studies on tribological wear behaviour for optimization of ...€¦ · international journal of...

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com July 2014, Volume 2 Issue 1 ISSN 2349-4476

1 Ramesh R.Burbure1, Dr.V.R.Kabadi2 Dr..Ganechari S.M.3

Keywords: Dual-phase steel, ferrite, martensite, carbon percentage, normal pressure, volumetric

wear rate

1. Introduction

Wear is one of the major phenomena reducing the effectiveness of mechanical components, directly or indirectly impact the nation financially in terms of material loss, associated equipment down time

for repairing and finally replacement of worn and corroded components [1]. The interactions among wear and corrosion could significantly increase total weight losses and reduction of either wear or

corrosion could considerably reduce the total weight loss. In order to decide whether to choose materials according to their mechanical properties or corrosive characteristics, for any particular applications, sufficient information will be necessary.In general, the wear rate ‘Wr’ depends on the

bearing pressure W/A (where W is the load carried by the contact ‘A’, its nominal area), on the sliding velocity ‘S’ and on the material properties and geometry of the surface [2].

Studies on tribological wear behaviour for optimization

of dual-phase steels

Ramesh R.Burbure1, Dr.V.R.Kabadi2 Dr..Ganechari S.M.3

1Department of Mechanical Engineering , K.L.E.Institute of Technology, Hubli-580 030, India.

2Department of Mechanical Engineering, B.E.College, Bagalkot-587 102, India.

3Thakur Polytechnic, Mumbai-400 101, India

Abstract

In order to study the Tribological wear behaviour of dual-phase steels containing different weight percentages of carbon from 0.2 to 0.6, volumetric wear rates have been investigated. The specimens of 0.2 wt% carbon steel were quenched from 723, 781 and 839oC and got about 25, 50 and 75%

martensite respectively. Specimens from 0.4 and 0.6 wt% carbon steels were quenched at 723oC to obtain specimens containing about 50 and 75% martensite respectively. It has been found that the

carbon of the individual phase of dual-phase steel plays a significant role in controlling the properties of each phase. Dry sliding wear tests have been conducted on dual-phase steels using a pin-on-disc wear testing machine under the wear pressures of 0.125, 0.375, 0.625 and 0.874 MPa,

sliding speeds of 1, 3, 5 and 7 m/s at ambient room temperature for a fixed sliding distance of 20,000 meters. Weight loss has been measured at the end of the experiment. Volumetric wear rate

has been estimated on the basis of volume loss after converting weight loss into volume loss by considering the density of the material. The analysis of volumetric wear rate and specific wear rate has been explained with the help of 2 and 3-Dimensional graphs and bar charts. At these

operational conditions, the mechanism of wear is primarily adhesive; two body abrasive, oxidative and delaminative which has been confirmed by SEM micrographs. X-ray diffraction patterns reveal

oxide layers on the wearing surface. Wear properties have been found to improve with the increase in martensite volume fraction in dual-phase steels.




Wr = f (W/A, S, Material properties, surface Geometry)………………(1.1)

The inbuilt material properties are not simply limited to friction and wear. Frict ion and wear are dependent on both the working conditions and the properties of materials. Widely varied wearing conditions cause wear of materials by various mechanisms. There are incredible changes in the wear

of contact surfaces due to small changes of load, speed, frictional temperature, environmental temperature and properties of materials including presence of different phases and microstructures.

Dual-phase steel (DP steel) is one of the family members of high strength low alloy steels which has a very good combination of strength and ductility. DP steels are characterized by the

microstructure consisting of the dispersion of hard martensite particles in a soft α-ferrite matrix. DP steel microstructures are produced by intermediate annealing of steels in the (α + γ) region of the

equilibrium phase diagram [3-4]. This unique microstructure results in characteristic mechanical properties like absence of yield point phenomena, large ratio of tensile strength to yield strength, high rates of work hardening, high total and uniform elongation, excellent forming characteristics

and high fracture toughness [5,6,7] The strength and ductility of DP steels are governed essentially by the two phases, martensite and ferrite respectively. Martensite is the major microstructure

component of DP steels used for structural applications which require ultra-high strength, excellent fatigue resistance and high wear resistance. In view of the potential of DP steel as a wear resistant material, it has already been employed in the field of mineral processing, mining and pipeline

transportation of slurry. These steels are also finding extensive usage in the manufacture of automobile components such as bodies, chassis, bumpers, wheel discs and rims due to their high strength to weight ratio [5-6]. Recent studies have shown that plain carbon dual-phase steels have a

good potential for use as farm implements where strength and wear resistant properties are of great concern.

