ENB231-T1-S1A-2009

ENB231-T1-S1A-2009 - Surname Given Name/s III-I..-...

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Unformatted text preview: Surname Given Name/s III-I..- Examination Paper SEMESTER: FIRST SEMESTER SUPPLEMENTARY/DEFERRED EXAMINATIONS 2009 UNIT: EN8231 MATERIALS AND MANUFACTURING 1 - THEORY 1 DURATION OF EXAMINATION: PERUSAL: 10 MINUTES WORKING: 2HOURS EXAMINATION MATERIAL SUPPLIED BY THE UNIVERSITY: EXAMINATION BOOKLETS - TWO (2) PER STUDENT EXAMINATION MATERIAL SUPPLIED BY THE STUDENT: WRITING IMPLEMENTS CALCULATORS - ANY TYPE INSTRUCTIONS TO STUDENTS: Students are prohibited from having mobile phones or any other device capable of communicating information (either verbal or written) in their possession during the examination NOTES MAY BE MADE QNLI ON THE EXAMINATION PAPER DURING PERUSAL TIME SEQ! ION - ALL FOUR (4) QUESTIONS ARE TO BE ATTEMPTED E TI N - ALL FOUR (4) QUESTIONS ARE TO BE ATTEMPTED ATTEMPT EACH SECTION IN A SEPARATE EXAMINATION BOOKLET ALL QUESTIONS ARE OF EQUAL VALUE Queensland University of Technology our QUT Gardens Point Kelvin Grove INSTRUCTIONS 0 All eight questions are to be attempted (100%) 0 All questions have equal marks 0 Use a separate answer book for each section SECTION A: MATERIALS RELATED QUESTIONS (50%) QUESTION 1 Solidification and Microstructures (21) Briefly describe the specimen preparations needed in order to examine the microstructure of your metallic samples using optical microscope. (b) The equation for the excess free energy of a small solid nucleus of radius, r in a molten metal is: 2 4 3 AGT 2 47zr 7—§7W Gv Explain the terms in this equation and why they arise. Derive an expression of the critical radius for nucleation. Explain how the degree of undercooling affects the kinetics of nucleation, and therefore the final microstructure of a solidified metal. QUESTION 2 Heat Treatments of Steels (a) Explain the following heat treatment processes: Martempering, Austempering, Ausforming. (b) Describe the effect of sulphur and phosphorous in steels. (c) How do austenite stabilising elements and ferrite stabilising elements affect the heat treatment of steels, i.e. indicate the effects of these types of alloying elements on features such as the eutectoid temperature and eutectoid composition in the Fe-Fe3C phase diagram. ENBZ3lTlJ.O9l cont/. .. QUESTION 3 Phase Diagram of Steel A slowly cooled steel shows a microstructure containing 50% pearlite and 50% ferrite. Using the FC-F63C equilibrium phase diagram in Figure l, (a) Estimate the carbon content in this alloy. Show details of how you arrive at your answer. (b) Describe the microstructure that would be obtained and the phase proportions if this alloy is heated to 73 0°C (just above the eutectoid temperature). 1000 Austenite, y Temperature 800 Ferrite, OL 72 7C 600 400 0.00 0.40 0.80 1.20 1.60 2.00 Figure l: Fe—Fe3C Equilibrium Phase Diagram. Composition of Fe3C is 6.7%C. ENB231T1J.091 cont/. .. QUESTION 4 Hardenability of Steels The data in Figure 2 and Figure 3 are obtained from Jominy end quench for a long round steel bar using different cooling medium and conditions. (a) A component with a diameter of 100 mm must be “ideal quenched” (H=oo ). If the component must have a hardness of at least 45 HRC, which steel or steels should you choose. Explain the steps you follow to select the type of steel(s). (b) If the bar is quenched in oil Without agitation (H=0.2), determine the maximum size of bar of 1345 steel that will have a hardness in excess of 40 HRC at the centre. Relation between centre of a bar and the position along the Jominy bar, 180 170 160 150 140 130 120 4.. 0.4 00 Bar diameter (mm) (D O Distance from quenched end (mm) Figure 2. Graph relating J ominy end quench distance to equivalent bar diameter. Jominy End Quench Data for Three Steels. — AISI 1045, AISI 1345.-~---~-- AISI4‘I45 AISI 4145 Hardness. HRC. AlSl 1345 ' AISI 1045 0 5 10 15 20 25 30 35 4O 45 50 Distance from quenched end, mm. Figure 3. Representative J ominy end quench data for three steels. END OF SECTION A ENB231T1J.091 cont/. .. 4 SECTION B: MANUFACTURING RELATED QUESTIONS (50%) QUESTION 5 (a) Using appropriate sketches, describe the cast structure for a typical metallic alloy. (b) In casting experiments performed using a certain alloy and type of sand mold, it took 155 sec for a cube-shaped casting to solidify. The cube was 50 mm on a side. (1) Determine the value of the mold constant in Chvorinov's Rule. (ii) If the same alloy and mold type were used, find the total solidification time for a cylindrical casting in which the diameter = 30 mm and length = 50 mm. 2 Use: Solidification Time,T = QUESTION 6 (a) Define rolling in the context of the bulk deformation processes? (b) A single-pass rolling operation reduces a 20 mm thick plate to 18 mm. The starting plate is 200 mm wide. Roll radius = 250 mm and rotational speed = 12 rev/min. The work material has a strength coefficient = 600 MPa and a strength coefficient = 0.22. Determine (i) roll force, (ii) roll torque and (iii) power required 27: FLN USE F = L Y F = _..._ W (60,000)kW QUESTION 7 (a) What is springback in sheet metal bending? (b) A sheet metal with a thickness of 3 mm has a limiting drawing ratio of 2.4. Calculate the largest circular blank that could be used successfully in deep drawing a cylindrical cup with an internal diameter of 75 mm. Also calculate the punch force required when the sheet metal has an ultimate tensile strength of 530 MPa. USE: LDR = D0 /D,, F = 710,4, (UTS)[LDR — 0.7] ENB23 lTlJ.09l cont/. .. QUESTION 8 (a) Explain the different ways in which changing the die angle affects the extrusion process. (b) Assuming an ideal drawing process, what is the smallest diameter to which a 100-mm diameter rod can be drawn? (c) Briefly comment on the grain flow patterns in the extrusion process with respect to dead metal zone and the possible defects the phenomenon can induce in an extruded part. END OF SECTION B END OF PAPER ENB23lTlJ.091 ...
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This note was uploaded on 11/03/2011 for the course EN 40 taught by Professor Mcgregor during the Three '10 term at Queensland Tech.

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ENB231-T1-S1A-2009 - Surname Given Name/s III-I..-...

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