effect of abrasive particles on wear of hardfacing

5/28/2018 Effect of Abrasive Particles on Wear of Hardfacing

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RES. AGR. ENG., 55, 2009 (3): 101113 101

Wear by hard particles occurs in many differentsituations such as with earth-moving equipment,slurry pumps or pipelines, rock drilling, rock or orecrushers, pneumatic transport of powders, dies inpower metallurgy, extruders, or chutes. Accordingto Figure 1, the wear processes may be classifiedby different modes depending on the kinematicsand by mechanisms depending on the physical

and chemical interactions between the elementsof the tribosystem which result in detaching thematerial from the solid surfaces. Compared withthe unlubricated sliding wear, the value of the wearcoefficient k, i.e. the dimensionless quotient of theamount of volumetric wear WVtimes the hardnessof the wearing material Hdivided by the normalloadFNand the sliding distances, as estimated frompractical experience, can be substantially greater inabrasive or erosive wear (Z G 1998). Figure 1

can only represent a very rough estimation of thewear coefficient because of the wide variation ofthe wear mechanisms occurring in an actual tri-bosystem as a function of the operating conditionsand properties of the triboelements involved, whichcan result in changes of the kvalue by some ordersof magnitude.

In abrasive wear, the material is displaced or de-

tached from the solid surface by hard particles orhard particles between or embedded in one or bothof the two solid surfaces in relative motion, or by thepresence of hard protuberances on the counterfacesliding with the velocity v relatively along the surface.wo-body abrasion is caused by hard protuberancesor embedded hard particles while in three-bodyabrasion the hard particles can move freely (roll orslide) between the contacting surfaces. Accordingto S et al. (2007), the rate of the material

Supported by the Internal Grant Agency of the Czech University of Life Sciences in Prague, Faculty of Engineering, ProjectNo. 31140/1312/313113.

Effect of abrasive particle size on abrasive wear

of hardfacing alloys

R. C1, P. H1, M. M1, J. S2, M. J1,

M. N1

1Department of Material Science and Manufacturing Technology, Faculty of Engineering,

Czech University of Life Sciences Prague, Prague, Czech Republic2New Technologies Research Centre in Westbohemian Region NTC,

University of West Bohemia, Pilsen, Czech Republic

Abstract: Hardfacing is one of the most useful and economical ways to improve the performance of components submit-

ted to severe wear conditions. Tis study has been made for the comparison of microstructure and abrasion resistanceof hardfacing alloys reinforced with chromium carbides or complex carbides. Te hardfacing alloys were depositedonto NS EN S235JR low carbon steel plates by the gas metal arc welding (GMAW) method. Different commercialhardfacing electrodes were applied to investigate the effect of abrasive particle size on abrasive wear resistance. Teabrasion tests were made using the two-body abrasion test according to SN 01 5084 standard, abrasive cloths were ofgrits 80, 120, 240, and 400. Microstructure characterisation and surface analysis were made using optical and scanningelectron microscopy. Te results show the different influence of abrasive particles size on the wear rate for differentstructures of Fe-Cr-C system. Te structures without primary carbides are of high abrasive wear rate, which increasesnonlinearly with the increasing abrasive particle size. On the contrary, the structures containing primary carbides areof low abrasive rates and theses rates increase linearly with the increasing abrasive particle size.

Keywords: hardfacing alloy; abrasive wear; pin-on-disk; carbide


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102 RES. AGR. ENG., 55, 2009 (3): 101113

removal in three-body abrasion can be one order ofmagnitude lower than that for two-body abrasion,because the loose abrasive particles abrade the solidsurfaces between which they are situated only about10% of the time, while they spend about 90% of thetime rolling. Hard particles striking a solid surfacecarried either by a gas or a liquid stream can causeerosive wear whereby the wear mechanism dependsstrongly on the angle of incidence of the impactingparticles. Te interaction between hard particlesand the solid surface can be generally accompaniedby the events of adhesion, abrasion, deformation,heating, surface fatigue, and fracture. Figure 2 showsschematically some general trends of the wear loss of

materials depending on the properties of the abra-sive particles and the wearing materials as well asthe operating conditions. With increasing hardnessof the abrasive particles, the wear loss can increaseby about one to two orders of magnitude from a lowto a high level (Figure 2).

