Download Properties of Materials Midterm Exam II: Steel and Alloys - Prof. E. J. E. Indacochea and more Study notes Civil Engineering in PDF only on Docsity! 1 CEMM 260 NAME___________________________ Properties of Materials I. D. # ___________________________ J. E. Indacochea University of Illinois at Chicago SAMPLE MIDTERM EXAM II PROBLEM 1 (20 points) [Refer to Figure 1] A proeutectoid steel contains approximately 5% cementite at the grain boundaries at room temperature: a) Calculate the carbon content of the steel. b) Sketch the microstructures and indicate the corresponding compositions of the phases present at 900ºC, 750º and 650C of the steel for the corresponding carbon content obtained in (a). Problem 2. (20 points) The Larson-Miller parameter (LMP) is a commonly used extrapolation procedure to predict service life of metals using higher temperature creep data. This is defined as LMP = T (C + log tR ) a) The Larson-Miller plot for the S-590 iron is shown in Figure 2. Determine the corresponding LMP for this alloy if it operates at an applied stress of 20,000 psi. b) Using the parameter obtained above, predict the rupture life if this alloy is to operate at a temperature of 800°C. For this alloy C = 20. c) If the alloy were to be used at an applied stress of 30,000 psi, what would the maximum service temperature it could be used, if a service life of 200 hours is required? PROBLEM 3 (15 points) For a bronze alloy, the yield stress is 40,000 psi, and the modulus of elasticity is 16.7 x 106 psi. a) What is the maximum load that may be applied to a specimen with a cross-sectional area of 0.5 in2 without plastic deformation? b) If the original specimen length is 4.5 in, what is the maximum length to which it may be stretched without causing plastic deformation? 2 PROBLEM 4. (25 points) [Short answer questions; 5 points each] a) What does the transition temperature in Charpy Impact testing represent? Do all materials show a transition temperature? b) Sketch a creep curve (strain vs time), and label the different regions of creep and instantaneous strain. Indicate or sketch the effect of applied stress on the creep curve. c) List three mechanisms responsible for strengthening metals. What are the three stages of annealing for a cold worked metal. d) Two samples of 4340 steel were heat treated at a temperature of 800ºC to produce 100% austenite. Sample A was heat treated for 30 minutes, and then quenched in water at room temperature, while Sample B was heat treated for 4 hours and then quenched in water also at room temperature. What are the corresponding microstructures? e) Sketch the fatigue curve for a ferrous alloy and a second plot for a nonferrous alloy labeling the corresponding axes and other pertinent information. PROBLEM 5 (20 points) (Refer to the ITT diagram in Figure 3). Describe the heat treatment steps to obtain the following microstructures if the steel is initially 100% pearlitic: a) 50% coarse pearlite and 50% martensite. b) 50% upper bainite 25% lower bainite and 25% martensite. c) 100% tempered martensite. d) 50% fine pearlite and 50% lower bainite. BONUS PROBLEM (10 points) (Refer to Figure 4) a) Label the phase diagram, and mark the lines corresponding to the liquidus, solidus and solvus curves. Identify the alloy experiencing a congruent transformation and temperature. b) Write down the eutectic reaction, specifying the composition of the phases participating and temperature at which the reactions occurs. c) For the alloy containing 15 wt.. % Li sketch the microstructures and write the compositions of the phases at the following temperatures: 750°C, 620°C and 300°C.
