Module 3, Engineering Materials

Learning Outcome On completion of this module you will be able to 1.FERROUS METALS: INFLUENCE OF CARBON ON CAST IRON AND STEEL CLASSIFICATION ACCORDING TO THE CARBON CONTENT AND THE FORM OF CARBON IN: CAST-IRON: GREY AND WHITE AS WELL AS WROUGHT-IRON, LOW, MEDIUM AND HIGH-CARBON STEEL. CHIEF PROPERTIES AND USES, GIVING REASONS, FOR THE ABOVE MENTIONED CAST IRON AND STEEL. PURPOSE OF THE PROCESSES AND PROPERTIES GIVEN TO STEEL BY: HARDENING, TEMPERING, ANNEALING, NORMALISING AND CASE HARDENING. (KNOWLEDGE OF THE PRACTICAL EXECUTION OF EACH PROCESS IN PRACTICE IS NOT NECESSARY)

Learning Outcome On completion of this module you will be able to 1.NON FERROUS METALS: PROPERTIES AND USES OF: TIN, LEAD, COPPER, ZINC, ANTIMONY AND ALUMINIUM. 2.FERROUS ALLOYS: THE EFFECT OF THE FOLLOWING ELEMENTS WHEN ALLOYED WITH STEEL: CARBON, MANGANESE, NICKEL, CHROME, VANADIUM, TUNGSTEN AND COBALT.

Learning Outcome On completion of this module you will be able to 2.FERROUS ALLOYS (continue): THE PROPERTIES AND USES OF THE VARIOUS ALLOYS WHICH ARE MANUFACTURED IN THIS WAY: HIGH SPEED STEEL, MANGANESE STEEL, NICKEL STEEL, CHROME STEEL, NICKEL-CHROME STEEL, STAINLESS STEEL AND VANADIUM STEEL. 3.NON FERROUS ALLOYS: COMPOSITION, PROPERTIES AND USES OF: BRASS, BRONZE, SOLDER, WHITE METAL AND DURALUMIN. (Percentages of the content of the alloys are not required.)

Learning Outcome On completion of this module you will be able to 3.NON FERROUS ALLOYS (continue): KNOWLEDGE OF THE MANUFACTURING PROCESSES AND APPROPRIATE FURNACES IS NOT REQUIRED. FINER CATEGORIZING OF MATERIALS IS NOT REQUIRED. 4.PLASTICS THERMOPLASTICS CHARACTERISTICS AND USES OF THERMOPLASTICS: NYLON, POLIMETHYMETHACRYLATE (PERSPEX),POLIVINYL CHLORIDE (P.V.C)

5.THERMOSETTING PLASTICS CHARACTERISTICS AND USES OF THERMOSETTING PLASTICS(THERMOSETTS): BAKELITE AND EPOXY RESINS.

Physical properties of materials - terminology Some of the terms used to describe the various physical properties and characteristics of materials: Brittleness - brittle materials are unable to flex or deform when subjected to an applied load or sudden shock load, but will snap, shatter, or crumble. Examples of brittle materials are glass and improperly tempered hardened steel

Physical properties of materials - terminology Compressibility - the ability of a material to deform by reducing its volume without fracturing when compressed. Examples of compressible materials are cork, sponge, and rubber

Physical properties of materials - terminology Compressive strength - the ability of a material to resist deformation when compressed. Concrete is an example of a material having relatively high compressive strength.

Physical properties of materials - terminology Conductivity electrical conductivity is the ability of a material to convey or carry an electric current (has low electrical resistance). thermal conductivity is the ability of a material to conduct heat. Copper is an example of a material that has both characteristics.

Physical properties of materials - terminology Ductility - the property that allows materials to stretch or become elongated under tension or bend or twist when subjected to bending or twisting forces without rupturing. Examples of materials exhibiting this property are wrought iron and various grades of steel.

Physical properties of materials - terminology Tensile strength - the ability of a material to resist deformation when under tension or stretched, bent or twisted. Steel is an example of a material having relatively high tensile strength.

Physical properties of materials - terminology Elasticity - the ability of a material to stretch when under tension, or bent or twisted and return to its original shape and form when the force is removed. Rubber bands exhibit elasticity and so does steel although it appears to be much more rigid. Steel will return to its original shape and form when the force is removed as long as its elastic limit has not been reached.