Most of the studies reported on the Tribology of DP steels have been carried out by developing DP steels with different proportions of martensite and ferrite from one particular plain

carbon steel [8-17].

A thorough review of the published literature on wear characteristics of dual-phase steels based on their percentage carbon content, microstructure combinations, wear pressures and sliding speeds reveal the following:

Majority of the researchers have carried out investigation on one particular percentage of carbon and varying in volume fraction of martensite.

1. By varying the percentage of carbon in dual-phase steel, effect on mechanical properties and in particular wear resistance properties of dual-phase steel has not been investigated.

2. No systematic studies on wear characteristics have been carried out so far, based on different volume fraction combinations of ferrite and martensite for different percentages of carbon content in dual-phase steel.

3. Majority of the researchers have carried out their investigation on mechanical properties and wear resistance properties of dual-phase steels containing very low carbon content, mostly less

than 0.2wt%. 4. The effect of normal pressure, which is a combined measure of the applied load and contact

area, on wear behaviour of dual-phase steels has not yet been studied thoroughly.

5. The effects of frictional temperature changing the mechanical properties of the contact material and hence its wear resistance have not yet been examined thoroughly so far.




6. The martenistic phase of dual-phase steel studied so far for wear behaviour does not contain a fixed percentage of carbon and hence the same will have different hardness and wear resistance

depending upon the carbon content in the dual-phase steel. From the above information, it can be concluded that there is still some potentiality for studying in detail the wear behaviour of dual-phase steels under different operational conditions like normal

pressure, sliding speed in ambient temperature for different combinations of volume percentage of ferrite and martensite and for carbon percentages from 0.2 to 0.6 wt% in dual-phase steel. The results

of the study will lead to optimization of dual-phase steel for best wear resistance properties.

The work reported is part of a study carried out on DP steels containing 0.2, 0.4 and 0.6 wt%

carbon with different volume fractions of martensite and ferrite and examine their effect on wear behaviour under different normal pressures and sliding speeds.

2. Experimental Details

For the present investigation of dual-phase steels, 10 mm diameter plain carbon steel bars containing 0.2, 0.4 and 0.6 wt% carbon were selected and chemical compositions were analyzed by optical spectrometer.

Plain carbon steel pin specimens of 10 mm diameter x 32mm long containing 0.2, 0.4 and 0.6 wt %

carbon were prepared as per G-99 for wear tests and were subjected to controlled heating to reach lower critical temperature of 723oC, isothermalized for 30 minutes and subsequently were water quenched to produce the following specimens 1, 2 and 3 containing different volume fractions of

ferrite and martensite (Fig. 1).

Table 1. Details of Specimen 1, 2 & 3.

Specimen No. % C % Ferrite Vol. % Martensite vol.

1 0.20 75 25

2 0.40 50 50

3 0.60 25 75

Plain carbon steel pin specimens as per G-99 containing 0.2 wt % carbon were subjected to

controlled heating to inter critical temperatures of 781oC and 839oC respectively and isothermalized for 30 minutes and subsequently were water quenched to produce the following specimens 4 and 5

containing different volume fractions of ferrite and martensite (Fig. 1).

Table 2. Details of Specimen 4 & 5

Specimen No. % C % Ferrite Vol. % Martensite Vol.

4 0.20 50 50

5 0.20 25 75




Fig.1. Iron-Carbon diagram of hypo-eutectoid steels.

Wear tests were conducted with a pin-on-disc type wear and friction monitor machine. The experimental set up is shown in Fig. 2. The disc was made up of AISI 316 Austenitic stainless steel

with hardened surface of 65RC.

Fig. 2 Experimental set up of DUCOM Pin-on-Disc wear testing machine.

