1
Q
casting alloys
A
- Those that are cast to approximate a finished shape without deformation
2
Q
Wrought alloy
A
- When the metal is fabricated by deformation process an alloy designed to have good ductility
3
Q
blast furnace
A
- Both Iron and steel have their start in the blast furnace
- Mixture of iron, coke, and limestone, blast of hot air is supplied through the mixture from near the bottom to provide oxygen for composition of the core
- Temps of 1650C ( 3000F) developed in the melting zone
- Near the bottom of the furnace the iron and slag will combine with limestone melt and accumulate in a well
- slag is disposed of either as trash or for byproduct use
- Iron is run into open molds top solidify as pigs
4
Q
Pig iron
A
- Product of the blast furnace whether liquid or solid is called pig iron
- Pig: Crude casting , covienent for transportation, storage, remelting of any metal
- pig iron: Metal trapped from the blast furnace whether in liquid or solid state
- ALWAYS contains 3%-4% carbon
- In solid state, pig Iron is weak, is too hard to be machined and has no ductility to permit deformation work
5
Q
Early steel
A
- oldest method of making carbon steel consisted of reheating wrought iron and powdered charcoal together in the cementation process
- at 1148C ( 2098F) carbon is soluble in iron up to 2 %
- much of the slag in the wrought iron migrated to the surface and formed surface blisters ; Blister steel
- even after waiting two weeks carbon was not uniformly dispersed throughout the material so requires more work
6
Q
Crucible steel
A
- further reduction of slag and uniformity of carbon and closer controls were later achieved by crucible process
- Made from the cementation process were remelted in a clay or graphite crucible in which slag floated to the surface
- produced steel of high quality but obsolete now
7
Q
open- hearth steel
A
- Developed in the 1850s along with the Bessemer converter was used for the majority of steel produced in the US until superseded by the Bessemer process
- Principal reducing action take place between the. Iron ore and the carbon of the pig iron, the final carbon content of the steel being controllable by the proper proportions of the charged material
- Main difference between this and early steel making was that the preheating of the entering combustion air
8
Q
Bessemer Steel
A
- Consist of molten pig iron. Steel scrap may be added to help control the temp
- Process can be used to reduce the carbon content to about .05%
- inability to reduce phosphorus content of the metal restricted its use. By 1968 was replaced into the US
9
Q
Electric furnace steel
A
- Furance heated by electric arc or induction
- steel of the highest quality is produced by this method
10
Q
Basic Oxygen Process
A
- by 2000, 60% of the worlds steel was made by this method
- Steel made by this method can start from any grade of pig iron, scrap is useable in large quanties so that the process becomes the cheapest method for melting and reusing scrap
- oxygen is the key to speeding up the process
11
Q
Steel
A
- lo cast irons are essentially pig iron with at most only. Minor modifications
- essential component of pig iron in addition to iron is the 3 to 4% carbon
- when carbon content is reduced to less than 2% new material is called steel
12
Q
Wrought iron
A
- First low carbon steel to be manufactured in quantity
- Material included slag, which floated to the top as long as the metal was liquid, the slag was mixed with purified iron
- while low in carbon and silicon contained 3 to 4% slag mostly si02
- reputation for corrosion and fatigue resistance
- wrought iron has a tensile strength of about 50,000 PSI and good ductility although the material is anisotropic because of slag stringers, principle use is for manufacture of welded pipe
- refers to any. Worked low carbon steel particularly a product shaped or worked by hand
13
Q
Low Carbon
A
- Steel with approximately 6 to 25 points of carbon ( .06 to .25%) rated as low carbon steel and are rarely heat treated to harden because the low carbon permits so little formation of hard martensite
- are readily brazed, welded and forged
14
Q
Medium carbon
A
- .25 to .5 % contain sufficient carbon that they can be heat treated for diserable strength, hardness, machinabiluty and other properties
- majority of the steel is furnished in the hot- rolled condition and is often machined for final finishing
- Can be welded, but it is more difficult to join by this method because of structural changes caused by welding heat in localized areas
15
Q
High carbon
A
- contains from 50 to 160 points of carbon ( .5% to 1.6%)
- Classed as tool or die steel in which hardness is the principal property desired
- nearly always must be water quenched
16
Q
alloy Steel
A
- refers to steels containing elements other than these in controlled quantities greater than impurity concentration or, in the case of manganese, greater than 1.5%
- carbon produces an increase in hardness and strength with a loss of ductility
- two steels with equivalent hardness and strength the one with finer grains will have better ductility which leads to improvised toughness
- carbon lowers corrosion resistance, nickel becomes effective in percentages of about 5% chromium is extremely effective in percentages greater than 10% stainless steels
17
Q
Low Alloy AISI Steels
A
- American iron and Steel institute ( AISI) Steels are alloyed primarily for improved hardenability
- Compared to plain carbon steel, they have 30 to 40% higher yield strength and 10 to 20 % higher tensile strength
- at= tensile and hardness, they can have 30 to 40% higher reduction area and twice the impact strength
- contain less than 8% total alloying elements, although most important commercially contain less than 5 %
18
Q
Stainless steels
A
- Most important of the higher alloy steels is a group of high chromium steels with extremely high corrosion and chemical resistance
- much better mechanical properties at high temps, first called Stainless steels referred to as heat and corrosion resistant steels
- in any as serious loss of corrosion resistance can occur if large amounts of chromium carbide form
19
Q
Martensitic stainless steel
