JOMINY END QUENCH EXPERIMENT

Andrew Braum

Mechanical Engineering Department

Loyola Marymount University

Los Angeles, California 90045

April 10, 2008

ABSTRACT

The purpose of this lab was to identify the correlation between carbon content and alloying

elements on the hardenability of steel and steel alloys. Three steels, 1040, 1090, and 4340, were

subjected to a Jominy End Quench Test. Hardness values along the length of the bars were

recorded in Rockwell C scale for comparison to literature. Results can be used by designers

during the materials selection process depending on the application and resources available. Key

results included the 4340 exhibiting relatively consistent hardness values along the bar length at

about 50-54, whereas the 1040 and 1090’s hardness values dropped off to 16 and 35

respectively. Initially the 1090 steel had the highest hardness values due to higher carbon

content (0.5% weight more carbon) in the steel. Alloying elements were identified as the key

factor in steel hardenability. Recommendations included performing additional Jominy End

Quench Experiments on other steel alloys to confirm the best combinations of alloying elements

as they correlate to hardenability.

Proofread by,

Tory Hanashiro

2

TABLE OF CONTENTS

Section Page:

Introduction 3

Theory and Analysis 4

Experimental Procedure 15

Results and Discussion 20

Conclusion and Recommendations 23

References 24

Appendices 25

Appendix A: Raw Data 26

3

INTRODUCTION

The purpose of this lab is to identify the correlations of carbon content and alloying elements on

hardenability of 1040, 1090, and 4340 steels. The hardenability is measured by the amount of

martensite formed throughout a Jominy bar sample. Rockwell C hardness values will be

recorded by a Wilson/Rockwell Hardness Testing Machine in 161 inch increments along the

length of the bar and plotted as a function of the distance from the end that was quenched by

water. Researched literature suggests that although increased carbon content allows for higher

hardness values near the quenched end, alloying elements will vastly affect the uniformity of

hardness, or hardenability, along the length of the samples. Identification of key factors

affecting hardenability, and more specifically which steels are more hardenable than others,

helps designers to select appropriate materials based on application and resources available.

Hardenable steel alloys like 4340 are expensive and thus should be used in critical applications

such as aircraft landing gear.

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THEORY AND ANALYSIS

There are many ways to strengthening steel. The key element that makes steel a steel is the

addition of carbon. Carbon, or in the form of Cementite ( )CFe3 , exponentially improves the

strength of steel. The following Figure 1 shows the relationship between the hardness (Rockwell

C scale) and the carbon content of the steel tested.

As shown above, hardness is used as in indicator of strength. Hardenability is another term used

to describe the hardness in respect to the depth below the steel’s surface (McGannon, 1971).

Favorable hardenability means that the steel or alloy has consistent hardness properties

throughout the thickness of the specimen. This is important because certain alloys exhibit better

hardenability characteristics, and thus prove to be essential in critical applications. Other

strengthening techniques for steel are solution hardening, grain size effect hardening, dispersed-

phase hardening, or work hardening (Thelning, 1984).

Figure 1. Rockwell C hardness as a function of the weight percent carbon added in a steel

(Askeland & Phule, 2006).

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Addition of alloying elements inherently increases steel’s resilience to hardenability loss

(Thelning, 1984). This means that adding alloying elements increases steels hardenability and

thus improves its strength. The exact parameters behind this effect are attributed to “many

factors” as stated by Thelning (1984).

In addition to equilibrium reactions, there are non-equilibrium reactions such as age hardening

and the Martensite reaction. The Martensite reaction, specifically, is not shown on the phase

diagram and is a result of diffusionless solid-state transformation (Askeland & Phule, 2006). For

steels containing less than 2% carbon, austenite (FCC) transforms into martensite (BCC). For

steels with higher carbon content, the martensite is not BCC, but rather a body centered

tetragonal (BCT) crystalline structure. The following picture (Figure 2) illustrates the crystalline

structure of a body centered tetragonal structure. The graph to the right shows how the addition

of carbon changes the length of the c-axis and a-axis (Askeland & Phule, 2006).

