sci course lecture-1

R&D-PRC-SRC

Surface Conditioning & Interaction courseFocus areas: Rolls, Defects & Inspection

Champion: Sudhansu Pathak

Lecturer: Dr Henk Bolt & Dr Lene Hviid

March 2013 - Jamshedpur

2Surface Conditioning & Interaction course

Time schedule

1. Rolls training2. SIS training



Two sessionsin plants (choice)

7th of March

15.00 to

16.00

LUNCH

11.30 to

12.45

BREAK

10.45 to

11.30

BREAK

9.00 to 10.30Thursday

Exercise customer defect

complaint

Lec. 8 A3 solving method for defects

Lec. 7Inspection & Coilgrading

Lec. 6 Surface

inspection and control

Lec. 5 Quality controlSDC

6th of March

16.15 to

17.15

BREAK

15.00 to

16.00

LUNCH

11.30 to

12.45

BREAK

10.45 to

11.30

BREAK

9.00 to 10.30Wednesday

Exercise Rolls/lubric. problem

Lec. 4Lubrication

Lec. 3 Rolls failure

& Rolls database

Lec. 2Performance of rolls & surface

Lec. 1Importance of Rolls

5th of March

16.15 to

17.15

BREAK

15.00 to

16.00

LUNCH

11.30 to

12.45

BREAK

10.45 to

11.30

BREAK

9.00 to 10.30Tuesday

3Rolling Mill Rolls are high-impact key assets

the work horses of any rolling mill

This lecture will highlight the importance & impact of rolls in multiple

aspects costs, product quality, process & daily operations, supply security

A focus on rolling mill rolls within Tata Steel

Importance of Rolling Mill RollsLecture 1

5Importance of Rolls

Supply security

Ensure rolls are defect-free & fit-for-purpose

roll shop operations transport, handling, storage

roll inspection

Heart of the rolling process

Harsh operating conditions

Impact on product quality

Cooling/mill hardware & scheduling requirements

High total cost of ownership

Impact on mill operations,downtime, capacity, capability

Roll failure risk

6 Rolls technology: Core area for Tata Steel mills and R&D Rolls procurement: Strategic function with lead buyer for Tata Steel Group

Rolls: high-impact key assets for rolling mills

High costs roll purchasing roll shop texturing, Cr-platingmill downtime for rollchanges & failuresworking capital tied upin roll fleetstorage space

High impact on

product quality surface defects rougness / texturetransferstrip gauge & shape rollability of product mix

High impact on

operational levelmill scheduling /planned roll changesunplanned roll changessafety aspects, rollfailures & preventionmill pacingmill vibrations, frictioncooling requirements transport/handling

Supply security lead times can be verylong & roll consumptioncan fluctuatemills require tailoredroll properties ratherthan off-the-shelfproducts from rollsuppliers

Roll use = core competency for Tata Steel rolling mills cannot be left / outsourced successfully to third parties

Need for cooperationwith top quality roll suppliers

Importance of rolls

7 Rolls technology: Core area for Tata Steel mills and R&D Rolls procurement: Strategic function with lead buyer for Tata Steel Group



High impact on


High impact on





Importance of rolls

8Financial impact of roll use in tandem cold strip mills

Roll costs per tonne - year 2003 .

0

2

4

6

8

10

Port Talbot Llanwern CSPY- CM21 CPP-

IJmuiden-

CM11

CPP-

IJmuiden-

CM12

p

o

u

n

d

s

p

e

r

t

o

n

n

e

Miscellaneous, chocks, ..

Roll stock costs

Mill downtime costs

Roll shop costs

Material costs

not included: cost of roll-related coil rejections / repairs / downgrading consequential damage of roll failures (other than loss of roll life)

roll purchasing costs of new rolls constitute only a minority fraction of the total costs of roll usage (TCO = total cost of ownership).

