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Fretting Wear Behavior of a Low Alloy Steel (42CrMo4) after Quenching and Tempering

Sebhi Amar1, Douib Nadirl2, Osmani. Hocine3

1,2Dpartment Mechanical Engenering, Faculty of Technology, University Med Boudiaf Msila 3Optics and Precision Mechanics Institute, University of Ferhat Abbes , Setif, Algeria

International Journal of Research in Mechanical Engineering

Volume 3, Issue 1, January-February, 2015, pp. 24-30 ISSN Online: 2347-5188 Print: 2347-8772, DOA : 24012015

IASTER 2014, www.iaster.com ABSTRACT

The major concern of researchers is to improve the tribological performance of the products with the aim to gain security, energy efficiency and lifetime. The behavior of 42CrMo4 (EU standard) steel to the various influent parameters such as load, stress, and exposure time has been studied. The study of such parameters has been done after different heat treatments. The weight loss as a function of applied load and the exposure time was determined at a constant frequency. In order to evaluate wear or materials degradation such as the formation of debris, initiation and crack propagation, it is important to evaluate what types and magnitude of imposed mechanical stresses. Contact mechanics is the first serious attempt to converge the formalism of friction and wear. The friction contact surfaces undergo damage which can be defined as a change in the topography of ithe microstructure or surface layers.

This results generally, in the superimposing in many processes and effects. The analysis and identification of surface degradation is complex. One must consider the changes in the microstructure, such as phase changes, precipitation, aging etc. The weight loss as a function of time at different loads was studied in order to draw conclusions and identify the likely causes of the phenomena causing fretting wear. Keywords: Friction, Exposure Time, Tribology, Weight Loss, Wear.

1.0 INTRODUCTION Whenever two mechanical components are in contact, important solicitations are created to massifs and can give rise to damages. The finding of damage is not easy and may cause the malfunction of the mechanism, if the foresight is not made in advance, [1]. The tribological study of phenomena engendering the contact interface allows one to avoid disasters and possible incidents, [2].

The selection of materials for defined solicitations is generally very difficult due to the complexity of the generated phenomena. The types of wear are known and classified: adhesive, abrasive, corrosive and fatigue wear; yet to attribute each wear shape to the place where it is created and link these provocative parameters together with the aim to predict solutions to the problem on time, [3].

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The Fretting wear refers to the surface degradation process that appears between two surfaces in contact with a vibrant oscillatory motion of small amplitudes. This may result in malfunctioning of the mechanism, gap appearance between the parts and even failure functionality more or less dangerous depending on the type of wear, [4]. Expressed in many cases by crack initiation, which, not controlled, may induce a brutal and catastrophic components failure, [5, 6, and 7]. The recent researches suggest the hardening by heat treatment of contact surfaces [8]. 2.0 EXPERIMENTAL PROCEDURE The experimental device for fretting wear, allows performing linear track bearing steel and sample forms pin configuration (Figure 1). This radial type device consists of a lead screw, a spring rappel, a stop, a variable mass, a swing of the specimen, a base, a locking pin of the connecting rod (machining center 5axe). The experimental fretting wear, allows configuration steel track testing - sample; of which the rotational speed (tribological parameter) is 3000 r / min. The sample is attached to a small cutter holder which rotates and moves along the bearing steel track Z200 C13 with 2% C and 13% Cr (new X200Cr13 Standard); whose shape is semi-cylindrical. The sample is of complementary shape (semi-spherical) of 5mm diameter, is made a stroke of 60 mm with a speed of 2 m / min on the 4mm radius of track (Figure 1). The material to be studied is a low alloy steel type 42CrMo4 (42CD4, EU standards) whose chemical composition is given in the table below.

Table- 1 Chemical Composition of 42crmo4 Steel in Weight Percent C Si MO P Co Ni P

0.42 0.2 0.77 0.16 1.08 0.16 0.07 The heat treatment furnace is a natural gas furnace. It can reach up to 1800 C. It is equipped with a digital display to fix the desired temperature. Three types of treatment have been carried out:

1. A quenching carried out at 850 C for 30 minutes. 2. A tempering carried out at 400C for 30 minutes 3 A tempering carried out at 200C for 30 minutes

The specimens to be treated have been cut in 2cm diameter by 1cm in height. After heat treatments the specimens have to be polished in order to remove any kind of metal fragments which can be possibly suspended. In the following step the specimens will be subjected to fretting tests. The applied loads are as follows: 500g (5N); 1000g (10N); 1500g (15N). Firstly, the load is fixed while the time varied. The specimens are weighed before and after each test. In order to explore the contact surfaces; an optical microscope is used, with the objective 100/0.25 to determine the types of wear and the cumulative debris on the contact surface.

