Tabulated are data that were gathered from a series of charpy impact tests on a tempered 4140 steel alloy.

temperature,
o
c
impact energy, j

100 89.3

75 88.6

50 87.6

25 85.4

0 82.9

-25 78.9

-50 73.1

-65 66

-75 59.3

-85 47.9

-100 34.3

-125 29.3

-150 27.1

-175 25

(a) plot the data as impact energy versus temperature.

(b) determine a ductile to brittle transition temperature corresponding to the average of the maximum and minimum impact energies.

(c) what is the minimum temperature at which you can use this steel if you wish to have at least 70 j of charpy impact energy?