high manganese steel conference trip maraging steels short version

Alloy design of nanoprecipitate-hardened high-Mn maraging-TRIP and -TWIP steels

D. Ponge, O. Dmitrieva, J. Millán, S. Sandlöbes, P. Choi, A. Kostka, G. Inden, D. Raabe

WWW.MPIE.DEd.raabe@mpie.de

Dierk Raabe

Düsseldorf, Germany

2

OverviewOverview

Introduction

Compositions and processing

Mechanical properties and microstructures

Characterization of precipitations

Conclusions

Formation of new austenite during aging

3

Good combination of strength, ductility, price

Controlled precipitation hardening

Ductile low carbon martensite matrix

Small amount of austenite (TRIP, TWIP)

IntroductionIntroduction

Steel for automotive applications:

Lean Maraging TRIP Steels

4

OverviewOverview

Introduction

Compositions and processing

Mechanical properties and microstructures

Characterization of precipitations

Conclusions

Formation of new austenite during aging

5

Low carbon: ductile martensite

Compositions in mass%: classical maraging steelCompositions in mass%: classical maraging steel

Steel C Ni Co Mo Ti Al Mn Fe

Maraging 0.01 18 12 4 1.6 0.15 0.05 Balance

Precipitation hardening

Expensive for automotive applications !

Optimised for very high strength + toughness

We want high strength + ductility

6

Low carbon: ductile martensite

Steel C Ni Co Mo Ti Al Mn Fe

Maraging 0.01 18 12 4 1.6 0.15 0.05 Balance

09MnPH 0.01 2 - 1 1.0 0.15 9 Balance

12MnPH 0.01 2 - 1 1.0 0.15 12 Balance

15MnPH 0.01 2 - 1 1.0 0.15 15 Balance

Precipitation Hardenable

Mn (+Ni): austenite (TRIP)

Compositions in mass%: new lean maraging steelsCompositions in mass%: new lean maraging steels

PH

PH

PH

Raabe, Ponge, Dmitrieva, Sander: Adv. Eng. Mat. 11 (2009) 547

7

Vacuum induction melting

Annealing

Hot deformation

Quenching

Solution heat treatment

Aging (450°C)

ProcessingProcessing

“Maraging“

Martensite + retained austenite

retained + new austenite

Dmitrieva et al. Acta Mater 59 (2011)

8

OverviewOverview

Introduction

Compositions and processing

Mechanical properties and microstructures

Characterization of precipitations

Conclusions

Formation of new austenite during aging

9

0100 101 102 103 104 105

180

200

220

240

260

280

300

320

340

360

380

400

420

440

460

480

Vic

kers

har

dnes

s H

V5

Time at 450°C (min)

09MnPH09MnPH

12MnPH12MnPH

15MnPH15MnPH

a’a’ gg

Hardness during aging at 450°CHardness during aging at 450°C

12MnPH09MnPH 15MnPH

Dmitrieva et al. Acta Mater 59 (2011)

10

precipitates in a`

no precipitates in

12MnPH after aging (48h 450°C)12MnPH after aging (48h 450°C)

nmDtxDiff 302

nmxDiff 2

Dmitrieva et al. Acta Mater 59 (2011)

11

0 5 10 15 20 250

300

600

900

1200

1500

1800

2100

2400

Eng

inee

ring

Str

ess

(MP

a)

Engineering Strain (%)

0 5 10 15 20 250

300

600

900

1200

1500

1800

2100

2400

Eng

inee

ring

Str

ess

(MP

a)

Engineering Strain (%)

0 5 10 15 20 250

300

600

900

1200

1500

1800

2100

2400

Eng

inee

ring

Str

ess

(MP

a)

Engineering Strain (%)

Ni-Maragingaged (450°C/48h)

quenched

12MnPHaged (450°C/48h)

quenched

Tensile testsTensile tests

(X3NiCoMoTi18-12-4)

D. Raabe et al. Scripta Materialia 60 (2009) 1141

12

OverviewOverview

Introduction

Compositions and processing

Mechanical properties and microstructures

Characterization of precipitations

Conclusions

Formation of new austenite during aging

13

Atom Probe, 12MnPH aged (48h, 450°C) Atom Probe, 12MnPH aged (48h, 450°C)

Ni a‘+particles g (no particles)

Mn enrichment in interface ?

