Pearlite, Bainite and Martensite in Carbon Steel - Report
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Added on 2020-05-28
Pearlite, Bainite and Martensite in Carbon Steel - Report
Added on 2020-05-28
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Question A.1(a)Discuss the differences between Pearlite, Bainite and Martensite in carbon steels. Sketch themicrostructures and discuss the properties of each phase (e.g. stiffness, strength, toughness,ductility) with reference to typical applications.Pearlite, Bainite and martensite all contain alpha –ferrite and cementite phases.Pearlite has two phases of ferrite and cementite both in different layers. Pearlite hasboth these phases and they will alternate with each other. Bainite consists of veryfine and parallel needles of ferrite that are separated by elongated particles ofcementite. Martensite is nothing but transformed austenite to room temperature byrapid quenching process (Gensamer, 2012). Pearlite microstructure:Bainite microstructures:Upper and lower Bainitic microstructures:Martensite microstructures:Properties of each phase of the Iron-Iron carbide diagram:Pearlite:Pearlite mechanical properties are between the soft ferrite and that of hardcementite. It is not too soft like ferrite and at the same time not too hard likecementite. Hardness of the material is less brittle than cementite. Pearlite and itshigh strength is mainly useful in enabling the material to draw into thin wires.1
Bainite:Toughness of bainite is different for upper and lower bainitic regions. The toughnessof the upper bainitic regions is less tougher than the lower bainitic regions. Lowerbainitic microstructure material is used for the sake of tool steel making applicationswhere there is need for moderate toughness. Bainite enables good weldability aswell is good for making forging steels and related materials.Martensite:The specific characteristic of martensite is its high brittleness. The material is brittleas well is also harder than other microstructures. Martensite is employed for makingcutting tools employed for making utensils etc.(b)With the aid of a diagram, explain the micro-structure of Ferrite-Martensite Dual Phase (DP)steels and discuss the advantages of using DP steels incarmanufacturing(Sun,2002)Ferrite and martensite dual phase steel as the name implies will contain both the ferrite andmartensite constituents in the microstructure. They are actually produced by quenching low andmedium carbon steel from above A1 temperature and below A3 temperatures. The processemployed is a continuous cooling transformation process. Overall behavior, morphology andcharacteristic properties of the material are actually governed by the volume fraction, morphologyand other related properties of the microstructure. The key properties of the micro structure consistsof low yield strength, higher initial strain hardening rates, good fatigue resistance. The uniqueproperty profile of the material is mainly due to the presence of the micro constituents of thematerial. Multi material concept is equally competent like any other high strength and low densitymaterial like aluminum etc. Using such materials for car industry is equally advantageous for carmaking applications like sheet metal forming etc and hence multi material concept is useful for carmaking requirements and being used at present more commonly.2
Question A.2As an engineer working for a major car company you have been asked to investigate the possibilityof manufacturing a composite bumper using a thermoplastic polymer and chopped carbon fibres. Inyou report(a)Describe the manufacturingprocess.Carbon fiber reinforced polymer composite material is the material being discussed in the currentcontext. CFRP can be beneficial to use in the car company. The material has all the attributesrequired for making good components for running a car. Typical operations that can be employedfor making CFRP with thermo plastic polymer and chopped carbon fibres include Wet layup as wellas pre-peg processes.Wet-Layup ensures moderate properties to the material, typical steps in making the materialinclude the following,Mould preparation,Fabric cutoutApplying the patent agentResin preparationKeeping the carbon fabricApplication of resin on carbon fabricApplying resin and placing the layerCuring of the resin will yield final materialPrepeg process and key steps involved in,Thawing the materialPrepeg cut into the required shape and sizeBacking paper will be removedSqueezing roller to remove the entrapped air between the sheetsVaccum bagging is performed my removing all the file, breeder, barrier film, breather and bagging material.Keeping into the autoclaveCure cycling is done using the computer cycleAfter cooling vaccum bag is removed and the part is taken out.(b)If the fibres are 10 μm in diameter, the tensile strength of the fibres is 3500 MPa and the fibre-matrix fibre strength is 100MPa, what is the criticallength?Equation for critical length is Length (l) /10*10-6 = (3500*106)/2*(100*106)Hence the length(l) = 0.175mm (critical length) or alternatively = 175 micro meters(c)A number of manufacturing production routes have been developed for producing CFRPcomponents. One that has generated a great deal of interest is Automated Tape Laying. Withthe aid of diagram explain the operation of Automated Tape Layingmachine.Automated tape laying operation consists of laying composite material tapes for making the compositematerial components. 3
Principally the device either will use gantry style systems or even robotic systems for the sake ofdelivering the fiber to the part. The tight and strong overhead of the machine will keep the tape andfibers intact on to the component. Thermoplast or Thermoset resins are employed with the machine forthe sake of automated tape laying requirements.(d)What are the advantages of Automated TapeLaying?The process is highly automated and hence precision and quality as expected will always beavailable.Manual interference will be minimized and hence the process is fasterContamination as well negative impacts on the human body are totally eliminatedApplicable for diverse range of componentsQuestion B.1(a)Outline the property requirements of hot roller tool steel for steel rolling operation and discuss theadvantages of precipitation hardening intoolsteels.Hot roller tool steel need to have hardness, toughness and strength to take up the high loads athigher temperature. Material also should have high thermal and corrosion resistance particularly athigh temperatures. Precipitation hardening will provide high strength and good corrosion resistance. Also the materialwill provide high fatigue strength, good resistance to galling. Also the material will possess goodcorrosion resistance as well.(b)Explain how precipitated particle (e.g. carbides) will enhance the strength of a material withreference to particledislocationinteractions.Precipitated particle will contribute to the increase in the strength requirement for the movementof the particle in the lattice. Actual precipitation will act as an obstacle for the dislocation motion.Once precipitation occurs, there it will be required to apply more stress to move the dislocationthrough the lattice. This will make the alloy harder and stronger in the material (Martin, 2012).4
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