9Financial impact of roll use in HSMs

total roll-related costs in Corus Hot strip mills;

year=2004

0

2.000.000

4.000.000

6.000.000

8.000.000

10.000.000

12.000.000

14.000.000

16.000.000

18.000.000

20.000.000

HSM

Port Talbot

HSM

Llanwern

HSM2

IJmuiden

t

o

t

a

l

r

o

l

l

-

r

e

l

a

t

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c

o

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t

s

Mill downtime costs for roll changes

Miscellaneous, chocks, ..

Roll stock costs

Roll shop costs

Roll material costs

roll-related costs per tonne in Corus Hot strip mills;

year=2004

0

1

2

3

4

5

6

HSM

Port Talbot

HSM

Llanwern

HSM2

IJmuiden

r

o

l

l

-

r

e

l

a

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d

c

o

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t

s

p

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t

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n

e

Mill downtime

costs for roll

changes

Miscellaneous,

chocks, ..

Roll stock

costs

Roll shop

costs

Roll material

costs

roll material costs per tonne

in Corus Hot strip mills; year=2004

0,00

0,50

1,00

1,50

2,00

2,50

3,00

HSM Port Talbot HSM Llanwern HSM2 IJmuiden DSP

IJmuiden

r

o

l

l

m

a

t

e

r

i

a

l

c

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t

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p

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Edger & HSB rolls

Back-up Rolls

Rear Finishing Mill Work Rolls (EC/IC)

Early Finishing Mill Work Rolls (HiCr/HSS)

Roughing Mill Work Rolls

roll material costs per km strip

in Corus Hot strip mills; year=2004

10

20

30

40

50

HSM Port Talbot HSM Llanwern HSM2 IJmuiden DSP

IJmuiden

r

o

l

l

m

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p

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p

Edger & HSB rolls

Back-up Rolls

Rear Finishing Mill

Work Rolls (EC/IC)

Early Finishing Mill

Work Rolls (HiCr/HSS)

Roughing Mill Work

Rolls

10

Raw material price development

TSG-SDS raw material prices

0

10

20

30

40

50

60

70

80

90

100

dec-03

jun-04

dec-04

jun-05

dec-05

jun-06

dec-06

jun-07

dec-07

jun-08

dec-08

jun-09

dec-09

jun-10

dec-10

N

i

,

M

o

,

V

p

r

i

c

e

s

i

n

/

k

g

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

C

r

,

s

t

e

e

l

s

c

r

a

p

p

r

i

c

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s

i

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/

k

g

NickelMolybdenumVanadiumChrome

Steel Scrap

TSG-SDS raw material price indices

(April-2010 = 100)

0

50

100

150

200

250

300

350

400

dec-03

jun-04

dec-04

jun-05

dec-05

jun-06

dec-06

jun-07

dec-07

jun-08

dec-08

jun-09

dec-09

jun-10

dec-10

p

r

i

c

e

i

n

d

e

x

Nickel

Molybdenum

Vanadium

Chrome

Steel Scrap

Raw material price fluctuations large impact on roll prices

11

Rolls procurement in TSG (May 2011)

Spend: estimated at US$ 100 Million per annum on rolls in TSG

Since May 2011: Some decrease in roll spend (TSE: less roll consumption & destocking; raw material prices ) Forecast FY14, FY15: again around US$ 100 Million (with bigger share for TSL: more mill output)

Mills/works: > 50 mills/works across TSG using rolls

Items: > 1,000 different roll items across TSG

Delivery times: Ranging from 3 months for small rolls (mainly for long product mills) to >3 years for large (back-up) rolls

$20,800,000

$80,500,000

Asia

Europe

$3,100,000

$18,400,000

$35,500,000

$21,700,000

$22,600,000

Tungsten carbidediscs

Static castrolls/sleeves

Spin cast work rolls

Forged work &intermediate rolls

Cast & forged back-up rolls

12

Rolls technology: Core area for Tata Steel mills and R&D Rolls procurement: Strategic function with lead buyer for Tata Steel Group



