Callister - An introduction - 8th edition

11.8 Heat Treatment of Steels • 433
Solution
First, evaluate the cooling rate (in terms of the Jominy end-quench distance)
at center, surface, mid-, and three-quarter radial positions of the cylindrical
specimen. This is accomplished using the cooling rate–versus–bar diameter
plot for the appropriate quenching medium, in this case, Figure
11.17a. Then, convert the cooling rate at each of these radial positions into
a hardness value from a hardenability plot for the particular alloy. Finally,
determine the hardness profile by plotting the hardness as a function of
radial position.
This procedure is demonstrated in Figure 11.19, for the center position.
Note that for a water-quenched cylinder of 50 mm (2 in.) diameter, the cooling
rate at the center is equivalent to that approximately 9.5 mm 1 3 8 in.2 from
the Jominy specimen quenched end (Figure 11.19a). This corresponds to a
hardness of about 28 HRC, as noted from the hardenability plot for the 1040
steel alloy (Figure 11.19b). Finally, this data point is plotted on the hardness
profile in Figure 11.19c.
Diameter of bar (in.)
4
3
2
1
Center
(a)
0
0 1 1 3 1
4 2 4 1 1 4
Distance from quenched end (in.)
Figure 11.19 Use of hardenability data
in the generation of hardness profiles.
(a) The cooling rate at the center of a
water-quenched 50-mm- (2-in.-)
diameter specimen is determined. (b)
The cooling rate is converted into an
HRC hardness for a 1040 steel. (c) The
Rockwell hardness is plotted on the
radial hardness profile.
60
Hardness, HRC
50
40
30
1040
(b)
20
0
1 1 3 1 1 1 3
4 2 4 1 4 1 2 1
2
4
Distance from quenched end (in.)
60
Hardness, HRC
50
40
30
20
2 in.
(c)