the development of ultra-high strength wire a joint development project by and

The Development of Ultra-High Strength Wire

A joint development project by

and

Application DemandsPermanent Mooring Cables

• Deepwater activities for long term fields.

Application DemandsPermanent Mooring Cables

• High strength to weight ratio– Large diameter wire.

• Field life performance. – Corrosion Performance.

– Fatigue performance.

Opportunities for Development

Strength Progression

5000

7500

10000

12500

15000

17500

20000

22500

25000

100 110 120 130 140 150

Spiral Strand Diameter (mm)

MB

L (k

N)

1570 MPa Grade1770 MPa Grade1860 MPa Grade

Development Target – 1960 MPa

Application DemandsProject Objective

• 5mm diameter final hot dip galvanised wire

• 1960MPa grade • Achieving a 10% improvement

in strand breaking strength• maintaining corrosion &

fatigue performance.

The Development of Ultrahigh Strength Wire

Alloy Development Phase

Shaun Hobson

Corus RD&T – Swinden Technology Centre - UK

ObjectiveObjective

To design a steel composition, capable of attaining a minimum UTS of 1960MPa in the hot dip galvanised wire(~5mm dia) condition, enabling a 10% improvement in cable strength.

BackgroundBackground

(a) MICROSTRUCTURE

A fully pearlitic microstructure is required, to optimiseUTS / ductility / drawability.

When designing a new steel for rod/wire, the following need to be considered:-


As-Rolled Rod Microstructure


As-Rolled Rod Microstructure

Microstructure after 80% reductionfrom wire drawing Drawing Direction

MicrostructureMicrostructure

Laying TemperatureControls austenite grain size

Forced Air Blast / Conveyor SpeedControls cooling rate, hence

transformation products

Martensite

Bainite

Austenite

Tem

pera

ture

, °C

Pearlite

Time (Log Scale)

Interlamellar Spacing (S)

Cooling S (nm)

TS (N/mm²)

Rod Mill 130 1000

Patenting 5.5mm 50 1180

12mm 80 1100

Plain 0.7% C Steel

Microstructure : Lead Microstructure : Lead PatentingPatenting

Isothermal Transformation diagram


(a) MICROSTRUCTURE


(b) WIRE PROPERTIES

Definition of the various ductility tests.

When designing a new steel, for rod/wire, the following need to be considered:-

Wire PropertiesWire Properties

Torsional Ductility

Length of wire is gripped at one end, whilst theother end is rotated at a fixed speed. The numberof twists to fracture is recorded , along with thefracture type. A type is preferred ductile fracture.


Torsional Ductility


A Type B Type C Type


Torsional Ductility


Reverse Bend Ductility

Length of wire is repeatably bent through 90°over a specified radius in opposite directionsuntil fracture. The number of reverse bendsis recorded.

2nd bend 1st bend

A Type B Type C Type


(a) MICROSTRUCTURE


(b) WIRE PROPERTIES

Definition of the various ductility tests.

(c) AGEING RESPONSE

Dynamic / static strain ageing of wire.

When designing a new steel, for rod/wire, the following need to be considered:-

Immersion Time at Galv Temp, s

Tensi

le S

trength


Mean N

o o

f T

wis

ts t

o F

ail

ure

Ageing Response of Drawn WireAgeing Response of Drawn Wire

C Clustering & Pearlite Spheroidisation

Dislocation lockingby C migration

Delaminations (C type)

Recovery

A Type

Immersion Time at Galv Temp

Tensi

le S

trength


Mean N

o o

f T

wis

ts t

o F

ail

ure


Increasing Temp

Increasing Temp

Drawing strain, scheduleand speed also influence theageing response duringgalvanising.

Immersion Time at Galv Temp

Tensi

le S

trength


Mean N

o o

f T

wis

ts t

o F

ail

ure


Ideal position, just enough to recovertorsions, without too much loss of UTS

Torsional recoveryto type A fractures

Three Stage Development Programme

(1)Laboratory assessment of experimental compositions

(2) Small scale production trial of most suitable steel

(3) Full scale trial cast, and cable manufacture

Development ProgrammeDevelopment Programme

Stage 1 – Lab AssessmentStage 1 – Lab Assessment

60Kg Ingots

Rolled and Ground to 10mm Rod Samples

Patented (using a laboratory saltbath)

Drawn to 4.4mm Wire (single hole drawbench)

Simulated Galvanising (using laboratory saltbath)


Steel C Si Mn Cr

1 0.90 0.60 0.50 0.20

2 0.90 0.90 0.50 0.20

3 0.90 1.20 0.50 0.20

CMaximise strength, and refine pearlite.(need to avoid proeutectoid cementite / segregation)

SiSolid solution strengthening of pearlitic ferrite, suppressescementite formation and influences the ageing response during galvanising.

