Jominy End-Quench Harden Ability Test

J.N.Astoveza. Jominy End-Quench Hardenability Tes of an AISI 1020 Steel. Page 1 of 9

Jominy End-Quench Hardenability Test

of an AISI 1020 Steel

J.N.Astoveza

Department of Mining, Metallurgical and Materials Engineering

University of the Philippines, Diliman [email protected]

Abstract

The Jominy End-Quench Hardenability Test was used in this experiment to characterize the

hardenability property of an AISI 1020 steel sample which was initially austenitized at 868ᵒC

on a muffle furnace for 1 hour and transferred to a Jominy apparatus to cool for 20 minutes

with water jet. Following the standard procedures of the test, two parallel surfaces were

ground on the opposite side of the specimen after which indentions for hardness readings and

photomicrographs were taken from one of the sides with specified spacing between the

indentions considered according to the standards settings. The Hardenability Curve indicated a gradual decrease in hardness values while the microstructures varied from martensite to

non-martensitic (pearlite, bainite, ferrite) as the distance moved away from the quenched end.

The first derivative plot suggested a high rate of hardness drop with a maximum of 12 HRC

per inch at close distances from the quenched end.

1. Introduction

Hardenability is defined as the ability of a ferrous

material to acquire hardness after austenitization

and quenching. It entails two major aspects

including determination of (1) the extent to which a

certain level of hardness is attained along the cross

section of a material (depth of hardening) and (2)

the ability to attain a specific value of hardness. [1]

1.1 Major Factors Affecting

Depth of Hardening

a) Carbon Content

Among the various factors to which hardenability

depend, the amount of dissolved carbon during austenitizing is considered to be the most critical.

This may be inferred upon recalling that this amount

of carbon takes part in the austenite-to-martensite

transformation [1] and that the degree of martensite

formation during heat treatment is directly

indicative of the overall hardness yield of the

material. Generally therefore, steel types with higher

carbon content are expected to exhibit higher

hardenability.

b) Alloying Elements

“The general effect of alloying elements dissolved

in austenite is to decrease the rate of austenite

transformation at subcritical temperature… thereby

facilitating ultimate transformation to martensite or

lower bainite..” [2]. Presence of alloying elements

therefore makes it possible to attain high extent of

martensite formation even at a slower cooling rate

which is well depicted in the following figure.

Figure 1. Hardenability of Unalloyed versus

Alloyed Steel for (a) water quenching and (b) oil

quenching conditions (From G. Spur (Ed.), Handbuch der

Fertigungstechnik, Band 4=2, Wa¨rmebehandeln, Carl Hanser, Munich,

1987, p. 1012.)

Manganese, chromium and molybdenum are

considered to be some of the most economical alloying elements added with the goal of increasing

hardenability while nickel is the most expensive per

unit. The latter however produces an alloyed steel

product with good machinability property due to the

increased toughness that results upon its addition.

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c) Grain Size

“The hardenability of a carbon steel may increase

as much as 50% with an increase in austenite grain

size from ASTM 8 to ASTM 3” [2]. However, using

coarser-grained steels usually invoke setbacks

associated with a compensated notch toughness property.

d) Shape and Size of Cross Section

Heat extraction during quenching is highly

influenced by the geometry and size of the cross

section of the sample material during a hardenability

test. Bars of rectangular cross sections always

achieve less depth of hardening than round bars of

the same cross-sectional size which may be

accounted to the greater effective surface area

exposed for the latter shape.

e) Quenching Media

Quenching media and condition significantly

affect the degree of hardenability that can be

attained. For this reason, this factor is usually

eliminated from correlations by applying similar

condition for a specific hardenability test.

f) Austenitizing Time and Temperature

Operating under sufficient austenitizing time and temperature is necessary in achieving complete

initial transformation to austenite phase to

consequently aid in complete martensite formation

upon quenching the steel sample.

Other variables being considered include grinding

of the flats of the test bar, prevention of grinding

burns, accuracy of measured distance from the

quenched end, water temperature (if water-

quenched), free water-jet height, and transfer time

from the furnace to the quenching fixture [1].

1.2 Hardenability Determination

Two of the most widely applied hardenability

determination methods are the Grossmann’s

Hardenability Concept and the Jominy End-Quench

Hardenability Test.

