Understanding Cemented Carbide · 12/5/2016 · basic cemented carbide structure from which other types of cemented carbide have been developed. In addition to the straight tungsten

UnderstandingCemented Carbide

S A N D V I K H A R D M A T E R I A L S

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The material with staying powerThe most valuable property ofcemented carbide is that it offers asafer and more dependable solutionthan any other known material toone of the toughest problems whichengineers have to contend with –reliability.

Reliability is often a problemof wear. And wear resistance is themost outstanding feature of cemen-ted carbide. If the material also hasto withstand deformation, impact,heavy load, high pressure, corrosionand high temperature, cementedcarbide is often the only materialthat can fulfil these requirementssatisfactorily.

It has long been a well-knownfact that the use of cemented carbide

provides an optimal solution in thecase of tools for metal cutting androck drilling. Over the years cementedcarbides have also proven theirsuperiority in a great number of othertooling and engineering applications.

Looking at industrial equipmentand consumer products in general,failures are often caused by thebreakdown of a single componentor structure. The solution may beto switch to a high-performancecarbide part.

Experience shows that designsolutions result from the close co-operation of engineers representingthe application and carbide techno-logies. The best results are attainedwhen these contacts have been

established at an early stage of adevelopment project, when it is stillpossible to adjust the design andtake full advantage of the carbide.

The purpose of this documentis to serve as a reference manual onthe design and application of cemen-ted carbide.

The data and graphs shownrepresent typical values from labora-tory tests.

Recommendations regardingthe selection of grades for specificapplications are based on bothlaboratory tests and experience, andcan be used only to indicate thefitness in other similar applications.

The term “hard materials”refers to materials harderthan the hardest steel. The

hardest of these is diamondfollowed by cubic boron

nitride and ceramics. Afterthese comes cemented

carbide – currently the mostimportant technical hardmaterial which covers a

wide range of hardness andtoughness combinations.

Diamond

Cubic boron nitride

Ceramics (KIC 2-8 MN/m3/2)

Cemented carbides (KIC 5-25MN/m3/2)

High speed steels(KIC 5-25MN/m3/2)

Transverse rupture strength, N/mm2

Hardness, HV


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Cemented carbides are a range ofcomposite materials which consistof hard carbide particles bondedtogether by a metallic binder. Theproportion of carbide phase isgenerally between 70-97 % of thetotal weight of the composite andits grain size averages between 0.4and 10 µm.

Tungsten carbide (WC), thehard phase, together with cobalt(Co), the binder phase, forms thebasic cemented carbide structurefrom which other types of cementedcarbide have been developed. Inaddition to the straight tungsten

carbide – cobalt compositions –cemented carbide may contain vary-ing proportions of titanium carbide(TiC), tantalum carbide (TaC) andniobium carbide (NbC). These car-bides are mutually soluble and canalso dissolve a high proportion oftungsten carbide. Also, cementedcarbides are produced which havethe cobalt binder phase alloyed with,or completely replaced by, othermetals such as iron (Fe), chromium(Cr), nickel (Ni), molybdenum (Mo),or alloys of these elements.

Thus, there are three individualphases which make up cemented

carbide. In metallurgical terms, thetungsten carbide phase (WC) isreferred to as the �-phase (alpha),the binder phase (i.e. Co, Ni etc.) asthe �-phase (beta), and any othersingle or combination of carbidephases (TiC, Ta/NbC etc) as the �-phase (gamma).

Other than for metal-cuttingapplications, there is no internation-ally accepted classification ofcemented carbides. However, thecemented carbide grades developedby Sandvik fall into four main groupsas described on the next page.

Cemented carbide types

The application range ofstraight grade cemented

carbide.

Cobalt content, % by weight

22002000

18001600

1400

1200

1000

800

Hardnes

s, HV 30

Percussivemining toolsMining and civilengineering toolsMasonry andstone cutting tools

Rolls forhot rolling

Cold forming tools

Metal cutting tools

DrawingdiesWood

workingtools

Tools forcompositemachining

WC-grain size, µm

Front cover illustration:Microstructure of extracoarse grained WC-Cocemented carbide after

electrolytic etching.Magnification: 1500x.


WC-Co gradesThis group contains WC and Coonly (i.e. two-phases) and a fewtrace elements. These grades areclassified according to their cobaltcontent and WC grain size.

The grades with a binder con-tent in the range 10-20 % by weightand WC-grain sizes between 1 and5 µm have high strength and tough-ness, combined with good wearresistance.

