Materials and Design 32 (2011) 3099–3105

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Materials and Design

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Technical Report

Investigation of the correlation between thermal properties and hardenabilityof Jominy bars quenched with air–water mixture for AISI 1050 steel

Mehmet Çakir a,⇑, Abdullah Özsoy b

a Süleyman Demirel University, Graduate School of Natural and Applied Sciences, Department of Mechanical Engineering, 32260 Isparta, Turkeyb Süleyman Demirel University, Faculty of Technical Education, Department of Mechanical Education, 32260 Isparta, Turkey

a r t i c l e i n f o a b s t r a c t

Article history:Received 8 October 2010Accepted 15 December 2010Available online 21 December 2010

0261-3069/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.matdes.2010.12.035

⇑ Corresponding author. Tel.: +90 246 211 19 05; faE-mail address: cakirm@sdu.edu.tr (M. Çakir).

In this study, the hardenability of AISI 1050 steel has been investigated in different cooling media usingJominy test. The temperature values were recorded using the thermocouples that were placed on sample.The relations between the cooling media and the cooling curves, heat flux, hardenability and heat con-vection coefficient were shown in graphics. The correlation between thermal properties and hardenabil-ity was established. When Jominy water pressure decreased, hardenability decreased in Jominy bar. Buthardenability of steel quenched by air–water mixture cooling media was observed that increasing sur-prisingly. As a result of air–water mixture quenching, heat transfer accelerated and the hardenabilityincreased in the Jominy bar.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

The distribution of hardness constituted in a steel usingquenching operation from the surface to the inside is defined ashardenability. The Jominy end-quenching test is one of the mostreliable and common methods used for the hardening of steels.

Köksal et al. [1] noted that the hardening behavior of steel cov-ers two concepts namely both the maximum hardness that can bereached and the hardenability that can be achieved. During thedetermination of hardening depth the type of the cooling media,its composition, the temperature and the thermal effects betweenthe environment and the sample all take very important roles.While the steel is cooled in quenching media, Fernandes and Pra-bhu [2] observed that three different phases (the vapour phase,nucleate boiling and convective stage) are constituted betweenthe quenching media and the sample. During the first stage ofquenching the cooling rate is slow. In the first moments a thin filmof vapour forms over the surface of the sample. This vapour filmhinders the heat flow between the sample and the cooling media[3]. It is important to determine in which conditions this layer isformed or not and it has to be investigated. In the Jominy test dur-ing the quenching the cooling starts from the end of the sample.For this reason the heat transfer on the surface is important. Theimportance of the surface heat transfer coefficient is directlyproportional with the surface temperature, the changes inconditions of quenching media and the condition of the surfaceof sample [4]. Beloshapko et al. [5] examined the hardening of steel

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x: +90 246 211 18 77.

KhPT-250 in media of cooling with oil, water and air–water mix-ture. The cooling with air–water mixture was observed that itcaused less tension compared to the quenching operations usingonly water. The cooling capacity of air–water mixture was foundhigher than that of the oil media. They acquired different coolingparameters changing the water flow and cooling time in coolingmedia. While a hardness of 53 HRC (Rockwell C Hardness) was ob-served on the surface as a result of quenching for 2 min 15 s inpressure water, the air–water mixture used for quenching for 10and 20 min caused respectively 55 and 57 HRC hardness on thesurface of the sample.

Ghrip et al. [6] investigated the relations between thermalproperties, Rockwell hardness value and microstructure in steelsC48, 42CrMo4 and 35NiCrMo16. They calculated the heat convec-tion coefficient and heat diffusion coefficient using the Photo-ther-mal Deflection Technique (PDT). They said that the hardness valuecould be determined without any measurements provided that oneknows the heat convection and diffusion coefficients at any dis-tance from the Jominy end. Kazakov et al. [7] cooled springs witha 16 mm diameter and made of steel 60S2. For this purpose theyquenched the samples in air–water mixture changing the air pres-sure and water percentage at determined ratios. The distribution ofhardness acquired with the air–water mixture showed better re-sults than cooling in oil media. The best results were achievedusing a mixture of air with 3 atm pressure and 80% of water. Pysh-mintsev et al. [8] quenched the samples made of steel 42CrMo4and AISI 4140 at 250–720 mm diameter interval, 1500–6000 mmlength interval and 1–20 tones of weight interval in oil media, highand low pressure air–water mixture media. For this purpose theyaimed to control the hardenability in steels with large diametersand heavy masses. They determined that using intense air–water

Fig. 1. State of thermocouples in Jominy specimen.

