Steels Ponge Marie-Curie Summer School

7/28/2019 Steels Ponge Marie-Curie Summer School

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Max-Planck-Institut fr Eisenforschung GmbHMax-Planck-Institut fr Eisenforschung GmbH

Structural Materials - Steels

Structural Materials - Steels

D. Ponge

Marie Curie Summer School, Hrtgenwald


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ContentContent

Steels for Constructions:

High Strength LowAlloyed (HSLA) Steels

Steels for Automotive application


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success story: HSLA-steels up toReH=1100 MPa

fields of application:

offshore

pressure vessel

shipbuilding pipelines

cranes

automotive

bridges

success story: HSLA-steels up toReH=1100 MPa

fields of application: offshore

pressure vessel

shipbuilding pipelines

cranes

automotive

bridges

weight: 96 t

lifting capacity: 800 t

standard steels:lifting capacity: 140 t

until 1970s: St 37(S235), St 52 (S355)

oil-shocksin the 70s

motivation to save raw materials and energy

development of high strength low alloyed (HSLA) steels

High Strength Low Alloyed (HSLA) SteelsHigh Strength Low Alloyed (HSLA) Steels


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basic requirements:

high yield strength (Re)

high toughness even at low temperatures(ductile to brittle transition temperature (DBTT) should be low)

good weldabili ty(0.2%C (1) , limit for alloying elements)

High Strength Low Alloyed (HSLA) SteelsHigh Strength Low Alloyed (HSLA) Steels

(1): all compositions are given in mass%


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Strength and ToughnessStrength and Toughness


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Eng

ineering

stress[M

Pa]

Engineering strain [%]

ReH

ReL

Yield strengthYield strength


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S690QS690Q

S460NS460N

S355S355

S235S235

Engineering

stress[M

Pa]

Engineering strain [%]

Engineering stress-strain curvesEngineering stress-strain curves

minimum

ReHin MPa


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ToughnessToughness

Liberty shipsLiberty ships

Numberofb

rokenships

Totalnum

berofships


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m

H

h

sample

Av

0

300

Toughness: ducti le to britt le transit ion temperatureToughness: ducti le to britt le transition temperature

impact

notch


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Impact transition curveImpact transit ion curve

upper shelf

Lower shelf

transition

Test temperature in C

Impactenergyin

J

glossy

crystallinespot

mate


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Impact transition curveImpact transit ion curve


Impacte

nergyin

J

bcc

fcc

27J

DBTT

DBTT: ductile to brittletransition temperature


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Effect of carbon content on toughnessEffect of carbon content on toughness

0.11 %C

after F. B. Pickering in

Constitution and Properties

of Steels, p. 55, VCH 1992

0.31 %C

0.80 %C


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ImpactenergyinJ

standard steel

fine grained HSLA steels

DBTT

Grainrefinement

Effect of grain refinement on toughnessEffect of grain refinement on toughness


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Increase strengthIncrease strength

Increase the strength ofsteel is easy !Increase the strength ofIncrease the strength ofsteel is easy !steel is easy !

But it has a price But it has a priceBut it has a price


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-10

-5

0

5

10

0 2.5 5.0 7.5 10.0Increase of yield strength in MPa

Change

oftransitiontemperatureinC

Solids

olution

hardeningb

ycarbo

n

Solids

olution

hardening

bycarb

on

Strengthenin

gbydisloca

tions

Strengthenin

gbydisloca

tions

Precipitationhard

ening

Precipitationhard

ening

Grainrefinem

ent

Grainrefinement

Effect on strengthening mechanisms on toughnessEffect on strengthening mechanisms on toughness


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WeldabilityWeldability


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Iron-Cementite DiagramIron-Cementite Diagram

LiquidLiquid

as cast iron

Fe3C

(austenite)face centered cubic (fcc)

Max. C solubility: 2.06%

(ferrite)body centered cubic (bcc)

Max. C solubility: 0.02%


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Cooling time t8/5 [s ]

