Ferrous Materials Flashcards
What does a ferrous material contain
Iron
How do you make steel
Pure iron is remelted where carbon is introduced, the amount of carbon give the required characteristics.
What is iron melted in
A blast furnace
Low carbon
0.1-0.3% Carbon
Medium carbon
0.3-0.5% Carbon
High carbon
0.5-1.05% Carbon
Alloying with Sulphur
Decrease ductility
Alloying with Manganese
Adds strength and hardness
Alloying with Silicon
Adds strength and hardness (worst the
An manganese)
Alloying with Phosphorus
Increases strength, hardness and corrosion resistance
Alloying with Nickel
Increases hardenablity and impact strength
Alloying with Chromium
Increases corrosion resistance and oxidation resistance
Alloying with Molybdenum
Increases the hardenablity and impact strength
Alloying with Vanadium
Increases yield strength and tensile strength
Alloying with Titanium
Improves toughness
What does AISI stand for
American iron and steel institute
Digits in the AISI
First two = alloying element
Last two = percentage of carbon
What is Tempering
A method used to decrease the hardness, thereby increasing ductility and toughness.
Relieves stresses
What is Hardening
Material is heated above its critical temperature, allowing carbon to disperse uniformly into the iron,
Cooled rapidly by quenching, if too quick its structure will become to brittle
What is annealing
Softens and relieves its internal stresses, the steel is heated to its critical limit, soaked at this temperature, cooling very slowly.
What is Normalising
Steel is heated to 100 F above critical limit, soaked for a prescribed time and cooled at room temp,
Relieving internal stresses
What is Quenching
The rate at which steel will cool down, it is governed by the quenching medium, brine is the best quench.
What does CRES stand for
Corrosion resistant steel
Properties of CRES
Corrosion resistance, strength, toughness and resistance to high temperature
Negative properties of CRES
Greater coefficient of expansion and not suitable in high temperature environments
Austentic
Chromium or nickel and chromium nickel magnese alloy Non magnetic Limited use 200/300 series Cannot be heat treated
Ferritic
15-30% chromium 400 series Small amounts of aluminium Carbon below 1% Magnetic Cannot be heat treated
Martensitic
12-18% chromium 400 series High carbon content Heat treatable Least corrosion resistance
Precipitation hardening
Little carbon 15-17% chromium 4-7% nickel Heat treatable Corrosion resistance
High strength low alloy steel
Iron based
Can be hardened to high strengths
300M used on landing gear
Hydrogen embrittlement
Occurs in ferrous and titanium alloy
Hydrogen migrated through the material, reacts producing methane, build up in pressure then cracks occur
What is stress concentrations
The misuse of tools leading to scratches, general damage to surface finish
Types of surface protection
Cadmium Paint Aluminium spraying Silver plating Chromium and nickel plating
What is Galvanic corrosion
Potential is a measure of how dissimilar metals will corrode when placed against each other
Case hardening
Some steel components require a hard durable surface
Two methods of case hardening
Carburising
Nitriding
Carburising
Produces a thin layer of high carbon steel on the surface
Heating to 900 C
Followed by heat treatment
Carbon absorbed 1mm every 5-6 hours
Pack carburising
Heating to 1700 F
Surrounded by charcoal
Carbon penetrates surface to harden it
Metal is quenched
Gas Carburising
Object placed in furnace
Filled with carbon rich gas
Liquid Carburising
Object heated to a sensible temp
Put in salt bath at 900 C
Flame hardening
Steel heated with a oxy actene touch
Quenched with a jet of water
Induction hardening
Whole circumference heated by an induction coil
Nitriding
Improves final surface finish
Hardened, tempered and ground
Introduction of nitrogen
