Page 149 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

|28 Chapter 4 Metal Alloys: Their Structure and Strengthening by Heat Treatment

4.20. Describe the differences between case hardening and 4.26. Explain why, in the abscissa of Fig. 4.18c, the percent-
through hardening, insofar as engineering applications of age of pearlite begins to decrease after 0.8% carbon content
metals are concerned. is reached.
4.2I. Describe the characteristics of (a) an alloy, (b) pearlite, 4.27. What is the significance of decarburization? Give some
(c) austenite, (d) martensite, and (e) cementite. examples.
4.22. Explain why carbon, among all elements, is so effec- 4.28. Explain your understanding of size distortion and
tive in imparting strength to iron in the form of steel. shape distortion in heat-treated parts, and describe their
4.23. How does the shape of graphite in cast iron affect its causes.
properties? 4.29. Comment on your observations regarding Fig. 4.2Ob.
4.24. In Section 4.8.2, several fluids are listed in terms of 4.30. Design a heat-treating cycle for carbon steel, including
their cooling capacity in quenching. Which physical proper- temperature and exposure times, to produce (a) pearlite-
ties of these fluids influence their cooling capacity? martensite steels and (b) bainite-martensite steels.
4.25. Why is it important to know the characteristics of
heat-treating furnaces? Explain.

QUANTITATIVE PROBLEMS

|]4.3 I _ Using Fig. 4.5, estimate the following quantities for |]4.33. A typical steel for tubing is AISI 1040, and one for
a 20% Cu-80% Ni alloy: (a) the liquidus temperature, (b) music wire is 1085. Considering their applications, explain
the solidus temperature, (c) the percentage of nickel in the liq- the reason for the difference in carbon content.
uid at 1400°C, (d) the major phase at 1400°C, and (e) the
ratio of solid to liquid at 1400°C.
|]4.32. Extrapolating the curves in Fig. 4.16, estimate the
time that it would take for 1080 steel to soften to 53 HRC at
(a) 200°C and (b) 300°C.

SYNTHESIS, DESIGN, AND PROIECTS

4.34. It was stated in this chapter that, in parts design, Make a simple qualitative sketch showing the hardness distri-
sharp corners should be avoided in order to reduce the ten- bution across the diameter of the bar. Would the shape of the
dency toward cracking during heat treatment. If it is essential curve depend on the bar’s carbon content? Explain.
for a part to have sharp corners for functional purposes, and 4.38. Throughout this chapter, you have seen specific exam-
it still requires heat treatment, what method would you rec- ples of the importance and the benefits of heat treating parts
ommend for manufacturing this part? or certain regions of parts. Refer to the bibliography at the
4.35. The heat-treatment processes for surface hardening end of this chapter make a survey of the heat-treating litera-
are summarized in Table 4.1. Each of these processes involves ture, and then compile several examples and illustrations of
different equipment, procedures, and cycle times; as a result, parts that have been heat treated.
each incurs different costs. Review the available literature, 4.39. Refer to Fig. 4.26, think of a variety of other part
contact various companies, and then make a similar table shapes to be heat treated, and design coils that are appropriate
outlining the costs involved in each process. for these shapes. Describe how your designs would change if
the parts have varying shapes along their length (such as from
4.36. It can be seen that, as a result of heat treatment, parts
a square at one end to a round shape at the other end).
can undergo size distortion and shape distortion to various
degrees. By referring to the Bibliography at the end of this 4.40. Inspect various parts in your car or home, and identi-
chapter, make a survey of the technical literature, and report fy those that are likely to have been case hardened. Explain
quantitative data regarding the distortions of parts having your reasons.
different shapes.
4.37. Figure 4.20b shows hardness distributions in end-
quench tests, as measured along the length of the round bar.