Figure 2. (a) Body centered tetragonal (BCT) crystalline structure and (b) a graph of the a-axis

and c-axis as a function of weight percent carbon in the martensite (Askeland & Phule, 2006).

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As mentioned before, martensite formation is a diffusionless solid-state transformation which

means that the reaction does not follow normal diffusion rules specified by Avrami’s equations.

However, the presence of martensite is important because it has very favorable strength. The

BCT crystalline structure has no close-packed slip planes where dislocations lines can move,

thus giving martensite its inherent strength. Specifically during martensite formation, austenite

rapidly transforms to ferrite but the carbon remains in solid solution in the iron−α . Since there

is less space in the ferrite structure than the austenite structure, the ferrite structure is expanded

into its new crystalline structure; a body centered tetragonal (BCT) martensite supersaturated

with carbon (Thelning, 1984). As mentioned, the lattice is expanded and thus there is a notable

volume change during the formation of martensite from austenite. Due to very little migration,

or diffusion, of the carbon atoms the reaction is classified as non-equilibrium (Thelning, 1984).

There are two different structures of martensites, lath and plate martensite, which form

depending on the carbon content of the steel. Low carbon content ( )%6.0< is conducive to lath

martensite which consists of flat, narrow bundles tightly knit next to each other. Higher carbon

content ( )%6.0> , on the other hand, is conducive to form plate martensite which, as its name

suggests, consists of larger flat, narrow plates (Thelning, 1984). Figure 3 below shows a

magnification of the two martensite structures (Thelning, 1984). Figure 4 below Figure 3, shows

the transition of lath martensite to plate martensite as the carbon content increases (Thelning,

1984).

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Figure 3. Magnification of (a) lath martensite and (b) plate martensite (Thelning, 1984).

Figure 4. Diagram of late martensite to plate martensite as the carbon content of the steel

increases (Thelning, 1984).

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Martensite is the hardest and most brittle microstructure that forms in temperatures under Co450

(McGannon, 1971). Brittle characteristics are not desired in steel applications; however a

balanced composition of both martensite and austenite creates a balance of both strength and

ductility. In order to obtain this delicate balance, extremely careful attention is paid to the

undercooling rate to control the martensite growth. Martensite nuclei formation is highly

favored by supercooling due the increasing driving force during the temperature change

(Thelning, 1984). Slow nucleation of martensite occurs at higher temperatures, whereas lower

temperatures accelerate martensite nucleation. This goes to mention a critical cooling rate where

initially the steel must be cooled fast enough through the higher temperature range, but cooled

slowly at the lower temperature ranges to encourage martensite formation (Thelning, 1984).

Also, by quickly bypassing the higher temperature ranges, the risk of undesired equilibrium

transformations is avoided (McGannon, 1971). As indicated in Figure 5 below, holding steel at

elevated temperatures can produce different crystalline structures. The following diagram is

known as a time-temperature transformation (TTT) diagram (Askeland, 2006).

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The TTT diagram clearly shows that at elevated temperatures, say for a 0.8% carbon steel held at

Co650 , will produce austenite and pearlite after 1 second, and form all pearlite after 10 seconds.

Martensite is formed at much lower temperatures and thus requires an extremely fast cooling rate

to bring the steel’s temperature down within the martensite formation range. To illustrate this

Figure 5. TTT diagram for different steels with (a) 0.8% carbon, (b) 0.45% carbon, and (c)

1.0% carbon content. A = austenite, B = bainite, C = cementite, F = ferrite, P = pearlite, M =

martensite, and s

M indicates the start of martensite formation (Thelning, 1984).

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best, a different diagram is needed. A continuous cooling transformation diagram, or CCT

diagram, shows the different microstructures formed as a function of the cooling rate. The

following two charts (Figure 6) are CCT diagrams for 1080 steel, and 4340 steel (Askeland &

Phule, 2006).

