Jominy End Quench Hardenability Test

Tejas AtyamIII Sem- BE (Prod.)

HardenabilityOne of the important properties of (processed) metals

is hardenability

Hardenability is the capability of an alloy to be hardened by heat treatment

Measures the depth of hardness obtained by heat treatment/quenching

Hardenability is not the same as hardness.

The Hardness of a steel refers to its ability to resist deformation when a load is applied, whereas hardenability refers to its ability to be hardened to a particular depth under a particular set of conditions.

Jominy TestThe Jominy End Quench Test measures

Hardenability of steels.

As we already discussed, hardenability is a measure of the capacity of a steel to be hardened in depth when quenched from its austenitizing temperature.

Why Jominy Test?Information gained from this test is

necessary in selecting the proper combination of alloy steel and heat treatment to minimize thermal stresses and distortion when manufacturing components of various sizes.

Steps to conduct Jominy Test 1. First, a sample specimen cylinder either 100mm in length and

25mm in diameter, or alternatively, 102mm by 25.4mm is obtained

2. Second, the steel sample is normalized to eliminate differences in microstructure due to previous forging, and then it is austenitised. This is usually at a temperature of 800 to 900°C.

3. Next, the specimen is rapidly transferred to the test machine, where it is held vertically and sprayed with a controlled flow of water onto one end of the sample

4. This cools the specimen from one end, simulating the effect of quenching a larger steel component in water

(Because the cooling rate decreases as one moves further from the quenched end, one can measure the effects of a wide range of cooling rates from very rapid at the quenched end to air cooled at the far end.)

Steps to conduct Jominy Test ….. Contd…5. Next, the specimen is ground flat along its

length to a depth of .38mm (15 thousandths of an inch) to remove decarburized material.

6. The hardness is measured at intervals along its length beginning at the quenched end. For alloyed steels an interval of 1.5mm is commonly used where as with carbon steels an interval of .75mm is typically employed.

24°C water

specimen (heated to g phase field)

flat ground

Rockwell Chardness tests

Steps to conduct Jominy Test ….. Contd…7. And finally the Rockwell or Vickers hardness values are

plotted versus distance from the quenched end.

Hardness versus distance from the quenched end

 The Jominy Test data illustrates the effect of alloying and microstructure on the hardenability of steels.

Har

dnes

s, H

RC

Distance from quenched end

End-Quench hardenability test (Jominy Test) - Summary

Quenching mediaWaterBrineOilMolten saltsAirCaustic solutionsPolymer solutionsgases

Round test bar is austenized (heated to the proper temperature to form 100% austenite)

Bar then quenched at one end

Hardness decreases away from the quenched end of the bar

Commonly used elements that affect the hardenability of steel are carbon, boron, Chromium, Manganese, Molybdenum, Silicon, and Nickel.

Carbon is primarily a hardening agent in steel, although to a small degree it also increases hardenability by slowing the formation of pearlite and ferrite. But this affect is too small to be used as a control factor for hardenability.

Boron can be an effective alloy for improving hardenability at levels as low as 0005%. 

Boron is most effective in steels of 0.25% Carbon or less.

And FinallySlowing the phase transformation of

austenite to ferrite and pearlite increases the hardenability of steels.

Chromium, Molybdenum, Manganese, Silicon, Nickel and Vanadium all effect the hardenability of steels in this manner.

Chromium, Molybdenum and Manganese being used most often.

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Why Hardness Changes with Position• The cooling rate varies with position.

Adapted from Fig. 11.13, Callister 7e. (Fig. 11.13 adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1977, p. 376.)

distance from quenched end (in)Ha

rdn

ess

, H

RC

20

40

60

0 1 2 3

600

400

200A ® M

A ®

P

0.1 1 10 100 1000

T(°C)

M(start)

Time (s)

0

0%100%

M(finish) Martensite

Martensite + Pearlite

Fine Pearlite

Pearlite

Hardenability vs Alloy Composition

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• Jominy end quench results, C = 0.4 wt% C

• "Alloy Steels" (4140, 4340, 5140, 8640) --contain Ni, Cr, Mo (0.2 to 2wt%) --these elements shift the "nose". --martensite is easier to form.

Adapted from Fig. 11.14, Callister 7e. (Fig. 11.14 adapted from figure furnished courtesy Republic Steel Corporation.)

Cooling rate (°C/s)

Har

dne

ss, H

RC

20

40

60

100 20 30 40 50Distance from quenched end (mm)

210100 3

4140

8640

5140

1040

50

80

100

%M4340

T(°C)

10-1 10 103 1050

200

400

600

800

Time (s)

M(start)M(90%)

shift from A to B due to alloying

BA

TE

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Quenching Medium & Geometry• Effect of quenching medium:

Mediumairoil

water

Severity of Quenchlow

moderatehigh

Hardnesslow

moderatehigh

• Effect of geometry:

When surface-to-volume ratio increases: --cooling rate increases --hardness increases

Positioncentersurface

Cooling ratelowhigh

Hardnesslowhigh

Jominy Test Dimensioning

Jominy Test Apparatus

Jominy Results exmapleUsed Jominy Test Piece