Models for two-body abrasion have been devel-oped to a substantially greater depth than thosefor three-body abrasion. Penetration of a slidingabrasive particle into a metallic surface results inmicroploughing or microcutting depending onthe attack angle. Below a critical attack angle, themetallic material is mainly elastically-plasticallydeformed and flows around and beneath the sliding

Figure 1. Values of wear coefficient kas a function of wear mechanism without lubricating media (Z G 1998)

Figure 2. Schematic representation ofwear loss by hard particles as a function

of material properties such as hardnessof abrasive particle (Z G 1998)

Wear mode

Sliding wear

Abrasive wear

Erosive wear

WVHWear coefficient k= FN s

107 106 105 104 103 102 101100Wear mechanism

Softst

eel(200H

V)

Wear

loss

W

Hardness of abrasive particle

Glass Flint Garnet Al2O

3 SiC

500 1 000 1 500 2 000 2 500

Cement

edcar

bides(

WC-Co

)

Hard

ste

el(

700HV)

Brittle

ceram

ic(Al2O

3)


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RES. AGR. ENG., 55, 2009 (3): 101113 103

particle but no material is removed from the surface.

Increasing the attack angle leads to a transition frommicroploughing to microcutting, i.e. material flowsup the front face of the abrasive particle and is de-tached from the wearing surface in the form of a chip(Z G 1998; C & V 2003a).

Hence, a more general model was developed whichdescribes abrasive wear by distinguishing four typesof interaction between the abrasive particles andwearing material (Figure 3), namely microplough-ing, microcutting, microfatigue, and microcracking.In the ideal case, microploughing, due to a singlepass of one abrasive particle, does not result in anydetachment of material from the wearing surface. Aprow is formed ahead of the abrading particle andthe material is continuously displaced sideways toform ridges adjacent to the groove produced. Te

volume loss can, however, occur owing to the action

of many abrasive particles or the repeated action of a

single particle. Te material may be ploughed asiderepeatedly by passing particles and may break off bylow cycle fatigue, i.e. microfatigue. Pure microcut-ting results in a volume loss by chips equal to the

volume of the wear grooves. Microcracking occurswhen highly concentrated stresses are imposed byabrasive particles, particularly on the surface ofbrittle materials. In this case, large wear debris isdetached from the wearing surface owing to thecrack formation and propagation. Microplough-ing and microcutting are the dominant processeson ductile materials while microcracking becomesimportant on brittle materials (Z G 1998;S & E 2006; S et al. 2007).

Composites can offer the answer for achievinghigh hardness and sufficient fracture toughness toavoid brittle fracture. Second phases, e.g. hard ce-

Figure 3. Schematic rep-resentation of differentinteractions between slid-ing abrasive particles andthe surface of materials(Z G 1998)

Figure 4. Interaction between slid-ing hard or soft abrasive particles

and reinforcing phases (Z G1998)


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104 RES. AGR. ENG., 55, 2009 (3): 101113

ramic particles or fibers, can be incorporated intoa softer and more ductile matrix. Te abrasive wearresistance of such composites depends on differentmicrostructural parameters such as the hardness,shape, size, volume fraction, and distribution of theembedded phases, the properties of the matrix andthe interfacial bonding between the second phase

and the matrix. Figure 4 shows different interactionsbetween abrasive particles and a reinforcing phase.Hard and soft abrasive particles, i.e. harder or softerthan the reinforcing phase, and also small and largesizes of the reinforcing phase are distinguished. Hardabrasive particles can easily dig out small phases andcut or crack larger ones. Soft abrasive particles areable to dig out small phases or produce large pits.Te indentation depth of soft abrasive particles issubstantially reduced by hard reinforcing phases ifthe mean free path between them is smaller than the

size of the abrasive particles. Large phases deficientlybonded to the matrix can be pulled out. However,large phases strongly bonded to the matrix can bluntor fracture soft abrasive particles (C & V2003b; B et al. 2005).

