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Enhancement of Dry Sliding Wear Characteristics of CK45 Steel Alloy by Laser Surface Hardening Processing

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Procedia Materials Science 6 ( 2014 ) 1639 – 1643

Available online at www.sciencedirect.com

2211-8128 © 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Selection and peer review under responsibility of the Gokaraju Rangaraju Institute of Engineering and Technology (GRIET) doi: 10.1016/j.mspro.2014.07.148

ScienceDirect

3rd International Conference on Materials Processing and Characterisation (ICMPC 2014)

Enhancement of Dry Sliding Wear Characteristics of CK45 Steel

Alloy by Laser Surface Hardening Processing

Adel K. M.

a

*

aMechanical Engineering Dept., College of Engineering, University of Diyala, Baqoubah, Diyala - Iraq,

Abstract

Laser surface hardening processing has been applied to Ck45 steel cylindrical rod specimens using Nd: glass laser. Laser surface hardening processing parameters examined in the present study included three energies (0.25, 0.51 &0.64) J and number of laser beam sizes, after investigation found that the melting is occur for Ck45 steel alloy at laser energy equal or above to 0.64J while the laser surface melting processing don’t take place below this value and no significant effect has been observed below 0.25J. The Ck45 steel samples were examined using X-Ray diffraction technique to determine the phases of microstructure. Also examined structural and mechanical properties especially the hardness and wear resistance after laser processing. It was found that the significant increasing in hardness value at the highest energy (0.64J) and high increasing in the dry sliding wear resistance after laser surface hardening processing.

© 2014 The Authors. Published by Elsevier Ltd.

Selection and peer-review under responsibility of the Gokaraju Rangaraju Institute of Engineering and Technology (GRIET).

Keywords: Laser surface hardening, dry sliding wear, Ck45 steel alloy ;

1. Introduction

High power lasers are currently use to transformation hardening of many surfaces and mechanical components such as cylinder, liners, crankshafts, bearing gears and ring grooves in order to improve hardness, fatigue and wear resistance, Molian et. al. (1986). In practical, laser surface hardening is now been accepted as effective as other conventional techniques, Munir et. al. (2001). Laser surface hardening provides the extra advantage localized hardened region. This may be considered as an economic factor that compensates for the high initial capital of laser equipment as compared to conventional methods requirements, Rykalin et. al. (1978)& Ready et. al. (1978). Transformation hardening due to scanning laser beam or pulses was studied by many workers. The resulting phases in the microstructure depend upon the laser beam characteristics, this on one hand and on the composition of the processed steel on the other hand. The heat affected zone (HAZ) is characterized by dendritic structure, martensite, pearlite, ferrite and retained austenite could be present in a laser processed steel surface. Noticeable increasing in hardness was also found due to laser processing, Sandren (2003). However scatter in surface hardness is expected when microstructure is not uniform and when hard compound form due to laser glazing, Eckersky (1996). Laser surface hardening response of steel as expected increase with the carbon content, Danileko et. al. (1986) & Riabkina et. al. (1985). Nicolas (1984) used Pulsed solid state lasers for surface hardening of

low carbon steel, he had obtianed that the hardness increase and favorable microstructure modifications. Similar processing on tool steel has produced variation in chemical compositionMolian et. al. (1986), in addition obvious surface modification.

The objective of this paper is to improve the material properties that are responsible for success or failure of laser heat treatment. In earlier studyby Adel et.al. (2001), the author studied the laser surface modification of ductile iron, while this paper represents additional investigation of surface heat treatment of medium carbon steel using pulsed laser beam.

© 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Selection and peer review under responsibility of the Gokaraju Rangaraju Institute of Engineering and Technology (GRIET)

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* Corresponding author. Tel.:009647904427514.

E-mail address: adel_alkayali@yahoo.com

2. Experimental procedure

In this study samples of circular CK45 steel alloy were subjected to dry sliding wear study before and after surface treating by laser. The test specimens were (15mm) in length and (10mm) in diameter. Chemical composition of the Ck45 steel alloy is shown in table 1. Pin on disc sliding machine was used for this study. The wear rate was measured by weight loss method using a Mettler AE200 microbalance of (10^-4 gm) sensitivity. The wear rate was calculated according to the following relationship:

Wear rate = 'W/SD (gm/cm) (1) Where: 'W= Weight loss (gm)

SD=Sliding distance (cm)

'W=W1-W2 (2) Where: W1= Initial weight of the test specimen (gm)

W2= Finial weight of the test specimen (gm)

The applied normal load was 30N and three linear sliding speeds (0.7, 0.99 & 1.49) cm/sec. The hardness of the disc was 385Hv. The duration of each test was 10 minutes and the test was carried out at room temperature and normal atmospheric conditions.