High impact on


High impact on





Importance of rolls

13

Supply security

Unique geometrical designper mill and per roll type

Rolls tailor-made to customers order

Lead times can be very long

+

Fluctuating roll consumption rates

Rolling mill rolls are not available of-the-shelf

Variations in mill output, product mix, rolling process, mill condition, excess

roll consumption

challenging task to ensure that: mills will always have sufficient rolls to keep on rolling

whilst avoiding excessive stock

Once, work rolls were transported

by airplane from Brazil (!) to

The Netherlands to prevent DSP

mill stoppage due to lack of rolls

14

Supply security tailored rolls

mill-specific roll requirements (microstructural) material properties

A successful roll grade in a certain mill may perform poorly or even fail in a different rolling application

standard roll grades offered by suppliers still need to be fine-tuned

especially for more demanding rolling applications

Maintain fruitful bilateral relations with several key roll suppliers

ensure an adequate level of technology exchange

roll supplier needs to know the mill and grasp its key requirements

roll user should understand the capabilities and limitations of the roll manufacturer

15




High impact on


High impact on





Importance of rolls

16

High impact of Rolls on product quality

(1) Gauge & shape

Rolls are the work horses of any rolling mill

The tool to deform slab, bar or strip dimensions required for the customer or for downstream operations.

Gauge & shape control within tight tolerances roll wear (work rolls, intermediate rolls, back-up rolls) has to be sufficiently low and

homogeneous

Work roll change build-up of thermal crown thermal properties of roll important Cold rolling: rapid build-up of a stable thermal crown required to limit length of out-of-

tolerance strip. Hot rolling: shape actuators must be able to compensate for thermal crown

17


(2) Surface properties

Work rolls critical influence on surface properties of rolled steel product

transfer of roughness / texture to the strip surface visual appearance processability in downstream/customer operations, coating thickness requirements

Trend: customer expectations requirements regarding strip surface roughness / texture E.g. automotive market: narrow Ra range combined with

high Peak Count (>75 cm-1 at bandwidth 1 m)

Rollrelated surface defects due to roll marks excessive roll wear premature work roll surface degradation

Tata Safari

18


(3) Tribological aspects

Work rolls = key component in tribosystem:

strip work roll lubricant (if any) process/loads

strip and the work roll may be coated. This coating may also be an oxide layer.

Lubricant may also be water

Tribo-system governs important parameters such as strip cleanliness and friction level in the mill requires insight in role & properties of work rolls. Some Cold Mills are using Cr-plated work rolls to avoid poor strip cleanliness

Cr-plating from Cr(VI) SHE issue restrictive EU legislation need for alternatives

DSP IJmuiden cannot use certain HSS rolls due to high friction/mill vibrations

Friction level roll properties mill force and power requirements

product rollability limits for a mill (grade/gauge/width-combinations)

Roll design limits can be more restrictive for product rollability than mill power

19




High impact on


High impact on





Importance of rolls

20

High impact of Rolls on operational level

(1) scheduled roll changes

Mill operations generally scheduled into rolling campaigns

work roll changes scheduled before each new campaign

maximum # coils & sequence of coils to be rolled within a campaign are strongly determined by the behaviour, capabilities and limitations of the work rolls

some mills: different campaign types with different work roll requirements

ground cambers

surface finish

Work rolls determining factor for mill logistics

Work roll changes = daily routine at mills

frequencies up to several times per shift depending on the mill type and campaign type

Trend in certain markets customers requesting smaller orders with shorter lead times

some mills confronted with shorter average campaign length roll change frequency

due to logistical constraints regarding the coil sequence in a campaign

Aspirational target: Schedule-free rolling

eliminate (majority of) planned work roll changes

allow maximum scheduling freedom

Mills will generally not be able to implement schedule-free rolling with current roll fleet development, trialling and implementation of new work roll types

21


(2) unplanned roll changes

unplanned roll changes disturb the normal routine

disproportionally high effect on mill operations

Particularly in cases of roll failure / serious roll damage occurs

extensive mill downtime

effort to remove havoc & get mill ready for restart

Disturbance of upstream operations are also disturbed

E.g: roll failure in DSP / TSCR mill abortion of casting process; slabs in furnace scrapped

Special safety precautions required in cases of spallings or serious damage of a roll type with high residual stresses

compressive stress levels 500 MPa at the hardened barrel surface

forged rolls

CPC-HSS rolls

22


(3) roll shop operations

Roll shop comprises large & vital part of operations associated with any rolling mill

Roll shop task: ensure that rolls are prepared correctly & in time for next rolling campaign.