HardnessHV10

M

icrostructure[%]

Continuous-cooling-transformation (CCT) diagram of S355NContinuous-cooling-transformation (CCT) diagram of S355N

Time [s]

Temperat

ure[C]

Austenitization: 900C for 5 min

Chemical composition in mass%:

phase transformation phase transformation

170435


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Heating by weldprocess

Welding rod

Heat Affected Zone (HAZ):

Zone, in which the parent

material is affected (usually adegradation) by the weldtemperature cycle

Affection of base material by weld temperature cycleAffection of base material by weld temperature cycle

Temperature in C

TimeHAZ

HAZ

Temperature cycle

in the weld region

Temperature cycle

in the weld regionfusion zone


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S235 (St37-2) C=0.15 E360 (St70-2) C=0.45

not welded

welded

Brit tle fracture due to

excessive hardening (martensite)

C 0.2%

max.hardness:

350 HV

Effect of carbon contentEffect of carbon content


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cold cracks

Cause:

Cooling rate to high

Avoiding cold cracks by preheatingAvoiding cold cracks by preheating

Steels with a high hardenability have to bepreheated before fixing and welding

Effect: cooling rate is reduced => avoiding

untempered martensite (no excessive hardening)Preheating temperature: 100C to 400C

Eff t f iti ld k tibil it


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%massin

15

NiCu

5

VMoCr

6

MnC)IIW(CE

++

++++=

Besides C also other elements can increase the hardenability:

if CE(IIW) 0,40 %: low cold crack susceptibility

Effect of composition on cold crack susceptibil ityEffect of composition on cold crack susceptibil ity

Carbon equivalent CE:

International Institute for Welding

C fC l i f t l d i


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Conclusions for steel designConclusions for steel design

improves weldability

improves toughness decreases strength

Increasing strength mainly by: grain refinement (improves also toughness)

precipitation hardening (microalloying)

Decreasing carbon content:

(Carbon content 0.2%)


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Normalized structural steelsNormalized structural steels

example: S460N

N li iNormali ing


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+ Ac3

Temp

erature

Conventional hot rolling

Ar3

Ar1

+ Pearlite

normalizing

Time

approx. 50C

Pearlite

NormalizingNormalizing

Austenite Austenite

PearliteFerrite

R t d ti f t it i th b AlNRetardation of austenite grain growth by AlN


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900 1000 1100 1200 1300 1400

12

10

8

6

4

2

0

-2

-4

Austenitizing temperature in C

ASTM

grainsize

number Coarse grain

Coarse grain

Fine grainFine grain

0.047% Al

0.017% N

0.004% Al

0.010% N

Austenitization time: 30 minAustenitization time: 30 min

Retardation of austenite grain growth by AlNRetardation of austenite grain growth by AlN

Austenite grain size as function

of austenitization temperature

Austenite grain size as function

of austenitization temperature

AlN: retards grain growth

Effect of microalloying additions on austenite grain coarseningEffect of microalloying additions on austenite grain coarsening


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after G. R. Speich, L..J.

Cuddy, G. R. Gordon, A.J.DeArdo, in: Phase

Transformations in Ferrous

Allys: A. R. Marder et al.

(Eds.), Warrendale:TMS-

AIME, pp. 341-389

Effect of microalloying additions on austenite grain coarseningEffect of microalloying additions on austenite grain coarsening

V Al NbTi

Austenite

Austenite C-Mn


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Thermomechanically rolled steels (TM)Thermomechanically rolled steels (TM)

example: S460M

Effect of finishing rolling temperature on transformationEffect of finishing rolling temperature on transformation