The grades with binder contentsin the range 3-15 % and grain sizesbelow 1 µm have high hardness andcompressive strength, combined withexceptionally high wear resistance.

The Sandvik grade programmealso includes WC-Co grades whichutilise a range of ultra-fine WCgrain sizes (< 0.5 µm). With suchfine, uniform grain sizes, a uniquecombination of hardness, wearresistance and toughness can beachieved.

Corrosion resistant gradesThis group contains cemented car-bide grades in which the binder phasehas been specifically designed toimprove corrosion resistance abovethose grades which contain cobaltalone.

This is achieved by alloying thecobalt binder phase with elementssuch as nickel and chromium, orcompletely replacing it with a morecorrosion resistant alloy.

Dual Property (DP) gradesThis group contains grades whichhave had the distribution of theirbinder phase modified in such away as to create a material withdifferent properties in the surfacezone compared with the bulk.

This entirely new concept,developed by Sandvik, enablescomponents to be produced whichcontain distinct microstructuralzones, each with a different binder

content. Thus, each zone hasdifferent properties – hence theterm “Dual Property”.

More information on DPCarbide can be found on page 17.

Grades containingcubic carbidesThis group consists of grades con-taining a significant proportion of�-phase, (Ti, Ta, Nb)C togetherwith WC and Co, (i.e., three-phasematerials).

The main features of the �-phase are good thermal stability,low grain growth, and resistance tooxidation.

These grades have been de-signed to provide a good balance ofwear resistance and toughness inapplications in which there is intimatecontact with ferrous materials andin which a high temperature is gene-rated. Typically, these conditionsarise in metal cutting or high pres-sure sliding contact situations wherewelding and galling of the surfacesare encountered.

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Microstructure of WC-Co grade Microstructure of �-phase grade

5 µm


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Grain size classificationSandvik Hard Materials uses the following grain size classification for all standard grades.

Ultra fine Extra fine Fine Medium Medium coarse Coarse Extra coarse< 0.5 µm 0.5 - 0.9 µm 1.0 - 1.3 µm 1.4 - 2.0 µm 2.1 - 3.4 µm 3.5 - 5.0 µm > 5.0 µm

5 µm


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Wear resistanceThe most important characteristicof cemented carbide is its wearresistance. This property, or morecorrectly, combination of properties,is related to surface phenomena.

When two surfaces slide againsteach other, material will be removedfrom both of them. At a low load,this loss of material will take placethrough the loss of single grains orparts of single grains. This processis generally referred to as attrition.

At higher load, the loss ofmaterial takes place by clusters ofgrains becoming detached. Thisprocess is known as abrasion.

Both these processes, leadingto loss of surface material, contri-bute to wear. In practice, the materialloss is often also affected by thelocal environment, particularly ifcorrosion or oxidation is encountered.

The nature of wear is verycomplex and the wear rate dependson many variables. General valuesfor comparative purposes should beviewed critically. However, evalua-tions of wear resistance can be donein the laboratory under standardisedconditions. Such evaluations indi-cate the ranking between the testedmaterials under these specifiedconditions only.

Materialproperties

In a test based on ASTM B611-85,the test sample is pressed against

the periphery of a rotating disc,partly immersed in a slurry of

alumina (Al2O3) particles inwater. The abrasive wear

resistance is influenced by thecobalt content and the tungsten

carbide grain size as shown in the diagrams.

Wear resistance as a function of the Co content atdifferent WC grain sizes according to the ASTM B611-85test method.

Wear resistance as a function of hardness (ASTM B611-85).

cm-3

Extra fine

Medium

Medium coarse

% Co by weight

cm-3

Extra fine

MediumMedium coarse

Vickers hardness

Steel disc

Test specimen

Mixing bladesAbrasive slurry

F

Wear resistance Wear resistance


ToughnessWhen components are exposed toexternal loads, static or dynamic,mechanical stresses occur within thematerial. The mechanical strengthand deformability of the materialare therefore important. In manycases, particularly when dealing withshock loading, both these propertiesmust be considered simultaneously.This forms the background to theterm “toughness” which can be de-fined as “the ability to resist fracture”,i.e. a complete separation into atleast two parts.

Toughness can be defined anddetermined in many ways. With theabove definition, the integrated pro-duct of force and deformation tofracture, can be used as a toughnessvalue.

A method commonly used for determining the toughness ofcemented carbides is the Palmqvistmethod. In this case, the fracturetoughness of the material is repre-sented by its critical stress intensityfactor KIC.

