An investigation of the abrasive wear behavior of ductile cast iron

An investigation of the abrasive wear behavior of ductile cast iron
An investigation of the abrasive wear behavior of ductile cast iron

An investigation of the abrasive wear behavior of ductile cast iron

Zhen-Lin Lu a,*,Yong-Xin Zhou a ,Qi-Chang Rao b ,Zhi-Hao Jin b

a

School of Material Science and Engineering,Xi'an University of Technology,Xi'an 710048,PR China b

School of Material Science and Engineering,Xi'an Jiaotong University,Xi'an 710049,PR China

Received 2J anuary 2000

Abstract

The abrasive wear behavior of ductile cast iron with four different matrix microstructures was determined by the pin-on-disc abrasion

test,the three-body abrasion test and the impact three-body abrasion test.The results indicate that the abrasive wear resistance of ductile cast iron tested in pin-on-disc abrasion and three-body abrasion is approximately linearly proportional to its hardness,so that the abrasive wear resistance of martensitic matrix ductile cast iron and martensitic matrix with dispersed eutectic carbide ductile cast iron is the best,followed by the bainitic matrix,with the pearlitic matrix being the worst.However,under the conditions of the impact three-body abrasion test,the abrasive wear resistance of ductile cast iron has a relationship to its hardness and toughness,i.e.it requires the appropriate combination of its hardness and toughness.Therefore,the abrasive wear resistance of martensitic matrix ductile cast iron is the best,the pearlitic and the bainitic matrix being the next best,with the martensitic matrix with eutectic carbides being the worst.#2001Elsevier Science B.V .All rights reserved.

Keywords:Abrasive wear behavior;Ductile cast iron;Martensitic matrix

1.Introduction

Ductile cast iron,which has excellent mechanical proper-ties,has been used widely in the machine industry,the automobile industry,the mining industry,and so on as a structural material [1±5].However,as a wear resistant material,its application is still limited.In the 1960s,grind-ing balls made of ductile cast iron with medium manganese (5±6%Mn)were developed and applied in the mining industry [6,7],but this material has become gradually obso-lete because of its serious fatigue spalling and breakage in service caused by a great deal of retained austenite and eutectic carbides in its matrix.In recent years,the use of ductile cast irons to make grinding balls has been investi-gated,such as martensitic ductile cast iron [7±10],bainitic ductile cast iron [11],austempered ductile cast iron [12],and as-cast pearlitic ductile cast iron [13].Because ductile cast iron has an appropriate cooperation of impact fatigue resis-tance and abrasive wear resistance,as well as having lower breakage,lower fatigue spalling and lower production cost,it is used to make grinding balls that are used in the cement,mining and power industries,and a better utilization effect

has been obtained [14].In this paper,the abrasive wear behavior of ductile cast iron is studied in order to provide the proper matrix structures for wear resistant parts of ductile cast iron required to be employed under different conditions.2.Experiment procedure 2.1.Material preparation

Ductile cast iron for testing was melted in a 60kg induction-melting furnace.The melts were poured at a temperature of 13508C into 50mm thick Y-block dry sand molds,and the castings were allowed to cool to room temperature in the molds.Subsequently,the castings were machined into different size samples for testing.The che-mical compositions,heat treatments and mechanical proper-ties of the samples are presented in Tables 1and 2.Eutectic carbide appears in the microstructure of ductile cast iron with the addition of chromium,and its amount would increase with increasing chromium.2.2.Abrasion test

The pin-on-disc abrasion test [15]using Al 2O 3abrasive paper which size corresponded to 120grit was carried out.The wear pin specimen for the pin-on-disc tests was

a

Journal of Materials Processing Technology 116(2001)176±181

*

Corresponding author.Present address:School of Material Science and Engineering,Xi'an Jiaotong University,Xi'an 710049,PR China.Fax: 86-29-3237910.

E-mail address :luzl@https://www.360docs.net/doc/969363792.html, (Z.-L.Lu).

