Chapter 8 Flashcards
Metal Structures can combine to form what 3 forms and are referred to as atoms
Solid
Liquid
Gas
Increase in temperature in metal will cause atoms to?
vibrations of the atoms continue to increase causing the spacing to increase and the metal to expend. once the interatomic spacing is so great the atoms are no long attached enough to form a specific structure and become liquid
Further heating would eventually turn the liquid into a gas (vapor point)
Decrease in temperature in metal will cause atoms to?
move closer together in turn causing the metal to contract
What is the internal energy and interatomic spacing
Solid Metal?
Liquid Metal?
Gas?
Solid Metal
- Lowest internal energy and shortest interatomic spacing
Liquid Metal
-Higher internal energy and greater interatomic spacing
Gas
- Considered Unstructured - Highest internal energy and greatest interatomic spacing
When a metal solidifies it always does so in a
A metal solidifies in to a(an) _________ by a process know as?
crystalline pattern
Nucleation & Growth
The smallest number of atoms that can complete describe their orderly arrangement is referred to as a?
Unit cell
The most common crystal structures or phases in metals are…
BCC - Body-centered cubic
FCC - Face-centered cubic
HCP - Hexagonal close packed
BCC?
Which metals?
Body-centered cubic
Iron, Carbon steel, Chromium, Molybdenum & Tungsten
FCC
Which metals?
Face-centered cubic
Aluminum, copper, nickel & austenitic
HCP
Which metals?
Hexagonal close packed
Titanium, Zinc, Cadmium, Beryllium, & Magnesium
Allotropic
A metal crystal possessing different structures but the same chemical composition
Mechanical properties can be dependent upon…?
The GRAIN size of the Materials
Fine-grained materials are preferred for what type of temurature
Because?
Room and low temperature services
They generally exhibit better ductility, notch toughness and fatigue properties.
Coarse-grained materials are preferred for what type of temperature
Higher Temperatures
Metals are___________ __________ formed by atoms in an ________ _________ . This arrangement is know as a ________ and is described as a ______ ____
Crystalline structures
ordered patterns
phases
unit cell
The junction between individual grains are referred to as a
Grain boundary
The grain size will dictate?
The amount if grain boundary are present
& determines to a certain degree the mechanical properties of the metal.
Smaller atoms such as carbon, nitrogen and hydrogen tend to occupy sites Between the atoms that form the lattice structure of the base metal
interstitial allowing
Allowing elements with atoms close to the size of those of the bas metal tend to occupy __________ sites know as
substitutional alloying
Types of smaller Atoms metals
carbon, nitrogen and hydrogen
Types of larger Atoms metals
copper in nickel
and nickel in copper
Heat treatments
annealing, normalizing, quenching, tempering, preheating, and thermal stress relieving
Annealing def?
Properties?
How?
Heat treatment - softening treatment used to increase the metals ductility at ht expense of its strength.
Metal is raised to the austenitic range and held, them cooled very slowly in a furnace, the to room temperature
Normalizing def?
How?
Properties?
Weldable?
Heat treatment - softens metal, not as significantly as annealing. Considered “homogenizing’ heat treatment. makes metal uniform throughout its cross section
Heated up and slow cooled in still air
Harder. stronger metal with better ductility than annealing
Easily weldable
Quenching
How?
Properties?
Weldable?
Heat treatment - Raising metal demo to austenite range, holding then rapidly coming to room temp by submerging it in quenching medium (water, oil, salt water (brine))
Increased hardens and strength and decreased ductility
Tempering
a heat treatment which reduces the strength and hardness of as-quenched steels and restores ductility and toughness
- reheating quenched material below transformation temp 1333F
Preheating
- used to slow down cool rate of the base metal
- improves ductility without significantly degrading the metals strength. temp not as high as post heat treatments
additional preheat required if there in an increase in carbon equivalent
Post heating
- used to reduce residual stresses and to temper hard, brittle phases formed during cooling or quenching
- temp higher then pre heat treatments
stress relieving
a heat treatment which relieves a metal’s residual stress by heating, holding at temp. and cooling per a prescribed cycle.
Thermally, or mechanically
lamellar
Layered, or plate like
diffusion
moment of atoms within a solution (solid, liquid or gas )
Peening
- Severe mechanical deformation of a metal.
- Also a mechanical treatment
- use of a heavy hammer to flatten the face of the weld which reduces residual stresses of the weld.
- not used on root pass or final layer
Thermal stress relief
a large area of the weed zone is heated uniformly and held fora period of time. bELLOW LOWER TRANSFORMATION TEMP 1333deg F then uniformly cooled to room temp.
eliminates distortion
strength reduced while temp is increased
Vibratory treatment stress relief
a sound wave is introduced during or after welding to prevent build up of stresses
Diffusion
Changes of atoms in the solid state
gold and lead example) also (solid solubility
Solubility
As the temp increases the more the metals can mix together
Hydrogen cracking is oft referred to as
underbead or delayed cracking
Hydrogen in welding
- try to eliminate hydrogen when welding
- clean surface
- use low hydrogen rods should be kept dry and care taken after seal of package has been broken.
- hydrogen will diffuse out of most metals at temp of 200-450F
Pack carburizing
Heating metal up with carbon below their melting point to allow diffusion to occur and give the base metal additional properties. makes the steel harder
Steal is packed into carbon particles and heated some carbon will dissolve and diffuse in the surface of the steel
Nitriding
Process whereby nitrogen is dissolved into the surface of carbon steel.
hardening technique using ammonia instead of carbon to use diffusion. ammonia and steal are heated up and then the ammonia breaks down and the nitrogen atom enter the steel surface.
Stainless steal
5 classes of SS
- Classified as having a least 12% chromium
- Ferritic - Weldable with proper filler
- martensitic - most difficult to weld. (need post/pre heat)
- austenitic - Weldable with proper filler
- (PH) precipitation hardening - weldable
- duplex grades - weldable
duplex grades
stainless steel - half ferrite & half austenite at room temp.
- improved resistance to chloride stress corrosion cracking
Sensitization
When heating to welding temp chromium and carbon present in the metal combine (@1250F) resulting in corrosion dues to less resistance qualities
Pearlite
Steel is heated into austenitic range, the resulting microstructures will contain pearlite
- generally very soft and ductile.
Heat input formula
Heat input =
welding current X Welding Voltage X 60
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
welding travel speed (in/min)
Cementite
Rapid quenching of a steel from the austenitic range results in a hard, brittle structure