The CCT diagrams show that for rapid cooling rates like sec140 Co for 1080 steel and sec8 Co

for 4340 steel allow the formation of all martensite. Slower cooling rates like sec40 Co for

1080 steel and sec3.0 Co for 4340 steel allow the formation of martensite plus pearlite and

(a)

(b)

Figure 6. CCT diagrams for (a) 1080 steel and (b) 4340 steel (Askeland & Phule, 2006).

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martensite plus bainite, respectively. It should also be noted the significant difference of cooling

rates between the nonresulphurized carbon steel (10XX series) and the 1.8% nickel, 0.5-0.8%

chromium, 0.25% molybdenum (43XX series). The 10XX series tend to require a much faster

cooling rate to achieve higher concentrations of martensite whereas the 43XX series can do so at

much lower cooling rates. In respect to hardenability and considering current cooling techniques

and limitations, the 43XX exhibits much more favorable hardenability properties than the 10XX

series.

Since the formation of martensite is a function of cooling rates, naturally the outside will cool

faster than the inside of a sample. Depending on how hardenable a material is, the depth of

martensite will vary. This means that inner sections may not cool quick enough to form

martensite and will contain retained austenite. By leaving the retained austenite as is, the sample

will exhibit ductile properties. However, for samples which are rapidly cooled and form a high

percentage of martensite, brittle characteristics may be limiting for certain applications and thus

additional treatments must be performed. Some of these techniques are known as tempering

which can help relieve the internal stress and allow for ductility recovery. Tempering allows for

the precipitation of carbide from the supersaturated martensite structure at elevated temperatures.

Tempering is applied immediately after quenching (when martensite formation starts) to avoid

cracks (due to non-uniform cooling rates between the surface and the center) and increase

ductility (McGannon, 1971). Rapid cooling in a hot agitated salt bath followed by air cooling to

a uniform temperature is called martempering (McGannon, 1971). Martempering allows for

additional retained austenite to form and improve the steel’s ductility (Thelning, 1984). Figure 7

below shows the formation of cracks on the surface due to non-uniform cooling rates between

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the surface and center (Askeland & Phule 2006). Figure 8 (under Figure 7) shows the graphical

correlation between the surface and center temperature as a function of time, the compression

and tension internal stresses accumulated on the surface and center, and the resulting net residual

stress on the sample surface and center (Thelning, 1984).

A popular method for measuring hardenability is with the Jominy End Quench test. Jominy bars

are typically 1 inch in diameter and 4 inches in length with a tapered head that rests in the cutout

Figure 7. Progressive diagram over time of the formation of cracks due to the non-uniform

cooling rates of the surface compared to the center (Askeland & Phule, 2006).

Figure 8. Diagram of (top) center and surface temperature as a function of time, (bottom left)

tension and compression stresses accumulated from the sample center to the sample surface,

and (bottom right) the net residual stress from the sample center to the sample surface

(Thelning, 1984).

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of the Jominy Quench Tank (McGannon, 1971). The steel alloy is heated to its austenizing

temperature and placed in a Jominy Quench Tank which constantly sprays water on the bottom

of the sample. The water rapidly quenches one end of the sample whereas the other end is

cooled in the air at a slower rate. The sample is cooled to around room temperature and hardness

samples are taken along the bar in 161 inch intervals. Plots can be created showing the

hardness as a function of the length along the bar. The genius behind this test is that the bar

represents a cross-sectional analysis of hardness along the bar length. The more uniform the

hardness along the length, the more hardenable the material is. For larger industry samples in

which cross sectional hardness tests may be impossible (or impractical), Jominy allows designers

to select the proper alloy steel which will give desired hardenability parameters. Figure 9

illustrates a simple Jominy bar being quenched and how the hardness correlates to the bar length

(Askeland & Phule, 2006).

Figure 9. Diagram of a Jominy bar held in a Jominy Quench Tank with water jetted at the

bottom and how harness correlates to the Jominy distance down the length of the bar

(Askeland & Phule, 2006).

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When different steel’s hardness values are superimposed on the same plot, the resulting diagram

should resemble Figure 10 below (Askeland & Phule, 2006).

