Manufacturing Process -Ferrous Metal & Alloys

MANUFACTURING PROCESSMANUFACTURING PROCESS(BMFG 2323)(BMFG 2323)

LECTURE 3LECTURE 3

FERROUS METALS AND ALLOYSFERROUS METALS AND ALLOYS

FERROUS METALS AND ALLOYSFERROUS METALS AND ALLOYS 1

@jurie 2007 – Lecture 3

- Due to the wide range in mechanical, physical, and chemical properties, ferrous metalsand alloys are among the most useful of all metals.

- Contains of iron as their base metal; general categories are carbon and alloy steels, stainless steels, tool and die steels, cast irons, and cast steels.

Produced product:

Sheet steel for automobiles, appliances and containers.

Plates for boilers, ships, and bridges.

Structural members such as I-beams, bar products, crankshafts and railroad rails.

Tools, dies and molds.

Fasteners such as bolts and nuts.



IRON AND STEEL MAKINGIRON AND STEEL MAKING

- The three basic materials used in iron and making steel are:1) Iron ore.2) Limestone.3) Coke.



1) Iron Ore- After it is mined, the ore is crushed into small particles and the impurities are removedby using the magnetic separation techniques.- The ore is formed into pellets by using water and various binders.- Typically, this pellets contains 65% of pure iron and about 25mm in diameter.



Iron ore(after cleaning)

Iron orestorage area

2) Limestone-Function: to remove impurities from molten iron.-It reacts chemically with impurities, acting like a flux which causes the impurities tomelt at low temperature.- It also combines with the impurities to form a slag, where this slag will float over themolten metal.



Limestone (CaCo3 & MgCO3)[after cleaning]

Limestone’s storage area



Limestone mineLimestone mine





3) Coke-Coke is obtained from special grades of bituminous coal, that are heated invertical coke oven to temperatures of up to 11500C and then cooled with waterin quenching towers.

- Functions:i)Generate high level of heat required for the chemical reactions in iron making.ii)Producing CO (removes the O2), which is then used to reduce iron oxide to iron.

Coal mineCoal mine CoalCoal(after cleaning)(after cleaning)





IRON MAKINGIRON MAKING



- All three basic materials – carried to the top of the blast furnace and dumped rightto the bottom section of the furnace.

- Basically, the furnace is a large steel cylinder lined with refractory heat-resistance brick.- The height of the furnace can goes up to 10 story building.- The charge mixture is melted in reaction at 16500C together with air which pre-heated about 11000C, blasted into the furnace through nozzles called tuyeres. - The basic reaction: between O2 and C to produce CO which then reacts with the iron oxideand reduces it to iron.- Preheating the incoming air is necessary because the burning coke alone does not producesufficiently high temperatures for these reactions to occur.- In the blast furnace, the molten metal accumulates at the bottom of the furnace whilethe impurities float on top of the molten metal.

- Slag has many commercial use, and is rarely thrown away.- It often reprocessed to separate any other impurities that may contain.- Slag is used in making cement, fertilizers, building materials and road ballast.

Steel worker at blast furnace tap



Slag



Slag pouredinto ladles

The slag’s storage area

ELECTRIC FURNACESELECTRIC FURNACES

1) Direct Arc



- Source of heat in this furnace is a continuouselectric arc which formed between the threegraphite electrodes (750mm in dia. and 1.5m to2.5m in length) and the charged metal.

- Temperature: 19250C.- Steel scrap, carbon and limestone are droppedinto the electric furnace thru’ the open roof.- The roof then is closed and the electrodes arelowered – turned on the power, and within 2H,the metal melts.

- Next, the current is shut off, the electrodes are raised, thefurnace is tilted, and the molten metal is poured into a ladle.

- The capacities can range: 55 to 82 tones of steel per day.



2) Indirect Arc

INDIRECT ARC TYPEINDIRECT ARC TYPE



3) Induction

- Used for small amount of quantities.

- The metal is placed inside a large pot (madefrom refractory material and surrounded with copper coils)

- The alternating current is passed thru’ thiscopper coils – form heat and melt the metals.

- This type of electric furnace are also usedfor remelting metal for casting.

INDUCTION TYPEINDUCTION TYPE



Scrap chargesScrap chargesoror

Electric furnaceElectric furnace

Electric furnaceElectric furnace

ContinuousContinuouscastingcasting





~ BASIC OXYGEN FURNACE ~~ BASIC OXYGEN FURNACE ~

- The most fastest steel makingprocess.