Dry sliding wear tests were carried out against the counter face of the hardened polished disc. The disc rotates with the help of a D.C. motor coupled; having a speed range 0-2000 rev/min., with disc size of 165 mm diameter x 8mm thick, which could yield sliding speed of 0.05 to 10 m/sec. Pressure

applied on the pin (specimen) was by dead weight provided through pulley string arrangement. The system has a maximum loading capacity of 200 N giving friction forces up to 200N. The machine

can accommodate pins having diameter from 3 to 12 mm and can wear for 0 to 2mm range. The system is capable of performing tests at elevated pin temperatures. A wide range of sliding speeds and normal pressures were considered to identify dominant wear mechanism.

To study the frictional temperature, 1.5 mm hole was drilled to a depth of about 3-4 mm near the edge of the wear specimen. The tip of the Iron-Constantan Fe3K thermocouple (J-type

thermocouple) was inserted into the drilled hole, followed by punching lightly at the periphery of the hole and the gap was filled by silver to fit the thermocouple in the hole. The thermocouple was then silver brazed with the pin. The silver was used as a filler material as it withstands even up to 7000C

temperatures. The procedure adopted for fabrication is shown in Fig 3

Fig.3. Fabrication of wear test pin




Following experimental parameters were selected for the investigation:

i) Sliding speeds of 1, 3, 5 and 7m/sec. ii) Normal loads of 1, 3, 5 and 7 Kgs. iii) Volume fractions of martensite and ferrite.

iv) Carbon wt % in plain carbon steel, i.e., 0.2, 0.4 and 0.6 wt % Variables noted during experiments were frictional force (N), rotational speed (rpm), wearing time

(minutes), surface hardness, surface roughness and frictional temperature. Pin loses its weight during wearing at normal pressure and sliding speed conditions and the loss of weight were measured by an electronic balance having an accuracy of 10-3 gm. Weight losses were

converted into volume losses by considering the density of the pin material. Frictional force generated on the specimen was monitored through the use of sensor attached to the pivoting arm and

the same was measured in Newton (N). The disc was driven with a given constant sliding speed for which the time was set. The disc smoothness was maintained for each set of reading [18].

The frictional force and the frictional temperatures were continuously monitored as wear occurs, and the changes were frequently indicative of a change in wear mechanism, although marked changes

were often seen during the early stages of wear tests as equilibrium conditions become established. The specimen orientation can be important if retained wear debris affects the wear rate.

The wear tests were run under different normal pressures in the range of 0.125 MPa to 0.874 MPa with sliding speeds in the range of 1 to 7 m/sec on a track diameter of 90 mm for a sliding distance of

20,000 meters. The hardness values (vpn) of the worn out surfaces were measured at the end of each run using Vickers micro hardness tester under 1 kg load for a dwelling time of 20 seconds using a diamond point indenter. The entire wear tests were carried out at room temperature. Humidity factor

was not taken into consideration during the tests. The density of the material was taken as 7.85 gm/cm3.

In general, the wear rate ‘Wr’ depends on the bearing pressure W/A (where W is the wear load carried by the pin specimen, A is the nominal contact area), on the sliding speed S and on the material properties and geometry of the surface.

Wr = f (W/A, S, Mat. Properties, Geometry) [19] -----2.1.

Sixteen experiments were conducted on each of the five specimens under the operational conditions of four normal pressures and four sliding speeds. Weight loss method was adopted for the calculation of wear rate.

Table No. 3 Estimation of rpm, time and normal pressures for the experimental sliding speeds and

normal loads. A – Cross section area of the pin - 78.54 mm2




D - The wear track diameter - 90 mm.

Fig.4 Optical microphotograph of Specimen – 1

Fig. 5 SEM micrograph of Specimen – 1 for the sliding speed of 3 m/s and

normal pressure of 0.8743 MPa.

Sl.No

Nor

mal Load

(Kg)

Nor

mal load

(N)

Slidin

g speed

(m/s)

rpm (4)*10

00*60/ (

Tim

e (min

)

Normal

pressure

(MPa) (3)/A

(1)

(2) (3) (4) (5) (6) (7)

1. 1 9.81 1 212.31 333.33

0.1249

2. 3 29.4

3 3 636.94

111.11

0.3747

3. 5 49.0

5 5

1061.5

7

67.6

7 0.6245

4. 7 68.6

7 7

1486.20

47.62

0.8743




3. Results and Discussion

Results of the studies carried out on five different specimens of dual-phase steels containing 0.20, 0.40 and 0.60 weight % carbon and different volumetric percentages of ferrite and martensite have been discussed with reference to the effects of the operational conditions of normal pressure

and sliding speed on the following parameters:

1. Volumetric wear rate and

2. Specific wear rate.

3.1 Volumetric wear rate

Failure impairs the relative movement between solid bodies and inevitably causes severe damage to the contacting surfaces. The consequence of failure is severe wear. Wear in these

circumstances is the result of adhesion between contacting bodies and is termed adhesive wear.

