solidification.

Classification of Aluminium (Cont…)

International Alloy Designation System

• Classification of Wrought Alloys

Wrought Aluminum Alloys• Primary Fabrication: Usually

semiconsciously cast by direct chill method.

• Ingots are homogenized and rolled. • Classification: According to major alloying

elements.• Four digits: First digit - major group of

alloying elements. • Second digit: Impurity limits.• Last 2 digits: Identify aluminum alloy.

Temper Designations• Temper designations are designated by

hyphen.• Example: 2024-T6

F – as fabricatedO – AnnealedH – Strain hardened.T – Heat treated to produce stable temper

H1 – Strain hardened alloy.H2 – Strain hardened and partially annealed.H3 - Strain hardened an annealed

T1 – Naturally agedT3 – Solution heat treated.T4 – Solution heat treated and naturally aged.T5 - Cooled and artificially aged.T6 - Solution heat treated and artificially aged.T7 - Solution heat treated and stabilized.T8 - Solution heat treated, cold worked and then artificially aged.

Cast Aluminum Alloys (Cont..)

Heat Treatment of Aluminium Alloys

• Precipitation Strengthening : Creates fine dispersion of precipitated particles in the metal and hinder dislocation movement.

• Basic steps :# Solution heat treatment: Alloy sample

heated to a temperature between solvus and solidus and soaked at that temp.

# Quenching: Sample then quenched to room temperature in water.

# Ageing: Solutionized and quenched sample is then aged to form finely dispersed particles.

Precipitation HardeningHeat treatment normally involves; (1) Solution treatment at relatively high temp. (To) within the single phase (α) region, in order to dissolve the alloying elements, (2)  Rapid cooling, usually to room temp. (T1) across the solvus line to exceed the solubility limit. This leads to obtain a supersaturated solid solution (SSSS) in aluminuim. Equilibrium structure is α+β, but limited diffusion does not allow β phase to form.

(3)   Controlled decomposition of the SSSS to form a finely dispersed precipitate, usually by ageing for convenient times and temp. (T2) where diffusion is appreciable – β phase starts to form.

Effects of Ageing on StrengthAgeing curve:

• Plot of strength or hardness vs. aging time.• As aging time increases alloy becomes stronger harder

and less ductile.

• Over-ageing decreases

strength & hardness.

5.5.2Copper And Its Alloys

(Chemical symbol Cu) - Element No. 29 of the periodic system, atomic weight 63.57. A characteristically reddish metal of bright luster, highly malleable and ductile and having high electrical and heat conductivity; melting point 1083°C; boiling point 2336°C; specific gravity 8.94. Universally used in the pure state as sheet, tube, rod and wire and also as alloyed by other elements as an alloy with other metals. i. Brasses

Copper base alloys in which zinc is the principal added element. Brass is harder and stronger than either of its alloying elements copper or zinc; it is malleable and ductile; develops high tensile with cold-working and not heat treatable for purposes of hardness development.

• Gilding Brass: 85% copper and 15% Zn is used for jewellery because it has a colour resembling that of gold.

 • Cartridge brass: 70% copper and 30% Zn is used in

the production of cartridge and shell cases.

• Muntz metal: 60% copper and 40% zinc is used for castings and hot-worked products. High strength brasses are developed from this by adding other elements such as 0.8% Pb .

• Duplex brass (’): 45% Zn is formed at a low temperature (453C). The presence of the ’ phase produces a drop in ductility but increase in tensile strength to the maximum value of brass. Duplex brass ’ have little industrial application but have good properties for hot forming processes, e.g. extrusion.

Types of brasses are as follows:

ii. BronzesBronzes that contain up to 8% Sn are bronzes and can be cold worked.

Phosphor bronze is might have about 95% Cu, 5% Sn and 0.02 to 0.4 %P. These alloys are used for electrical contact, clips, instrument components. Aluminium bronze is consist of copper and aluminium alloys. The contain about 10% Al are used for casting. It has high strength and good resistance to corrosion and wear. Typical applications of such materials are pump casing, gears, valves etc.

 Casting bronzes that contain Zn are called gunmetal. Gunmetal contains 88%Cu, 10% Sn and 2%Zn. This alloy finds general use for marine components.  Beryllium Copper that contain with 2-3 % beryllium with optionally fractional percentages of nickel or cobalt. Alloys of this series show remarkable age-hardening properties to give alloys with very high tensile strength (1400Mpa). Because of such hardness and good electrical conductivity, beryllium-copper is used in electrical switches, springs, etc.

5.5.3Titanium And Its AlloysTi has a relatively low density, 4,500kg/cu. m. It has a relatively low strength when pure but alloying gives a considerable increase in strength.

Ti is an expensive metal, its high cost reflecting the difficulties experienced in the extraction and formation of the material. Because of excellent corrosion resistance, commercially pure Ti is used for chemical plant components, surgical implants, marine and aircraft engine parts, etc.Ti alloy contain 92.5% Ti, 5% Al, 2.5% Sn are strong and maintain their strength at high temp. but are difficult to work. The alloys have good weldability and are used where high temp strength is required, e.g. steam turbine blades. The 90% Ti, 6% Va alloy can be readily welded, forged and machined. This alloy is used for both high and low temp. applications, e.g. rocket motor cases, turbine blades.

5.5.4Magnesium And Its Alloys

(Chemical symbol Mg.) - Element No. 12 of the periodic system; atomic weight 24.305. Mg has a density of 1,700 kg/cu. m with a melting point of approximately 627°C. A silver-white light malleable, ductile metallic element that occurs abundantly in nature. The metal is used in metallurgical and chemical processes; in photography and in the manufacture of pyrotechnics because of the intense white light it produces on burning. It has a low tensile strength, needing to be alloyed with the other metals to improve its strength. Mg has an HCP crystal structure is relatively soft and has a low elastic Modulus.

