C Si Mn r Ni MoV u mm in.
J6-80 = 95 C 0.00276 E2 C
-12.28 E + 0.898 E - 0.81G
+ 20Cr + 38Mo + 14Mn + 5.5Ni + 6.1Si + 39V + 96P - 13 + 6.1Si + 39V + 96P - 13
(Eq 34)
where E is the Jominy depth in mm, G is the ASTM grain size, and J is the calculated Rockwell hardness. This formula is applicable for steels with the following ranges: 0.13 to 0.55% C, 0.15 to 1.40% Si, 0.4 to 1.78% Mn, 0.11 to 2.07% Cr, 0 to 0.25% Mo, 0.01 to 2.02% Ni, 0.01 to 0.12% V, 0.008 to 0.035% P, and 6.5 to 10.5 ASTM grain size (G). The calculated Jominy curves for the steel described above with the core carbon content of 0.2% and a case carbon content of 0.4% are shown in Fig. 14.
Fig. 14 Prediction of the hardness profile on the basis of computed Jominy curve of a carburized steel (0.20%
C, 0.8% Mn, 0.6% Cr, 0.55% Ni, 0.20% Mo)
In order to determine the unknown hardness value HRC1, the equivalent Jominy distance, E1, must be determined. This Jominy depth, E1, can be estimated on the diagram proposed by Grossmann (Fig. 15). This diagram enables the computation of the equivalent Jominy distance as a function of the bar diameter and the value HG. The relationship between the E, D, and HG can be represented by the following equation:
{ }
logE= 0.23581 0.28155 ln− HG+0.18904 HG −0.000052D logD (Eq 35)
where the Jominy depth E and bar diameter D are in mm, and HG value is in in.-1. This formula is valid for 5 to 300 mm (0.2 to 12 in.) bar diameters and an HG value of 8 to 80 m-1 (0.2 to 2 in.-1).
Fig. 15 Curves showing correlation between rates of cooling in the Jominy specimen and rates of bars cooled in
various quenching media. The diagram applies to the surface of a cylindrical bar.
Substituting the corresponding values D and HG into Eq 35, E1 = 7.75 mm (0.3 in.) can be obtained. The use of the diagram in Fig. 15 leads to the same result. Knowing value E1, the hardness belonging to distance d1 can be obtained from the Jominy curve in Fig. 14, that is, HRC1 = 52.5 HRC.
Example 5: Determination of Required Carbon Profile for a Specified Case Depth in a Carburized Steel.