General trends include a drop in hardness for all steel alloys except for 4340. 4340 steel is

known to have very favorable hardenability characteristics but at an expensive cost (Es-said,

2008).

Figure 10. Superimposed chart of Rockwell C hardness for 4340 (top curve), 8640, 9310,

1080, 4320, and 1050 (bottom curve) at different Jominy distances (Askeland & Phule, 2006).

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EXPERIMENTAL PROCEDURE

Equipment used:

• Carbolite Furnace (Figure 11)

• Jominy Tank (Figure 12)

• Buehler Abrasimet Abrasive Cutter (Figure 13)

• Grinding Machine (Figure 14)

• Rockwell/Wilson Series 500 Hardness Tester (Figure 15)

• Jominy bar-shaped sample for the following steel samples (Figure 16)

o 1040 Steel

o 1090 Steel

o 4340 Steel

A brief overview of the experimental setup was as follows. Each sample was heated in a

Carbolite Furnace at Co885 for 1 hour and 20 minutes. A sample was placed in the Jominy tank

with the water turned on. After allowing the sample to cool down so steam was not visible when

a water droplet was placed on top, the sample was cleaned of excess oxidized scales. A grinding

machine was used to create a flat surface on the cylinder to allow for accurate hardness readings.

Careful attention was paid to the grinding rate so not to heat the sample and cause recovery,

recrystallization, or grain growth. Next, the end of the sample was sliced off with an abrasive

cutter. Then "161 marks were made up to "1 followed by "81 marks up to "2 . Every "81 mark

up to the "1 mark was made on the opposite side of the cylinder to avoid inaccurate hardness

values from strain hardening due to the close proximity of the test points. Lastly, hardness

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values were taken with a Wilson/Rockwell Series 500 Hardness Testing Machine. The

differential depth from a minor load of 10kg followed by a 150 kg major load on a diamond

indenter was recorded as Rockwell C. Entire procedure was repeated for the other two samples.

The following step-by-step procedure was used for Jominy end quenching:

• Heated each sample at Co885 for 1 hour and 20 minutes in Carbolite Furnace

• Placed in Jominy tank with water on

o Sample was ready to handle if no steam arose from a water drop

• Grinded smooth surfaces for hardness test

o Grinded slow to avoid recovery, recrystallization, or grain growth

• Used abrasive cutter to slice off end of sample

• Marked sample with "161 marks up to "1 followed by "81 marks up to "2

• Rockwell C Hardness values were recorded for each mark

• Procedure was repeated for each of the samples

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Figure 11. Picture of Carbolite Furnace (Patel, 2008).

Figure 12. Picture of Jominy Quench Tank (Patel, 2008).

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Figure 13. Buehler Abrasimet Abrasive Cutter (Patel, 2008)

Figure 14. Grinding Machine (Patel, 2008)

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Figure 15. Rockwell/Wilson Series 500 Hardness Tester (Patel, 2008)

Figure 16. Jominy bar-shaped sample (Patel, 2008)

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RESULTS AND DISCUSSION

All raw data can be found in Appendix A along with sample calculations in Appendix B. The

following table contained all raw data gathered during the experiment.

Using the data gathered from the Rockwell C Hardness tests, a graph was generated as a function

of the distance from the quenched end. The following Graph 1 summarized the data graphically.

Andrew Braum, 3/27/08, 1:45 PM, 1 ATM, 70°F

RAW DATA

Jominy End Quench Rockwell Hardness C Scale

Test Distance (in) 1040 1090 4340

0 61 64 55

1/16 56 64 53

1/8 54 63 50

3/16 42 60 53

1/4 34 45 51

5/16 31 47 52

3/8 30 45 51

7/16 30 44 52

1/2 28 45 51

9/16 29 44 51

5/8 27 45 48

11/16 28 42 50

3/4 25 42 48

13/16 26 42 50

7/8 25 42 49

15/16 26 42 49

1 24 40 48

1 1/8 25 40 49

1 1/4 18 40 50

1 3/8 22 39 49

1 1/2 22 38 51

1 5/8 22 37 49

1 3/4 19 36 49

1 7/8 21 34 49

2 16 35 49

Table 1. Raw data of Rockwell C Hardness values for 1040 Steel, 1090 Steel, and 4340 Steel

for distances from 0 inches to 2 inches in increments of 161 of an inch.

