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Hardenability refers to the ability of steel to harden to a certain depth when
quenched from its austenitizing temperature. It is typically measured by
assessing the extent or depth of hardness in a standardized test specimen of
fixed size and shape after a controlled quenching process. In the end-quench
test, hardenability is determined by the distance from the quenched end of the
specimen that corresponds to a specified hardness level.
The test involves quenching one end of a cylindrical specimen, 1.0 inch in
diameter, in water and then measuring the hardness response as it varies with
distance from the quenched end.
Grossman method described in ASTM A255
Overview
This method of Jominy Hardenability calculation from the chemical ideal
diameter (DI) on a steel is based on the original work of M. A. Grossman [1]
and described in ASTM A 255 standard [2].
The calculation method described here is applicable to the following range
of chemical compositions:
Element
Range, %
C
0.10–0.70
Si
0.15–0.60
Mn
0.50–1.65
Cr
≤ 1.35
Ni
≤ 1.50
Cu
≤ 0.35
Mo
≤ 0.55
V
≤ 0.20
However, to facilitate melting process control for higher alloy steels,
Hardenability Multiplying Factors have been included for calculating the DI
within the following chemical composition ranges:
ASTM A 255
Element
Range, %
C
0.01–0.90
Si
0.01–2.00
Mn
0.01–1.95
Cr
0.01-2.50
Ni
0.01-3.50
Cu
0.01-0.55
Mo
0.01-0.55
V
0.01-0.20
Zr
0.01-0.25
The procedure of hardennability curve calculation is the following.
First the ideal critical diameter should be calculated. To do this we need
to
Calculate the multiplying factor for each element.
Multply all the factors obtained above to obtain DI value in inches.
Convert the DI result to milimiters.
Then we need to calculate the hardness at the quenched end of the specimen.
Then using DI value to calculate a set of denominators for each distance
from the quenched end (1.5, 3, 5, 7, 9, 11, 13, 15, 20, 25, 30, 40, 45, 50 mm).
1. DI Calculation for Non-Boron Steels
TODO: describe the method applicable to boron steels
This calculation uses a set of hardenability factors for each alloying element
in the composition, which are multiplied together to determine the DI value in
inches ($DI_{in}$).
Only multiplying factors for DI in inch-pound units are provided for simplicity.
The effects of phosphorus and sulfur are not considered, as they tend to offset
each other. An austenitic grain size of No. 7 is assumed, as most steels with
controlled hardenability are produced using fine-grain practices. Experience
shows that a high percentage of heats conform to this grain size.
An example of a $DI_{in}$ calculation for an SAE 4118 modified steel is
provided below. The chemical composition of the steel along with the
corresponding multiplying factors for each element are listed in the table.
Chemical Composition and Multiplying Factors
Element
% Composition
Multiplying Factor
Carbon (C)
0.22
0.119
Manganese (Mn)
0.80
3.667
Silicon (Si)
0.18
1.126
Nickel (Ni)
0.10
1.036
Chromium (Cr)
0.43
1.929
Molybdenum (Mo)
0.25
1.75
Copper (Cu)
0.10
1.04
Vanadium (V)
0.05
1.09
To calculate the $DI_{in}$ value, the multiplying factors for each alloying
element are multiplied together:
The hardness at other positions along the end-quench specimen is found by
dividing the initial hardness by the appropriate factor. The formulas for these
factors are provided below.
To calculate the hardness at a specific distance from the quenched end use the
following formula:
$$HRC_d = \frac{HRC_M}{df}$$
Here:
$HRC_M$ is the initial hardness, which is a function of carbon content.
$df_k$ is the denominator for the distance $k$ millimeters from the quenched
end and is computed using the polynomial coefficients:
Grossman, M. A., Hardenability Calculated from Chemical Composition, .AIME Transactions, Vol 150, 1942, pp. 227–259 (2) Banerji, S. K., and Morral, J. E., Boron in Steel , AIME, Warrentown, Pa, 1980, pp. 106–126
ASTM A255 − 10 (2014) Standard Test Methods for Determining Hardenability
of Steel
SEP 1664 Ermittlung von Formeln durch multiple Regression zur Berechnung der Härtbarkeit im Stirnabschreckversuch aus der chemischen Zusammensetzung von Stählen