The results of toughness testsshow that this property increaseswith increasing binder content, andwith increased WC grain size.

In comparison with other me-tallic materials, carbide is on thelower part of the toughness scale,approximately at the same level ashardened steel.

By definition, and confirmed byexamining fractured surfaces, cemen-ted carbide must be classified as abrittle material, as practically noplastic deformation precedes frac-

ture. However, different cementedcarbides show large differences intoughness behaviour. This is bestexplained by a close look at themicrostructure. The types of frac-ture seen are cleavage fractures incarbide grains, grain boundaryfractures between carbide grainsand shear fractures in the binder.Generally, the amount of cleavagefractures increases with increasedgrain size and the amount of shearfractures with increased binder con-tent. Expressed as fracture energy,the major contribution to toughness,is from the latter, i.e. the crack paththrough the binder.

Modern fracture mechanics pro-vide a means of explaining tough-ness as it deals with the conditionsfor crack initiation and growth in non-homogeneous materials under stress.

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The Palmqvist method uses the corner crack length of aVickers hardness indentation to derive the fracturetoughness. The critical stress intensity factor is definedas:

Fracture toughness as a function of the Co content fordifferent WC grain sizes.

KIC = 6.2 (HV50)1/2 in MN/m3/2�L

MediumCoarse

% Co by weight

KIC, MN/m3/2

Extra fine

Ultra fine

L3

L2

L1

L4

Fracture toughness


HardnessHardness is normally determinedusing the Vickers indentation methodaccording to EN 23 878 (ISO 3878).This method allows a range of loadsbut HV30 is preferred. The force of a30 kg weight, 294 N, is used to createa measurable indentation withminimal cracking at the corners. Forthe hardest grades the size of theimpression and cracking contributeto reduced precision and accuracy.

Sometimes other methods areused such as Rockwell A (ISO 3738).The Rockwell method is similar toVickers, but is based on the use ofa diamond cone and the depth of theindendation is used as a measure ofthe hardness. There is no theoreticalbasis for conversion between thetwo. Instead actual determinationmust be used for comparisons.

Hardness increases with de-creasing binder content and de-creasing grain size. The hardnessrange extends roughly from that oftool steels, 700, up to 2200 HV30.

Hardness decreases with increas-ing temperature due to increasingplasticity.

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The Vickers method is based on inden-ting a polished carbide surface with a

diamond pyramid. The hardness isinversely proportional to the size of

the impression.

Hardness as a function of the Co content for variousWC grain sizes.

Relative hardness at different temperatures.

Wear resistance and tough-ness are two complex properties,both of which provide the ability towithstand the destruction of amaterial. A high wear resistance ispossible only if the demand forhigh toughness is reduced and viceversa. However, high wear resis-tance and high toughness can beachieved simultaneously, providedthese properties can be re-distributed.There are two ways of doing this:DP carbide or coating with thinlayers of wear resistant materials.There are numerous potential com-binations and, consequently, onlyhomogeneous, conventional carbidewill be dealt with below.

HV30

%

Extra fine

Ultra fine

Medium

Medium coarseExtra coarse

% Co by weight Temperature, °C

F0 F1

x

y

Hardness

Relative hardness

The transverse rupture strength is determined as thefracture stress in the surface zone:

k = chamfer correction factor (normally 1.00-1.02)


Mechanical strengthAll materials contain some amountof defects such as pores, inclusionsand micro-cracks. These defectslead to a reduced material strength.

In the case of a ductile material(copper, mild steels, etc.) defect fre-quency and mean size are importantfactors, whereas in the case of abrittle material (e.g. hardened steelsand carbide) the frequency above acertain size limits the strength. Con-sequently, this latter phenomenonmakes the mechanical strengthvolume dependent as the probabilityof finding a large defect increaseswith increased material volume.

Weibull has related the volumedependence of critical defects withina material to the material strength.The conclusion of the Weibulltheory is that the relationship canbe described using the formula:

where �1 and �2 are the fracturestresses corresponding to the volumesV1 and V2, respectively, and m is afactor derived from the spread infracture stress of the material.

Modern high quality carbidehas an m-value of about 9. High m-values correspond with smallvariations in fracture stress and aless volume-dependent material.

In practice the stress distribu-tion is complex and the Weibulltheory only provides a partialdescription. However, a calculationof the fracture probability of a certaincarbide volume with a known stressdistribution is possible.

A high quality carbide is norm-ally regarded as an extremely defect-free material.

However, shaping processes,such as grinding and spark erosion,may lead to the introduction of largesurface defects, thereby reducing thestrength of the finished product.

