Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-14 GTBL042-Callister-v2 August 29, 2007 8:59

14.6 Heat Treatment of Steels • 587

Table 14.1 Surface Hardnesses for Oil-

Quenched Cylinders of 1060

Steel Having Various Diameters

Diameter(in.) Surface Hardness(HRC)

0.5 59

134

2 30.5

429

For example, the degree to which surface hardness decreases with diameter is

represented in Table 14.1 for a 1060 steel that was oil quenched. Furthermore, the

tempered surface hardness will also depend on tempering temperature and time.

As-quenched and tempered hardness and ductility data were collected for one

plain-carbon (AISI/SAE 1040) and several common and readily available low-

alloy steels, data for which are presented in Table 14.2. The quenching medium

(either oil or water) is indicated, and tempering temperatures were 540◦C

(1000◦F), 595◦C (1100◦F), and 650◦C (1200◦F). As may be noted, the only alloy-

heat treatment combinations that meet the stipulated criteria are 4150/oil-540◦C

temper, 4340/oil-540◦C temper, and 6150/oil-540◦C temper; data for these al-

loys/heat treatments are boldfaced in the table. The costs of these three materials

are probably comparable; however, a cost analysis should be conducted. Further-

more, the 6150 alloy has the highest ductility (by a narrow margin), which would

give it a slight edge in the selection process.

Table 14.2 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

As- Tempered at 540◦C Tempered at 595◦C Tempered at 650◦C

Alloy Quenched ( 1000 ◦F)( 1100 ◦F)( 1200 ◦F)

Designation/

Quenching Hardness Hardness Ductility Hardness Ductility Hardness Ductility

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

aThese 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 14.14, which

plots for an oil-quenched 4140 steel, tensile strength, yield strength, and ductility