3.1.1 Effect of normal pressure and sliding speed

From the Fig.3.1, it is observed that volumetric wear rate is increased with increase in the normal pressure for the sliding speed of 1 m/s. For the sliding speed of 3 m/s, the volumetric

wear rate is minimum and almost constant with increase in the normal pressure. For the sliding speeds of 5 and 7 m/s, the volumetric wear rate is increased with increase in the normal pressure.

Volumetric wear rate is decreased with increase in the sliding speed for the normal pressure of 0.1249 MPa. For the normal pressures of 0.3747, 0.6245 and 0.8743 MPa, the volumetric wear

rate is decreased with increase in the sliding speed up to 3 m/s, and then increased with further increase in the sliding speed.

From the Figures 3.1 to 3.5, it is observed that before and after the sliding speed of 3 m/s, volumetric wear rate is more. At the sliding speed of 3 m/s, the volumetric wear rate is minimum for all the

normal pressures. By increasing the sliding speed from 1 to 3 m/s, volumetric wear rate starts decreasing and approaches to constant values. On the other hand, wear mechanism changes from severe regime to mild one. At high normal pressures, a hard surface layer is formed, most likely

martensite on surface, because of high flash temperature, followed by rapid quenching as the heat was conducted into the underlying bulk material. The higher flash temperature also caused the local

oxidation rate to increase [20]. On the other hand, increasing the applied normal pressure caused work hardening of subsurface layers and surface oxide layer supported by the hardened sub layers. The higher oxidation rate formed thicker oxide layer on the surface. The formed oxide layer further

prevented direct metallic contact and reduced the volumetric wear rates.

Again from the figures, it is observed that the volumetric wear rate for the sliding speed of 1 m/s at low normal pressure i.e. under the low operational conditions, the corresponding wear mechanisms involved are mostly three body abrasive wear. Microscopic observation also reveals the presence of

the micro grooves on the worn-out surfaces of the specimen. Discontinued parallel grooves are observed on worn-out surface. This means that hard abrasive asperities are generated during wearing

and thus third body formation occurs at the interface. In this case, abrasive asperities would not always be much stronger than the mating surfaces [21]. The degree of adhesion at the contact interface would be closely related to the change of wear modes [22]. Hence, it can be stated that, the

particles should remain un-fractured during wear so that they can support the applied normal




pressure and act as effective abrasive elements. They may produce simple micro-grooves by plastic deformation and/or cutting action without producing any transfer material and the same remain on

the counter face [23]. This observation was made for low normal pressure where the particles could resist the fracture.

Also, it is observed that under high operational conditions of normal pressure and sliding speed, the volumetric wear rate is very high. Adhesive wear is directly proportional to normal load

and sliding distance [24]. When the normal pressure is low during wearing, the corresponding contacts are restricted to the peaks of the asperities only and hence there is lit tle interception against sliding, generating low friction forces and temperature. However, under the high normal pressure and

high temperature, the interception against the sliding direction occurs between the asperities of the two surfaces, due to their increased deformations and hence an increase of the corresponding wear

volume occurs with the result of high volumetric wear rate.

Fig.3.1 Effect of Normal pressure and Sliding speed on

volumetric wear rate for Specimen 1.

Fig.3.2 Effect of Normal pressure and Sliding speed on volumetric

wear rate for Specimen 2.

0.1249

0.3747

0.6245

0.8743

0.000

0.001

0.002

0.003

0.004

0.005

0.006

1

3

5

7

Specimen.1

Vol.W

ea

r ra

te (

mm

3/m

)

Sliding speed (m

/s)

Normal pressure (MPa)

0.1249

0.3747

0.6245

0.8743

0.000

0.001

0.002

0.003

0.004

0.005

0.006

1

3

5

7

Specimen.2

Vo

l.W

ea

r ra

te (

mm

3/m

)

Sliding speed (m

/s)





3.3 Effect of Normal pressure and Sliding speed on volumetric wear rate for Specimen 3.

3.4 Effect of Normal pressure and Sliding speed on volumetric wear rate for Specimen 4.

3.5 Effect of Normal pressure and Sliding speed on volumetric

wear rate for Specimen 5.

