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Ship Construction > Module 3 : Shipbuilding materials > Flashcards

Module 3 : Shipbuilding materials Flashcards

1
Q

Tensile Strength

A
  • Ability to withstand loads
  • One of the main criteria when referring to the properties of a metal
    Key words: stress, strain, ultimate tensile strength, yield stress, proof stress
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2
Q

Ductility

A
  • Ability to suffer permanent deformation without failure
  • Force to make an indent but not lead to failure
    ie. capacity for plastic deformation, drawing or hammering out without failure
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3
Q

Elasticity

A
  • Allows a metal to return to its original shape after the load has been removed
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4
Q

Hardness

A
  • Ability to resist plastic deformation
    ie. abrasive hardness, machinability
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5
Q

Brittleness

A
  • Allow to fracture quickly rather than deform
  • Opposite of ductility
  • Not ideal for machine industry
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6
Q

Toughness

A
  • Ability to absorb energy or deform plastically
  • Cross between brittleness and softness
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7
Q

Malleability

A
  • Allows a metal to be shaped by beating or rolling
  • Similar to ductility
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8
Q

Strain

A
  • Elongation (or deformation) of a body under stress (or load)
  • Expressed as the ratio of total deformation to the initial dimension of the body
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9
Q

Module of elasticity

A

The slope of the straight line of the graph where stress is proportional to strain

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10
Q

Yield point

A

aka yield stress
- Point at which the metal starts to act in a plastic nature
- Aluminum does not have clear yield point

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11
Q

Ultimate tensile stress

A
  • Maximum load that the metal can be subjected to before it fractures
  • Ship structures are designed to withstand working stresses within the elastic range and much lower than UTS to allow for a factor of safety
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12
Q

Steel Components

A
  • Alloy of iron and carbon
  • Ship building normally uses mild steel : carbon content 0.15%-0.23% with relatively high manganese content
  • Certain other alloys can be added during the molten stage to produce steels of different properties
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13
Q

Carbon content in steel

A
  • Strong impact on strength of the steel but offset by ability to weld
  • More carbon = harder to weld
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14
Q

Silicon content in steel

A
  • Added as a de-oxidizer during the solidification of the metal
  • Promotes a more uniform distribution of elements leading to improved weldability
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15
Q

Manganese content in steel

A
  • Similar to carbon but to a lesser degree
  • Tends to improve steel’s mechanical properties including both tensile and impact strength
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16
Q

Nickel content in steel

A
  • Used to increase strength and corrosion resistance
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17
Q

Chromium content in steel

A
  • Used in conjunction with nickel to make stainless steel
  • Also used in shafting to avoid wear patterns of bearings or seals
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18
Q

Aluminum content in steel

A
  • Effective de-oxidizer and grain refinement agent
  • Increases steel’s weldability and notch resistance
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19
Q

Niobium content in steel

A
  • Used in special steels to provide an increase in tensile strength
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20
Q

Other beneficial alloy components

A
  • Copper
  • Vanadium
  • Titanium
  • Molybdenum
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21
Q

Detrimental elements to add to steel

A
  • Sulfur : cause embrittlement during welding leading to hot cracking
  • Phosphorus : cause embrittlement during welding leading to hot cracking
  • Nitrogen : changing of tensile strength and brittleness during processes where metal is shaped or drawn
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22
Q

Advantages of Steel over Aluminum

A
  • Strength
  • Weldability
  • Cost of acquisition & fabrication
  • Toughness
  • Ductility
  • Malleability
23
Q

Disadvantages of steel over aluminum

A
  • High weight to strength ratio
  • Susceptible to corrosion
  • Can be brittle
24
Q

Steel Categorization

A

Four basic groups:
1. Carbon Steel
2. Alloy Steel
3. Stainless Steel
4. Tool Steel

25
Q

Sourcing steel for ship building or repair

A
  • Must come from an approved manufacturer
  • Will be inspected and certified prior to acceptance by classification society
  • Inspection would be destructive/ non-destructive techniques and chemical analysis
  • Information is marked on mill test certificate prior to shipping
26
Q

Steel Grades

A
  • Options are A, B, D, and E
  • A : mild steel with carbon context at 0.15% - 0.23%
  • E has higher strength and more crack resistance due to increased carbon and manganese.
  • Can also have F : a grade conceived by classification societies, above grade E
  • Higher grades mean higher quality, can be used for high stress areas. Can have thinner plates but they’re more expensive
27
Q

Distinction “H”

A
  • A designation for high tensile steel, used in conjunction with A, D, E and F
  • Each designation has a certain tensile yield strength:
    AH is 27S = 265 N/mm2
    DH is 32
    EH is 36
    FH is 40 = 390 N/mm2
28
Q

Steel Identification _ SAE designation

A

4 - digit code:
1. General category grouping steels
2. Presence of major elements that may affect properties of steel (if none, leave as 0)
3 & 4 : indicate carbon concentration as multiple of 0.01%