This includes:

Adequate redressing of the barrel surface remove surface layers affected by wear, thermal fatigue and work hardening

Application of the correct ground profile and surface finish

Routine Non-Destructive Testing (NDT) of rolls before each new rolling campaign shield the mill from potential harmful incidents caused by rolls with a defect or remnant damage

from a previous mill incidents

Perform/arrange roll repairs salvaging of damaged rolls arrange repair of rolls with worn journals

Mounting and dismounting of roll sets

(Re)chamfering barrel edges

Roll fleet management

23


(4) transport + handling

extensive transport & handling operations associated with roll usage inside roll shops as well as between the roll shop and the mill

Frequent roll changesComprehensive (roll shop)

activities on each roll+

Even more for some mills not located in same building as their roll shop Sometimes routine transport of rolls via public motorways

Some roll shops are serving multiple mills complex logistics, operations & roll fleet management E.g: Cold Strip Mill IJmuiden roll shop, serving:

CM21, CM22, TM21, HDGLines#1,#2,#3 IJmuiden Segal HDGLine in Lige HDGLine in Moerdijk (JV Wupperman/Tata Steel) BUR grinder also in use for other mills

M4 motorway between Llanwern

and Port Talbot (100 km)

24

High impact of Rolls on operational level(5) implications for mill hardware & process

Work roll cooling essential for all hot & cold rolling mill

Carefully designed cooling systems high, stable & homogeneous heat transfer Optimum coolant flow rates are (a.o.) dependent on work roll properties & rolling speed Inhomogeneous cooling can lead to

premature local roll surface degradation strip surface defects poor strip shape rolling process instability

Roll cooling systems must also exhibit a very high reliability complete roll cooling system failure (e.g. valve not opening) or even partial roll cooling failure (e.g. blocked nozzles)

Hot rolling: additional strip surface cooling devices also required interstand cooling, chilling/skin cooling headers (a.k.a. anti-peeling headers), edge spays

suppress formation of Fe2O3-rich oxide scale abrasive for work roll surface diminish thermal degradation of the work roll barrel avoid roll-in oxide defects on the strip surface.

Also in this respect, work roll properties are important, as they influence the optimum strip cooling requirements, and determine the resilience of the work rolls if the mill is operating outside the optimum window respect to strip

cooling/strip surface temperature

rapid catastrophic roll failure

25


(7) friction, chattering, rolling loads limitations

Friction work roll properties A change in work roll material properties can substantially affect the friction coefficient

E.g. HSMs experience: HiCr Iron work rolls HSS work rolls friction

Friction at mill campaign start behaviour of the roll in the grinding process

friction evolution during rolling campaign work roll surface evolution

In some mills, chattering (mill vibrations) is a serious problem related to the previous topic friction and dependent on work roll properties

Roll material strength limits impose maxima to rolling loads

maximum allowable torque, bending force, total and specific rolling forces, rolling pressure, and Hertzian contact stress.

installed mill power can exceed strengthlimits of rolls.

6-high mill with IMR shifting asymmetrical distribution of loads and contact stresses can easily lead to exceeding the rolls Hertzian stress limit.

changes in product mix and/or rolling practice roll fleet still fit-for-purpose?

26

Roll change reasons Hot Strip Mills (2004)

CSPY - HSM2

8%

5%

8%

0,02%

80%

0,3%

0,27%

5,2%

0,02%

0,09%0,6%

1,1% 0,005%

0,25%

CSPY - DSPheavy bruise

0,1%

medium/heavybanding

9%

Fire cracks0,6%

Defect freeor orange peel

70%

Other30%

tail marks6%

Vibration/grinding lines

0,7%

medium/heavycomets2%

light comets4%

light banding7%

End of programme (EOP)

EOP for logistics

IRC - planned

IRC - extra

BUR change

Shape

Slip / skids / roughness deviation

Vibrations / shudder

Cobble

Pinch / tail marks

Other roll marks / rolling incidents

Roll failure in mill (spall etc.)