Physical properties of materials - terminology Flexibility - the relative ease with which the shape of an item may be changed is a measure of its flexibility (rigidity is the opposite of flexibility). It may or may not return to its original form when the force is removed.

Physical properties of materials - terminology Fusibility - the relative ease with which a material changes state from solid to liquid when heated. Examples of materials exhibiting high fusibility are lead and tin.

Physical properties of materials - terminology Hardness - the ability to resist abrasion, cutting or scratching. Examples of materials exhibiting hardness are diamond, ceramic materials, tungsten carbide, and hardened steels.

Physical properties of materials - terminology Malleability - the ability to be permanently extended or formed in all directions by hammering or rolling without fracture. Examples of materials exhibiting malleability are lead, wrought iron and a variety of steels.

Physical properties of materials - terminology Molecular structure - the characteristics of all materials are fundamentally defined by their molecular structures and the way in which the molecules are aligned with respect to each other in the body of the material. This is of particular importance in relation to hardening, tempering and annealing of materials.

Physical properties of materials - terminology Tenacity - the ability of materials to resist deformation or fracture when being stretched, compressed, bent or twisted.

Physical properties of materials - terminology Toughness - a measure of tenacity combined with hardness - the ability of a material to withstand repeated deformation without fracture.

Physical properties of materials Choosing the correct material for a particular job demands a thorough knowledge of the chemical nature and the physical properties and characteristics of each material. A more complete handling of the atomic and molecular structures of the various elements and compounds that will be introduced is outside the scope of this module. However, some understanding of the crystalline structure of materials, and in particular metals, is necessary in order to appreciate the effects of heat treatment when hardening, tempering and annealing various metals.

Physical properties of materials Several allotropes of carbon exist depending on the way in which the carbon atoms are bonded to each other resulting in different crystalline structures. The two forms depicted here are diamond and graphite.

Ferrous Metals - Iron and Steel Iron is extracted from iron-ore by smelting in a blast furnace together with coke and limestone. The pig iron obtained from this process is relatively soft and also brittle due to its crystalline structure. Iron has few practical uses in this form. Further processing delivers a purer form of iron and together with appropriate heat treating and normalizing results in iron that can be successfully cast and forged or wrought.

Ferrous Metals - Iron and Steel The practical uses of iron in this form still remain limited, and only once it is alloyed with small amounts of carbon to form steel do the applications of this material become virtually unlimited. Plain carbon steels low carbon steel (mild steel) - 0,05 to 0,3% carbon content medium carbon steel - 0,3 to 0,75% carbon content high carbon steel - 0,75 to 1,5% carbon content Through heat treatment, i.e. heating and quenching, the presence of carbon (above 0,3%) allows a dramatic alteration of the physical properties of the metal in relation to its strength and hardness by introducing subtle changes to its crystalline structure.

Ferrous Metals - Iron and Steel Steel can also be alloyed with other metals to dramatically enhance its physical characteristics and allow it to be used for a wide variety of applications. A variety of elements can be used to create these alloys: Tungsten Chromium Molybdenum Vanadium Nickel Manganese Cobalt

Non-ferrous Metals A wide variety of other metals that don’t contain any iron also exist and these can be used for a multitude of engineering applications. These are referred to as non-ferrous metals and include: Copper Zinc Tin Lead Aluminium Antimony

Non-ferrous Alloys Just as steel can be alloyed with other elements, so too can non-ferrous metals. These are referred to as non-ferrous metal alloys and include: Brass Bronze Duralumin White metal Solder

Rare Metals A variety of uses have also been developed for other metals that due to the fact that they are not abundantly available or otherwise difficult to obtain are referred to as rare metals. These include: Vanadium Uranium Thorium Titanium

Heat Treatment Processes - Carbon Steels A variety of heat treatments can be applied to carbon steels to significantly alter physical characteristics such as hardness, toughness and wear resistance. These processes include: Hardening Annealing Tempering Normalizing Case Hardening In order to deliver the required characteristics consistently, these heating and cooling processes must be accurately controlled in relation to maximum and minimum temperatures, rates of heating and cooling, and the atmospheric exposures of the metals being heat treated.

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