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Alloying atoms can either fit into _____ between atoms (______) or can replace atoms in lattice structure (________)
- voids
- interstitial
- substitional
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Definition of phase
A homegenous portion of a system that has uniform chemical and physical characteristics
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Phase diagram
A graphical represntation of contraints (t,p,c) and regions of phase stability
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Solution is _____ phase
single
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Mixtures is what phase
More than one type
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If we know T and C0 then we know (2)
- What phases are present
- Their compositions
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Steel contains three main phases at room temperatures
- Ferrite
- Cementite
- Pearlite
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Carbon content percentage and application
- <0.25% Structural
- 0.25-0.5% Reinforcing steel
- 0.5-1.5% Pre stressing steel
- 2.5-4.5% Ornamental work
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Types of annealing
Stress relief:
Process anneal:
Spheroidize
Full Anneal (steels)
Normalize (steels)
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Heat Treatments
- Quenching
- Annealing
- Tampered Martensite
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Quenching/Hardening
Steel is heated above the transformation range and held until the austenite is formed. the steel s then quenched by immersing into oil, water or brine. Rapid cooling locks the iron into a martensite BCC structure, rather than allowing transfrmation to ferrite structure
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Alloy agents are added to to improve: 4
- 1. Strength
- 2. Ductility
- 3. Corrosion resistance
- 4. Hardenability
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Alloy agents and their effects:
- Aluminium (2.0%) Aids nitirding; remove oxygen in steel making
- Sulfur >0.5% Adds Machinability, reduces weldability and ductility
- Chronium resistance to corrosion, increase hardenability
- Increases High temperature strength
- Nickel Increases hardenability and toughness
- Coppper
- Manganese
- Silicon
- Molybdenum
- Vanadium
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Aluminium
Aluminium (2.0%) Aids nitirding; remove oxygen in steel making
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Sulfur
>0.5% Adds Machinability, reduces weldability and ductility
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Chronium
resistance to corrosion, increase hardenability
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Nickel Increases hardenability and toughness
Increases hardenability and toughnes
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Silicon
improves toughness, removes oxygen , increases hardenability
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Structural steel properties 3
- Low carbon
- High strength low allow
- Corrosion resistant high strength low alloy
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Structural steel mechanical properties
- Yield strength
- Tensile or ultimate stress
- Percent elongation
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