The use of inferior quality car-bide, in which defects already exist,

increases the risk of both early fail-ure and variations in performance.

Transverse rupture strengthTransverse rupture strength (TRS)or bending strength testing is thesimplest and most common way ofdetermining the mechanical strengthof cemented carbide. According tothe standardised method EN 23 327(ISO 3327), a specimen of a specifiedlength with a chamfered, rectangularcross section is placed on two sup-ports and loaded centrally untilfracture occurs.

TRS is taken as the median ofseveral observed values. TRS reachesa maximum at a cobalt content ofabout 15 % (by weight) and amedium to coarse WC grain size.

The small portion of plasticdeformation is generally disregardedas it is only noted in the toughestcarbides.

The test pieces should be eitheras sintered or ground.

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�2 = (V1)1/m�1 V2

The probability of a large defect occurring is higher in a large volume.

Rbm = 3FLk2bh2

V1 V2

b

F

h

L


A careful grinding, conductedwithout any introduction of cracksor surface defects, will increase theTRS values compared to valuesobtained from assintered specimens.

The carbide rotary toolmakingsector in industry has adopted amodified TRS testing method moreapplicable to the geometry of solidcarbide tooling and allowing a rapidtesting procedure.

In this test a modification of thestandard test specimen according toEN 23 327 (ISO 3327) is used. Thiscomprises a cylindrical specimen,Ø 3.25 x 38 mm. This modified testhas been adopted as an industrystandard and is now proposed to beincluded in the ISO-standard. Byusing this cylindrical test specimen,the edge effect of the rectangularstandard specimen is avoided.

As a result, the data gainedfrom this test shows higher TRSvalues than with the rectangulartest piece. Typically, the TRS valuesobtained from the cylindrical speci-mens exceed the level of the squarespecimens by about 20%. Thus,caution must be used when data arecompared.

Transverse rupture strengthdecreases with increasing tempera-ture. At prolonged load times andhigh temperatures, the cementedcarbides will exhibit creep behaviour.

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Volume dependence of transverse rupture strength.

Transverse rupture strength as a function of Cocontent. Above 20% Co, the relationship is disturbedby interference from other fracture mechanisms.

Relative transverse rupture strength as a function ofthe temperature for an 11% Co, medium WC grain sizecemented carbide.

Volume ratio V2/V1

Rbm2/Rbm1

%

Temperature, °C % Co by weight

Complex fracture

Simple fracture

Transverse rupture strength

Relative transverse rupture strength

Relative transverse rupture strength N/mm2

Medium


Tensile strengthTensile strength testing of brittlematerials is difficult. The accuracyof the test is extremely sensitive tosample preparation (the surface mustbe “perfect”) and to superimposedloads from the fixtures, resulting incomplex additional stresses.

However, by using the Weibulltheory, it is possible to derive thetensile strength from the TRS value.With m=9 the tensile strength is56% of the TRS value.

Compressive strengthOne of the most important propertiesof cemented carbides are theirextremely high compressive strengthunder uniaxial loads. The stressmode with this type of load doesnot actually lead to “compressivefracture”, but to a situation closerto a shear fracture. The shear stressat fracture of the compressed speci-men is about half of the compressivestress which is much higher thanthe pure shear strength.

A suitable method of compres-sive strength determination is definedby EN 24 506 (ISO 4506). To obtainaccurate values with cemented car-bide, a modified specimen geometrymust be used in order to overcomethe edge and contact effects associ-ated with a simple cylindrical testpiece.

When the load is applied, thereis first an elastic deformation, butprior to fracture there will also be acertain amount of plastic deformation.The stress/strain curve can be char-acterised in the normal fashion, with,the inclination from the origin (Young’s modulus), one or more

residual strain values and the fracturestress. The degree of plastic defor-mation decreases with increasingcompressive strength.

The compressive strength in-creases with decreasing bindercontent and decreasing grain size.A carbide grade with a small WCgrain size and a low binder contenthas a typical compressive strengthapproaching 7000 N/mm2.

The compressive strength de-creases with increasing temperature.The proportion of plastic deformationincreases dramatically with tempera-ture, leading to a barrel shaped speci-men before fracture, thereby makingresults uncertain.

Shear strengthPure shear tests are difficult to carryout. Studies of fractured pieces, how-ever, indicate that the shear strengthis at the same level, or slightly higher,than that of the tensile strength.

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Compressive strength as a function of the Co contentfor different WC grain sizes.