Hardfacing made using flame, electric arc, orplasma, are used in industry. Hardfacing makes astrong metallurgical point between the deposit andsubstrate. Filler materials in the form of coated elec-trodes, cored electrodes, welding rods and powderrepresent a wide assortment of metal and composi-tion materials of various properties. Te choice offiller material and hardfacing technology depends onthe part forms and dimensions, chemical composi-tion of the substrate, mode of stress, wear type, andtotal cost for hardfacing. ribological propertiesdepend on the filler material chemical compositionand on the hardfacing technology. In the first layer

of the deposit, the mixing of the filler material andsubstrate occurs. Terefore, the required propertiesare reached mostly in the second layer of multilayers(G & K 2003; Y 2006; C- et al. 2007a,b).

Hardfacing materials of major volume of carbidicphase in the deposit are of a very good abrasion

resistance. For usual temperatures, hardfacingmaterials on the basis of Fe-Cr-C are used, aboveall for their relatively low price. Complex depositFe-Cr-C-M (where M means Nb, W, i, Mo andtheir combination) are of higher abrasion resistance.Te commercially produced hardfacing materialsare usually of 35.5% carbon content (A& B 1990; A et al. 2003). By theuse of these electrodes on the low carbon steel assubstrate and one layer deposit, the hypoeutectic oreutectic structure is reached. In the case of complex

alloyed deposit, the hypoeutectic structure withprimary carbides of MC type (e.g. NbC, WC) oc-curs. Te carbides M7C3with high Cr contents canbe reached only in the second and next layers (PL et al. 2004; C 2008; Jet al. 2008).

EXPERIMENAL PROCEDURE

Materials and welding conditions

Steel according to SN EN S235JRwas used asthe substrate. Its composition, determined usingthe GDOES method, is presented in able 1. Tesubstrate plate used for surfacing was of dimensions100 25 300 mm.

On this substrate plate, the filler materials were de-posited. Teir nominal chemical composition is pre-sented in able 2, welding conditions in able3.

Hardness measurement

Te bulk hardness of the hardfacing deposits was

measured by the Vickers hardness method, while a

able 1. Chemical composition of substrate plate (weight %)

C Mn S P Fe

0.074 0.33 0.006 0.0025 balance

able 2. Chemical composition of electrodes (weight %)

C Cr Nb Mo W V Si Mn Fe

Hardfacing 1 (H1) 3.2 29 1.0 balance

Hardfacing 2 (H2) 3.5 35 1.0 balance

Hardfacing 3 (H3) 4.4 23.5 5.5 6.5 2.2 1.5 balance

Hardfacing 4 (H4) 3.8 33 0.5 1.2 balance

Hardfacing 5 (H5) 4.5 17.5 5 1.0 1.0 1.0 0.5 0.5 balance

Hardfacing 6 (H6) 3.5 22 3.5 0.4 0.4 0.9 balance


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RES. AGR. ENG., 55, 2009 (3): 101113 105

microhardness tester allowed measuring the hard-ness of the phases in the microstructure by using aVickers indenter with a load of 0.1 kg.

Microstructure analysis

Optical and scanning electron microscopes wereused to analyse the microstructure of the specimens.Secondary electron imaging allowed morphologicdescription of the worn surfaces, while backscat-tered electron imaging and EDX compositional wereused to describe qualitatively the chemical composi-tion of the phases in the microstructure.

Abrasive wear

he abrasive wear resistance was tested using

the tester with bonded abrasive according to SN01 5084 (1974). For the test, the abrasive cloth of 80,120, 240, and 400 grits and the load of 2.35 kg werechosen. Te mass lost was determined using theanalytic balance of 0.0001 accuracy. Te pin-on-disktesting machine (Figure 5) consists of a uniformlyrotating disk whereon the abrasive cloth is fixed. Tetested specimen is fixed in the holder and pressed

able 3. Welding conditions

Electrode diameter (mm) 1.6

Arc voltage (V) 27

Welding current (A) 250

Electrode polarity positive

Welding speed (cm/min) 13

Preheating no

Deposition rate (kg/h) 14.3 Figure 5. Diagrammatic representation of the pin-on-disktesting machine: 1 abrasive cloth, 2 specimen, 3 holder,4 weight, 5 screw, 6 nut with cogs, 7 limit switch,8 pin, 9 horizontal plate

able 4. Chemical composition of weld deposit layers (weight %)