Grossman’s Hardenability Concept basically

involves using a several pieces of cylindrical steels bars having different diameters which are uniformly

austenitized initially then are quenched employing

different quenching media and conditions. The

respective cross sections are examined and the one

having 50% martensite at its core is accounted to

have the critical diameter. This may then be

correlated to several other variables using

Grossman’s chart for ideal critical diameter.

Moreover, this method of hardenability

determination utilizes a quantity called quenching

severity factor, H, where the correspondence of a

specific quenching medium and condition to the

ideal critical diameter may be determined. However,

objections concerning the assumption of a single H

value for a quenching condition have risen. The need for a more generalized method was recognized

when it was determined that the heat transfer

coefficient at the interface between the metal

surface and the surrounding quenchant changes

dramatically during different stages of the

quenching process for a vaporizable fluid [1].

Another method, the Jominy End-Quench

Hardenability Test, developed by Jominy and

Boegehold is used worldwide, described in many

national standards, and available as an

international standard [1]. The test has the following significant advantages: (1) it

characterizes the hardenability of steel from a

single specimen, allowing a wide range of cooling

rates during a single test; and (2) it is reasonably

reproducible [1]. This method essentially involves

austenitizing a steel sample (following the standard

parameters and procedures), soaking, and quickly

quenching it through a jet of water in a Jominy

apparatus. The Jominy Hardenability Curve is

plotted after obtaining hardness readings across the

length taken per 1/16” interval on a ground side of the sample. As all other factors are standardized (ie

quenching media, austenitizing type, atc.),

hardenability may be directly related to the distance

from the quenched end.

This experiment focused on the hardenability

determination of an AISI 1020 steel sample as the

method of Jominy End-Quench Hardenability Test

was employed.

2. Methodology

The steel specimen used by the group for the

Jominy End-Quench Hardenability Test was an

AISI 1020 steel 25.4mm (1inch) in diameter and

around 100mm (4 inches) in length following the

standard dimensions set for the method (refer to

Figure 2). It was austenitized at the temperature of

868ᵒC for 1 hour, and quickly transferred to the

Jominy apparatus for quenching for 20 minutes

(refer to Figure3).

Figure 2. The AISI 1020 steel sample


Figure 3. The Jominy Apparatus

It must be noted that this transfer to the Jominy

apparatus has to be done as quick as possible to

prevent delayed quenching which is known to

induce a discontinuous cooling rate throughout the

length of the sample. In effect, delayed quenching

may substantially increase the depth of hardening

and may compensate for lower hardenability of the

steel [1].

Figure 4. Effect of delayed quenching to the

Hardenability Curve of an AISI 4140 steel sample. (From B. Lisˇcˇic ,́ S. Svaic, and T. Filetin, Workshop designed system for

quenching intensity evaluation and calculation of heat transfer data. ASM

Quenching and Distortion Control, Proceedings of First International

Confererence On Quenching and Control of Distortion, Chicago, IL, 22–

25 Sept. 1992, pp. 17–26.)

Parallel flats were then ground on the opposite

sides of the specimen where hardness test and

metallographic readings were employed afterwards.

For the two replicates of hardness readings,

indentions were made at 1/16” gaps for the first

inch, 1/8” for the next inch, and ¼” for the rest of

the length On the other hand, 500x optical

magnification of the Scanning Electron Microscope

was used in obtaining the photomicrographs of the sample.

A Hardenability Curve was plotted for both

replicates to portray the trend of hardness values in

relation to the microstructure in a point of a certain

distance from the quenched end.

3. Results and Discussion

A table summarizing the data obtained from the

experiment is presented in Table 1 of the

Appendices. From these data, the Jominy

Hardenability Curves for replicates 1 and 2 were

plotted with polynomial trendlines as shown in

Figure 5 (refer to the Appendices). Polynomial

trendline was chosen as it yields the curve with the

most accurate fit to residuals as opposed to

exponential, power, logarithmic and linear

trendlines. The decreasing trend of the curves was

as expected since the extent of martensite formation is greater in areas which are exposed to faster

cooling rates (near the water-quenched end). In

order to elaborate the characterization, the first

derivative plots for the Jominy Hardenability Curves

were generated with a polynomial trendline as

shown in Figure 6 (refer to Appendices). These plots

were taken with the absolute values of the slopes

(|Δy/Δx|) plotted against the corresponding

distances from the quenched end. It can be inferred

from the graph that the rates of hardness reduction

were greatest at around 5 to 12 HRC per inch, for the first inch from the quenched end. As the distance

moved away from the quenched end, the rate of

hardness reduction also decreased significantly

(between the second to the third inch) at 1 to 3 HRC

per inch though a gradual increase was again

observed from the third going to the fourth inch at 2

to 8 HRC per inch. This result suggested that the

highest rate of hardness drop as the distance moved

away from the quenched end occurred along the

area which was directly quenched with water.