Compressive strength as a function of the temperaturefor 13% Co, coarse grain size carbide.

N/mm2

% Co by weight

Extra fine

Medium

Extra coarseMedium coarse

F

F

%

Temperature, °C

Compressive strength

Relative compressive strength


Fatigue strengthThe fatigue strength of cementedcarbide under pulsating compressionloading is normally 65-85% of thestatic compressive strength at 2x106

cycles. No definite fatigue strengthlimit, which corresponds to an in-finite life, has been found as in thecase of steel and other metals.

The fatigue strength increaseswith decreasing WC grain size anddecreasing binder content.

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Wöhler curves from compressive fatigue testing ofdifferent carbides. Lower load limit is 250 N/mm2.

Young´s modulus, shear modulus and Poisson’s ratio

Young’s modulus and Poisson’s ratio as a function ofthe Co content.

Cemented carbide is a very rigidmaterial. Its modulus of elasticityor Young´s modulus (E) is 2-3 timeshigher than that of steel and increaseslinearly with decreasing binder con-tent. Additions of �-phase reduceYoung´s modulus. Accurate measure-ments are hard to accomplish bymeans of stress/strain curves alone.Thus, resonance measurements oftransverse or longitudinal waves areused to provide more reliable results.Young´s modulus is determinedaccording to EN 23 312 (ISO 3312).

The shear modulus (G) is bestdetermined in a similar way usingtorsion waves. Values for cementedcarbide lie between 180 and 270kN/mm2.

With E- and G-values, Poisson’sratio (�) can be calculated accordingto the formula:

� = E -12G

N/mm2

Number of loading cycles

Ultra fine, 6 wt-% Co

Fine, 6 wt-% Co

Coarse, 8 wt-% Co

Coarse, 15 wt-% Co

kN/mm2

% Co by weight

E

�

�

Compressive fatigue strength

Young´s modulus and Poisssons´s ratio


Linear expansion coefficientAs tungsten carbide has a very lowlinear expansion coefficient, WC-Co cemented carbides have valuesof approximately half that of ferriticand martensitic steels while the ratioto austenitic steels is about 1:3.

If titanium carbide is included,the values will be slightly higherthan for straight WC-Co cementedcarbides.

Thermal properties

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Density as a function of the Co content.(WC-Co carbides only).

Density is determined according tothe standard EN 23 369 (ISO 3369).The wide variation in the densityof the constituents of cementedcarbide (i.e. WC=15.7 g/cm3,Co=8.9 g/cm3, TaC 13.2 g/cm3 andTiC=4.9 g/cm3) result in large vari-ations in the density of cementedcarbides in line with their compo-sition.

Typically, the density of thecemented carbides can be 50-100%greater than that of the steel. Thisis an important consideration whenweight is a major factor in componentdesign.

Density

Thermal expansion as a function of the Co content fortwo different temperature intervals.

g/cm3

% Co by weight

10-6/°C

% Co by weight

20-800 °C

20-400 °C

Density

Linear expansion coefficient


Thermal conductivityThe thermal conductivity of WC-Co cemented carbides is approxi-mately twice that of unalloyed steelsand one third of that of copper. Thetungsten carbide grain size has aminor effect but the presence of �-phase decreases the thermal con-ductivity considerably.

Specific heat capacityAt room temperature, the specificheat capacity for straight WC-Cogrades is about 150-350 J/(kg•°C),which is nearly half the value ofunalloyed steels.

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Electrical andmagnetic properties

ResistivityWC-Co cemented carbides havelow resistivity and a typical value is20 µ� cm. Cemented carbides with�-phase have a higher resistivity.

ConductivityAs a consequence of the low resis-tivity, the WC-Co cemented carbidesare good conductors, having a valuearound 10% of the copper standard.Alloying with �-phase forming car-bides, e.g. titanium carbide, reducesthis value considerably.

Due to the presence of cobalt(and nickel) in the binder phase,cemented carbides show ferromagne-tic properties at room temperature.

Curie temperatureThe transition of the cobalt binderphase from the ferromagnetic to theparamagnetic state occurs in a tem-perature range between approxi-mately 950 to 1,050 °C dependingon the alloy composition.

PermeabilityAlthough WC-Co cemented carbidescontain a ferromagnetic binder phase,they usually have low magneticpermeability. It increases with thecobalt content and the typical rangeof values is 2 to about 12 when thevacuum value is equal to 1.

Thermal conductivity as a function of temperature,different microstructures and WC grain sizes.