A
- Material responds to heat treatment much as any low alloy steel
- May be hardened by heat treatment similar to that used on plain carbon or low alloy steels
- are called martensitic and the most used ones have 4 to 6 % chromium
- magnetic, offer good corrosion resistance at normal temp
20
Q
Ferric stainless steel
A
- with larger amount of chromium as great as 30 % or more, Austentite is surprised. Steel loses its ability to be hardened by normal steel heat treating procedures
- useful when high corrosion resistance is necessary in cold worked products
- magnetic, offer good corrosion resistance at normal temperatures
21
Q
Austentic stainless steels
A
- with high chromium and the addition of 8% or more nickel or combinations of nickel and manganese, ferrite is suppressed
- most typically contains 18 % chromium and 8 % nickel are referred to as austentite stainless steels
- addition of small amounts of other elements makes some of them hardenable by a solution precipitation reaction
- are paramagnetic, most expensive, but posses the best impact properties at low temps, highest strength and corrosion resistance at elevated temp and the best appearance
22
Q
cast Steel
A
- Steel castings may be produced with greater ductility than even malleable iron
- principal advantage of steel as a structural element mainly the ability to control properties by composition and heat treatment apply for both the wrought and the cast material
- cast steel is isotrophic
- eutectic temperature: Single tempo at which a mixture of substances in fixed proportions melts and solidifies that is lower than the melting points of the separate constituents of any other mixture of them
- majority of steel castings are produced in the medium carbon range because nearly all are heat trate ti develop good mechanical properties
23
Q
Aluminum alloys
A
- Can be divided into two major categories: casting alloys and wrought alloys
- Some wrought can be strengthened by therma treatment while others can only be cold worked
- Casting alloys some can be heat treated, while others are not heat treatable and used in the as cast condition
- four ignition system is used for identification of wrought aluminum and wrought aluminum alloys
24
Q
Basic temper designations
A
- F as Fabricated
- O- Annealed: wrought products that are annealed may be flowed by a 0 or other digits
- H- Strain Hardened * wrought products only) H followed by two more digits
- V- Solution heat treated: only applicable to alloys that spontaneously age at room temp after solution treatment
- T - Thermally treated to produce Stable Tempers other than F, O, H
25
Wrought aluminum Alloys
* alloys in the 2 series, 6 and 7 can be strengthened by heat treatment
* consist of solution het treatment at high temps 467 to 538 C ( 870 to 1000F) and rapid cooling ( quenching) in water or polymer solution
* After quenching soft, alloy aged at room temp or artificially aged at 121 to 177 C
* 2024, 7050, 7075 have poor weldability
* Aluminum alloys have good ductility and machinability most have good weldability
* density 1/3 that of steel 2.7g/cm3
* Good corrosion resistance in most environments can be improved by the use of chemical conversions coatings and anozdiing, clad pure aluminum coatings
26
cast Aluminum alloys
* Good fluidity, low melting point, rapid heat transfer from the molten aluminum to the mold, chemical stability good as cast surface finish, good weldability
* hydrogen only gas with solubility in aluminum that can be controlled
* many Aluminum alloys are relatively free from hot short cracking and tendencies
* mostly produced by pressure die, permanent mold, green and dry sand, plastic mold casting methods
27
Copper
* One of the heavier trcutural metals with a density about 10 % greater than that of steel
* range from 30,000 to 125,000 PSI
* ductility is excellent easy to work with by deformation process either hot or cold
* most machinable ore those containing lead or tin additives fir improving machinability
* has outstanding electrical and thermal conductivity and excellent corrosion resistance particularly under marine conditions
28
Nicke and nickel alloys
* nickel and manganese are metals that have mechanical characteristics similar to iron
* nearly 3/4 of all nickel produced is sued either as plating material for corrosion resistance or as an alloying element in steel
* high temp nickel chromium or cobalt have better properties at high temp than SS but cost more and more difficult to process
29
Cobalt alloys
* Cobalt as the principle element referred to as cobalt based alloys
* Usefull structurally at temps as high as 1000C ( 1832F) which they have good corrosion resistance and tensile strength as great as 13,000 PSI
30
Magnesium and its alloys
* Berylium is the lightest metal available, high cost makes magnesium the lightest metal commercially available, density 2/3 that of aluminum
* good strength, alloys range up to 50,000 PSI for wrought alloys and 40,000 for cast alloys
* corrosion resistance good in ordinary atmosphere but more severe conditions some surface protection is necessary. 8 % or more aluminum hardening treatment possible
* Principal drawback is its crystalline structure having a closed packed hexagonal structure high rate of strain hardening, impractical to press work
* high strain rate results in notch sensitivity. Subject to failure
Can burn easily in air
31
Titanium and titanium alloys
* high strength moderate density ( 1/2 of steel and 70% higher than aluminum)
* high strength from 25,000 to 200,000 PSI
* corrosion resistance not resistant to attack from reducing acids ( sulfuric, hydrochorlic
* oxidation resistance effective up to 480C ( 900F) but higher willl lead to the growth of a brittle surface oxide ( alpha case)
* Useful in biocompatibility, useful in implants since body wont reject
* close packed hexagonal structure, high rate of strain hardening which limits the amount of cold work that can be done without re crystallization
* produced in wrought form at elevated tempsin the770C to 1150C 1350F to 2100F
* stress levels high at notches and discontinuities ( notch sensitivity )
32
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