Furthermore it was previously established that the

performance of steels depends on the properties

associated with their microstructures, that is, on the

arrangements, volume fractions, sizes, and

morphologies of the various phases constituting a

macroscopic section of steel with a given

composition in a given processed condition [2].

Referring to the photomicrographs taken at points

with different distances from the quenched end (see

Figures 7-20 in the Appendices), the change in grain

size and amount of cementite formation were highly

indicative of the hardness yield at the specific points. For instance, it can be seen that the

metallography in Figure 7 (microstructure nearest to

the quenched end) was constituted with fine grains

and high amount of cementite (black areas)

throughout the region. Cementite structures are long

and plate-like which form along grain boundaries

inducing an increased brittleness throughout the

region. The structure in Figure 7 resembled that of a

martensite and therefore was expected to yield the


greatest hardness reading. As the distance moves

away from the quenched end, the grain sizes

increased while the amount of cementite formation

along the grain boundaries decreased. The

microstructures varied from martensite to bainite to

pearlite respectively as the distance moved away from the quenched end due to the difference in

cooling rates at these sections of the sample.

Consequently, hardness readings continued to

decrease towards a greater distance from the

quenched end.

The standard cooling rate employed in a Jominy

End-Quench Hardenability Test is that produced via

water quenching the end of the sample at

approximately 0.7 Kelvin/sec. When the critical

cooling rate however is not attained, the standard

test may not be sufficient to characterize hardenability since there will be no substantial

change in the hardness curve because martensite

will be obtained at every distance along the Jominy

specimen [1]. This case is known to be that for air-

hardening steels which may be aided by increasing

the upper mass of the specimen with the use of

stainless steel cap (refer to Figure 21) which would

result to a decreased, more attainable, critical

cooling rate of the upper portion of the specimen.

Figure 21. Modified Jominy Test using stainless steel cap (From A. Rose and L. Rademacher, Stahl Eisen 76(23):1570–

1573, 1956 [in German].)

The effect of changing the quenching condition

with the use of a different media, say oil (a more common quenching media for industrial

applications), may be depicted referring back to

Figure 1 where it can be seen that no essential

hardness increase was attained with oil quenching

for the unalloyed steel sample since the critical

cooling rate was not achieved. On the other hand,

through hardening was attained for the alloyed steel

sample which was water-quenched since the cooling

rate for this condition surpassed the critical cooling

rate required to achieve hardening up to the core of

the sample. Although quenching with water yields

higher hardenability, “steels are not necessarily

better because they are higher in hardenability… There are many applications for which minimum,

rather maximum, hardenability is needed” [2].

Cracking and undesirable patterns of residual

stresses are usually expected to form for steels

having high hardenability values.

Finally, some of the factors that may be accounted

as the sources of error in the experiment include: (1)

delayed quenching, (2) uneven surfaces subjected to

hardness and metallographic testing, and (3) other

deviations from the standard procedures and

material specification indicated for a Jominy End-Quench Hardness Test. Although it was previously

established that Jominy End-Quench Hardness Test

was highly reproducible yielding consistent results

for the same material test at varying laboratories, it

was also known that slight deviations from the

procedures can yield highly deviated result.

4. Conclusions

Hardenability of an AISI 1020 steel sample was

characterized in this experiment employing the

standard procedures for a Jominy End-Quench Test.

Hardness readings decreased as the distance moved

away from the quenched end which was directly

related to the microstructure obtained at different

points along the length of the specimen. Fine-

grained martensitic microstructure was observed at

regions near the quenched end while coarse-grained

non-martensitic (pearlite, bainite, ferrite) phases where dominant at regions distant from the

quenched end. Additionally, the First Derivative

Plot of the Hardenability Curve portrayed the largest

rate of hardness reduction with 12 HRC per inch

about 1/16 inch away from the quenched end

corresponding to the highest hardness drop at the

region as the distance moved away from the

quenched end.