3.1.2 Effect of normal pressure

A linearly increasing pattern of wear rate with increasing normal pressure is observed in the present study for all the dual-phase steels. The specimen-2 which contains about 50% martensite, has

0.1249

0.3747

0.6245

0.8743

0.000

0.001

0.002

0.003

0.004

0.005

0.006

1

3

5

7

Specimen.3

Vo

l.W

ea

r ra

te (

mm

3/m

)

Sliding speed (m

/s)


0.1249

0.3747

0.6245

0.8743

0.000

0.001

0.002

0.003

0.004

0.005

0.006

1

3

5

7

Specimen.4

Vo

l.W

ea

r ra

te (

mm

3/m

)

Sliding speed (m

/s)Normal pressure (MPa)

0.1249

0.3747

0.6245

0.8743

0.000

0.001

0.002

0.003

0.004

0.005

0.006

1

3

5

7

Specimen.5

Vo

l.W

ear

rate

(m

m3/m

)

Sliding sp

eed (m

/s)Normal pressure (MPa)




shown least volumetric wear rate compared to that observed in other dual-phase steels at all the normal pressures used in the present study. Specimen- 3 also has almost the same hardness but

volume fraction of martensite is nearing 75%. From the literature survey, it is observed that up to 72% of martensite has better wear resistance properties [13]. In the high volume fraction of the matensite, the impact shock loads during wearing on the martensite phase will not be absorbed by the

soft matrix of ferrite, hence during wearing; martensite will break easily and wear out the particles in the form of debris.

Sp-1, Sp-2 and Sp-3 have almost the same hardness of the martensite, but increase in the volume fraction of the martensite in multiple of about 25%. It is known that as the volume fraction of

the martensite increases, the wear resistance increases. During wearing, initially ferrite phase will wear and permit contact of the martensite phase with the rotating disc. During wearing, the shock

will occur on the martensite phase and these shocks are absorbed by the softer ferrite phase. If the volume fraction of ferrite is low, then these shocks are not absorbed by the ferrite phase and result in more wear rate. Sp-3 and sp-5 have higher volume fraction of martensite .Their volumetric wear rate

is higher than the Sp-2 and Sp-4 respectively.

Fig.3.6 Effect of Normal pressure on volumetric wear rate

for a sliding speed of 1 m/s.

Fig.3.7 Effect of Normal pressure on volumetric wear rate for a sliding speed of 3 m/s.

0.1249 0.3747 0.6245 0.8743

0.000

0.001

0.002

0.003

0.004

0.005

0.006

Sliding speed (1 m/s)

Vol

umet

ric w

ear r

ate

(mm

3 /m)


Specimen - 1

Specimen - 2

Specimen - 3

Specimen - 4

Specimen - 5

0.1249 0.3747 0.6245 0.8743

0.000

0.001

0.002

0.003

0.004

0.005

0.006

Sliding speed 3 m/s

Volu

met

ric w

ear r

ate

(mm

3 /m)


Specimen - 1

Specimen - 2

Specimen - 3

Specimen - 4

Specimen - 5

0.1249 0.3747 0.6245 0.8743

0.000

0.001

0.002

0.003

0.004

0.005

0.006

Sliding speed 5 m/s

Volu

met

ric w

ear r

ate

(mm

3 /m)


Specimen - 1

Specimen - 2

Specimen - 3

Specimen - 4

Specimen - 5






3.1.3 Effect of sliding speed

From the Fig. 3.10, it is observed that the volumetric wear rate for low normal pressure of 0.1249

MPa is decreased with increase in the sliding speed for all the specimens. The general effect of increasing sliding speed under low normal pressure is to cause a reduction in the rate of wear, because during wearing the metal is first transferred to the disc from the wear pin and wear debris is

produced from this deposited layer. The size of the transformed fragment decreases as the speed increases, as sufficient time is not available for the junction growth; this means that the frequenc y of

metal transfer will decrease with the increase of sliding speed resulting in a progressive fall in the rate of wear [24].

Fig.3.10 Effect of Sliding speed on volumetric wear rate for a

Normal pressure of 0.1249 MPa.