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high finishing roll ing temperature low

conventional rolling controlled rolling

partiallytrans-formedmicro-structure

partiallytrans-formedmicro-

structure

micro-structurebefore

trans-formation

micro-structurebefore

trans-formation

-recrystallization

Effect of finishing rolling temperature on transformationEffect of finishing rolling temperature on transformation

acceleratedcooling

grain

matrix

deformation band nuclei in matrix

: additional nuclei due to controlledrolling or accelerated cooling

: additional nuclei due to controlledrolling or accelerated cooling

magnified

after I. Kozasu in

Constitution and Properties

of Steels, p. 189, VCH 1992

Retardation of austenite recrystall ization by NbRetardation of austenite recrystall ization by Nb


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1000

900

800

10 10 10 10

-1 0 1 2

Rollingtem

peratur

einC

Time to start of recrystallization in s

0 mass% Nb

0.04 mass% Nb

Maximumstrain induced

NbC precipitation

Maximumstrain induced

NbC precipitation

Retardation of austenite recrystall ization by NbRetardation of austenite recrystall ization by Nb

Change of Yield strength and DBTTChange of Yield strength and DBTT


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Change of Yield strength and DBTTChange of Yield strength and DBTT

Increaseo

fyieldstrengthinMPa

Changeoftransitiontemperaturein

C

Grain size in mm-1/2 Grain size in mm-1/2

Grain

refin

ementP

recipitation

h

ardening

Precipitatio

n

hardening

S355 with 0.05% Nb or 0.1%V or 0.1% TiS355 with 0.05% Nb or 0.1%V or 0.1% Ti

TM steelsTM steels


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Goal: decrease pearl ite content and carbon equivalent at the

same or even higher strength

10 m

Ferrite: very soft (approx. 60 HV)

Cementite: very hard (approx. 800HV)

Pearlite

TM steelsTM steels

[1]

[2]

from [3]

[1]: J.J. Irani, D. Burton, J.D. Jones , A. B.

Rothwell: Strong tough structural steels, London

1967 (Spec. Rep. Iron Steel Inst. No. 104) pp.

110

[2]: W. E. Duckworth, R. Phillips, J. A.

Chapman, J. Iron Steel Inst. 203 (1965) p. 1108

[3]: B. Msgen, H. de Boer, H. Frber, J.Petersen, Normal and High Strength Structural

Steels, in Steel Vol. 2, Springer Verlag

Stahleisen 1993, p. 40

Comparison microstructure normalized and TM- steelComparison microstructure normalized and TM- steel


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S355 J2G3S355 J2G3 S355 MCS355 MC

NormalizedNormalized Thermomechanically rolled (TM)Thermomechanically rolled (TM)

Comparison microstructure normalized and TM steelComparison microstructure normalized and TM steel

pearlite

ferrite

Typical compositions of normalized steel and TM steelsTypical compositions of normalized steel and TM steels


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Typical compositions:

Typical compositions of normalized steel and TM steelsyp p


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Quenched and tempered HSLA-steelsQuenched and tempered HSLA-steels

example S690Q, S1100Q

Quenched and tempered HSLA-steelsQuenched and tempered HSLA-steels


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Water quenching:

martensite (0,2%C)

HSLA:at relative high temperingtemperatures

(typically 600-680C)for sufficient ductility

hardeninghardening temperingtempering+

pp

Time [s]

Temperatu

re[C]

Development of HSLA-steelsDevelopment of HSLA-steels


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1850 1900 1950 2000

0

200

400

600

800

1000

1200

Minim

umy

ield

strengt

hinMPa

Year

Hot rolled: S235

normalized

S355J2G3; S355N

thermo-

mechanically(TM) rolled

S700MC

S420MC

quenched and

tempered:

S960Q

S890Q

S690Q

S1100QLS960M

TM+accelerated

cooling (ACC)

and tempering

p


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New Developments

Mechanical PropertiesMechanical Properties


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Normalised Ultra Fine

Grain

Ultra Fine

Grain

TMCP

Ferrite Grain Size, dF (m)40 10 5 3 1

2 6 10 14 18 22 26 30 34

dF-1/2 (mm-1/2)