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Clearly the trends have shown that both the 1040 and 1090 steels had a significant drop in

hardness as hardness values were taken further and further away from the quenched end. The

4340, on the other hand, showed a relatively level trend, which suggested nearly uniform

hardness values everywhere on the sample. As compared to Figure 10 (discussed in the Theory

and Analysis section), the 4340 steel exhibited a similar trend of uniform hardenability

throughout the entire depth of the test sample. The 1040 and 1090 samples had similar trends in

that as the Jominy test distance increased the hardness values decreased. It should also be noted

Jominy End Quench Hardness vs. Test Distance

0

10

20

30

40

50

60

70

0

1/8

1/4

3/8

1/2

5/8

3/4

7/8

1

1 1/4

1 1/2

1 3/4

2

Jominy Test Distance (inches)

Rockwell Hardness C Scale

1040 Steel 1090 Steel 4340 Steel

Graph 1. Rockwell C Hardness values for 1040 Steel, 1090 Steel, and 4340 Steel as a

function of the distance from the quenched end.

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that the 1090 samples had the highest hardness values at and near the quenched end of the

sample. This was consistent with the theory because the 1090 had more carbon content ( )%9.0

than both the 1040 and 4340 ( )%4.0 . The higher carbon content of the 1090 steel correlated to

higher hardness values but the addition of alloying elements correlated to the higher

hardenability of the 4340 steel.

Figure 10 showed that 4340 also had an initial hardness value less than 1080 (close to a 1090

steel) or 1050 steels (close to a 1040 steel) which were also consistent with data from Chart 1.

Figure 10 suggested hardness values for 4340 to be around 60; for 1050 to go from about 62

dropping to 16; and for 1080 to go from about 68 dropping to about 30 in Rockwell C scale

hardness. Data from the lab showed hardness values for 4340 to be around 50 to 54; for 1040 to

go from 61 dropping to 16; and for 1090 to go from 64 dropping to 35 in Rockwell C scale

hardness.

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CONCLUSIONS & RECOMMENDATIONS

The following are conclusions made for this experiment:

• The 1040 and 1090 steels’ hardness drops off as the Jominy test distance increases.

• The 4340 steel’s hardness stays relatively level at about 50-54 in Rockwell C hardness as

the Jominy test distance increases.

• The 1090 steel has initial hardness values higher than those for the 1040 and 4340 steels

because of the higher carbon content (0.5% weight more carbon).

• Trends for the 1040, 1090, and 4340 steels are consistent with referenced literature for

1050 (comparable to 1040), 1080 (comparable to 1090), and 4340 steels.

• Carbon content increases the hardness of the sample but only near the quenched end.

• Alloying elements are the determining factor in steel’s hardenability.

The following are recommendations made for this experiment:

• Perform additional Jominy End Quench Experiments on other steel alloys to confirm the

best combination of alloying elements as they correlate to hardenability.

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REFERENCES

Askeland, D.R., & Phule, P.P. (2006). The Science and Engineering of Materials. Thomson

Canada Ltd., Toronto, Ontario, Canada.

Es-Said, O. (2008). Personal communication (lecture notes). Los Angeles, CA: Loyola

Marymount University.

McGannon, H.E. (1971). The Making, Shaping and Treating of Steel, United States Steel, 9th

edition. Herbick & Held, Pittsburgh, PA.

Patel, D. (2008). Experimental Pictures. Los Angeles, CA: Loyola Marymount University.

Saniei, N., & Es-Said, O. (2007). Laboratory Manual, MECH 342 Mechanical Engineering Lab

II. Department of Mechanical Engineering. Los Angles, CA: Loyola Marymount

University.

Thelning, K.-E. (1984). Steel and its heat treatment, 2nd edition. Butterworths, London, Great

Britain.