0.1249 0.3747 0.6245 0.8743

0.000

0.001

0.002

0.003

0.004

0.005

0.006

Sliding speed - 7 m/s

Vol

umet

ric w

ear r

ate

(mm

3 /m)


Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5

1 3 5 7

0.000

0.001

0.002

0.003

0.004

0.005

0.006

Normal pressure 0.1249 MPa

Volum

etric

wea

r rat

e (m

m3 /m

)

Sliding speed (m/s)

Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5

1 3 5 7

0.000

0.001

0.002

0.003

0.004

0.005

0.006


Volum

etric

wea

r rat

e (m

m3 /m

)

Sliding speed (m/s)

Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5




1 3 5 7

0.000

0.001

0.002

0.003

0.004

0.005

0.006


Volum

etric

wea

r rat

e (m

m3 /m

)

Sliding speed (m/s)

Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5



Fig.3.13 Effect of Sliding speed on volumetric wear rate

for a Normal pressure of 0.8743 MPa.

3.2 Specific wear rate

Specific wear rate is defined as the volumetric wear rate per unit load (m3/Nm). Material with

specific wear rate of 10-14 m3/Nm or higher would be classified as not particularly wear resistant. Materials with good wear resistance would exhibit specific wear rate of about 10-16 m3/Nm or

lower. Materials with specific wear rate as low as 10-17 or 10-18 m3/Nm have also been developed.

3.2.1 Effect of normal pressure and sliding speed

Fig.3.14 Effect of Normal pressure and Sliding speed on Specific wear rate for Specimen 1.

1 3 5 7

0.000

0.001

0.002

0.003

0.004

0.005

0.006


Volu

met

ric w

ear r

ate

(mm

3 /m)

Sliding speed (m/s)

Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5

0.1249

0.3747

0.6245

0.8743

0.00E+000

1.00E-008

2.00E-008

3.00E-008

4.00E-008

5.00E-008

6.00E-008

7.00E-008

8.00E-008

9.00E-008

1

3

5

7

Specific

wear

rate

(m

m3/(

N*m

m)

Sliding sp

eed (m/s)

Normal Pressure (MPa)

Specimen-1





Fig.3.16 Effect of Normal pressure and Sliding speed Specific wear

rate for Specimen 3.


0.1249

0.3747

0.6245

0.8743

0.00E+000

1.00E-008

2.00E-008

3.00E-008

4.00E-008

5.00E-008

6.00E-008

7.00E-008

8.00E-008

9.00E-008

1

3

5

7

Spe

cific

we

ar

rate

(m

m3/(

N*m

m)

Sliding speed (m

/s)Normal Pressure (MPa)

Specimen - 2

0.1249

0.3747

0.6245

0.8743

0.00E+000

1.00E-008

2.00E-008

3.00E-008

4.00E-008

5.00E-008

6.00E-008

7.00E-008

8.00E-008

9.00E-008

1

3

5

7

Sp

ecific

we

ar

rate

(m

m3/(

N*m

m)

Sliding speed (m

/s)Normal Pressure (MPa)

Sspecimen - 3

0.1249

0.3747

0.6245

0.8743

0.00E+000

1.00E-008

2.00E-008

3.00E-008

4.00E-008

5.00E-008

6.00E-008

7.00E-008

8.00E-008

9.00E-008

1

3

5

7

Specimen - 4

Sp

ecific

we

ar

rate

(m

m3/(

N*m

m)

sliding sp

eed (m/s)






3.2.2 Effect of normal pressure

From the figures it is observed that effect of normal pressure on specific wear rate at the sliding

speed of 1 m/s, the variation is more amongst the specimens. The same is minimum and almost constant between the specimens. At the sliding speed of 5 m/s, the values are increased with the normal pressure but variation amongst the specimen is again minimum. At the sliding speed of 7 m/s

the specific wear rate values are increased little more compared with the sliding speed of 5 m/s.

Fig.3.19 Effect of Normal pressure on Specific wear rate for Sliding speed of 1 m/s.

Fig.3.20 Effect of Normal pressure on Specific wear

rate for Sliding speed of 3 m/s.