900

800

700

600

500

400

300

200

YieldStreng

thR

eH

(M

Pa)

p

Yield Strength Yield Strength

Transition

Temperature (0C)(50% FATT)

0

- 80

- 40

-120

-160-200

-240

Transition

Temperature

bergangstemp

Hall-

Petch

Cottrell-Petch

Mechanical PropertiesMechanical Properties


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ReH or Rp0,2, MPa after Nagai200 300 400 500 600 700

CMnSi

%N0m

Steel:

0.1%C

0.7%Mn0.2%Si

0.005%NdF=10m

Steel:0.1%C

0.7%Mn0.2%Si

0.005%NdF=10m

dF: 2 1m

dF: 5 2m

dF: 10 5m

Mn: 0.7

3.0%

N: 0.0050.02%

Si: 0.21.0%

Streckgren

ze

p

MicrostructureMicrostructure


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0.2% C; 1.5%Mn; 0.2%Si0.2% C; 1.5%Mn; 0.2%Si

Further reading: Microstructure and crystallographic texture of an ultrafine grained CMn steeland their evolution during warm deformation and annealing, R. Song, D. Ponge, D. Raabe, R.Kaspar, Acta Materialia 53 (2005) 845858

ContentContent


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Steels for Constructions:

High Strength LowAlloyed (HSLA) Steels

Steels for Automotive application

Fraction of conventional and high strength steel for carsFraction of conventional and high strength steel for cars


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0

20

40

60

80

fractio

nin%

conventional high strength

1990 1995 2000 2005

Steel grades for car bodySteel grades for car body


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Mehrphasen-Sthle

Dualphasen-Sthle

DP 280/600

DP 300/500DP 350/600

DP 400/700

DP 500/800

DP 700/1000

CP 700/800

Misc.

BH 210/340BH 260/370

IF 300/420

HSLA 350/450

MS 950/1200

MS 1250/1520

1%4%

30%22%

4%

3%

8%

7% 1%4% 6% 4%2%1%

3%

TRIP 450/800

CP 700/800

Martensit-Sthle

Fraction of different steel grades in a car body (Porsche Cayenne)

Car body

Porsche Cayenne

Application ofhigh strength steelswith UTS up to 1000 MPa

High strength Dual Phase steel

TRIP-steel

Martensitic

steels

Dual Phase

steels

Multiphasesteels

Ductil ity/Strength combinations of steels for automotive applicationsDucti lity/Strength combinations of steels for automotive applications


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TRIP(Mn+Al) (Mn+Si) Mn+Si+Nb

TRIP(Mn+Al) (Mn+Si) Mn+Si+Nb

austeniticstainless

Fe-Mn-Al-C

Fe-Mn-Al-SiTWIPFe-Mn-Al-SiTWIP

Fe-Mn-Al-SiTRIPFe-Mn-Al-SiTRIP

Al-alloys

Fe P06

Fe P01-P05HSLA

HSLABH(P)

DualPhase(DP)

CPCP

MartensiticMartensitic

BH t l

Bake-hardening effectBake-hardening effect


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Stress

Strain

C

After

press

forming

Bake

hardening

Work

hardening

Conventional

steel

Baking

BH steel

after M. Kurosawa, S. Sato,

T. Obara, K. Tsunoyama,

Age-hardening behaviour

and dent resistance ofbake-hardenable and extra

deep-drawable high strengh

steel, Kawasaki Steel Tech.