29
Q

SAE type categories

A

1XXX - Carbon Steels (most common, cheapest, easier to find)
2XXX - Nickel steels
3XXX - Nickel-chromium steels
4XXX - Molybdenum steels
5XXX - Chromium steels
6XXX - Chromium-vanadium steels
7XXX - Tungsten steels
8XXX - Nickel-chromium-molybdenum steels
9XXX - Silicon-manganese steels

Price increases as category increases

30
Q

Other classification factors

A
  • Composition
  • Production method (continuous casting, electric furnace, etc)
  • Finishing method (cold rolled, hot rolled, cold drawn)
  • Form or shape (bar, rod, tube, pipe, plate, sheet, structural, etc)
  • De-oxidation process (killed, semi-killed, etc)
  • Microstructure (ferritic, pearlitic, martensitic, etc)
  • Physical strength (ASTM standards)
  • Heat treatment (annealed, quenches, tempered, etc)
  • Quality nomenclature (commercial quality, drawing quality, pressure vessel quality, etc)
31
Q

Hull distribution of materials

A

Classification societies lay down the grade of steel, thickness, and welding techniques for all shell and deck plating. Factors accounting for this decision are: loading, corrosion, erosion, and temperature.
Grade “E” is often used for areas like the sheer strake, bilge strake, garboard strake, keel strake.
Classification societies use classes O, I, II, and III
The hull is broken down into sections that require certain classes of plating or sections to be used.

32
Q

Aluminum

A
  • Used extensively for areas where weight is a factor
  • Used in both plate and sectional form
  • Lightweight, good corrosion resistance
  • Will melt at low temperatures compared to steel
  • Can see galvanic action with other materials and must prevent contact with certain metals
33
Q

Aluminum Identification

A
  • Commercially Pure
  • Heat- Treatable alloys
  • Non-heat-treatable alloys
34
Q

Commercially pure Aluminum

A

The 1XXX series
99.000% pure or higher
- Last 2 digits are % above 99
- Excellent corrosion resistance, excellent workability
- High thermal and electrical conductivity
- Commonly used for transmission or power grid lines
1350 for electrical applications
1100 for food packaging trays

35
Q

Heat Treatable Alloys

A

2XXX series: copper is the principle alloying element and can be strengthened significantly through solution heat-treating
- Good combination of high strength and toughness, but does not have the level of atmospheric corrosion resistance as other alloys
- Generally painted or clad for exposure
2024 : aircraft alloy

6XXX series: Silicon and magnesium
- Versatile, heat-treatable, highly formable, weldable, moderately high strength, excellent corrosion resistance
- Architectural and structural applications
6061 : truck and marine frames

7XXX series: zinc primarily with a smaller amount of magnesium
- Heat-treatable, very high strength
7050 & 7075 : aircraft industry

36
Q

Heat Treating

A

Method of strengthening alloys
- Takes the solid, alloyed metal and heats it to a specific point
- The alloy elements (called solute) are homogeneously distributed with the aluminum, putting them in a solid solution.
- The metal is subsequently quenches (rapidly cooled) to freeze the solute atoms in place. These atoms consequently combine into a finely distributed precipitate.

37
Q

Non-heat-treatable alloys

A

3XXX series: manganese as major alloying element with smaller amounts of magnesium
3003 : general purpose, moderate strength & good workability; heat exchangers, cooking utensils
3004 : body of beverage cans

4XXX series: combined with silicon to lower the melting point of aluminum without producing brittleness
- Excellent welding wire and brazing alloys
4043: welding

5XXX series: magnesium as primary alloying element
- Moderate to high strength characteristics, good weldability and resistance to corrosion in the marine environment
- Building and construction, storage tanks, pressure vessels, marine applications
5052 : electronics
5083 : marine applications
5005 : architectural applications
5182 : beverage can lid

38
Q

Cold-working

A

Method of strengthening alloys
- Occurs during rolling and is the action of “working” the metal to make it stronger
- Builds up dislocations and vacancies in the structure, which then inhibits the movement of atoms relative to each other.
- Magnesium will intensify this effect, resulting in even high strength

39
Q

Aluminum treatments

A

F (fabricated) no special control over thermal conditions or strain-hardening used
O (annealed) to obtain lowest strength temper
H (strain-hardened) subjected to application of cold work after annealing (or after hot forming), or to a combination of cold work and partial annealing or stabilizing
W (solution heat-treated) unstable temper application only to alloys which spontaneously age at room temperature after solution heat treatment
T (thermally treated to produce stable tempers) applies to products which are thermally treated, with or without supplementary strain-hardening, to produce stable tempers other than F, O or H

40
Q

Aluminum advantages over steel

A
  • High resistance to corrosion
  • Light in comparison to most other metals (about 8x lighter than steel)
  • Non-magnetic (will not interfere with sensitive navigational equipment)
  • Totally recyclable
41
Q