0924-0136/01/$±see front matter #2001Elsevier Science B.V .All rights reserved.PII:S 0924-0136(01)01013-5

cylinder,with one end in contact with the abrasive paper on the disc.Its size was 4mm diameter and 30mm length.Following a ``run-in''period,tests were conducted at 2.5kg load over a wear path of about 11.22m on a fresh sheet of abrasive paper.After one running-in test,three tests were performed on each specimen.Three-body abrasion test was also carried out by the method described by Boyes [16].The linear velocity of specimens was about 0.55m/s.A vertical load of 4.83N/cm 2was applied on the specimen.The abrasive particles were 40±70mesh silica sand of angular shape.After 30min for the running-in test,three tests were performed on each specimen,each test running for 30min.The wear resistance tested in pin-on-disc and three-body abrasive wear is given in terms of the weight loss of the test materials related to the weight loss of a standard specimen of normalized steel,of which the composition was 0.45%C,0.23%Si,0.46%Mn,0.016%S,0.020%P and the hardness was HB210,as b

weight loss of the standard specimen g weight loss of the test specimen g

(1)

To use a standard sample simply gives a reference point and allows the reporting of data in terms of dimensionless numbers.

The impact three-body abrasion test was conducted in the abrasion test apparatus,a schematic diagram of which is shown in Fig.1.An upper specimen 10mm ?10mm ?30mm made of the test material was freely and repeatedly dropped on to a lower specimen which was made of normal-ized steel of 0.45%C and was rotating at a speed of 200rpm.The lower specimen was a ring of outside diameter 50mm.The upper specimen holder provided an impact energy of 3.0J to the test interface.The impact frequency was

200min à1.The abrasive particles ˉowing through the inter-face were 40±70mesh silica sand.After 30min running-in test,three tests were performed on each specimen,and each test running for 30min.The wear resistance was taken as the reciprocal of the weight loss,i.e.e

1

weight loss g

(2)

A balance with a sensitivity of 0.0001g was used to deter-mine all of the weight losses in the tests.

Table 1

Compositions of ductile cast irons for testing No.

Chemical composition (wt.%)C

Si Mn

P

S Cr

Mo

Cu

RE A-1 3.08 2.65 1.040.0630.0250.053A-2 3.08 2.65 1.040.0630.0250.053B 3.32 2.520.380.0600.020

0.290.350.43

0.067C 3.60 1.750.94

0.500.045D

3.66

1.88

1.020.061

0.61

0.049

Table 2

Heat treatments,microstructures and mechanical properties of ductile cast irons for testing a No.

Heat treatment

Microstructure Hardness (HRC)Impact toughness,a k (J/cm 2)A-18808C (1h)quenching in solution 200 C tempering (2h)M Ar G ;Ar <5%49.08.4A-28808C (1h)quenching in air 200 C tempering (2h)

P G ;F <5%

32.819.4B 8808C (1h)quenching in salt bath 200 C tempering (2h)B G Ar ;Ar $13%36.535.8C 8808C (1h)quenching in solution 200 C tempering (2h)M G 10à15%K 52.29.2D 8808C

(1h)

quenching

in

solution 200 C tempering (2h)

M G 15à20%K

51.0

11.9

a

P:pearlite,M:martensite,B:bainite,Ar:retained austenite,G:spheroidal graphite,F:ferrite,K:eutectic

carbides.

Fig.1.Schematic diagram of the impact abrasion tester:(1)hammer;(2)specimen holder;(3)upper specimen;(4)lower specimen;(5)abrasive particles.

Z.-L.Lu et al./Journal of Materials Processing Technology 116(2001)176±181

177

3.Results and discussions

The abrasion test results of different matrix structure ductile cast iron are shown in Table 3.It is known that the abrasive wear resistance,which differs from the strength limit and the hardness of materials,is the synthetic expres-sion of the physical and chemical characteristics of materials under de?nite ?eld conditions as systematic properties,but is not an inherent characteristic of materials.In other words,wear is determined by the summing up of all the processing appearing in usage,and its occurrence and development depends upon both the properties of the materials and the external ?eld conditions.