Bearing failure

Firecracks

Other reasons

Defect free or orange peel

Fire cracks

light banding

medium/heavy banding

tail marks

heavy bruise

Vibration/grinding lines

light comets

medium/heavy comets

CSP-UK Hot Strip Mill Llanwern

0,11%

14,4%

0,42%

0,48%

0,44%

1,5%

84,2%

0,02%

HSM Port Talbot

0,4%

0,06%

7%

0,03%

0,01%

0,06%

0,04%

0,08%

68%

25%

0,08%

0,02%

27

CSPY - Cold Mill 21

reasons for work roll changes

2003

End of program / Tonnage

43%

Pinch10%

Roughness

20%


1%

Bruises / cracks

0%

Burr marks

3%

Strip break

1%

Too fast out ("uitloper")

1%

Slip / skids

1%

Shape1%

Weld break

2%

Lines / streaks

1%

Other marks

(imprints/drag/pits/...)

13%

Other reasons

3%

End of program / Tonnage

Strip break

Weld break

Pinch

Burr marks

Bruises / cracks

Other marks(imprints/drag/pits/...)Lines / streaks


Too fast out ("uitloper")

Slip / skids

Roughness

Shape

Other reasons

Roll change reasons

Cold Mill 21 IJmuiden

discontinuous sheet mill

28

Roll Property Requirements - summary

Tensile strength Torsional strength Bending strength Toughness Ductility Fatigue strength Thermal shock resistance

Wear Resistance Cold mills, temper mills: good roughness and texture

retention Hot mills: abrasion resistance, thermal fatigue/

degradation resistance

Resistance to indentation / marks Corrosion resistance / ability to form a stable thin

oxide layer (hot mills) Resistance to bruising Resistance to localised overheating

Resistance to spalling Machinability/Grindability Strip cleanliness not jeopardised

Roll Core Roll Surface

Roll total

Resistance to catastrophic fracture Resistance to roll flattening Fast build-up of steady-state thermal crown Resistance to high contact pressures Value-for-money

29

Balancing roll requirements

Seemingly conflicting roll requirements need to be reconciled; roll properties need to be balanced for each application:

Roll barrel shell relatively hard; roll core&neck tough Compressive stresses in hardened shell tensile stresses underneath

Barrel hardness:WR (temper mil) > WR (cold strip mill) > IMR > BUR

Use of Cr-plated work rolls: to improve roughness/texture retention particularly for temper mills, sometimes tandem mills

for certain cold rolling mills strip cleanliness is a motivation expensive: not always cost-effective Cr(VI) bath => SHE issue.

30

Work rolls:

Balance wear resistance and incident resistance

mill / stand mapping

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Mill 2

roll mapping

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old rolls generation

current rolls generation

future rolls generation

developmentRoll type 2

Roll

type 1Match mill & roll

Match mill & roll


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Mill 2


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Mill 1

Mill 2

roll mapping

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Roll

type 1

roll mapping

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Roll

type 1Match mill & roll

Match mill & roll

31

Back-Up Rolls:

Cast versus Forged Back-Up Rolls

Primary concerns that affect BUR performance Bruises / impressions Wear Rolling contact fatigue

Lightly loaded mills (e.g. temper mills, DCR mills): cast iron back-up rolls make use of low wear rates offered by these grades

Heavy mill loads forged steel back-up rolls refined grain structure; induced longitudinal grain flow increased fatigue resistance / incident resistance

Cast steel back-up rolls: intermediate case.

