Steel Flashcards
What is the main component in steel apart from iron?
Carbon and coal
What is steel called if you have too much carbon and what is the percentage?
- Cast iron
- > 1.7% carbon
Why is cast iron not used in construction?
- More carbon = higher strength
- Higher strength = more brittle
- More brittle = no signs of warning before failure. We use ductile steel because it gives signs of warning before failing
- Cast iron is weak in tension compared to steel
What is toughness?
Property of a material to absorb energy (area from linear line to failure stress)
What happens to toughness when you increase strength?
Decreased toughness
How do you determine if a material is more ductile or not?
What is the most practical way to measure toughness?
- For brittle materials, use Charpy impact test
- For ductile materials, calculate area under curve starting from linear curve
What are 3 ways to strengthen steel?
- Strain-hardening
- Heat treatment: annealing (slow cooling)
- Alloying
What is the downside of using bolted connections with steel?
- When bolting 2 metals together, 1 of them is less noble (more reactive) than the other
- The metal that is less noble will corrode first
- This is called galvanic corrosion
What is the downside to bolts?
Bolts require more labour than welding
Classify the 3 materials in order of variability
- Steel (least variable)
- Concrete (variable)
- Wood (most variable)
Why is wood considered most variable?
- Defects in wood
- Wood is a natural material compared to concrete and steel which are manufactured materials
How does a brittle material fail?
90 degree plane perpendicular to axis of loading
How does a ductile material fail?
Cup and cone at 45 degrees
What are the common methods of corrosion for steel?
- Chemical
- Electrochemical
Which method is more dangerous?
Electrochemical because of the difference in electrochemical potential
What is the difference between corrosion of steel in water and corrosion of steel out of water?
Corrosion in water wont get passed the first stage of corrosion
What is the difference between low carbon steel and high carbon steel?
- Low carbon steel is easily weldable compared to high carbon steel
- With a lower carbon content, you trade strength for ductility which gives a warning sign before failure
- Low carbon content has coarse grains, low strength, high ductility, high toughness
- High carbon content has finer grains, high strength, low ductility and low toughness
Explain the method of strain hardening and its effects on toughness
- Load is applied past the yielding stress and steel strains hardens
- When unloaded, strain hardening increases strength but we reduce area under the curve
- Strain hardening reduces toughness (ability to absorb energy)
What are the 5 types of corrosion?
- General
- Galvanic
- Pitting
- Crevice
- Stress
Why is corrosion the worse at joints or connections?
- Crevice corrosion happens due to water inside a crevice increasing corrosion
- High stress regions in connections and in joints causes stress corrosion
- Crevice and stress corrosion combined makes for the worse corrosion
What is galvanizing steel and what is the sacrificial anode?
- Galvanizing steel is a method of protecting steel from corrosion by using a zinc coating
- The sacrificial anode refers to the metal coating that is more reactive than steel applied on top
- Zinc will act as a barrier for the steel and corrode first because it is more reactive, protecting steel
What is welding’s effect on steel strength?
- Welding causes temperature changes which change the microstructure
- stronger steel at weld point, weaker steel around weld point
What in the microstructure defines the properties of a low-carbon steel?
- Low carbon content = high ferrite content
- Mainly ferrite + a little of pearlite
- Ferrite responsible for high ductility and low strength of low-carbon steel