Dmitrieva et al. Acta Mater 59 (2011)

14

-5 -4 -3 -2 -1 0 1 2 30

10

20

30

40

50

60

70

80

90

Con

cent

ratio

n (a

t.%)

Distance (nm)

09MnPH450°C/48h

Fe

Ni

Mn

AlTi

matrix particle

-5 -4 -3 -2 -1 0 1 2 30

10

20

30

40

50

60

70

80

90

Con

cent

ratio

n (a

t. %

)

Distance (nm)

09MnPH450°C/192h

Fe

Ni

Mn

AlTi

matrix particle

09MnPH aging at 450°C, Proxigrams09MnPH aging at 450°C, Proxigrams

Dmitrieva et al. Acta Mater 59 (2011)

15

at. % in particles

Ni 39.99Mn 24.70Al 7.02Ti 3.91Fe 23.97

Chemical compositions (09MnPH; 450°C/48h)Chemical compositions (09MnPH; 450°C/48h)

at. % in particles

52.8832.669.285.17

0

47.11

Ni50(Mn,Al,Ti)50possible:

Dmitrieva et al. Acta Mater 59 (2011)

16

Aging time at 450°C 48 hours 192 hours

Volume fraction of particles 1.5% 4.3%

Number density of particles (m-3) 3.6x1024 1.9x1024

Mean diameter (nm) 4.7 ± 0.7 6.1 ± 2.2

10 nm

48 hours 192 hours

Iso-conc. surfaces:14 at.% Ni

only Fe and Ni shown

09MnPH aging at 450°C09MnPH aging at 450°C

Dmitrieva et al. Acta Mater 59 (2011)

17

PrecipitationsPrecipitations

After aging (48h 450°C) nanosized precipitations in martensite (Ø ~ 5nm; volume fraction ~ 1.5%)

Heusler Alloy (Ni2MnAl)? B2 or L21? Coherent ? Cut by dislocations ?

18

OverviewOverview

Introduction

Compositions and processing

Mechanical properties and microstructures

Characterization of precipitations

Conclusions

Formation of new austenite during aging

19

12 wt.% Mn, 0.01 wt.% C, 2 wt.% Ni, 1 wt.% Ti, 0.15 wt.% Al,1 wt.% Mo, 0.06 wt.% Si

TRIP effect(austenite transforms to martensite)

Maraging effect(precipitation hardening in martensite)

D. Raabe, D. Ponge, O. Dmitrieva, B. Sander, Scripta Mater. 60 (2009) 1141D. Raabe, D. Ponge, O. Dmitrieva, B. Sander, Adv. Eng. Mater. 11/7 (2009) 547

Effect of aging on ductilityEffect of aging on ductility

12MnPH

20

0 5 10 15 200

200

400

600

800

1000

1200

1400

Eng

inee

ring

Str

ess

(MP

a)

Engineering Strain (%)

0 5 10 15 200

200

400

600

800

1000

1200

1400

Eng

inee

ring

Str

ess

(MP

a)

Engineering Strain (%)

0 5 10 15 200

200

400

600

800

1000

1200

1400

Eng

inee

ring

Str

ess

(MP

a)

Engineering Strain (%)

as-quenched

aged 450°C/48h

-Fe (Martensite)-Fe (Austenite), vol. fraction 15-20%

increase of austenite

fraction during aging

Precipitationhardening

2

Effect of aging on ductilityEffect of aging on ductility

21

0 5 10 15 200

200

400

600

800

1000

1200

1400

Eng

inee

ring

Str

ess

(MP

a)

Engineering Strain (%)

0 5 10 15 200

200

400

600

800

1000

1200

1400

Eng

inee

ring

Str

ess

(MP

a)

Engineering Strain (%)

0 5 10 15 200

200

400

600

800

1000

1200

1400

Eng

inee

ring

Str

ess

(MP

a)

Engineering Strain (%)

as-quenched

aged 450°C/48h

-Fe (Martensite)-Fe (Austenite), vol. fraction 15-20%

increase of austenite

fraction during aging

Precipitationhardening

strain 0%

1

1 strain 15%2

2

?

Effect of aging on ductilityEffect of aging on ductility

22

Mn atoms, Ni atomsMn iso-conc: 18 at.%

APT results: Atomic map (12MnPH aged 450°C/48h)

70 million ionsLaser mode (0.4nJ, 54K)

Martensite decorated by precipitations

Austenite

?

?

23

OverviewOverview

Introduction

Compositions and processing

Mechanical properties and microstructures

Characterization of precipitations

Conclusions

Formation of new austenite during aging

24

Conclusions Conclusions

Martensitic Mn-steels (~0,01wt%C): good ductility

+ controlled amounts of Ni (2 wt%), Al (0.15 wt%), … increase strength during aging by formation of nanosized precipitations without significant reduction of ductility

By controlling the austenite stability (here by Mn) martensite can be refined and ductility can be further increased by retained and reverted austenite (TRIP)

Design of “Lean Maraging TRIP steel“ Precipitation hardening

Austenite (retained + new) Increase ductility

Increase strength