Table 1. The chemical composition of CK45 steel alloy.

Surface roughness estimated of samples before and after laser surface hardening by A Parthen – Perthometer type: 56 P_ ISO.

The hardness of samples was measured by using Lietz - GMBHD6330 Wetzlar- Hardness tester with load of 3kg for 30 seconds. The Vickers hardness Hv number is calculated by:

Hv = 1.8544 * P/ dav Kgf/mm2 (3) Where:-

P: Applied load (Kgf.)

dav: Average of indentation diameter (mm).

Olympus (Japan) optical microscope was connected to automatic camera. Olympus C-35 AD -2 Japan Serial No.259384 and digital controller to adjust exposure time automatically and scanning electron microscope "SEM" were used for examination of characters and microstructure of samples before and after laser surface hardening. X-ray diffraction technique was employed to evaluate the phases present in the CK45 steel alloy in the surface of samples before and after laser processing and to examine the effect of laser surface treatment on the processed sample surfaces. X-ray diffractometer instrument type: Philips PW-1050 with CukD radiations wavelength (O = 54838 nm) , Voltage 40 KV , Current 20 mA and with scanned rate of 1.5 20/min were used in this investigation to identify the present phases before and after laser surface hardening processing and estimated quantities of the present phases (martensite and retained austenite) in steel alloy by using Direct Comparison Method.

Three laser energies (0.25, 0.51& 0.64)J have been used for different focusing positions to obtain the best mechanical properties and fineness microstructure. After investigation , the results showed that the melting is occur for Ck45 steel alloy at laser energy equal or above to 0.64J while the laser surface melting processing don’t take place below this value and no significant effect has been observed below 0.25J.

Chemical composition (wt %)

C Si S Cr Mn Ni P Mo Al Cu

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3. Results and discussion

There are two basic types of microstructure may be produced in the laser modified surface. Short laser-substrate (CK45 steel alloy) interaction times (high solidification rate) produced a dendritic microstructure which consists of metastable austenite dendrites with an interdendritic cementite network. Long interaction times (low solidification rates) produced a lamellar microstructure consisting of large volume fraction in primarily ferrite matrix (with some retained austenite. Interaction cooling rates produced a mixed morphology consisting of both the dendritic and lamellar microstructures. The Nd:glass laser which is a solid state laser used in this research work in order to modify the microstructure of CK45 steel alloy, therefore the interaction time very short between CK45 steel alloy (substrate) and Nd: glass laser, this meaning very high solidification rates resulted in very fine acicular microstructure which consisted of acicular martinsite and metastable retained austenite as shown in figure 1, while figure 2 shows the X-Ray diffraction analysis results for CK45 steel alloy phases before and after laser processing. Acicular martensitic microstructure had a hardness ranging from 190Hv before laser treatment up to 850 Hv after laser surface modification.

Fig. 1. Shows the microstructure of Ck45 steel alloy after laser surface hardening.

Fig. 2. Shows X-ray diffraction analysis results of Ck45 steel alloy (a) before laser surface hardening processing; (b) after laser surface hardening processing.

The type of wear test was used adhesive and abrasive wear test. The laser induced rapid melting and resoldification generally produces a very hard wear resistant thin surface layer. The detailed wear data have been showed in figures 2 and 3. The effect of sliding time on the accumulative wear rate of CK45 steel alloy is shown in figure 3. It is clear that an accumulative wear rate increases with increasing sliding time, this increasing being more pronounced from the beginning to the end of the test for both of two metallurgical states of CK45 steel alloy before and after laser surface processing. This observation is due to the gradual flattening of the asperities with the sliding time and increasing other contact area was mentioned by some investigators Kheder et. al. (1996) and Sugishita et. al. (1981).

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The effect of sliding speed on the wear rate of both states laser processed& unprocessed CK45 steel alloy is shown in figure 4. The wear rate decreases with increasing sliding speed at all speeds used in the present study, this decreasing being more pronounced at the beginning of the test and then a steady state is reached. This behavior can be explained by taking the flash temperature into account. The flash temperature increases with increasing sliding speed up to the melting point at asperities, Kawamoto et. al. (1980), Chen et. al. (1988) and Chen et. al. (1988). The heat dissipation at higher sliding speed is lower than that at lower sliding speed , this agreement with study by Kheder et. al. (1996), this causes softening of asperities and reduces the forces required to shear the welded points so the wear- rate will be lower.

Fig. 3. Shows the sliding time versus the accumulative wear rate.

Fig. 4. Shows the sliding speed versus the accumulative wear rate.

From figures 3& 4 are obvious that the curves of wear rates in all conditions have the same trend namely, increasing the wear rate with sliding time and decreasing with sliding speed, but from same figures it is showed that an accumulative wear rate of the laser processed CK45 steel alloy could be reduced a factor of up to two, depending on the surface hardness.