0.1249

0.3747

0.6245

0.8743

0.00E+000

1.00E-008

2.00E-008

3.00E-008

4.00E-008

5.00E-008

6.00E-008

7.00E-008

8.00E-008

9.00E-008

1

3

5

7Spe

cific

We

ar

rate

(m

m3/(

mm

*N)

Sliding sp

eed (m/s)


Specimen - 5

0.1249 0.3747 0.6245 0.8743

0.0000000

0.0000001

0.0000002

Sliding speed 1m/s

Spec

ific

wea

r rat

e (m

m3 /(m

m*N

))


Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5

0.1249 0.3747 0.6245 0.8743

0.0000000

0.0000001

0.0000002Sliding speed 3 m/s

Spec

ific

wea

r rat

e (m

m3 /(m

m*N

)


Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5




1 3 5 7

0.0000000

0.0000001

0.0000002Normal pressure 0.1249 MPa

Spec

ific

wea

r rat

e (m

m3 /(m

m*N

)

Sliding speed (m/s)

Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5



3.2.3 Effect of sliding speed

From the figures it is observed that for all the normal pressures at the sliding speed of 1 m/s

the values of specific wear rate is more and minimum at the sliding speed of 3 m/s. but at the high normal pressures and at high sliding speeds the values of specific wear rate is also more.

Specific wear rate is volumetric wear rate per unit load. Volumetric wear rate is volume loss per unit sliding distance. At the low sliding speed of 1 m/s, the specific wear rate is high for all the normal

pressures and for all the specimens irrespective of the combinations of the phases. Under low sliding speeds, the frictional temperature is low and this frictional temperature is not sufficient to soften the asperities. So during the wear the asperities will break and roll between the wearing surfaces, and

result in three body abrasive wear, therefore volumetric wear rate per unit load is high. Under moderate operational conditions the values are minimum and almost the same amongst the

specimens. During wearing with increase in the operational conditions it is learnt that initially three bodies abrasive wear mechanism takes place, later with increase in the operational conditions, oxidative, laminative, delaminative and two bodies abrasive wear mechanism takes place. Two body

abrasive wear mechanism is that during wear under high operational conditions, the asperities adhere with the rotating disc and abrade the specimen surface.

0.1249 0.3747 0.6245 0.8743

0.0000000

0.0000001

0.0000002

Sliding speed 5 m/s

Spe

cific

wea

r ra

te (

mm

3 /(m

m*N

)


Specimen 1

Specimen 2

Specimen 3

Specimen 4

Specimen 5

0.1249 0.3747 0.6245 0.8743

0.0000000

0.0000001

0.0000002

Sliding speed 7 m/s

Spec

ific

wea

r rat

e (m

m3 /(m

m*N

)


Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5

1 3 5 7

0.0000000

0.0000001


Spec

ific

wea

r rat

e (m

m3 /(m

m*N

)

Sliding speed (m/s)

Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5




Fig.3.23 Effect of Sliding speed on Specific wear rate for a

Normal pressure of 0.1249 MPa

Fig.3.24 Effect of Sliding speed on Specific wear


Fig.3.25 Effect of Sliding speed on Specific wear rate for a Normal pressure of 0.6245 MPa

Fig.3.26 Effect of Sliding speed on Specific wear rate for a


Discussions

From the results, it is observed that specimen-2 containing about 50% martensite and 50% ferrite has shown minimum volumetric wear rate compared with other dual-phase steels. Specimen-

1, Specimen-2 and specimen-3 are developed from 0.2, 0.4 and 0.6 carbon percentage steels. Hardness of the martensite in all the specimens is almost equal. Sp-1 has 25% martensite embedded

1 3 5 7

0.0000000

0.0000001

0.0000002


Spec

ific w

ear r

ate

(mm

3 /(mm

*N)

Sliding speed (m/s)

Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5

1 3 5 7

0.0000000

0.0000001

0.0000002


Spec

ific

wea

r rat

e (m

m3 /(m

m*N

)

Sliding speed (m/s)

Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5

1 3 5 7

0.0000000

0.0000001


Spe

cific

wea

r rat

e (m

m3 /(m

m*N

)

Sliding speed (m/s)