Following the standard cooling rate is critical in

the test. Although the Jominy end-quench test is used mostly for low-alloy steels for carburizing

(core hardenability) and for structural steels, which

are typically through-hardened in oils and tempered

[1], several modifications were already developed to

accommodate variations from the standard

methodology. Air-hardening steels are usually aided

with the use of stainless steel caps to reduce the

critical cooling rate on the upper portions of the

sample. Moreover, utilization of other cooling

media with lower quenching severity factor affects


the depth of hardening with respect to the cross

section of the specimen.

Lastly, hardenability requirements are dependent

on the specific function of the product. High

hardenability is not always desirable since it corresponds to low toughness. To ensure therefore

that an appropriate type of material (with an

appropriate hardenabilty with respect to variations

in chemical composition) is chosen for a certain

application, hardenability band (H-band) was set as

one of the primary reference in purchasing steel

products.

5. References

[1] Totten, George. Steel Heat Treatment

Handbook. 2nd ed. Portland, Oregon, USA:

Taylor & Francis, 2007. eBook.

[2] ASM International Handbook Committee. ASM

Metals Handbook Vol I: Properties and

Selection: Irons, Steels and High Performance

Alloys. 10th ed. 1990. eBook.

[3] Pollack, Herman. Materials Science and

Metallurgy. 3rd ed. Reston, Virginia: A

Prentice-Hall Company, 1981. Print.

[4] Fong, H.S. “Further Observations on the Jominy

End Quench Test.” Journal of Materials

Processing Technology 38.1-2 (1993): n. pag.

Web. 31 July 2011.

<http://www.sciencedirect.com/science/article/

pii/092401369391198F>.

[5] Yazdi, A.Z. “Prediction of Hardness at

Different Points of Jominy Specimen Using

Quench Factor Analysis Method.” Journal of Materials Processing Technology 199.1-3

(2008): n. pag Web. 31 July 2011.

<http://www.sciencedirect.com/science/article/

pii/S0924013607007339>.

http://www.sciencedirect.com/science/article/pii/092401369391198F

http://www.sciencedirect.com/science/article/pii/092401369391198F


6. Appendices

6.1 Tables and Graphs

Table 1. Data obtained from the experiment

Distance from Quenched End Trial 1 Trial 2

1/16" 60 60

2/16" 61 60

3/16" 60 61

4/16" 61 60

5/16" 61 60

6/16" 61 59

7/16" 61 60

8/16" 60 59

9/16" 60 59

10/16" 61 59

11/16" 60 59

12/16" 60 59

13/16" 59 59

14/16" 59 58

15/16" 58 58

1" 59 59

1" and 1/8" 58 58

1" and 2/8" 58 58

1" and 3/8" 58 58

1" and 4/8" 57 58

1" and 5/8" 57 57

1" and 6/8" 58 57

1" and 7/8" 56 57

2" 56 56

2" and 1/4" 55 56

2" and 2/4" 55 56

2" and 3/4" 55 55

3" 55 55

3" and 1/4" 54 55

3" and 2/4" 54 55

3" and 3/4" 55 54

4" 54 55

4" and 1/4" 55 54


Figure 5. Jominy Hardenability Curves for replicates 1 and 2.

Figure 6. First Derivative Plots for replicates 1 and 2.

TRIAL 1: y = 0.4447x2 - 3.648x + 61.782

TRIAL 2: y = 0.2248x2 - 2.4572x + 60.558

53

54

55

56

57

58

59

60

61

62

0.06 0.31 0.56 0.81 1.06 1.31 1.56 1.81 2.06 2.31 2.56 2.81 3.06 3.31 3.56 3.81 4.06

Jominy Hardenability CurvesBrinell Hardness

versus

Distance from Quenched End (in inches)

Poly. (Trial 1) Poly. (Trial 2)

TRIAL 1: y = 1.504x2 - 7.6233x + 12.492

TRIAL 2: y = 1.8934x2 - 8.7368x + 11.132

0

2

4

6

8

10

12

0.06 1.06 2.06 3.06 4.06

First Derivative Plot|Δy/Δx|

versus Distance from Quenched End

Poly. (Trial 1) Poly. (Trial 2)


6.2 Microstructures of AISI 1020 Steel Sample (500x magnification)

Figure7. 4/16” from quenched end Figure8. 8/16” from quenched end

Figure9. 12/16” from quenched end

Figure11. 20/16” from quenched

end

Figure13. 28/16” from quenched end

Figure10. 1” from quenched end

Figure12. 24 /16” from quenched end




Figure17. 44/16” from quenched

end



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Jominy End-Quench Harden Ability Test