3100 M. Çakir, A. Özsoy / Materials and Design 32 (2011) 3099–3105

mixture for quenching would form hardenability in large steelparts and that the cooling could be controlled using the air–watermixture.

The cooling operation can be controlled by changing thequenching time and cooling media condition during quenchingoperations with water and air–water mixture [9]. Karaca [10]investigated cooling media mixed water and pressurized air at apressure lower than 65 mmWC (millimeter water column) in hisresearch on the hardenability of steel. He saw that the hardenabil-ity depth formed was at a higher level than those formed under65 mmWC and 130 mmWC pressures.

In this study, the AISI 1050 steel was quenched using the Jomi-ny end-quenched test. Air–water mixture was used for spreadingthe vapour phase that prevented heat transfer in quenched-end.This work aims to accelerate heat transfer and to increase hardena-bility in Jominy test bar. The relation between heat transfer andhardenability has been examined in Jominy bar. Especially, the ef-fect of air–water mixture investigated in Jominy end-quenchedtest.

Fig. 2. Test setup as show in the scheme.

2. Materials and methods

In the tests cylindrical bars with 32 mm diameter were taken assamples (composition of AISI 1050 steel are given in Table 1) fromthe AISI 1050 steel. The samples were wait at 860 �C temperaturesthat on 40 �C of the Ac3 temperature, for 30 min and were appliedto normalization annealing at placid air cooling media. Then, thesamples were prepared in Jominy sample sizes (25 mm diameterand 100 mm length) in the turning machine. The density and cp

values of the AISI 1050 steel used in the tests are given in Table2 [11].

K type thermo-couples were placed as shown in Fig. 1. The ther-mo-couples with 1.5 mm thickness were mounted inside the holeson the sample with 1 mm depth on vertical axis.

The samples were heated up to the austenite temperature(860 �C), and to provide a homogenous temperature distributionthey were kept inside the furnace for 30 min. The quenching oper-ation continued for 10 min. All samples were processed in thesame manner. The temperature values were transmitted to the sig-nal reader (Almemo 5990-2) via the thermo-couples. The valuesreceived from the signal reader were recorded in the computer.

The hardness was measured by the Rockwell C hardness test.The samples were ground at 0.4 mm depth. The samples weremould as bakelite for research under the optical microscope. Then,they were sandpapered respectively, 400, 600 and 1200 sand SiCwith emery at metal polishing machine. Next, they were polishedwith 0.25–1 lm polish. Then, they were washed with ethyl alcoholfor prevent satins at surface of the samples, and were dried bydryer. Etching process was made with a mixture of 3% nitric acid

Table 1Composition of AISI 1050 steel specimen (wt.%).

C Mn Si P S Cr Mo Ni Al Cu Sn

0.50 0.64 0.24 0.010 0.005 0.12 0.01 0.07 0.014 0.16 0.011

Table 2The density and cp values of AISI 1050 steel.

q (kg/m3) cp (J/kg �C)

7854 27 �C 127 �C 327 �C 527 �C 727 �C434 487 559 685 1169

and 97% ethyl alcohol. Then, microstructures of etched sampleswere photographed.

The quenching operation according to the Jominy test was ap-plied considering three conditions. 1. Standard water pressure at65 mmWC, (�18 �C), 2. Water pressure at 32.5 mmWC, (�18 �C),3. Water pressure at 22 mmWC (2,5 lt/m flow) water and air mix-ture (0.40 bars) (�18 �C) (This condition is equivalent to the stan-dard Jominy water pressure at 65 mmWC.) Under these conditions,after being heated up to the austenite temperature, the sampleswere subjected to the hardenability process in the test setup asshown in Fig. 2.