- 180 tones of pig iron + 82 tonesof scrap are charged into a vessel;fluxing agent (lime) are also added.

- Pure O2 is blown into the furnacefor about 20 min. thru’ a lance, under a pressure of 1250kPa.- Iron oxide is produced due to anoxidation process.

- The oxide react with the carbon inthe molten metal, producing CO +CO2.

- The lance is then retracted, and the furnace is tapped by tilting it – the slag is removed by tilting the furnace at the opposite direction.



The hot metal charge for basic-oxygen furnaceThe hot metal charge for basic-oxygen furnace



~ ~ CASTING OF INGOTSCASTING OF INGOTS ~ ~- Traditional method of making steel.- It is a shaping process of the molten steel into a solid form (ingot) before proceedto further processing such as rolling it into shapes or forging it.- The molten metal is poured from the ladle into ingot molds in which the metal solidifies.- The molds are usually made from blast furnace iron with 3.5% C.- The molds are tapered in order o remove the solidified metal.- At the bottom of the mold, it can be open or closed; if they are open, the molds areplaced on a flat surface.- The cooled ingots are removed from the molds and then lowered into soaking pits to reheated until reach the uniform temperature about 12000C for rolling process purposes.- The quality of the steel produced are depending on the certain reaction occurred duringthe solidification of ingots.- Example: O2 will dissolve in the molten metal during the steelmaking, and most of thisgases are rejected during the solidification of the metal due to when the limitation of solubility of gases in metal decrease sharply as the temperature decreases.- This rejected O2 combines with C to form CO, which causes porosity in the solidified ingot.



- There are 3 types of steel ingots depending on the amount of gases evolved duringsolidification.



1) 1) KILLED STEELKILLED STEEL

- Fully deoxidized steel – therefore, eliminated the porosity.

- In the process of deoxidization, the dissolved O2 in the molten metal will react withelements such as aluminum, silicon, manganese, as well as vanadium to form a metallicoxides, eg: aluminum killed steel.

- Free from any porosity, free of any blowholes, and relatively the mechanical and chemical properties of an ingots are uniform due to the shrinkage during solidification.

- Produce pipe on top of the ingots (shrinkage cavity).



2) 2) SEMI-KILLED STEELSEMI-KILLED STEEL- Partially deoxidized – contains some porosity (occurred at the upper central sectionof the ingot.- Little or no pipe.

3) 3) RIMMED STEELRIMMED STEEL- Has low amount of C (< 0.15%).- The evolved gas are controlled partially by the addition of other element such asaluminum.- The gases produce blowholes along the outer rim of the ingots.- Little or no pipe.- Ductile skin with good surface finish.- If not properly controlled – blowholes may break through the skin and the impuritiestend to segregate toward the center of the ingot.



Picture of Ingots



CONTINUOUS CASTINGCONTINUOUS CASTING(STRAND CASTING)(STRAND CASTING)

- Can produce higher quality steels at reduced cost.- The molten metal in the ladle is cleaned, and thenequalized in temperature by blowing the nitrogengas thru’ it (5 to 10 minutes).- The molten metal then is poured into a reservoir(tundish – can holds up to 3 tons of metal).- The molten metal travels downwards thru’water-cooled copper molds and start to solidify.

- Before starting with the casting process, a solidstarter bar, is inserted at the bottom portion of the mold.- The cooling rate develops a solidified skin(12 to 18mm of thickness).- Purpose, to support the metal itself during traveldownwards at speed ≈ 25 mm/s.



- Additional cooling is provided with water sprays along the travel path of the solidifying

metal.

- The molds – are coated with graphite or solid lubricants – to reduce the friction and

adhesion at the mold-metal interfaces.

- The molds are also vibrated to reduce friction and sticking.

- The continuous cast metal can be cut into desired length – by using techniques of shearing

or computer-controlled torch cutting.

- Sometimes it can be straight away fed into rolling mill for further reduction of the thickness

as well as for the shaping purposes such as channel or I-beams.

- Next, these steel plates will undergo few other processes such as:

a) cleaning by chemicals to remove the surface oxides.

b) cold rolling to improve strength and surface finish.

c) annealing.

d) coating (galvanizing or aluminizing) to improve resistance to corrosion.