W/(m •°C)

Temperature, °C

CoarseMedium

Fine

Low �-phase content

High �-phase content

Thermal conductivity


Corrosion of cemented carbide leadsgenerally to a surface depletion ofthe binder phase and, thus, the sur-face region will remain only as acarbide skeleton. The bonds betweenadjacent carbide grains are ratherweak and the deterioration rate willincrease accordingly. At low binderphase contents, the carbide skeletonis more developed and, accordingly,such grades exhibit a somewhathigher combined wear and corrosionresistance than corresponding gradeswith higher binder phase contents.

However, in practice, this effectis insufficient to offer a significantlife improvement. The limited cor-rosion resistance of straight WC-Cogrades often makes them unsuitablein applications where the corrosiveconditions are severe. For theseapplications Sandvik has developeda series of highly corrosion resistantgrades.

As shown in the diagram,straight WC-Co grades are resistantdown to pH 7. This is also valid forWC-Co grades containing cubiccarbides like TiC, TaC and NbC.The highest corrosion resistance isobtained for certain alloyed TiC-Nibased grades, which are resistantdown to about pH 1, but comparedto the straight WC-Co grades theyare brittle and have inferior thermalconductivity. They also have thedisadvantages of being difficult togrind and braze and, therefore, theyare only used in specific applica-tions with high demands on cor-rosion and wear resistance but inwhich mechanical strength andthermal shock resistance are lessimportant.

In most corrosion-wear situa-tions, the better choice is speciallyalloyed WC-Ni grades, which areresistant down to pH 2-3. Even incertain solutions with pH valuesless than 2 they have proved to beresistant to corrosion. As they haveWC as the hard principle, and Ni andCo are similar metals in most res-pects, their mechanical and thermalproperties are comparable to thoseof the straight WC-Co grades.

The pH value is one of themost important parameters whendetermining the corrosivity of amedium, but other factors alsohave a major influence, such as thetemperature and the electric con-ductivity of the medium. The latter

is dependent on the ion concentra-tion, i.e. the amount of dissolvedsalts in the solution. Thus, onecannot define the corrosivity of acertain medium in a simple wayand, accordingly, no general rulesare valid in all situations. However,as a first indication of the corrosionresistance of cemented carbides, theSandvik datasheet “Cemented carbideselection guide for corrosion resistance”shows different types of cementedcarbides exposed to some commonmedia.

For a particular choice ofgrade, we recommend that tests arecarried out in the medium consideredor, for orientation only, an analysisof the medium concerned.

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Corrosion resistance

Corrosion rate as a function of the pH value for different types of cementedcarbides tested in buffered solutions. These tests include a final surface weartreatment by tumbling in order to obtain a true value of the depth of thecorroded surface zone.

Corrosion rate

StraightWC-Cogrades

AlloyedWC-Nigrades

AlloyedTiC-Nigrades

Not resistant

Poor resistance

Resistant

High resistance

mm/year

Surface zone with ahigh volume of hardphase (WC) and a lowvolume of binder phase(Co) for increasedwear resistance.Compressive stressesguarantee increasedstrength.

Intermediate zoneenriched with Cobinder phase forhigh toughness.

Core with a Co binderphase content between thatof the two other zones.

Drawing mandrel of DP carbide.


The material properties required inthe core of many products are oftenquite different from those neededin their surface zone or on the verysurface of the finished part.

A stiff and rigid body mightbe needed from a mechanical pointof view, but high wear and corrosionresistance might be equally importantservice requirements for the compo-nent. Materials which meet thesedifferent demands do not necessarilyneed to have the same compositionand microstructure throughout thewhole body.

Compound steel is one exampleof a material which has been usedfor a long time to combine cheapand strong bulk materials with highlyalloyed and expensive corrosion-resistant surface materials. Similar

materials have also been developedfor cutting tool applications wherea thin coating offers suitable wearresistance and a cemented carbidethe mechanical strength needed inheavy operations. For wear parts,the situation is often very similar. Inthe case of a mandrel, the wearresistance of the surface is veryimportant but at the same timetoughness and mechanical strengthare needed to support the surfacezone. The wear on mineral tools andhighway engineering tools is oftensevere and requires high tool hard-ness, but a high tool toughness isalso needed to withstand shockloads.

As a result of an extensive re-search and development programme,Sandvik Hard Materials has intro-

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Gradient andcompound materials

duced two product concepts to offersolutions to such problems. Solutionswhich offer unique properties andwhich are not achieved with a singlehomogenous material.