Using the cp values in Table 2 [11], the equation given in Fig. 3was formed in order to find the cp value at a desired temperature.An equation was created for cp values at five different tempera-tures. In this equation, if the desired temperature instead of xwas inserted and solved cp value of the desired temperature wasfound.

In the sample heated up to the constant starting temperature Ti,

for a decrease in @T temperature in a period @t time after the start-ing of cooling operation;

qst ¼ �q � V � cp �@T@t

ð1Þ

shows the number of samples where a loss in heat has taken place.The heat transferred from the sample surface to the cooling mediais;

qconv ¼ �h � As � ðTs � T1Þ ð2Þ

which is also known as the Newton’s Law of Cooling. The fast cool-ing of the sample is effective during the hardening of the steel. Con-sequently, since the cooling media is in contact with the end of thesample, the immediate loss of heat is only at this end of the sample.If we equal the loss of heat in the sample to the heat received by thecooling media from the same sample;

c p (T) = 6E-09x4 - 3E-06x3 - 7E-05x2 + 0,5888x + 418,21

0

200

400

600

800

1000

1200

1400

0 100 200 300 400 500 600 700 800

Temperature (oC)

Cp

Valu

es (J

/kgo C

)

Cp Values

Fig. 3. Equation for cp values.

M. Çakir, A. Özsoy / Materials and Design 32 (2011) 3099–3105 3101

qconv ¼ qst

�h � As � ðTs � T1Þ ¼ �q � V � cp �dTdt

ð3Þ

is achieved. If we take out h, the heat convection coefficient in theEq. (3);

h ¼ qcpVAs

1t

lnT � T1Ti � T1

� �ð4Þ

is achieved.The heat energy loss from the sample in every stage of the time

was calculated with the Eq. (1). The heat convection coefficient val-ues released to the environment from the surface of sample werecalculated with the Eq. (4). The heat flux values (heats transferredfrom the unit surface) were calculated using the Eq. (5)

q0 ¼ qAs

ð5Þ

3. Results and discussion

In this study the relation between the hardenability curve ofAISI 1050 steel formed by the change in quenching parameter dur-ing the Jominy hardenability test and the heat transfer was viewed.

50

150

250

350

450

550

650

750

850

0 25 50 75 100 125

Time (

Tem

pera

ture

(o C)

Fig. 4. Cooling curves acquired from quenching

At the quenched-end of the sample, the relations between the cool-ing rate, heat convection coefficient and hardenability, and threedifferent quenching parameters were studied.

3.1. Cooling curves and the microstructure

At the end of the tests, the cooling curves depending on timewere acquired as given in Fig. 4.

Similarly to the studies of Yazdi et al. [12], when Fig. 4 ischecked, it was seen that the temperature decrease at 65 mmWCpressure level at the quenched-end of the sample became less inthe inner sections. The inner sections got cooled down slower.The quenched-end was cooled rapidly and respectively 5 mm,10 mm, 20 mm and 30 mm away from quenched-end on verticalaxis (specimen’s longitudinal axis).

In the continuous cooling diagram for AISI 1050 steel [13], cool-ing curves in the end of the sample for three different cooling med-ia were given in Fig. 5 and those at 5 mm and 10 mm distances invertical axis were given respectively in Figs. 6 and 7. The coolingcurves were superimposed on the continuous cooling diagram forAISI 1050 steel. Hardness values of these points were given in cir-cles at the bottom of the figures.

As it can be seen in the cooling curves the microstructure at theend of the sample for three different cooling parameters com-

150 175 200 225 250 275 300

seconds)

Quenched end5mm10mm20mm30mm

process at a water pressure of 65 mmWC.

1 10 100150

200

300

400

500

600

700

800

900

Time (seconds)

Tem

pera

ture

°C

Mf

MsB

P

F

A c = 785 °C

A c = 725 °C1

3

A

61 61

Air-water agitator

65 mmWC water pressure32.5 mmWC water pressure

QuenchedEnd

61

(Quenched end) 65 mmWC

Fig. 5. Cooling curves and microstructure in the quenched-end.