The laboratory abrasion test is to study mainly the rule of wearing phenomena under the laboratory test conditions,namely the wear process and the wear mechanism.There-fore,the analysis and discussions of the test results must be associated with the wear mechanism.3.1.Pin-on-disc test

The abrasive wear resistance of ductile cast iron with different matrix structures increased with increase in its hardness under the pin-on-disc abrasion test conditions,as shown in Fig.2.

It can be seen that there are a lot of grooves in Fig.3,and it can be seen also that deformation had taken place at both the edges of grooves.This is because pin-on-disc wear belongs

to stationary abrasive wear:the micro-cutting model is the predominant wearing mechanism.The wear resistance of ductile cast iron is determined by its hardness.

Khruschov [17]indicated in his early studies that the wear resistance of simple metal increased linearly with increase in its hardness when the hardness of the abrasive was higher than that of simple metal tested in the pin-on-disc test.An approximately linear relationship of the abrasion wear resistance of ductile cast iron and its hardness in the pin-on-disc test can be observed in Fig.2.This result shows that martensitic matrix ductile cast iron and martensitic matrix with dispersed 10±20%eutectic carbide ductile cast iron has the best abrasion wear resistance,followed by the bainitic matrix,with the pearlitic matrix being the worse.3.2.Three-body abrasion test

The wear resistance of ductile cast iron with different matrices also increased with increase in their hardnesses in the three-body abrasion test,as shown in Fig.4.

Because three-body abrasion test belongs to bulk abrasive wear,abrasive sliding and rolling existed at the surface of sample when tested.The abrasive sliding creates cutting wear;however,whether the cutting wear takes place or not is determined by the relative hardness between the abrasive and the tested material.Under the present test conditions,because the hardness of silica sand is higher than that of the material tested,numerous grooves can be observed in Fig.5.

Table 3

Abrasive wear resistances of different matrix ductile cast irons No.

Microstructure

Abrasive wear resistance Pin-disc,b

Three-body,b Impact three-body,e A-1M Ar G 74.7

1.31121.10A-2P G 23.8 1.17817.16B B G Ar 53.8 1.31416.12C M G 10à15%K 84.1 1.39714.87D M G 15à20%K

79.1

1.313

16.23

Fig.2.Relation between the wear resistance and the hardness of different matrix ductile cast irons in the pin-on-disc

test.Fig.3.SEM microphotograph showing the morphology of the worn surface of specimen A-1in the pin-on-disc test (?100).

178Z.-L.Lu et al./Journal of Materials Processing Technology 116(2001)176±181

Abrasive rolling would create trundle pits at the surface of the specimens and lead to repeat plastic deformation of the material.The fatigue crack initiation and propagation caused by the repeated plastic deformation would lead to fatigue spalling.Numerous rolling±pressing pits can be seen in Fig.5.Therefore,three-body abrasion is the combination of the micro-cutting wear mechanism and the plastic defor-mation wear mechanism.It is required to point out that fatigue spalling caused by repeated plastic deformation is a slow process of crack initiation and propagation.Because of the existence of numerous abrasive cuttings,the surface of the sample would be cut off by abrasive before fatigue spalling caused by repeated plastic deformation could take place.Micro-cutting,hence,is predominant under the con-ditions of the three-body hard abrasive wear test.The hard-ness of ductile cast iron is still the main factor that affects the three-body abrasion wear resistance.Therefore,the results show that under the conditions of the three-body hard abrasive test,the martensitic matrix ductile cast iron and martensitic matrix with dispersed 10±20%eutectic carbide ductile cast iron has the best abrasion wear resistance,followed by the bainitic,with the pearlitic being the worst.