Mg alloys are used in applications where lightness is the primary consideration, e.g. in aircraft and spacecraft. Mg – Al - Zn alloys and Mg – Zn – Zicronium are the main two groups of alloys in general use. A general purpose wrought alloy has about 93% Mg, 6% Zn, 0.3% Mn can be forged, extruded, welded and has excellent machinability.

5.5.5Nickel And Its Alloys

Ni has a density of 8,880 kg/cu. m and melting point of 1455C. Ni has good tensile strength at high temperature and can be both cold and hot working, has good machining properties and can be joined by welding, brazing and soldering.

Ni is used as the base metal for a number of alloys with excellent corrosion resistance. Monel is the name given to commercial alloys with Ni-Cu. Monel 400 has 66.5% Ni and 31.5% Cu has high strength, toughness and weldability. It is highly resistant to sea water, alkalis, many acids and superheated stem, hence its used for marine fixtures and fasteners, food processing plant components.

5.5.6Zinc And Its Alloys

Zn has a density of 7,100 kg/cu. m. Pure Zn has a melting point of only 419 C. Zn is frequently used as a coating on steel in order to protect that material against corrosion, the product being known as galvanized steel.

The main use of Zn alloys is for die casting. They are excellent for this purpose because of low melting points and the lack of corrosion of dies used with them. Zn alloys contain 95.6% Zn, 4.3%Al, 0.03%Cu, 0.06% Mg are ductile and tensile strength 285 Mpa. Zn alloys can be machined and to a limited extend, worked. Soldering and welding are not generally feasible.

REFRACTORY METAL -Properties: High melting temperatures, Large elastic moduli, hardnesses, and strengths.

For example;Tungsten (W), melts at 3,410°C, which is morethan double that of iron and ten times that of lead.

Because of their high melting points and ease of oxidation, refractory metals are usually worked in powder form. Powder metallurgy (PM) processes play an important role in the fabrication of refractory metals.

Five main elements of refractory metals widely used are Tungsten (W), Molybdenum (Mo), Niobium (Nb), Tantalum (Ta) and Rhenium (Re).

       PROPERTY W Re Ta Mo Nb(Cb)

Melting Point (ºC) 3410 3180 2996 2617 2468

Density (g/cm3) 19.3 21.0 16.6 10.2 8.6

Thermal Expansion (ppm/ºC) 4.5 6.2 6.3 4.8 7.3

Thermal Conduct. (W/cm-ºC) 1.70 0.40 0.52 1.40 0.54

Electrical Resistivity (µ ohm-cm) 5.3 18.5 13.1 5.4 14.4

  Tensile Strength 20ºC        (GPa)

0.7-3.5 0.7-2.0 0.2-0.5 0.7-1.4 0.4-0.7

           1000ºC    (GPa) 0.3-0.5 0.4-0.7 0.1 0.1-0.2 0.04-0.1

Young’s Modulus 20ºC        (GPa)

410 450 185 330 130

             1000ºC     (GPa) 365 360 170 280 110

REFRACTORY METAL (Cont…)

REFRACTORY METAL (Cont…)

Limitation of refractory metals: - some experience rapid oxidation at elevated temperatures.

Typical applications: extrusion dies, structural parts in space vehicles, incandescent light filaments, x-ray tubes, and welding electrodes.

REFRACTORY METAL (Cont…)

- Excellent strength at high temperatures. Even when heated to 10000C tungsten rocket nose cones still have twice the tensile strength iron has at room temperature.

- Very high melting point (2468 - 34100C). High melting points of tungsten, tantalum and molybdenum make them useful in processing molten metals and minerals such as glass making.

- Excellent wear and abrasion resistance. Refractory metals, often in alloy form extend the life of seals, bushings, nozzles, valve seats and many points of high wear. Alloys with gold and silver also make excellent long-life contact points or electronic equipment.

- High resistance to thermal shock. The stresses of rapid expansion due to heat would destroy most metal filaments in just a few on-off cycles. A tungsten filament, because of its high melting point and good non- sag characteristic, will withstand thousands of on-off cycles and still remain intact.

REFRACTORY METAL (Cont…)

- Hardness. Cutting tools today are made of tungsten carbide. For cutting, forming steel and other metals, even for drilling oil wells and in mining.

REFRACTORY METAL (Cont…)

SUPER ALLOYThe main characteristics of super alloys are as

follows:- Able to maintain high strengths at high temperatures.- Good corrosion and oxidation resistance at high temperatures, means that capable to withstand high temp. & oxidizing atmospheres for long time periods.- Good resistance to creep and rupture at high temp.

SUPER ALLOY (Cont…)

Typical applications of super alloys are as follows:aircraft turbines, gas turbine, nuclear reactors, andpetrochemical equipment and biomedical implants..

Generally, there are three main classes of super alloys:Nickel (Ni) – BaseNickel-Ferrous (Ni-Fe) – Base (cheaper than Ni-base)Cobalt (Co) – Base

NOBLE METAL

Properties- Highly resistant to corrosion or oxidation,

especially at elevated temperatures -Soft and ductile. -They tend to be very valuable.

Typical applications -Jewellery , dental restoration materials, coins,catalysts, and thermocouples.

Type of materialsGold (Au), silver (Ag), platinum (Pt), & palladium (Pd).

TQ