LECTURE 7 Flashcards
Steel Definition
An allow consisting primarily of iron but contains carbon and small amounts of other elements
How is steel made
By oxidizing crude or pig iron
An increase in carbon content mean
Increased strength, lower weld ability and lower ductility
alloying elements improve
strength weld ability ductility and corrosion resistance
What are the four operations required for production of most metals
mining, ore preparation, metal extraction from ore, refining
in ore preparation
metal compounds are separated from bits of sand and rocks
in metal extraction from ore
metal is chemically separated from other elements
What are the three general classes of ferrous metals
cast iron
wrought iron
steel
non ferrous metals in construction include
aluminum
copper
lead
Features of aluminum
lightwieght
machinable
weldable
features of copper
highly ductile
meleable heat and electricity conductor
features of lead
Low melting point, low strength
In north america most steel is made from
recyled steel scrap in “mini-mills”
Making steel step 1
extract, proportionate, and mix iron limestone and coal
making steel step 2
add iron limestone and coal to blast furnace
making steel step 3
recieve molten iron from the bottom of the blast furnace
making steel part 4
refinement by blowing oxygen into molten steel
remove impurities from steel such as carbon and silicon
making steel step 5
solidify the molten steel and form into desired shapes
Cast iron features
brittle and difficult to work with, strong in compression not as strong in tension carbon content 2-4%
first cast iron structure
late 1700s bridge in england
wrought iron features
little to no carbon
strong in tension weaker in compression
malleable
special welding techniques
steel features
carbon content less than 2
strong in both tension and compression
ductile
mild steel features
<0.3% carbon, small amounts of other metals improve strength toughness and other qualities
reasonably strong and highly ductile and easily welded
equal strength in tension and compression
as % carbon decreases
strength and hardness decrease
ductility and toughness increase
as carbon % increases
strength and hardness increase
ductility and toughness decrease
low alloy steels have
<5% non carbon addition
High alloy steels have
> 5% non carbon addition
Stainless steel contains ____ because___-
added nickel and chromium form a self protecting layer that provides long lasting protection against corrosion
galvanized steel sections are ____ because ___
hot dip galvanized with molten zinc for corrosion protection
GSA G40.21 Classes
W. weldable
WT. weldable notch tough
R. atmospheric corrosion resistant
A. atmospheric corrosion resistant weldable
AT atmospheric corrosion resistant weldable notch tough
Q. quenched and tempered low alloy steels plate
QT quenched and tempered low alloy notch tough steel plate
Type W steel is features
suitable for general welded construction where notch toughness at low temps is not a requirement
buildings and bridge compression members
WT steel features
meets charpy V-notch requirements and a suitable for welded construction where notch toughness at a lower design temperature is a design requirement
Type R steel features
Oxidized coat of weather steel, looks cool, can resist atmospheric corrosion
Static loading means
the load monolithically increases slowly from the initial value of zero to the final value
material response depends on load and…
loading rate and load cycling
in tensile steel tests we assume
stress is evenly distributed along cross section and strain is evenly distributed along the member
Engineering stress is
applied load over initial cross section
true Stress is
applied load over the true current cross sectional area as P acts (during necking it gets smaller)
When is engineering stress equal to. true stress
when strains are sufficiently small
when is the difference between engineering stress and true stress considerable
under large strains
True strain equation in terms of engineering strain
Et=ln(1+E)
linear behavior
the portion of the stress strain curve where stress over strain is constant
elsatic behavior
upon removal of the load, the strain returns to zero
Proportional limit
the point at which the behavior of steel remains linear
Elastic limit
the point at which the behavior of steel remains elastic
Modulus of elasticity
the slope of the stress strain curve in the linear elastic region (young’s modulus)
Yield strength 0.2% rule
a line parallel to the linear portion of the stress strain curve that passes through the yield strength will also pass through 0 at a strain of 0.002
ultimate stress
the ultimate engineering stress that the specimen experiences
Structural steel upper bound and lower bound yield point because
the stress required to initiate yield is greater than the one required to continue the yielding process (think gibbs ears)
Design assumption in stress strain curve points
proportional limit elastic limit and yield point are all equal
the modulus of resilience is
a measure of energy absorbed by a material up to the time it yields under load and is represented bu the area under the stress strain diagram to the yield point
modulus of resilience equation
U0=1/2sigmayieldepsilonyeild
toughness is
the ability of the steel to resist impact. also the area under the stress strain curve
Hardness is
the ability to resist abrasion or penetration on its surface
toughness vs hardness
the ability of steel to resist impact or dissipate energy is toughness the ability to resist abrasion or penetration on the surface is hardness
Necking is
a mode of tensile deformation where large amounts of strain localized into a small region