C Cr Nb Mo W V Si Mn FeFirst layer


Hardfacing 2 (H2) 2.04 30.3 0.1 0.76 0.13 balance

Hardfacing 3 (H3) 4.27 19.1 4.64 4.44 0.75 1.35 1.08 0.21 balance




Second layer







Tird layer




1 234 5 6 7

89


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106 RES. AGR. ENG., 55, 2009 (3): 101113

(a) H1 first layer

(c) H1 third layer

(e) H2 second layer

(d) H2 first layer

(f ) H2 third layer

(b) H1 second layer

(g) H3 first layer (h) H3 second layer

Figure 6. Structures of deposit using the optical microscopy

against the abrasive cloth by the weight of 2.35 kg.A screw makes possible the radial feed of the speci-men. Te limit switch stops the test. During the testthe specimen moves from the outer edge to the cen-

tre of the abrasive cloth and a part of the specimencomes in contact with the unused abrasive cloth.

RESULS AND DISCUSSION

Chemical composition and microstructure

able 4 presents the chemical compositions of theweld deposit layers. It is evident that the chemical


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RES. AGR. ENG., 55, 2009 (3): 101113 107

(i) H4 first layer

(k) H4 third layer

(m) H5 second layer

(l) H5 first layer

(n) H6 first layer

(j) H4 second layer

(o) H6 first layer

Figure 6. continued

composition approximately equal to the filler wirecomposition is reached in the second and furtherlayers. Te difference between the second and thirdlayers is not so much expressive and the layers struc-

tures are the same. Te lower content of carbon andalloying elements in the first layer is caused by mix-

ing the overlay and low carbon substrate materials.Tis problem can be solved e.g. by the use of powdergraphite and alloys added in the course of hardfac-ing. Tis method was successfully used e.g. by W

et al. 2006, when the powder graphite was added inthe welding flux. E.g. W tested the alloying using


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108 RES. AGR. ENG., 55, 2009 (3): 101113

a) b)

c) d)

e) f)

Figure 7. Structures of the some deposit using SEM

(c) E4V2, WD10.3 mm, SigSE, Spot 3.5, Mag5 000 x, 20.0 m

(a) E4V1, WD10.0 mm, SigSE, Spot 4.5, Mag1 500 x, 1 000.0 m

(b) E1V1, WD9.8 mm, SigSE, Spot 4.0, Mag1 500 x, 100.0 m

(d) E4V2, WD10.3 mm, SigBSE, Spot 4.5, Mag1 500 x, 100.0 m

(f) E1V2, WD9.8 mm, SigSE, Spot 4.0, Mag6 000 x, 20.0 m

(e) E1V2, WD9.8 mm, SigSE, Spot 4.0, Mag2 000 x, 50.0 m


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RES. AGR. ENG., 55, 2009 (3): 101113 109

powder of high carbon ferrochromium mixed withwelding flux for SAW surfacing method. Te resultscan be found e.g. in works of W (W et al.2007, 2008a,b,c).

Figure 6 shows the deposit structures corre-sponding to the chemical compositions presentedin able4. he structures of one layer deposits(H1, H2, H4, H6) are created by carbidic eutecticand austenite. Te morphology of carbidic eutecticconsisting of carbide (Fe, Cr)7C3and austenite isshowed in Figure 7a. Te deposits without primarycarbides contain this type of carbidic eutectic. Testructures of complex alloyed deposit materials(H3, H5) are created by carbidic eutectic on the basisof M7C3, austenite, and primary carbides of MC type(Figure 7b for H5).

Te structure of two layers deposit is created byprimary carbides, carbidic eutectic (Figure 7c), andaustenite. Te primary carbides of M7C3(Figure 7d)are in the weld deposits of H1, H2, H4, and H6.

