CASA 06A-FERROUS METALS

What defines a ferrous metal?

Any alloy containing iron as its chief constituent

What are examples of ferrous metals?

Steel, cast iron, titanium alloys and stainless steel

What is iron's appearance and basic properties in pure form?

Silvery white, fairly soft, malleable and ductile. Combines readily with oxygen to form rust (iron oxide)

What is cast iron and what are its aircraft applications?

Iron poured into moulds containing more than 2% carbon and silicon. Low strength-to-weight ratio limits use. Applied in valve guides and piston rings due to porosity and wear characteristics

What two elements are found in all steel?

Iron and carbon

What is the SAE four-digit numbering system for steel?

First digit: principal alloying element. Second digit: percentage of principal alloying element. Last two digits: average carbon content in hundredths of a percent

What are the SAE steel series designations?

1xxx Carbon. 2xxx Nickel. 3xxx Nickel-chromium. 4xxx Molybdenum. 5xxx Chromium. 6xxx Chromium-vanadium. 7xxx Tungsten. 8xxx Nickel-chromium-molybdenum. 9xxx Silicon-manganese

What are the properties of low-carbon (mild) steel?

Used in non-structural areas. Easily welded. Machines readily. Does not accept heat treatment

What are the properties of medium-carbon steel?

Accepts heat treatment. Adaptable for machining or forging. Used where surface hardness is desirable

What are the properties of high-carbon steel?

Very hard. Used in springs, files and some cutting tools

What does increasing carbon content do to steel?

Increases tensile strength and hardness. Decreases malleability and weldability

What does silicon do when alloyed with steel?

Acts as a hardener. In small quantities also improves ductility

What is mangalloy and what are its properties?

Manganese steel. Non-magnetic with extreme anti-wear properties. Resists abrasion. Can achieve up to three times surface hardness under impact without increased brittleness

What does manganese do when combined with sulphur in steel?

Forms manganese sulphide neutralising sulphur's harmful effects. Also improves forging characteristics by making steel less brittle at rolling and forging temperatures

What effect does sulphur have on steel and how is it managed?

Causes brittleness when rolled or forged. Removed in refining or countered by adding manganese. Small additions can improve machinability

What does phosphorous do in steel?

Raises yield strength and improves low-carbon steel's resistance to atmospheric corrosion

What does nickel do in steel?

Adds strength and hardness. Increases yield strength. Slows hardening rate increasing depth of hardening. Produces finer grain structure reducing warping and scaling

What does chromium do in steel?

Increases strength, hardness, wear and corrosion resistance. Used in antifriction bearing balls and rollers. Also deposited electrolytically on cylinder walls and bearing journals

What are the combined properties of nickel-chromium steel?

Nickel toughens and chromium hardens. Together produce steel suitable for high-strength structural applications

What does molybdenum do in steel?

Reduces grain size. Increases impact strength and elastic limit. Extremely wear resistant with great fatigue strength

What is chrome-moly steel and what is it used for?

Chrome-molybdenum steel. Machines readily. Easily welded by gas or electric arc. Responds well to heat treatment. Used for landing gear structures, engine mounts, cylinders and highly stressed engine parts

What does vanadium combined with chromium produce?

A strong, tough, ductile steel alloy. Used to make ball bearings (chrome-vanadium steel)

What is tungsten steel used for?

Control surface balance weights and breaker contacts in magnetos. Has extremely high melting point, high density and retains hardness at elevated temperatures

What is titanium steel alloy used for?

Very high tensile strength and toughness at higher temperatures. Lightweight with high corrosion resistance and ability to withstand extreme temperatures

What is stainless steel and where is it used?

Corrosion-resistant steel containing large amounts of chromium and nickel. Used in firewalls and exhaust system components

What is the purpose of steel heat treatment?

To change physical and mechanical properties without changing shape and size. Can increase strength, improve machinability and restore ductility

What is annealing of steel?

Heating steel, soaking for a specified time then slow cooling in furnace or packed in hot sand/ash. Softens steel and relieves internal stress

What is normalising?

Heating steel uniformly until heat-soaked then cooling in still air. Relieves stresses from forging, welding and machining. Important for welded parts

How does normalising differ from annealing?

Normalising cools in still air producing smaller carbon particles. Annealing cools slowly in the furnace producing larger carbon particles

What is hardening of steel?

Heating until carbon disperses uniformly then rapid quenching in water, oil or brine. Maximum hardness depends on carbon content

What are the quenching mediums for steel in order of speed?

Brine (fastest) then water then oil (slowest)

What is tempering?

Heating hardened steel to a set temperature and holding until heat-soaked then cooling in still air. Reduces brittleness and hardness. Relieves stress and improves ductility and toughness

What is case hardening and what steels suit it best?

Process to produce a hard outer surface with a tough core. Best suited to low-carbon and low-alloy steels. Used for bearings and gears

Why is high-carbon steel unsuitable for case hardening?

The hardness penetrates the core causing brittleness throughou