32

Some typical roll chemistries

< 1.5 Nb< 10.2 14 - 51.5 2.53 3.5Enhanced AIC

(super nickel grain iron)

< 0.1< 0.10.2 0.54 - 51.5 2.53 3.5alloy indefinite chill (AIC) iron

(nickel grain iron)

0.21 W0.2 - 12 - 40.5 1.511 - 141.5 - 2Cast HiCr steel

1 - 2

1 - 2

0.2 2

0.5 2

0.5 1.5

Ni

(%)

< 0.1< 0.10.5 217 - 192.8Cast HiCr iron

< 0.1< 0.10.1 - 0.61.5 - 60.7 - 1.0standard forged steel

< 1 W0.5 - 10.5 - 24 - 100.5 - 1.0forged semi-HSS

< 2 W0.5 - 30.5 - 38 - 130.8 - 1.5Forged HSS

2 8 W2 - 82 - 84 - 81 2Cast HSS

W / Nb

(%)

V

(%)

Mo

(%)

Cr

(%)

C

(%)Grade

Each rolling application requires tailored roll properties Wide variety of roll manufacturing routes, chemistries, heat treatments, microstructures

33

Schematic of Static Single Pour and Static Double Pour

Techniques

Static Single Pour Casting

Static Double Pour Casting

34

Schematic of Centrifugal Casting

Shell pouring during fast spinning

Solidified shellShell solidifies

Core top poured and spinning decreased

35

Schematic manufacturing route for forged rolls

Hardening

ESR (electroslag refining)

36

Electroslag Refining (ESR)

Molten electro-slag

Water cooled rising mould

Liquid steel

Solidified refined ingot

Benefits: Purification Steel structure

Application of ESR: In case of high content of alloying elements In case of high surface qualityrequirements (e.g. Al foil) For deep hardened rolls For roll conversion

Consumable electrode

37

Hardening and tempering

Elemental steps in hardening process: Austenising

roll heated above -Fe/-Fe transition temperature Quenching

water quench cryogenic cooling formation of Martensite & a small percentage of retained -Fe roll shell is hard but brittle

Tempering controlled softening; roll becomes less brittle

Differential hardening (neck isolated from barrel)

Hardening furnaces classical furnace static induction hardening dynamic induction hardening (single or double frequency)

38

Hardness versus tempering temperature

Forged 5%Cr steel rolls

650

700

750

800

850

900

100 150 200 250 300 350 400

Tempering temperature (C)

V

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h

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incident

resistance

wear

resistance

39

Effect of a rolling incident on roll damage:

influence of the tempering temperature

rolling incidents induce a local temperature peak

the lower the tempering temperature, the more extended the zone where the

microstructure of the roll is affected.

40

Explosive failure risk of forged rolls

Explosion risk

Enormous compressive stresses in shell

Compensated by enormous tensile stresses internally

Internal stress levels up to 1000 MPa !!!Crack in roll:

inherent explosion risk

Trend to roll life maximising greater depth of hardening better roughness retention => higher hardness

more critical for explosion risk

41

Some trends in last decades

Hardening depth increase

roughly from 30 to 120 mm on diameter

i.e. roughly from 15 to 60 mm on radius

Higher barrel hardness

Higher metallurgical purity

Higher alloying content (2%Cr -> 3-8%Cr steel; HiCr iron)

Automated roll inspection

Development of induction hardening techniques

Micro-alloying with strong carbide formers (e.g. 4%Cr-Mo)

Macro-alloying: forged semi-HSS and HSS grades

42

Breakthrough Technology:

Development & testing of forged HSS rolls

< 1.00.5 1.00.5 2.04.0 - 10.00.5 - 1.0Forged semi-HSS

< 2.00.5 - 3.00.5 - 3.08.0 - 13.00.8 - 1.5Forged HSS

< 0.1< 0.10.1 - 0.61.5 - 6.00.7 - 1.0Standard Forged

W (%)V (%)Mo (%)Cr (%)C (%)Grade

most promising current direction for breakthrough roll technology for cold rolling forged semi-HSS and most particularly forged HSS grades

finely dispersedhard carbides

enhanced wear resistance

high tempering temperature(~ 480C) possible

enhanced incident resistance

-1200

-1000

-800

-600

-400

-200

0

200

400

0 50 100 150 200 250

Depth in radius (mm)

A

p

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(

M

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)

Forged HSS

Forged 5% Cr steel

Lower residual stress levels

elimination of explosivefailure risk

sci course lecture-1

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