It needs to be pointed out that bainitic ductile cast iron has the appropriate combination of hardness and toughness because of the existence of ?ner lower-bainite and an appropriate amount of retained austenite formed at lower isothermal temperature in its matrix microstructures.Although its hardness is lower and its cutting wear resistance is less,it could resist the plastic deformation wear caused by abrasive repeated rolling because of its better toughness.Therefore,bainitic ductile cast iron could display better wear resistance under the conditions of the three-body abrasion test.It could not be deduced whether austenitic transformation took place during the test as the amount of retained austenite in the bainitic matrix specimen was not measured after the test.

3.3.Impact three-body abrasion test

The impact abrasion test with repeated impact load also belongs to bulk abrasive wear just as for three-body abra-sion,therefore,both cutting wear and plastic deformation fatigue wear existed simultaneously when testing,and the wear model would be affected by the value of existing impact work.With increase in the value of impact work,the portion of cutting wear would decrease and that of plastic deformation wear would increase.Thus,the weight loss of specimens under the conditions of different values of impact energy would be composed of a quantity of cutting wear and that of fatigue spalling caused by the repeated impact [18].The portion of weight loss caused by both of these two wear mechanisms was related to the mechanical properties of the material and the value of impact energy.Thus,it can be seen that the two main wear models,namely cutting wear and plastic deformation wear,must be viewed in association with the hardness and toughness of the material [18].

The results of the abrasion wear resistance of different matrix ductile cast irons under the condition of 3.0J impact energy tests are shown in Fig.6.It can be seen that the martensitic ductile cast iron has the best impact

abrasion

Fig.4.Relation between the wear resistance and the hardness of different matrix ductile irons in the three-body abrasion

test.

Fig.5.SEM microphotograph showing the morphology of specimen A-1in the three-body abrasion test (?

1000).Fig.6.Relation between the wear resistance and the hardness of different matrix ductile cast irons in the impact three-body abrasion test.

Z.-L.Lu et al./Journal of Materials Processing Technology 116(2001)176±181179

wear resistance,followed by the bainitic and the pearlitic,with the martensitic dispersed with some eutectic carbides being the worst.Clearly,the impact wear resistance of ductile cast iron has a relationship neither solely with the hardness of materials unlike the pin-on-disc and three-body abrasion tests,nor solely with the impact toughness of materials,but requires the appropriate combination of the hardness and toughness of the ductile cast iron.

Although bainitic ductile cast iron has the best impact toughness,its hardness is lower,so the morphology of long distance micro-cutting and of abrasives embedded in the matrix on the abraded surface can be seen in Fig.7.However,in spite of the greater hardness of ductile cast iron with martensitic matrix dispersed 10±20%eutectic carbides,its toughness is lower,thus numerous deep spalling pits can be seen in Fig.8because of its serious fatigue spalling under the conditions of the impact abrasion test.Short distant micro-cutting and shallow spalling pits are predo-minant in the morphology of the impact abrasion of mar-tensitic ductile cast iron,as shown in Fig.9.This is relative

to the appropriate combination of its microstructures and mechanical properties.As a result,martensitic ductile cast iron has the best impact abrasion wear resistance.

The wear resistance of ductile cast iron requires the appropriate combination of its hardness and toughness under impact three-body abrasion test conditions,so martensitic ductile cast iron has the best wear resistance.4.Conclusion

1.The wear resistance of ductile cast iron under the conditions of the pin-on-disc and three-body abrasion test has a approximately linear relationship with its hardness.With increase in the hardness of ductile cast iron,its wear resistance increases.Thus,martensitic ductile cast iron and martensitic ductile cast iron dispersed eutectic carbide have the best abrasive wear resistance,followed by the bainitic with the pearlitic being the worse.

2.The impact abrasion resistance of ductile cast iron does not have an apparently linear relationship with its hardness and impact toughness under the condition of the

3.0J impact work test.Therefore,martensitic ductile cast iron has the best wear resistance followed by the bainitic and the pealitic with the martensitic dispersed with some eutectic carbide being the worse.