The first group is based on theSandvik DP-carbide, which is com-posed of a cemented carbide withdifferent amounts of hard constituentsin the surface and the core to achievethe optimum combination of hard-ness, wear resistance and toughness.

The other group consists of acompound material – Sandvik Cast-in Carbide. This material is a combi-nation of two different materials, astiff and wear-resistant cementedcarbide, supported by tough castiron which is less expensive andeasier to machine.


For conventional cemented carbides,wear resistance and toughness arerelated in such a manner that animprovement in one property resultsin a deterioration in the other.

Sandvik has developed an en-tirely new type of WC-Co cementedcarbide in which wear resistanceand toughness can be improved in-dependently of each other. By meansof a controlled redistribution of thecobalt binder phase, cemented car-bide components can now be madewhich contain three distinct micro-structural zones, each of which hasdifferent properties. These gradients,together with the differences in ther-mal expansion, redistribute theinternal stresses. For example, it ispossible to create a very hard andwear-resistant surface layer whichis simultaneously pre-loaded withcompressive stresses to prevent theinitiation and propagation of cracks.

A carbide having such a distri-bution of properties has high wearresistance at the surface combined

with a tough core. These materialshave therefore been given the desig-nation DP – Dual Property. Theirinitial application area was in rockdrilling. Other applications, such astools for tube and wire drawingand cold heading dies, have alsoconfirmed improved performance.

The DP concept is covered bySandvik patents.

SANCIC – Sandvik Cast-inCarbideBy utilising granules or tiles ofcemented carbide as reinforcementof a cast iron surface, a new gene-ration of composite materials hasbeen developed. The high wearresistance of cemented carbide iscombined with the strength andtoughness of cast iron.

In the casting process a strongmetallurgical bond is establishedbetween the carbide and the iron.Granules are mainly used in products

exposed to high impact. Tiles areused in high erosion fields or togain sharp edges and corners. Gra-nules and tiles can, of course, bemixed in the same product.

The granules account for about50% of the volume in the compositezone and have an average size of 1-6mm.

A typical SANCIC product hasa wear resistance close to that ofsolid cemented carbide and 80-90 %of the strength of pure nodular castiron. Toughness is maintained withinthe range expected from conventionalengineering steels and as such con-siderably outperforms the highchromium and high nickel cast ironalloys.

SANCIC products have a wearresistance which is typically 3-15times that of conventional solutionsin steel, cast iron and designs withhardfacing or ceramics. SANCICcan be utilised in most componentshapes and sizes.

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Cemented carbide granules Cemented carbide tiles

Nodular cast iron

SANCIC is produced in the form of composite or clad material. In thefirst case, cemented carbide granules are cast together with nodular iron.Alternatively, cemented carbide tiles are embedded in the exposed surfacezone of the base material. The casting method used in both cases providesa metallurgical bond between the cemented carbide and the basematerial.

Sandvik DP Carbide

Young´s modulusCompressive strength


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Cemented carbide in comparisonwith other materials

Hardness

WC-Co

SiC

Al2O3

Al2O3

WC-Co

SiC

Si3N4

WC-Co

Al2O3

SiC

Toughness

WC-Co

Al2O3SiC

Steels

StellitesCast iron

Cast iron

Stellites

Cast iron

Steels

Stellites

Cast ironSteelsStellites

HV50

N/mm2 kN/mm2

MN/m3/2

The design and construction of com-ponents for demanding technicalapplications, frequently requiresmaterials with unique combinationsof properties. Finding the optimumsolution is not an easy task and theengineer has to have a broad know-ledge of many different groups of

materials. Cemented carbides have aunique combination of propertiesand can be the optimum solution inmany cases. To make your choiceeasier, the following tables areoffered as a guideline, with theproperties of WC-Co cementedcarbides compared with those of

some other materials. Note, forinstance, the interesting combinationof high compressive strength, rigid-ity, hardness and low thermal ex-pansion as well as the high electricaland thermal conductivity offeredby WC-Co cemented carbides.