Aluminum disadvantages over steel

A
  • Not as strong as steel
  • Melts at lower temperatures
  • High coefficient of expansion
  • High thermal coefficient
  • Expensive to manufacture as well as build into structures
  • Often highly reactive to other metals (galvanic)
  • Painting of aluminum requires special process (aluminum oxide coating and immediately prime)
42
Q

Heat Treatment

A
  • Means of obtaining certain desirable properties or to remove undesirable properties of steel
  • Limited by the size of the hull or components
  • Steel will pass through a transformation temperature range (will show as colours) during which the internal metallurgical structure (grain structure) changes and there is a pronounced effect on the properties of the metal
  • Lower transformation temperature : steel constituents begin to dissolve into each other
  • Higher transformation temperature : dissolving process is complete, but structure will coarsen with time and temperature
43
Q

Heat Affected Zone (HAZ)

A
  • Area or the portion of the base metal that was not melted during brazing, cutting or welding but whose microstructure and mechanical properties were altered by the intense heat
  • The extent and magnitude of property change depend primarily on the base material, the weld filler material, and the amount and concentration of heat input by the welding process.
  • This alteration can be detrimental, causing stresses that reduce the strength of the base metal, leading to catastrophic failure
44
Q

Types of heat treatment

A
  1. Preheating
  2. Annealing
  3. Normalizing
  4. Quenching
  5. Tempering
  6. Stress Relieving
  7. Case hardening
45
Q
  1. Preheating
A
  • Preheating is done by raising the temperature of the parent metal above ambient temperature
  • Effective at reducing cracking of the parent and weld materials
  • Slower cooling rate of the HAZ due to smaller temperature gradient between HAZ and surrounding parent metal.
  • Reduces hydrogen in the weld by evaporating any moisture off the metal prior to welding as well as allowing for better hydrogen diffusion due to slower cooling rate
  • Temperatures may range from 20 to 200, but generally 100 is sufficient for most welding procedures.
  • When applied, should extend along the full length of the area to be welded and for a distance of 75 mm in any direction from the joint edge
46
Q
  1. Annealing
A
  • Will help refine the structure of the metal and provide more even distribution of various elements
  • Helps improve the ductility but will adversely affect the strength and hardness
  • Full process involves raising the metal temperature to above the upper transformation temperature (850-900 C), maintaining this temperature for a period of time, then allowing to cool slowly in a furnace
47
Q
  1. Normalizing
A
  • Similar to annealing but the metal is permitted to cool more rapidly in still air
  • Tensile strength is reduced, but will improve notch resistance
  • Care must be exercised to not cause distortion or structural failure of welded structures
48
Q
  1. Quenching
A
  • Method used to harden metals
  • Temperature is brought above the upper transformation temperature, held there for a period of time after which the metal is rapidly cooled by immediate immersion into a liquid medium (water or oil)
  • Rapid cooling process traps the grain in the position attained by the increased temperature
  • Significantly increase in hardness, but likely increase in brittleness so very durable to erosion but easily breakable when subjected to certain directional loads
49
Q
  1. Tempering
A
  • Typically conducted after the metal has been quenched
  • Metal temperature is increased below its lower transformation temperature, held for a period of time, then rapidly cooled again in water or oil.
  • Will remove some hardness obtained during the quenching treatment but greatly improves the ductility of the metal
50
Q
  1. Stress Relieving
A
  • Post-welding heat treatment
  • Uniform heating of the metal to below the lower transformation temperature then allows to cool slowly in a uniform manner (probably still or circulating air).
  • Will help maintain specific characteristics such as tensile strength
  • Often called “process annealing”
51
Q
  1. Case hardening
A

AKA Carburizing
- Used to increase the surface hardness of metals
- Typically for machinery components that require high surface hardness but still need to be relatively ductile overall (such as a cutting edge or a shaft)
- Steel is wrapped in carbon-rich material then placed in a furnace and heated to a specific temperature range. The temperature is maintained for a period of time to allow the carbon atoms to penetrate the metal surface

52
Q

Material forming processes

A
  1. Casting - where molten metal is poured or forced into suitably shaped moulds
  2. Forging - shaping the metal when it is hot (but not molten)
  3. Extruding - forcing a metal through a suitably shaped die (usually rods or tubes) when the metal is hot
  4. Sintering - suitable metal powder is heated and compressed in a die to produce a particular shape of metal with certain qualities (not seen on ships!)
  5. Machining - process used to achieve a finished product (includes lathe, milling, bending, rolling, grinding, drilling, etc)
53
Q

Steel preparation

A
  1. Storage
  2. Heat treatment / De-scaling
  3. Sand blasting
  4. Priming / Painting
  5. Plate cutting
  6. Shaping
  7. Welding
  8. Assembly

Ship Construction (7 decks)

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