1 10 100150

200

300

400

500

600

700

800

900

Time (seconds)

Tem

pera

ture

°C

Mf

MsB

P

F

A c = 785 °C

A c = 725 °C1

3

A

53

48

Air-water agitator

65 mmWC water pressure32.5 mmWC water pressure

5mm

59

(5mm) Air-water mixture

(5mm) 65 mmWC

Fig. 6. Cooling curves and microstructure at 5 mm.

3102 M. Çakir, A. Özsoy / Materials and Design 32 (2011) 3099–3105

pletely consists of martensite. The microstructure has been givenas an example of 65 mmWC. The cooling curve of the air–watermixture at 5 mm level is the critical rate. The microstructure con-sists of martensite. The hardness at this point is 59 HRC. The hard-ness value at 65 mmWC pressure and 5 mm level is 53 HRC and themicrostructure consists of martensite and bainite. The microstruc-ture according to the cooling curve at 32.5 mmWC pressure and5 mm level consists less martensite and more bainite comparedto that in 65 mmWC pressure and the hardness is 48 HRC. If thecooling curves at 10 mm level were investigated, it was observedthat the microstructures in three cooling media had been similar.The hardness of the sample cooled down using air–water mixture

at 10 mm level is 32 HRC, whereas the hardness in other coolingmedia is 30 HRC. Also at this point, the sample cooled down withair–water mixture consisted of more martensite compared to othersamples.

3.2. Hardness and thermal properties

The hardness was measured by the Rockwell C hardness test.The changes in the hardness curves from the surface to a deep of10 mm for three different quenching media were given in Fig. 8.

In Fig. 8 the change in the water pressure and the effects of air–water mixture on hardenability were observed. The hardness

1 10 100150

200

300

400

500

600

700

800

900

Time (seconds)

Tem

pera

ture

°C

Mf

MsB

P

F

A c = 785 °C

A c = 725 °C1

3

A

30

30

Air-water agitator

65 mmWC water pressure32.5 mmWC water pressure

10mm

32

(10 mm) 65 mmWC

Fig. 7. Cooling curves and microstructure at 10 mm.

Fig. 8. The hardenability curves for three different cooling media at 10 mm distance.

Fig. 9. The change in cooling rate, according to the temperature in the quenched-end of the sample for three different cooling media.

M. Çakir, A. Özsoy / Materials and Design 32 (2011) 3099–3105 3103

curves overlapped up to 3 mm depth for three different coolingparameters however they differentiate after the level of 3 mm.The hardness values in a–b–c points at 3 mm depth are nearly 59

HRC. Hardness at point d, which is 6 mm away from thequenched-end, was observed 41 HRC. Hardness at e and f pointswas observed respectively 47 HRC and 55 HRC.

Fig. 10. The change of heat convection coefficients in time for three different cooling media parameters.

Fig. 11. The change in heat flux for three cooling media in the quenched-end of the sample.

3104 M. Çakir, A. Özsoy / Materials and Design 32 (2011) 3099–3105

Yazdi et al. [12] recorded the temperature values in differentpoints of Jominy sample during cooling process and observed a de-crease in the temperature curves as the distance increases from thequenching end to the inner sections and also a similar decrease inthe hardness value. Similarly to the study of Yazdi et al. [12], thechange of the cooling rate, according to the temperature in theend of the sample for three different cooling media, is given inFig. 9.

The maximum value of the cooling rate of the air–water mix-ture is at 600 �C; whereas the maximum value is at 680 �C forthe other two cooling parameters. Vapour phase was disintegratedin air–water mixture cooling media. So, cooling rate of air–watermixture occurred a major difference compared to that of othermedia. This difference can also be observed considering the hard-ness values. As mentioned by Borisov [14] in his study, the coolingprovided with air–water mixtures is faster than the cooling pro-vided with water, and this is also as Fig. 9. The change of the heatconvection coefficient in the quenching end for three cooling med-ia parameters is given in Fig. 10.

Until the first three seconds, in cooling operation with air–water mixture the heat convection coefficient is lower comparedto the other. However in the forth second, the sample exceedsthe peak values of the others and reaches the maximum level. Itwas observed that it was at higher levels compared to others inthe 5th and 6th sec. On the heat transfer surface, (at thequenched-end) the heat flux occurred in time for three environ-ments is given in Fig. 11.