Specimen-1

Specimen-2

Specimen-3

Specimen-4

Specimen-5




in ferritic matrix. During wearing, the impact shocks will be affecting the complete matrix. The ferrite phase wears first due to its softness. Later the shocks will act on martensitic phase. Martensite

is hard phase and it will not wear so easily. Also the wearing shocks are transferred to the softer matrix through martensitic phase. Hence the effective load on the martesitic phase is less. Also the same logic will be applicable to the specimen-2 and specimen-3. In the specimen-2 the contact area

of the martensite with the rotating disc is more but shock absorption by the ferrite phase is low, even though most shocks are absorbed by the ferritic phases and due to more contact area of the

martesntie, the effective load on the martesnte is low, hence the wear loss is low. Whereas for the specimen-3, the contact area of the martesnite is quite high with the rotating disc. But the shock absorption ferrite phase contact area is low. The impact load during wearing is transferred to the

ferrite phase through the martesnitic phase but the volume fraction of the ferrite is so low that the complete shocks are not absorbed by the ferrite phase. Hence, some impact load will act on the

martensite only and the martensite will break easily and results in more wear. Hence, dual-phase steel containing about 50% martensite and 50% ferrite phases has shown low wear rate.

Specimen-4, also has near about 50% martensite and 50% ferrite. Even then the wear rate is more than the specimen-2, because the hardness of the martesntie of the specimen-4, is less than the

hardness of the martensite for the specimen-2, in view of the low carbon content.

Volumetric wear rate is volume loss per unit sliding distance and specific wear rate is volumetric

wear rate per unit load. From the graphs of specific wear rates it is observed from all the graphs that the specific wear rate is decreased with the increase in the operational conditions and thereafter increased with further increase in the operational conditions.

During wearing initially three body wear mechanism takes place. Thereafter oxidative wear,

laminative wear, delaminative wear, fatigue wear, pitting wear and at the end two body abrasive wear takes place. Among the wear mechanisms, abrasive wear is severe wear and adhesive wear is medium wear and oxidative wear is mild wear. So from the specific wear rate graphs it is observed

that initially severe wear takes place; afterwards with increase in the operational conditions the wear mechanism changes to mild wear, later again severe wear takes place at the higher operational

conditions.

During initial sliding wear was severe, causing the adhesive transfer of thin layers of metal

from one surface to the other. The transferred fragments build up with further sliding, losing their individual identities by agglomeration and plastic shearing until they eventually became detached as

wear particles [25]

4. Conclusions

Dual-phase steels containing different proportions of martensite and ferrite as well as containing different percentages of carbon have been subjected to wear tests on pin-on-disc wear

testing machine under different normal pressures and sliding speeds. This is to understand the effect of carbon content in the martensite which intern affects the hardness and wear resistance properties

of the martensite phase. This intern affects the overall wear resistance property of the dual-phase steel.

Following are the findings:

1. With increase in the normal pressure, the volumetric wear rate is increased.




2. With increase in the sliding speed, the volumetric wear rate is decreased. 3. Mild wear is observed at the sliding speed of 3 m/s for all the DP steels.

4. Oxidative wear mechanism is observed at 3 m/s for all the DP steels. 5. With increase in the volume fraction of martensite up to 50% for 0.4% carbon DP steel,

volumetric wear rate is decreased and with further increase in the volume fraction of

martensite, volumetric wear rate is increased. 6. It is observed for all the specimens that specific wear rate is high at low operating conditions

of normal pressure and sliding speed 7. It is observed for all the specimens that specific wear rate is decreased with increase in the

operating conditions up to medium level and thereafter increased with further increase in the

operating conditions 8. Specimen-2 which is developed form 0.4% carbon steel has shown low volumetric wear rate

amongst the remaining DP steel specimens.

References

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Mater. Perform. 23(7), (1993), pp. 50. [2] M.F. Ashby & S.C. Lim, Wear-Mechanism Maps, Script Metallurgica et Materialia,

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abrasive wear behaviour of plain carbon dual- phase steel, Microstructure and Texture in

steels (Book), Springer, London, pp. 483-488. [16] IA EI-Sesy, Z.M. EI-Baradie, Influence of carbon and /or iron carbide on the structure and

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[17] O.P.Modi, B.K. Prasad , Rupa Dasgupta and A.H. Yegneswaran, Low stress abrasive behaviour of 0.2%C steel : Influence of microstructure and test parameters , Tribology

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August (1999), pp. 2019-2026. [19] M. F. Shbey and S. C. Lim, Wear-Mechanism maps, Scripta Metallurgical Material, Vol. 24,

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