Callister - An introduction - 8th edition

11.8 Heat Treatment of Steels • 435
Table 11.11
Surface Hardnesses for Oil-
Quenched Cylinders of
1060 Steel Having Various
Diameters
Diameter (in.) Surface Hardness (HRC)
0.5 59
1 34
2 30.5
4 29
As-quenched and tempered hardness and ductility data were collected
for one plain carbon steel (AISI/SAE 1040) and several common and readily
available low-alloy steels, data for which are presented in Table 11.12. The
quenching medium (either oil or water) is indicated, and tempering temperatures
were 540C (1000F), 595C (1100F), and 650C (1200F). As may be
noted, the only alloy–heat treatment combinations that meet the stipulated
criteria are 4150/oil–540C temper, 4340/oil–540C temper, and 6150/oil–540C
temper; data for these alloys/heat treatments are boldfaced in the table. The
costs of these three materials are probably comparable; however, a cost analysis
should be conducted. Furthermore, the 6150 alloy has the highest ductility
(by a narrow margin), which would give it a slight edge in the selection
process.
Table 11.12
Rockwell C Hardness (Surface) and Percent Elongation Values for 1-in.-Diameter
Cylinders of Six Steel Alloys, in the As-Quenched Condition and for Various
Tempering Heat Treatments
Tempered at Tempered at Tempered at
As-Quenched 540C (1000F) 595C (1100F) 650C (1200F)
Alloy Designation/ Hardness Hardness Ductility Hardness Ductility Hardness Ductility
Quenching Medium (HRC) (HRC) (%EL) (HRC) (%EL) (HRC) (%EL)
1040/oil 23 (12.5) a 26.5 (10) a 28.2 (5.5) a 30.0
1040/water 50 (17.5) a 23.2 (15) a 26.0 (12.5) a 27.7
4130/water 51 31 18.5 26.5 21.2 — —
4140/oil 55 33 16.5 30 18.8 27.5 21.0
4150/oil 62 38 14.0 35.5 15.7 30 18.7
4340/oil 57 38 14.2 35.5 16.5 29 20.0
6150/oil 60 38 14.5 33 16.0 31 18.7
a These hardness values are only approximate because they are less than 20 HRC.
As the previous section notes, for cylindrical steel alloy specimens that have
been quenched, surface hardness depends not only upon alloy composition and
quenching medium, but also upon specimen diameter. Likewise, the mechanical
characteristics of steel specimens that have been quenched and subsequently tempered
will also be a function of specimen diameter. This phenomenon is illustrated
in Figure 11.20, which plots for an oil-quenched 4140 steel, tensile strength,
yield strength, and ductility (%EL) versus tempering temperature for four
diameters—12.5 mm (0.5 in.), 25 mm (1 in.), 50 mm (2 in.), and 100 mm (4 in.).