Rep. 18 (1988), pp. 61-65


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AdvancedAdvanced HighHigh--StrengthStrength

and Supraand Supra--Ductile LightDuctile Light--WeightWeight

SteelsSteelsG.G. FrommeyerFrommeyer and U.and U. BrBrxx

MaxMax--PlanckPlanck--InstitutInstitut for Iron Researchfor Iron Research

DuesseldorfDuesseldorf, Germany, Germany

Further reading: Supra-Ductile and High-Strength Manganese-TRIP/TWIPSteels for High Energy Absorption Purposes, G. FROMMEYER, U. BRX andP. NEUMANN, ISIJ International, Vol. 43 (2003), No. 3, pp. 438446

Engineering stress-strain curvesEngineering stress-strain curves


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0 20 40 60 80 1000

200

400

600

800

1000

1200

TRIPLEX-steel

X110 MnAl 26 11

TRIP-steel

X5 MnAlSi 15 3 3

TWIP-steel

X5 MnAlSi 25 3 3

stress[

MPa]

plastic strain pl

[%]

characteristic stress-strain-curves of TRIP-, TWIP-

and TRIPLEX-steels (strain rate = 10-4s-1)&

Twinning Induced Plasticity

Transformation Induced Plasticity

Dominant deformation mechanismsDominant deformation mechanisms


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TWIPdeformation twinning

TRIP Martensitetransformation

Austenitic FeMn [Al, Si]Steels

Austenitic / Ferritic FeMn [Al, Si] Steels

Temperature-dependence of mechanical propertiesTemperature-dependence of mechanical properties


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TWIP steel (X5 Mn Al Si 25 3 3)

-200 -100 0 100 200 300 4000,0

200

400

600

800

1000

1200

1400

III II I

un

f

Rp0,2

Rm

Strength[

MPa]

Temperature T [C]

0

20

40

60

80

100

St

rain

[%]

= 10-4 s-1.

M:1000x

T = 400 C, = 50 %T = 50 C, = 78 %

DuctilityDuctility


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TWIP steel (X5 Mn Al Si 25 3 3)TWIP steel (X5 Mn Al Si 25 3 3)

Undeformed sampleUndeformed sample

Sample after tw isting by 1080 (T = 20 C)Sample after twisting by 1080 (T = 20 C)

Undeformed sampleUndeformed sample

Deformed sample (uniform elongation of 70%)Deformed sample (uniform elongation of 70%)

High Strength TRIPLEX Light-Weight SteelHigh Strength TRIPLEX Light-Weight Steel


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TEM images of a high carbon Fe-Mn-Al-C steel

revealing a fine shear band structure (BF) (a),SADP of the twinning region (b),

E21-structured -carbides (DF) (c),theoretical SADP of-matrix and E21-carbides (d)

fcc(111)

fcc(111)

fcc(111)

fcc(002)

fcc(111)

E2 (001)1

E2 (110)1E2 (001)1

E2 (110)1

7 874 /3

Density vs. Al-concentration of quaternary Fe-Mn-Al-C alloysDensity vs. Al-concentration of quaternary Fe-Mn-Al-C alloys


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12 14 16 18 20 226,4

6,5

6,6

6,7

6,8

6,9

7,0

7,1

7,2

7,3

7,4

7,5

18

16

14

12

10

8

6

Mn content [At.-]

,

, ,

, ,

, ,

, ,

, ,

, , resulting density

aluminium content [At.-%]

density

[g/cm

3]

Eisen

= 7.874 g/cm3

percentagereductioninden

sity

(0-)/0*100

: 8

: 9 : 17

: 10 : 19

: 11 : 21

: 12 : 22

: 13 : 23

: 16 : 24

density reduction resulting

from the lattice dilatation

ApplicationsApplications


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TRIPTWIP

TRIPLEX

Lightweight constructionand

crashresistent

High strengthand safety against brittle failure

High toughness

at low temperatures

since

Development of steels with high strength and formabilityDevelopment of steels with high strength and formabili ty


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0 10000 20000 30000 40000 50000

2002

1996

1996

1990

1990

1990

1985

1985

1981

1978

1975

FeMnAlC TRIPLEX steels

high manganese TWIP steels

high manganes TRIP steels

Conventional TRIP steels

SULC steels

Isotropic streels

highstrength IF steels

Bake-Hardening steels

Dualphase steels

Phosphorus alloyed steels

Microalloyed steels

ultimate tensile strength * total elongation [MPa %]

Steels Ponge Marie-Curie Summer School

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