REFININGREFINING

- A process of eliminating or separating the impurities, residuals from the melting metal.

- The eliminating process occurs in melting furnace or ladles.

- Create a uniform properties and a greater consistency of composition – produce high-grade

steels and alloys for high performance and critical applications.



~ ~ CARBON AND ALLOY STEELS CARBON AND ALLOY STEELS ~~

TABLE 5.1Product Steel Product SteelAircraft forgings,

tubing, fittingsAutomobile bodiesAxlesBall bearings and racesBoltsCamshaftsChains (transmission)Coil springsConnecting rodsCrankshafts (forged)

4140, 8740

10101040, 4140521001035, 4042, 48151020, 10403135, 314040631040, 3141, 43401045, 1145, 3135, 3140

Differential gearsGears (car and truck)Landing gearLock washersNutsRailroad rails and wheelsSprings (coil)Springs (leaf)TubingWireWire (music)

40234027, 40324140, 4340, 87401060313010801095, 4063, 61501085, 4063, 9260, 615010401045, 10551085

- The most commonly used metals and have a wide variety of applications.- Available in various basic product shapes such as plate, sheet, strip, bar, wire, tube,castings and forgings.



EFFECTS OF VARIOUS ELEMENTS IN STEELSEFFECTS OF VARIOUS ELEMENTS IN STEELS

- Various elements are added to steels in order to impart the properties of materials:harden, strength, toughness, wear resistance, weldability, machinability.

- Generally the higher the percentage of the elements in the steels, the greater the

properties that impart; eg: the higher the C content, the greater the hardenability of

the steels, as well as greater in strength, hardness, and wear resistance. On the other

hand, the higher the C content, there are a reduction of ductility, weldability, and

toughness.



CARBON STEELSCARBON STEELS

- Generally are classified by their proportion (by weight) of carbon content.

- Can be divided into three types:i)Low-carbon steel (mild steel).

-Has less than 0.30% C.-Used for common industrial products and machine components;eg: bolts, nuts, sheet, plate, and tubes).- Do not require high strength.

ii) Medium-carbon steel.- Has 0.30 to 0.60% C.- Generally used in applications which requires higher strength than low-carbonsteel; eg: machinery, automotive, and agricultural equipments parts: (gears,axles, connecting rods, crankshafts, railroad equipment, and parts for metal working machinery.



iii) High-carbon steel.-Has more than 0.60% C.-Generally used for parts requiring strength, hardness, and wear resistance;eg: cutting tools, cable, music wire, springs, and cutlery.- The parts usually are heat treated and tempered after being manufacturedinto shapes.

- Carbon steel containing sulfur and phosphorus which known as resulfurized carbon steels,and rephosphorized carbon steels.



ALLOY STEELSALLOY STEELS

- Steel containing significant amount of alloying element which called alloy steels.

- This type of steels can be heat treated to obtain the desired properties.

- Structural-grade alloy steels are used mainly in construction and transportation industries

due to their high strength.

- Other of alloy steels are used in applications where strength, hardness, creep and fatigue

resistance, and toughness are required.



HIGH-STRENGTH LOW ALLOY STEELSHIGH-STRENGTH LOW ALLOY STEELS

- To improve the strength-to-weight ratio of steels, a number of high-strength low alloysteels (HSLA) have been developed.- These steels have a low carbon content (usually less than 0.30%).- These type of steels are also characterized by a microstructure consisting of fine-grainferrite as one phase and martensite together with austenite as a second phase.- HSLA steels usually are produces in a form of sheet by microalloying and controlledhot rolling.- Other shapes: plates, bars, and structural shapes.- The ductility, formability, and weldability of HSLA steels, however generally are inferiorto those of conventional low-alloy steels.- Therefore, to improve the properties, a process which called dual-phase steels aredeveloped.- Application: parts of automobile bodies, mining, agricultural; HSLA plates are widelyused in ships, bridges, building construction, and other shapes such as I-beams, channels and angles used in buildings.



MICROALLOYED STEELSMICROALLOYED STEELS

- One of the HSLA steels which recently developed.

- Have superior properties; can eliminate heat treatment, hence not required other

manufacturing process such as quenching, tempering, and stress relieving – therefore

this type of steels are much more cheaper compared to medium-carbon steels.

- Contains of ferrite-pearlite microstructure with fine dispersed particales of carbonite;

0.5% C, 0.8% Mn, and 0.1% V.

