carbide grade design. © 2010 kennametal inc. l all rights reserved. l proprietary and confidential...

Carbide Grade Design

© 2010 Kennametal Inc. l All rights reserved. l Proprietary and Confidential l 2 of 47

FEED, DOC, Interruptions (Fracture Resistance)

SPEEDThermal

DeformationResistance

Superhards (PCD, PCBN)

Ceramics

CermetsCoated

Carbides Co-HSS HSS

Cutting Tool Materials


Cutting Material Market Share

HSS

Carbide

Adv. Mtls

0

20

40

60

80

100

1990 2000 2010

Adv. Mtls

$.8 B ==> $1.8 B

CAGR = 9.3%

Total Market

$8.6 B => $12.1B

CAGR = 3.5%


• Substrate– Deformation resistance, fracture resistance,

thermal & mechanical shock resistance

• Coating– Wear resistance, lubricity, reduced frictional heat,

surface finish

• Macro-geometry– Chip control, cutting efficiency

• Micro-geometry (Edge Preparation)– Cutting force, surface finish

Cutting Tool Development – A Systems Approach


Basic Substrate Elements

W Tungsten

C Carbon

WC Tungsten Carbide

Co Cobalt Binder

Hard


Cemented Carbide(Hard carbide particles bound or cemented by soft binder such as cobalt)

WC

Co

Basic Substrate Elements


Cemented Carbides

Straight carbides WC-Co(Cast iron &

Non-ferrous alloymachining)

Mixed carbidesWC-(W,Ti,Ta,Nb)C-Co

(Steel machining)


Composition / Grain Size vs. Properties

Fine grained

(1 µm)

Coarse grained

(5 µm)

1 5 µm

5 12%5 - 12% Cobalt

1 5 µmWC grain size

5 - 12% Cobalt and 1-5 µm carbide grain size


Hardness

• Determines resistance to abrasive wear– Higher hardness at higher abrasion resistance

• Depends on:– Composition

(primarily WC content)– Microstructure

(WC grain size)

• Measured by Rockwellor Vicker’s method


High Temperature Hardness

Hardness decreases steadily with increasing temperatures

Micro hardness based on 1kg load

Grades with medium WC grain size

A: WC-3CoB: WC-6CoC: WC-12(Ti,Ta,Nb)C-8CoD: WC-2TaC-12Co

% of Cobalt


Compressive Strength

• Measure of deformationresistance

• Compressive strength ofcarbide is higher than mostother materials

• Like hardness, compressivestrength decreases with increasing cobalt, increasing grain size, or increasing temperatures

Carbide inserts get their strength for their thickness


Transverse Rupture Strength

• TRS measures the bending fracture strength of carbides

• TRS = f (composition, microstructure, porosity)

• Excellent quality control tool


Transverse Rupture Strength

Straight WC-Co Alloys


Fracture Toughness

• Measures resistance to fracture• Determines intrinsic tool toughness• Less sensitive than TRS to

– Specimen size and geometry– Surface finish– Flaws such as porosity

• Depends on:– Composition (more cobalt higher toughness)– Grain size (coarser grains higher toughness)


Fracture Toughness

Fracture toughness increases as Co% and WC grain size increase.


Thermal Shock Resistance

• Required in operations like milling• No laboratory test developed yet• Various empirical parameters used

e.g. KIc • k

E • awhere KIc

= fracture toughness

k = thermal conductivityE = Young’s modulusa = thermal expansion coefficient


Engineered Substrates: Cobalt-Enrichment

Strength (toughness) of WC-Co tools is a strong function of cobalt content.

Str

en

gth

/To

ug

hn

ess

(Re

sis

tan

ce t

o

Fra

ctu

re)

% Cobalt


Cobalt - Enrichment Technology

• Higher cobalt (& lower or no cubic carbides) at the insert periphery gives high edge strength while the bulk with lower Co provides deformation resistance

• Applicable to a broad range of machining


Cobalt - Enriched Tool


Tool Material Design

Metalcutting environment:

– heat (thermal deformation)

– pressure (deformation, fracture)

– wear (pure abrasion, chemical wear, notching)

– interrupted cuts (thermal & mechanical cycling)

Substrate Property Considerations in Tool Material Design

Turning / Drilling:– High speed finishing requires deformation

resistant substrate – General purpose machining requires an optimum

combination of deformation resistance and edge strength

– Roughing operations require bulk toughness



Milling:– Since milling involves thermal and mechanical

cycles, the cutting tool is subjected to thermo-mechanical fatigue.

– Low magnetic saturation alloys have higher resistance to crack initiation arising from thermal fatigue.

– Higher cobalt contents impart resistance to mechanical fatigue.



Milling:– For finish milling, choose a substrate with high

Transverse Rupture Strength (TRS).– For general purpose milling, select a tool with high

cobalt and cubic carbides (dry milling) or no cubic carbides (wet milling).

– Rough milling operations require straight WC-Co grades.


CVD-Coated Tools

• CVD-coated carbides comprise ~70% of all coatedWC-Co tools.

• Employed in a variety of applications: turning,boring, threading, grooving, parting, and milling

• Used in machining of carbon, alloy, and stainlesssteels, gray & ductile irons, and Ni-based alloysover a range of speeds and feeds.


CVD-Coated Tools with Cobalt-Enriched Substrates

• These tools combine the wear resistance of hardcoatings with edge-toughened substrate

• Broad applications (medium to heavy roughing to semi-finishing operations)

• Machining of carbon, alloy, and stainless steels,gray and ductile cast irons, and high temperature alloys


Medium-Temperature CVD Coated Tools

• Microstructures of these tools show negligibleeta phase at the coating-substrate interface.

• Generally exhibits columnar microstructure.

• Suitable for roughing to finish machiningover a wide range of workpiece materials


PVD-Coated Tools

• Advantages: Smooth, low-friction, fine-grained, and crack-free coating even over sharp edges with compressive residual stresses

• Lower cutting forces with sharp edged tools

• Reduced tool-tip temperatures

• Finer workpiece finish


Coating Property Considerations in Tool Material Design

• TiC: Applied by CVD. High hardness at lower temperatures but hardness decreases rapidly with increasing temperature. Good for abrasive wear resistance.

• TiN: (CVD or PVD) Less hard than TiC. Often used as top coating layer for cosmetic appeal and used edge identification. Also used as interlayers between other coatings to refine grain size and possibly enhance adherence. Chemically more stable than TiC.


Coating Property Considerations in Tool Material Design

• TiCN: Applied by the normal temperature or medium temperature CVD, or PVD process. Intermediate in hardness between TiC and TiN. Has good balance of abrasion resistance and toughness.

• Al2O3: Not as hard as Ti-based coatings at lower temperatures, but harder at higher temperatures. Has high chemical stability (excellent resistance to crater wear and notching).


Application of CVD Coated Tools

Turning 1045 steel with 2.5mm doc and 0.40mm/rev feed rate(Tool life based on 0.25mm flank wear)


PVD-Coated Tools

• Particularly useful in threading, grooving, parting, finish-turning, milling, and drilling operations

• Typical workpiece materials:– Carbon, alloy, and stainless steels– hardened steels– high-temperature alloys– titanium alloys

carbide grade design. © 2010 kennametal inc. l all rights reserved. l proprietary and confidential...

Documents

cobalt slide

cobalt wc

carbide grain size slide

alloys slide

thickness slide

medium wc grain size

carbide grade design

steel machining slide