Mn / CrIncrease the hardenability, i.e. reduce the temperatureat which pearlite begins to transform from austenite, thus refining the pearlite and increasing the UTS.


1800

1850

1900

1950

2000

2050

2100

0 20 40 60 80 100 120

Immersion Time, s

Te

ns

ile

Str

en

gth

, M

Pa

0.6% Si

0.9% Si

1.2% Si

0

5

10

15

20

0 20 40 60 80 100 120

Immersion Time, s

Me

an

No

of

Tw

ists

to

Fa

ilu

re, n

0.6% Si

0.9% Si

1.2% Si


1800

1850

1900

1950

2000

2050

2100

0 20 40 60 80 100 120

Immersion Time, s

Te

ns

ile

Str

en

gth

, M

Pa

0.6% Si

0.9% Si

1.2% Si

0

5

10

15

20

0 20 40 60 80 100 120

Immersion Time, s

Me

an

No

of

Tw

ists

to

Fa

ilu

re, n

0.6% Si

0.9% Si

1.2% Si

Increasing Si

Increasing Si


SteelUTS, MPa

Tensile Ductility, %

Reverse Bends, n

Torsional Ductility, n (fracture type)

1 1835 39 11 18 (C)

2 1840 40 11 26 (A)

3 1905 45 13 28 (A)

Steel 3 was deemed the most promising composition and was progressedthrough to stage 2.

Stage 2 – Small Scale ProductionStage 2 – Small Scale Production

Steel C Si Mn Cr

3 0.90 1.20 0.50 0.20

60kg Vac Melt

Forged and welded onto ‘carrier’ billets

Rolled to 12mm rods

Lead Patent

Wire Drawing (5.3mm)

Hot Dip Galvanise (5.4mm)

Corus RD&T

Corus ScunthorpeRod Mill

Bridon InternationalDoncaster

Stage 2 – Small Scale ProductionStage 2 – Small Scale Production

Dia, mm

UTS, MpaTensile Ductility,

%Torsions, n

(fracture type)Reverse Bends, n

Patented Rod

12.0 1445 30 - -

Wire 5.30 2030 56 32 (A) 18

Galv Wire

5.40 1975 49 26 (A) 12

For an 80% drawing reduction, the target properties were met, without any processing difficulties. Therefore a full-scale commercial trial was recommended.

Stage 3 – Full-Scale ProductionStage 3 – Full-Scale Production

A full cast (300t) of steel 3 was successfully made at Scunthorpe Works.This was cast to bloom, rolled to billet and supplied to the rod mill.

8.0 – 13.5mm diameter rod was produced at Scunthorpe Rod Mill.All the rod was fully pearlitic.

No production problems with :-

(a) Mill loads / hot stiffness(b) Increased hardenability(c) Scale / descalability (high Si)


1000

1050

1100

1150

1200

1250

1300

1350

1400

1450

1500

7 8 9 10 11 12 13 14

Rod Dia., mm

UT

S, M

Pa

Plain 0.90C


1000

1050

1100

1150

1200

1250

1300

1350

1400

1450

1500

7 8 9 10 11 12 13 14

Rod Dia., mm

UT

S, M

Pa V-Microalloy

Plain 0.90C


1000

1050

1100

1150

1200

1250

1300

1350

1400

1450

1500

7 8 9 10 11 12 13 14

Rod Dia., mm

UT

S, M

Pa

UHC-Si-Cr (steel 3)