Te neighbourhood of these carbides is austenitic.Te second layer of the complex alloyed deposit iscreated by primary carbides MC a M7C3, carbidic

eutectic, and austenite (Figure 7e). he eutecticmorphology is shown in Figure 7f.

Hardness

Te Vickers hardness (HV) values are presentedin able 5 for one-layer, two-layer, and three-layerdeposits. Te hardness of the deposit correspondsto the structure. Te lowest hardness values weredetermined in one-layer deposit materials alloyedonly with chromium. Te hardness of these depositsis influenced by the proportion of phases. Te de-posit containing the highest amount of austenite isof the lowest hardness. Te hardness increases withthe carbidic eutectic quantity. Te complex alloyeddeposits in the second or third layers with primarycarbides contents are of the highest hardness values.Te hardness values of these deposits increase withthe carbidic phase amount and size. Except the de-posit bulk hardness, the hardness of single phases

is also determined (if the phase size is sufficient forHV0.01measuring). able 6 shows the hardness ofsingle microstructure phases of deposits.

able 5. Hardness of hardfacing layers (HV30)

Hardfacing 1 Hardfacing 2 Hardfacing 3 Hardfacing 4 Hardfacing 5 Hardfacing 6

First layer 617 492 714 465 612 606

Second layer 680 564 812 560 778 646

Tird layer 696 638 595

able 6. Hardness of phases in the hardfacing

Phase Austenite (HV 0.02) Eutectic (HV 0.02) MC (HV 0.1) M7C3(HV0.1)

H2 first layer 650 930

H2 second layer 612 950

H2 third layer 965

H3 first layer 700 1 130 1 850

H3 second layer 730 1 150 1 850 1 600

H4 first layer 642 940

H4 second layer 635 1 050 1 550

H4 third layer 640 1 020 1 560

H5 first layer 1 120 1 800

H5 second layer 720 1 150 1 800 1 635

H6 first layer 873

H6 second layer 650 870 1 600


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110 RES. AGR. ENG., 55, 2009 (3): 101113

Abrasive wear and roughness

Figures 813 show the abrasive wear resistance

results of the hardfacings tested. From the resultsit follows that the structure is of a significant influ-

ence on the wear resistance. With the hardfacing ofeutectic or hypoeutectic structures, the dependencebetween the wear rate and abrasive particles mean

diameter is linear. Te wear rate of these hardfacingsdepends significantly on the proportions of carbidic

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 50 100 150 200 250 300

Mean diameter of abrasive particles (mm)

Wearrate(mg/m)

Hardfacing 1 (first layer) Hardfacing 1 (second layer)

Hardfacing 1 (third layer)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 50 100 150 200 250 300


Wearrate

(mg/m)



0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.61.8

2.0

0 50 100 150 200 250 300


Wearrate(mg/m)


Figure 10. Hardfacing 3 rela-

tion between wear rate andabrasive particles size

Figure 8. Hardfacing 1 relation be-tween wear rate and abrasive particlessize

Figure 9. Hardfacing 2 rela-tion between wear rate andabrasive particles size

(m)

(m)

(m)


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RES. AGR. ENG., 55, 2009 (3): 101113 111

eutectic and austenite. Te higher the carbidic eu-

tectic content in the hardfacing structure, the lowerthe wear rate.With the occurrence of primary carbides in the

structure, the wear rate increases linearly with the

abrasive particle size. Te wear rate decreases with

the carbidic phase amount. In the first layer, thehardfacing 3 contains a higher quantity of primarycarbides MC than the hardfacing 5 and the carbidiceutectic and austenite matrix shows a higher repre-

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 50 100 150 200 250 300


Wearr

ate(mg/m)



0.0

0.2

0.4

0.6

0.81.0

1.2

1.4

1.6

1.8

2.0

0 50 100 150 200 250 300


Wearrate(mg/m)




0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 50 100 150 200 250 300


Wearrate(mg/m)


Figure 13. Hardfacing 6 rela-

tion between wear rate andabrasive particles size

(m)