3.The micro-cutting model is predominant under pin-on-disc test conditions,so the greater is the hardness of ductile cast iron,the better the abrasion wear resistance.The three-body wear model is mainly micro-cutting wear,associated with some plastic deformation wear,thus the wear resistance of ductile cast iron still depends mainly on its hardness.Since both micro-cutting wear and plastic deformation wear exist together under impact abrasion test conditions,the wear resistance of ductile cast iron requires the appropriate combination of its hardness and

toughness.

Fig.7.SEM morphology of the worn surface of martensitic matrix ductile iron (?

200).Fig.8.SEM morphology of the worn surface of bainitic matrix ductile iron (?

200).

Fig.9.SEM morphology of the worn surface of martensitic matrix ductile iron with 15±20%eutectic carbides (?200).

180Z.-L.Lu et al./Journal of Materials Processing Technology 116(2001)176±181

References

[1]C.Vishnersky,J.F.Wallace,Effect of heat treatment on impact

properties of ductile cast iron,Trans.AFS71(1963)290±295. [2]S.I.Karsay,Production of thin as-cast ductile cast iron,Trans.AFS

73(1965)204±213.

[3]J.Akiyama,Application of ductile cast iron for civil engineering,

Trans.AFS75(1967)284±291.

[4]M.Johansson,Austenitic±bainitic ductile cast iron,Trans.AFS85

(1977)117±122.

[5]D.Z.Gou,D.K.Shi,Study on the strength and toughness of

austenitic±bainitic ductile cast iron,J.Xi'an Jiaotong Univ.,23 (Suppl.2)(1989)251±260(in Chinese).

[6]Yang Jia Zhang Zi Mining Bureau,Production technology of rare

earth magnesium treated medium manganese ductile cast iron grinding balls,Metal Mine(4)(1973)25±28(in Chinese).

[7]S.L.Cheng,H.X.Wang,C.L.Sun,A review of new grinding media

studies,industry productions and applications in our country,in: Proceedings of the First Conference on Grinding Media and Wear Resistant Materials,Beijing,China,1992(in Chinese).

[8]Z.Z.Yue,Study on grinding balls of martensitic ductile cast iron,

Foundry Technol.(4)(1983)42±46(in Chinese).

[9]C.G.Li,Q.D.Zhou,G.S.Song,Z.S.Fang,Influence of

carbon content of martensitic matrix and retained austenite on

wear of martensitic ductile cast iron,Wear162±164(1993) 75±82.

[10]Y.Z.Gao,Z.-L.Lu,B.L.He,Q.-C.Rao,Q.D.Zhou,An investigation

on martensitic ductile cast iron grinding balls,China Building Mater.

Equipment(1)(1990)19±22(in Chinese).

[11]B.Q.Wei,L.Ji,Z.D.Gao,Study of new wear resistant ductile cast

iron,J.Mach.Eng.27(6)(1991)51±55(in Chinese).

[12]S.Shepperson,C.Allen,The abrasive wear behavior of austempered

spheroid cast iron,Wear121(1988)271±287.

[13]S.C.Zhang,Q.-C.Rao,Y.S.Deng,Study on abrasive wear behavior

and impact fatigue resistance of as cast pearlitic ductile cast iron, Hydraulic Electrical Mach.(6)(1991)25±30(in Chinese). [14]Z.-L.Lu,Y.S.Deng,K.Z.Sang,The grinding balls of martensitic

ductile cast iron and their application,J.Xi'an Univ.Technol.12(2) (1996)112±116(in Chinese).

[15]R.C.D.Richardson,Wear and impact resistant white cast irons,Wear

10(1967)291±301.

[16]J.W.Boyes,Development and use of an abrasion test for cast iron and

steels,Iron Steel(February1969)57±63.

[17]M.M.Khruschov,The effect of wear on the compressive stress in the

sphere on plane configuration,Wear28(1974)69±78.

[18]Q.-C.Rao,Y.P.Ma,K.Z.Sang,Characteristics of martensite steel in

three-body impact abrasion,J.Iron Steel Res.3(1)(1991)47±52(in Chinese).

Z.-L.Lu et al./Journal of Materials Processing Technology116(2001)176±181181

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