The heat flux in the sample end at 65 mmWC and 32.5 mmWCpressure levels reaches to the peak level in 3 s. However, the air–water mixture reaches to the peak level in the 4th sec.

Replacement of water spray quenching by water–air mixture insteel rolls was observed an increase in surface hardness from 51HRC to 56 HRC [5]. This situation is supported this article.

4. Conclusions

The hardenability of the AISI 1050 steel has been examinedusing the Jominy test for three different quenching media. As theresult of the relations between hardenability and the thermalproperties, the following points have been reached:

(1) During the Jominy end-quenched test, when the quenchingpressure was decreased below the standard value, it wasobserved that hardenability decreased a little. However,lowering the water pressure and forming a mixture withpressurized air (65 mmWC) caused an increase in thehardenability.

(2) In the continuous cooling diagram of AISI 1050 steel thecooling curve at 5 mm away from the quenched-end inair–water mixture media equalized to the critical coolingrate. The structure consisted of martensite.

(3) The hardenability formed by the air–water mixture in theJominy sample was higher than the hardenability formedduring standard cooling process.

M. Çakir, A. Özsoy / Materials and Design 32 (2011) 3099–3105 3105

(4) Hardenability was increased with the accelerating heattransfer from the quenched-end. Air–water mixture coolingmedia was accelerated heat transfer from the quenched-end.

Acknowledgement

This study was supported by Unit of Scientific Research Projectsof Süleyman Demirel University (Project Number: 1531 YL-07).

References

[1] Köksal NS, Uzkut M, Ünlü BS. Differences in mechanical properties of steels ofdifferent carbon concentration by heat treatment D.E.U. Fac Eng J Sci Eng2004;6:95–100.

[2] Fernandes P, Prabhu KN. Effect of section size and agitation on heat transferduring quenching of AISI 1040 steel. J Mater Process Technol 2007;183:1–5.

[3] Heming C, Xieqing H, Jianbin X. Comparison of surface heat-transfercoefficients between various diameter cylinders during rapid cooling. J MaterProcess Technol 2003;138:399–402.

[4] Smoljan B. Prediction of mechanical properties and microstructure distributionof quenched and tempered steel shaft. J Mater Process Technol2006;175:393–7.

[5] Beloshapko MV, Shmyrev IP, Mazanik VF, Bondereva LM, Zimoveiskaya SI.Water–air hardening of KhPT-250 mill 9Kh2MF steel rolls. Met Sci Heat Treat1982;24:101–3.

[6] Ghrib T, Bejaoui F, Hamdi A, Yacoubi N. Correlation between thermalproperties and hardness of end-quench bars for C48, 42CrMo4 and35NiCrMo16 steels. Thermochim Acta 2008;473:86–91.

[7] Kazakov YS, Pozharskii AV, Makarov VA. Quenching hot-coiled springs in waterand water–air mixture. Met Sci Heat Treat 1980;22:88–91.

[8] Pyshmintsev Y, Éismondt YG, Yudin YV, Shaburov DV, Zakharov VB.Hardening of large forgings in water–air mixture. Met Sci Heat Treat2003;45:103–8.

[9] Astaf’ev AA, Levitan LM. Controlled quenching: sprayer and water-air cooling.Met Sci Heat Treat 1999;41:54–7.

[10] Karaca SÖ. Jominy test and the effect of the test parameters on the test. Y.T.U.Graduate School of Applied and Natural Sciences, _Istanbul. M. Sc. Thesis; 1993.p. 166.

[11] Incropera FP, DeWitt DP. Fundamentals of heat and mass transfer. 4th ed. NewYork; 1996. p. 886.

[12] Yazdi Z, Sajjadi SA, Zebarjad SM, Moosavi NSM. Prediction of hardness atdifferent points of Jominy specimen using quench factor analysis method. JMater Process Technol 2008;199:124–9.

[13] Topbas� MA. Çelik ve Isıl _Is�lem Atlası. Prestij Yayıncılık, _Istanbul; 1996. p. 199.[14] Borisov IA, Goland LF, Zhigalkin IG. Water–air cooling in heat treatment of

large parts. Met Sci Heat Treat 1996;38:499–502.