(m)

(m)



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112 RES. AGR. ENG., 55, 2009 (3): 101113

sentation of austenite. Te works of S pres-ent that this austenite, if deformed, transforms intomartensite. In the second layer of hardfacings 3 and 5,the carbides MC and M7C3occur. Te quantities ofM7C3and its sizes is almost identical and therefore thewear rate is of the same value. A slightly lower wearrate is found in the hardfacing 3, evidently because

of the higher content of MC phase.E.g. in the first layer of hardfacings 4 and 6 no

primary carbides occur and the structure consistsof carbidic eutectic and austenite. In the third layerof hardfacing 4 and in the second layer of hardfac-ing 6 primary carbides M7C3already occur and thewear rate decreases significantly. Te character ofthe wear rate dependence on the abrasive particlessize changes to linear.

CONCLUSION

Te knowledge obtained can be summarised inthe ollowing points:

he hardness of hypoeutectic hardfacings in-creases with the carbidic eutectic part and type.Te hardness of hypereutectic hardfacing increaseswith the increasing proportions of carbidic phasesMC and M7C3.

Te abrasive wear rate of hypoeutectic hardfacingdepends on the structural components portions. Ahigher part of alloyed eutectic reduces the wear rate.

Te dependence of hypoeutectic deposit abrasivewear rate on the abrasive particles size is not linear.Tis fact can be caused by the abrasive particle criti-cal size, which erodes the carbidic eutectic softerphase and in this way uncovers the carbidic phasewhich can crumble away. Tis dependence of theabrasive wear rate increase on the increase of theabrasive particle size is almost constant.

Te abrasive wear rate of hypereutectic hardfacingdecreases with the increasing proportions of carbidicphases MC and M7C3. In this decrease, the MC phaseparticipates more because it is harder. Tis is shown

in comparing the hardfacings 3, 4, 5, and 6.Te dependence between the hypereutectic hardfac-

ings wear rate and the abrasive particle size is linear.

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Received for publication October 10, 2008

Accepted after corrections May 6, 2009

Corresponding author:

Ing. R C, Ph.D., esk zemdlsk univerzita v Praze, echnick fakulta,katedra materilu a strojrensk technologie, Kamck 129, 165 21 Praha 6-Suchdol, esk Republika

tel.: + 420 224 383 274, fax: + 420 234 381 828, e-mail: [email protected]

Abstrakt

C R., H P., M M., S J., J M., N M. (2008): Vliv velikosti abra-zivn stice na abrazivn opoteben nvarovch materil. Res. Agr. Eng., 55: 101113.

Nvarov vrstvy jsou jednou z cest ke zven odolnosti proti opoteben a zrove jsou i ekonomickou cestou. Studie

porovnv mikrostrukturn charakteristiky nvarovch materil a odolnost vi abrazivnmu opoteben. Studiumbylo provdno na nvarovch materilech, kde ve struktue byly chromov karbidy a karbidy komplexn. Nvarov

materil byl nanesen na nzkouhlkovou ocel S235JR metodou odtavujc se elektrody v ochrann atmosfe. Rznkomern nvarov materily byly studovny z hlediska efektu velikosti abrazivn stice na abrazivn opoteben.

est abrazivnho opoteben byl provdn na brusnm pltn o zrnitosti 80, 120, 240 a 400 podle SN 01 5084. Cha-rakteristika mikrostruktury a analza povrchu byla provdna postupy optick a elektronov mikroskopie. Vsledky

ukazuj rozdln vliv velikosti abrazivn stice na rychlost opoteben pro rzn struktury systmu Fe-Cr-C. Struktu-ry bez primrnch karbid maj vysokou rychlost abrazivnho opoteben; tato rychlost roste nelinern se zvtujc

se velikost abrazivn stice. Naopak struktury s primrnmi karbidy maj nzkou rychlost abrazvnho opotebena tato rychlost roste linern se zvtujc se abrazivn stic.

Klov slova: nvarov materil; abrazivn opoteben; pin-on-disk; karbidy

effect of abrasive particles on wear of hardfacing

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