Examination by optical microscope of the worn surfaces of both laser processed and unprocessed samples has shown that the average wear particle size of the laser processed samples is much smaller than that of unprocessed samples, this observations agree with studies by Chen et. al. (1988). This decreasing in wear particle size, resulting

from increased hardness (included localized decomposition of the metastable austenite phase wherever, the

concentration of retained austenite phase after laser processing was 8.35%) and refined microstructure is thought to be the direct cause of improved and enhanced dry sliding wear resistance.

Ck45 steel alloy 0 5 10 15 20 25 0.7 0.99 1.49 Sliding Speed(cm/s) W e a r R a te (g /c m )* 1 0 ^ -5

wear rate after L.processing wear rate before L.processing

CK45 STEEL ALLOY 0 10 20 30 40 50 60 10 20 30

Sliding Time (minute)

A ccu m u lat ive Wear R ate (g /C m )* 10 ^ -5

wear rate after laser wear rate before laser

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4. Conclusions

Laser surface processing of Ck45 steel alloy has been shown to produce a complex microstructure involving 91.65% acicular martensite microstructure and 8.35% retained austenite. Laser processing parameters, such as laser energy, beam size and control of the melting surface produce distinctive type of microstructure. A very fine acicular martensitic matrix microstructure, with hardness up to 850 Hv. While the dendritic retained austenite microstructure, with a hardness 400-600 Hv is produced at high solidification rates.

Dry sliding wear resistance of laser processed Ck45 steel alloy surface has been found to be significantly enhanced by laser refined microstructure and the presence of a mechanically metastable austenite phase which was its concentration in microstructure 8.35%. The retained austenite phase is found to transform martensitically, producing localized hardening in high deformation regions and a transformation induced wear resistant surface.

The wear rates of Ck45 steel alloy in all conditions have the same trend namely, increasing the wear rate with sliding time and decreasing with sliding speed. The accumulative wear rate of the laser processed Ck45 steel alloy reduced a factor of up to two, depending on the surface hardness. The wear particle size of the laser processed Ck45 samples is much smaller than that of unprocessed samples, this decreasing in wear particle size resulting from increased hardness (included localized decomposition of the metastable austenite phase) and refined microstructure is thought to be the direct cause of improved and enhanced dry sliding wear resistance.

Acknowledgements

This work was supported by Production Engineering & Metallurgical Department, University of Technology-Baghdad and Laser Institute for Postgraduate Studies, University of Technology-Baghdad, Iraq.

References

Adel, K. M. and Kheder, A.R.I. 2001. The 4th Jordanian International Mechanical Engineering Conference, Amman- Jordan, pp. 395 - 406.

Chen, C.H, Ju, C.P. and Rigsbee, J.M. 1988. Part-1, Materials Science and Technology, 4, pp. 161 – 166.

Chen, C.H, Ju, C.P. and Rigsbee, J.M. 1988. Part-2, Materials Science and Technology, 4, pp. 167-172.

Danileko, Y.K., Prokhorov, A. M., Pechelintser, A. I. and Sidorin, A. V. 1986. Sov.Journal, Quantum Electron, 16, (12): 105-115. Eckersky, J.S. 1996. Laser application in metal surface hardening, pp. 200 - 210.

Kheder, A.R.I., Al-Arji, N. and Khalaf, A.A. 1993. Journal of Engineering and Technology, 12, (10): 35 -– 41

Kawamoto, M. and Okabayashi, K. 1980. Wear, 58, pp. 59 - 95.

Molian, P. A. and Mather, A. K. 1986. Journal of Engineering Materials and Technology, 5, pp. 108 - 233.

Munir, A. M., Hussain, L.B. and Yaseen, S. K. 2001. The 4th Jordanian International Mechanical Engineering Conference, Amman-Jordan, pp.409.

Molian,P. A. and Rajasekhara, H.S.R. 1986. Journal of Materials Science, 5, pp. 1292 - 1294. Nicolas,G. 1984. Etca, 1, pp. 169 - 83.

Rykalin, N., Uglov, A. and Kokora,A. 1978. Laser machining and welding, Mir. Publisher, Moscow, pp. 500 - 505. Ready, J. F. 1978. Industrial application of lasers, Academic Press, New York, pp. 301 - 305.

Riabkina, M. and Zahavi, F.J. 1985. Journal of Materials Science, 23, pp. 1547 - 1552

Sandren, O. A. 2003. Final Report, The Navel Research laboratory, Washington, Dc 20375 Contract No.0014- 82- C 2373 Sugishita, J. and fujiyoshi, A. 1981. Wear, 68, pp. 7 - 20.

References

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