Fig-1 Fretting Wear Tribometer

The electrical balance with a digital display 1/10000 precision is used to determine the weight of each specimen before and after each fretting test.

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Fig. Balance

After cutting, the specimens are processed in the oven and then pass the grinder for grinder for grinding by various sandpaper. After rinsing with a liquid detergent, acetone is cleaned to remove metal fragments which can be optionally suspended. The loads applied are progressive 500 G (5N); 1000g (10N); 1500g (15N). For each specimen, the load and varying the testing time is fixed; then we go to the weighed. For exploration of the contact surfaces; manification microscope 100 / 0.25; determines some forms of wear and debris accumulated on the contact surface. 3.0 RESULTS AND DISCUSSION Figure 3 shows the weight loss of the smple as a function of time with an applied load of 5, 10, 15 Newton. This test is carried out before heat treatment (as received). It is noticed from the curve that the wear rate increases as a function of time. The form of the curve is nearly linear. The values are very low (60 min 61*10-4 gr = 6.1 mgr under an applied 5N; 6.5 mgr under 10 N; 7 mgr under F=15N).

0

20

40

60

80

15 30 45 60

5N

10N

15N

Fig-3 Weight Loss as Function of Time before Heat Treatment

Figure 4 shows the weight loss of the specimen as function of time under the different loads. In this case the specimen has undergone a quenching treatment. It has been heated at a temperature of 850C for 30 min; the specimen was quenched in water. One can notice from the curve that the wear rate is not significant between 15 and 45 minutes, but more than value it increases sensitivity as function of time. The form of the curve is nearly linear. The values are almost negligible (60min1.5 mgr under load 5N; 3.8 mgr under 10N; 4.1 mgr under 15N).

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0

10

20

30

40

50

15 30 45 60

5N

10N

15N

Fig-4 Weight Loss as Function of Time Under after Quenching 850C

Figure 5 shows the weight loss as function of time under the under various loads, after quenching from 850C followed by a tempering at 200C. It can be seen that between 15 and 30 minutes there no significant weight loss (4 mgr under 5N; 5 mgr under 10N and 15N), but beyond this the wear rate increases linearly. Income had its effect on wear and more resistant.

0

10

20

30

40

50

15 30 45 60

5N

10N

15N

Fig-5 Weight Loss as Function of Time (Quenched From 850Cand Tempered at 200C)

Figure 6 shows the weight loss of the sample as a function of time with a load of 5 and 10 Newton with a quenching of 850 C and returned to 400 C. From the curve, the wear rate increases with time and the pace is almost linear. Probably due to the low wear income 400 C, which balances the metallographic microstructure.

0

10

20

30

40

15 30 45 60

Colonne1

Colonne2

Fig-6 Weight Loss as Function of Time (Quenched from 850C and Tempered at 400C)

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010203040506070

15 30 45 60

Wei

ght l

oss

*10-

4[gr

]Temps [min]

S.T

850C850R200850R400

Fig-7 Weight Loss as Function of Time Under 5N at Different Treatment

Figure 7 shows the weight loss as function of time under a load of 5 Newton at different heat treatments. As can be noticed from this figure, the weight loss is not significant after the quenching at a temperature of 850C. After quenching from 850C and tempering at 200C, compared to the as received specimen or which has been quenched and tempered at 400C, there is no substantial difference. This can be explained by the fact that after quenching and tempering at very low temperatures, the obtained phases and microstructures are specially made of martensite which very hard. Consequently, the wear will be very small and not significant.

01020304050607080

15 30 45 60

Wei

ght l

oss

*10-

4[gr

]

temps [min]

S.T850C850R200850R400

Fig-8 Weight Loss as Function of Time Under 15N at Different Heat Treatments

In figure 8 and 9 we can give the same conclusion as in figure 7 except that the weight loss is more significant for the sample before quenching. After quenching and tempering, the different curve overlaps. The wear is very low (15min 0.7 mgr; 60min 4 mgr, figure 8); and (15min0.6mgr; 60min5mgr figure 9).