V-Microalloy

Plain 0.90C


1000

1250

1500

1750

2000

2250

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

True Strain

Ten

sile

Str

engt

h, M

Pa

Work Hardening Curves

Plain 0.90C

Direct drawn


1000

1250

1500

1750

2000

2250

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

True Strain

Ten

sile

Str

engt

h, M

Pa


V-Microalloy

Plain 0.90CDirect drawn

Patented


1000

1250

1500

1750

2000

2250

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

True Strain

Ten

sile

Str

engt

h, M

Pa


UHC-Si-Cr

V-Microalloy

Plain 0.90C Direct DrawnPatented


Wire Size,Mm

ConditionUTS, Mpa

Torsions, n (fracture type)

Elong to Fracture, %

Reverse Bends, n

5.204.90

As-drawn20952100

33 (A)29 (A)

--

--

5.305.00

Galvanised20402070

11 (C)8 (C)

8.18.3

-10


Wire Size,Mm

ConditionUTS, Mpa

Torsions, n (fracture type)

Elong to Fracture, %

Reverse Bends, n

5.204.90

As-drawn20952100

33 (A)29 (A)

--

--

5.305.00

Galvanised20402070

11 (C)8 (C)

8.18.3

-10

5.0Galvanised

Non-Std2025 26 (A) 10.0 9

Ageing response at galvanising is influenced by :-Microstructure, Drawing Strain, Drawing Speed, Galvanising Times/Temps

Stage 3 – Full-Scale ProductionStage 3 – Full-Scale ProductionFatigue Testing of Single Wires (Fatigue limits at 2 x 106 cycles)

Tests were conducted to BS 5896 for 2 x 106 cycles. Industry standard uses max. stress = 45% of grade UTS, with min. stress changed until a fatigue limit is reached

Fatigue limit increases with strength, but reduces as % of grade

200

400

600

1500 1600 1700 1800 1900 2000

Grade

Str

ess

ran

ge,

Ds

, MP

a

21

22

23

24

1500 1600 1700 1800 1900 2000

Tensile Grade

Fat

igu

e lim

it, D

s, %

of

gra

de

Summary of Steel DevelopmentSummary of Steel Development

1000

1250

1500

1750

2000

2250

12mm Rod PatentedRod

5mm GalvWire

UTS

, MPa

Plain C

V-Microalloy

UHC-Si-Cr

The galvanised wire was supplied to the ropery at Bridon, where it was spirally spun to a full sized mooring cable.

Opportunities for Development

Strength to Weight

5000

7500

10000

12500

15000

17500

20000

22500

25000

100 110 120 130 140 150

Spiral Strand Diameter (mm)

MB

L (

kN)

DNV CN 2.5Bridon SPR2Bridon SPR2plusBridon Xtreme10% targettest resulttest resulttest result

Fatigue Performance

-1.60

-1.40

-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

2.00 3.00 4.00 5.00 6.00 7.00 8.00

Number of Cycles (log)

Rat

io o

f ten

sion

rang

e to

refe

renc

e br

eaki

ng s

treng

th (l

og) Spiral Strand

Six Strand Wire Rope

Common Chain Links

NRM = K

Where Log K = a – b.Lm

Fatigue Performance

Test 1 Test 2

Conditions 30% ± 10% 20% ± 10%

Achieved N 384,650 808,279

Expected:

Spiral Strand 562,220 1,239,595


166,878 316,418

Mode of Fatigue Failure

Fatigue Performance

-1.60

-1.40

-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

2.00 3.00 4.00 5.00 6.00 7.00 8.00

Number of Cycles (log)

Ra

tio o

f te

nsi

on

ra

ng

e to

re

fere

nce

bre

aki

ng

str

en

gth

(lo

g)

Spiral Strand


Common Chain Links

Xtreme Spiral Strand estimate

NRM = K

Where Log K = a – b.Lm

Fatigue Performance

Conventional Grade

Spiral Strand

UHC-Si-Cr Grade Spiral

Strand


Fittings / Common

Chain

Life Span

1.8 x 106 yrs 1.2 x 106 yrs2.2 x 105

yrs9.45 x 104 yrs

Commercial Application

• Three full scale mooring systems manufactured.

• Assessment of alternative applications.– Bridges– Structures

• Next stage of strength improvement initiated.

The Development of Ultra-High Strength Wire

A joint development project by

and

the development of ultra-high strength wire a joint development project by and

Documents

corrosion performance

ratiolarge diameter

cable strength

pearlitic microstructure

field life performance

new steel

steel composition

rod microstructurebackgroundas