MSE 230 Assignment 10 Fall 2013 due 11 7 11 8 Problems with an by them will not be graded but solutions will be provided In this homework assignment problems 3 6 7 and 9 will be graded 1 Three samples of an alloy containing Al with 4 wt Cu phase diagram in Fig 11 24 are rapidly cooled from 550 C to 0 C One sample is heated to 50 C a second to 200 C and a third to 350 C All are kept at their respective temperatures for one hour Assuming that no diffusionless transformations occur order the expected strengths of the alloys from the weakest to the strongest and explain your ordering Also make a sketch of the microstructure you expect to observe in each case 2 Using the isothermal TTT diagram for steel with the eutectoid composition Fig 10 22 determine the constituents and their approximate proportions at the end of the following isothermal heat treatments Assume that each heat treatment begins at 800 C and that all quenching is instantaneous a Quench to 600 C and hold for 100 s quench to room temperature b Quench to 700 C and hold for 100 s quench to room temperature c Quench to 350 C and hold for 100 s quench to room temperature 3 Using the same TTT diagram as in Problem 2 specify the heat treatment temperatures and approximate times necessary to produce the following microstructures from the given starting structures You should start and end at room temperature a Martensite from coarse pearlite b Coarse pearlite from fine pearlite c Coarse pearlite from martensite 4 Name the microstructural products of eutectoid iron carbon alloy 0 76 wt C specimens that are first completely transformed to austenite then cooled to room temperature at the following rates a 200 C s b 100 C s c 20 C s 5 Callister 10 D4 a For a 1080 steel that has been water quenched estimate the tempering time at 425 C to achieve a hardness of 50 HRC b What will be the tempering time at 315 C necessary to attain the same hardness 6 Spheroidite and tempered martensite are fabricated by very different heat treating routes Spheroidite is made by annealing coarse pearlite for an extended period of time 24 h near the eutectoid temperature while tempered martensite is formed by rapidly quenching austenite and then heating the material to 400 C for 1 hour a Sketch the microstructures for spheroidite and tempered martensite based on the processing routes discussed above Label the phases present b Which material will exhibit the greater hardness Briefly explain 7 A carbon steel of eutectoid composition 0 8 wt C a k a 1080 steel is required to have a Brinell hardness of 550 Specify the heat treatment s you would use to obtain this hardness value All the information you need to solve the problem is provided in Chapter 10 figures 8 Is it possible to produce a precipitation hardened 2014 aluminum alloy having a minimum yield strength of 380 MPa and a ductility of at least 15 elongation If so specify the precipitation heat treatment If it is not possible then explain why See chapter 11 9 for data relevant to 2012 aluminum 9 Callister 11 28 Construct radial hardness profiles for the following and be sure to explain where you obtained the information e g the figures used from the reading to produce the profiles and a brief explanation of how you used the information to produce the profiles a A 50 mm 2 in diameter cylindrical specimen of an 8640 steel alloy that has been quenched in moderately agitated oil b A 70 mm 2 75 in diameter cylindrical specimen of a 1040 steel alloy that has been quenched in moderately agitated water c Briefly explain why the radial hardness profiles of 8640 steel and 1040 steel are different 10 Callister 11 D9 A cylindrical piece of steel 90 mm 3 1 in in diameter is to be quenched 2 in moderately agitated water Surface and center hardnesses must be at least 55 and 40 HRC respectively Which of the following alloys will satisfy these requirements 1040 5140 4340 4140 8620 8630 8640 and 8660 Justify your choices using data from Figs 11 17a 11 14 and 11 15
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