010203040506070

15 30 45 60

Wei

ght l

oss

*10-

4 [g

r]

Temps [min]

S.T

850

850R200

850R400

Fig-9 Weight Loss as Function of Time Under 10N at Different Heat Treatments

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a) b)

Fig-10 Microstructures of the Worn Surfaces Under 15N Quenched at 850C A) Load=5N; B) Load=10N

A) B)

Fig-11 Microstructures after Fretting of the Specimens Quenched at 850C A) Load=5n; B) Load=10n

Figures 10 and 11 show some microstructures of the worn surfaces of the ball and the specimens. It of importance to say that after fretting wear procedure the appearance of the surface may give some clarifications on the surface state. On figures 18 and 19 it is clear that imprints left after fretting on the ball and on the steel specimens are of debris shucked on the ball, and fractured imprints on the specimens. 4.0 CONCLUSION Through this study it can be concluded that: The weight loss as function of time for different applied loads increases almost linearly; The influence of quenching and tempering shows a linear and slow growth of the wear rates according to the studied parameters.

One can also notice that the weight loss after quenching shows a small increase compared to tests on untreated samples, this may be due to the sticking debris of the ball on the samples hardened by quenching. This can be shown by the microstructures in figures 17 and 18. It is important to note that after quenching, the most notable structure is the martensite which is characterized by its high hardness. After tempering at low temperatures (here 200C), the residual stresses will be reduced but the martensitic structure does not change and keeps its high hardness. This can be explained by the fact that we do not notice a great difference in weight loss in the case of quenched samples and samples quenched and tempered at 200 C. On the other hand, the weight loss of the samples quenched and tempered at 400 C is almost the same as in the case of the untreated samples. This can be explained by the fact that after tempering at 400 C, there is a return to the phase equilibrium state. Finally, this work will be completed in the future by studying the evolution of the imprint in terms of other influential parameters.

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5.0 ACKNOWLEDGMENTS Was this modest work started at the Laboratory of Mechanics and Engineering, Mechanical and Engineering Department Then completed in Unit Industrial Equipment Maintenance (IEM) Algeria Sonelgaz Group. The authors express gratitude to the Ministry Their of Higher Education and all the people who have collaborate closely or by far in this work. REFERENCES

[1] M .Kalin, Fretting wear mckanism in contact of steel and silicone nitrade ceramics; P.H.D University of Lijubana Slovenie 1999.

[2] Jasppers and al., (2002), Material Behaviour in Conditions Similar to Metal Cutting: Flowstress in the Primary Shear, Science and Engineering. A383. pp. 201-212.

[3] Grzesik, W., and Nieslony, P. (2004), Prediction of Friction and Heat Flow in Machining Incorporating Thermophysical Properties of the Coating-Chip Interface, Journal of Wear, 256: pp. 108-117.

[4] Satish Achanta, Dirk Drees, Jean-Pierre Celis ; Friction and Nanowear of Hard Coatings in Reciprocating Sliding at milli-Newton loads, Tribology Iternational,Volume 259, (1-6),

July-August 2005, Pages 719-729.

[5] S. Fouvry, V. Fridrici, C. Langlade, Ph. Kapsa, L. Vincent ; Palliatives in fretting: A Dynamical Approach ; Article Tribology International, Volume 39, (10), October 2006, Pages 1005-1015.

[6] C. Petiot, L. Vincent, K. Dang Van, N. Maouche, J. Foulquier, B. Journet ; An Analysis of Fretting-Fatigue Failure Combined with Numerical Calculations to Predict Crack Nucleation, Article Tribology International, Volumes 181-183, (Part 1), February 1995, Pages 101-111.

[7] A. Neyman, O. Olszewski, "Research on Fretting Wear Dependence of Hardness Ratio and Friction Coefficient of Fretted Couple", Wear of Materials, International Conference No. 9, San Francisco CA, USA (13/04/1993). Wear, vol. 162-64, (Part B), pp. 939-943, 1993.

[8] Stachowiak G.W. and Batchelor A.W, Engineering Tribology, (2005), 3rd ed., Elsevier, Oxford, UK.