Electrical resisitivity

Thermal conductivity

Density


19

Data on properties and Recommendations StatementThe properties and data listed in this brochure represent averagevalues based on laboratory tests conducted by the manufacturer. Theyare indicative only of the results obtained in such tests and should notbe considered as guaranteed values. Any statements in this brochurereferring to a specific alloy for a particular application, or to the useof one of our products, are merely recommendations based onmanufacturer tests or experience. Therefore, such statements cannot beconsidered as warranties. Our products, and any recommendedpractices, should be tested by the user under actual service conditionsto determine their suitability for any particular purpose.

g/cm3

WC-Co

µ�cm

WC-Co

CuAl

SiC

Al2O3

10-6/°C

WC-CoAl2O3

SiC

WC-Co

SiC

Al2O3

�

WC-Co SiC

Al2O3

W/(m•°C)

Cast ironSteelsStellites

Cast iron

SteelsStellites

Cast iron SteelsStellites

Cast iron

Steels

Stellites

Cast ironSteels

Stellites

Poisson´s ratio

Linear expansion coefficient

Sandvik Hard Materials in brief

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The Sandvik Group, established in 1862 and headquartered in Sandviken, is one of Sweden´s largestexport companies with more than 300 wholly owned subsidiaries and representation in 130 countries.The Group has annual sales of SEK 40 billion, with 34,000 employees. More than 90% of sales are tocustomers outside Sweden. Sandvik is highly research-oriented. Investments in R&D related to newproducts and processes amount to approximately SEK 1.6 billion annually.

THE SANDVIK GROUP

The Sandvik Group’s operations are based on three core business areas: Sandvik Tooling (SandvikHard Materials, Sandvik Coromant and CTT Tools), Sandvik Specialty Steels (Sandvik Steel, SandvikProcess Systems and Kanthal) and Sandvik Mining and Construction (Sandvik Tamrock, VoestAlpine-Eimco, Driltech Mission and Roxon).

Sandvik Hard Materials supplies a wide range of cemented carbide products from more than tenmanufacturing plants around the world.

BLANKS FOR TOOLMAKERS

The toolmaking industry is supplied with blanks or semifinished cemented carbide products for cuttingand forming metals, composite materials, wood, bricks, concrete and rock. Tool blanks are available inthe form of rods, saw tips, drill tips, discs and inserts in designs and dimensions based on industrystandards.

ENGINEERING COMPONENTS

Cemented carbide is often the only material that can satisfactorily withstand wear in addition todeformation, impact, heavy load, high pressure, corrosion and high temperature. In this area, weprovide the industry with carbide components such as seal rings, bearings, pistons, valves and nozzles.

ROLLS FOR THE STEEL INDUSTRY

Sandvik Hard Materials has long held a leading position as a supplier of solid cemented carbide rolls forthe steel industry. Composite rolls based on cemented carbide and nodular cast-iron represent a newspeciality in this field.

NOT JUST CEMENTED CARBIDE

The operations of Sandvik Hard Materials also encompass the manufacture of products in new hardmaterials, for example, PCD (polycrystalline diamond) and PCBN (polycrystalline cubic boron nitride).

• Argentina: 01-484 32 41 • Australia: 049-24 21 00 • Austria: 1-277 37 • Belgium/Luxembourg: 02-702 98 50 • Brazil: 011-525 26 11 / 011-55 11 55 26

• Canada: +1-800-533-6067 • Chile: 2-623 54 43 • China: 10-6590 86 00 • Czech Republic: 02 2425 33 11 • Denmark: +46-8-726 63 00 • Estonia: +46-8-726 63 00

• Finland: 09-87 06 61 • France: 04-75 31 38 00 • Germany: 0211-502 75 57 • Hungary: 1-269 63 91 • India: 020-7 14 64 91 • Indonesia: 021-830 84 11 • Ireland: 01-295 20 52

• Italy: 02-30 70 51 • Japan: 078-992 09 92 • Korea: 02-785 17 61 • Lithuania: +46-8-726 63 00 • Latvia: +46-8-726 63 00 • Malaysia: 03-756 21 36 • Mexico: 05-729 39 00

• Netherlands: +32-02-702 98 50 • New Zealand: +61-02-49 24 21 00 • Norway: +46-8-726 63 00 • Philippines: 02-807 63 72 • Peru: 1252-1111 • Poland: 22 43 21 51

• Portugal: +34-93-86 29 413 • Singapore: 265 22 77 • Slovak Republic: 02 73 54 86 • South Africa: 011-914 34 00 • Spain: 93-862 94 00 • Sweden: 08-726 63 00

• Switzerland: 056-417 61 11 • Taiwan: 03-452 31 72 • Thailand: 02-379 44 61 • Turkey: +43-1-277 37 • UK: 02476-85 69 00 • USA: 800-343 06 36 • Venezuela: 02-93 09 22

www.hardmaterials.sandvik.com

Documents

Understanding Cemented Carbide · 12/5/2016 · basic cemented carbide structure from which other types of cemented carbide have been developed. In addition to the straight tungsten