-With carefully controlled cooling (usually in air), these materials develop improved

uniform strength.



STAINLESS STEELSSTAINLESS STEELS- Characteristics: corrosion resistance, high strength and ductility, and high chromium content.

- Other alloying elements in stainless steels: nickel, molybdenum, copper, titanium, silicon,

manganese, columbium, aluminum, nitrogen, and sulfur.

- This kind of steels have low carbon content, therefore the corrosion resistance is high.

- Produced by using electric furnaces or basic-oxygen process and the techniques are similar

to those used in steelmaking – can be in a form of variety of shapes.

- Application: cutlery, kitchen equipments, health care and surgical equipment, chemical,

food-processing, and petroleum industries.

- Generally can be divided into five types:

i) Austenitic (200 and 300 series).

ii) Ferritic (400 series).

iii) Martensitic (400 and 500 series).

iv) Precipitation-hardening (PH).

v) Duplex structure.



i) AUSTENITIC (200 AND 300 SERIES)i) AUSTENITIC (200 AND 300 SERIES)

- Composed of chromium, nickel, and manganese in iron.

- Non-magnetic metal and excellent in corrosion resistance, but susceptible to

stress-corrosion cracking.

- Harden by cold working process; if increase the cold work will reduce the formability.

- The most ductile of all stainless steels and can be formed easily.

- Application: kitchenware, fittings, welded construction, lightweight transportation

- equipment, furnace and heat exchanger parts, components for severe chemical

environments.



ii) FERRITIC (400 SERIESii) FERRITIC (400 SERIES))

- Contains high chromium content (up to 27%).

- They are magnetic and good corrosion resistance.

- Lower ductility compared to austenitic.

- Hardened by cold working process and are not heat treatable.

- Application: generally used for nonstructural application such as kitchen equipment

and automotive trim.

iii) MARTENSITIC (400 AND 500 SERIESiii) MARTENSITIC (400 AND 500 SERIES))

- Most of this steels do not contain nickel.

- Chromium content ≈ 18%.

- Magnetic, high strength, hardness and fatigue resistance, good ductility, moderate

corrosion resistance.

- Hardened by using heat treatment process.

- Application: cutlery, surgical tools, valves, springs.



iv) PRECIPITATION-HARDENING (PH)iv) PRECIPITATION-HARDENING (PH)- Contain chromium and nickel, copper, aluminum, titanium, molybdenum.

- Good corrosion resistance and ductility and high strength at elevates temperatures.

- Application: aircraft and aerospace structural components.

v) DUPLEX STRUCTUREv) DUPLEX STRUCTURE- Mixture of austenite and ferrite.

- Good strength, higher resistance to corrosion (in most environments), higher stress

corrosion cracking if compared to austenitic steels 300 series.

- Application: water treatment plants, heat exchanger components.



TOOL AND DIE STEELSTOOL AND DIE STEELS- Special alloyed steels designed for high strength, impact toughness, and wear resistanceat room and elevated temperatures.- Application: commonly used in forming and machining of metals.

HIGH SPEED STEELS (HSS)HIGH SPEED STEELS (HSS)- The most highly alloyed tool and die steels.- Maintain their hardness and strength at elevated operating temperatures.- Generally, there are two types of high-speed steels:

i) molybdenum type (M-series).ii) tungsten type (T-series).

- The M-series steels contain up to about 10% molybdenum with chromium, vanadium, tungsten, and cobalt as other alloying elements.- The T-series steels contain 12 to 18% tungsten with chromium, vanadium, and cobalt asother alloying elements.- The M-series steels have higher abrasion resistance, under go less distortion in heattreatment, and less expensive compared to T-series steels.- HSS tools can be coated with titanium nitride and titanium carbide for the enhancementof wear resistance.



DIE STEELSDIE STEELS

HOT-WORK STEELS (H-SERIES)- Designed for use at elevated temperatures.- High toughness as well as high resistance to wear and cracking.- Alloying elements are: tungsten, molybdenum, chromium, and vanadium.

COLD-WORKS STEELS (A, D, AND O-SERIES)

- Used for cold-working operations.- High resistance to wear and cracking.- Available as oil-hardening or air-hardening types.

SHOCK-RESISTING STEELS (S-SERIES)- Designed for impact toughness – suitable in the application as header dies, punches,and chisels.

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Manufacturing Process -Ferrous Metal & Alloys