Metal Casting Conference – South Africa 2017

TU Bergakademie Freiberg | Foundry Department | Bernhard-von-Cotta-Str. 4 | 09599 Freiberg |

Tel.: 03731 / 39-4000 | www.gi.tu-freiberg.de | Dr.-Ing. Claudia Dommaschk | South Africa 2017

Chances and limits of High silicon ductile iron

Dr.-Ing. Claudia Dommaschk

TU Bergakademie Freiberg, Foundry Department

Introduction

By using Si-contents between 3 and 4.3 % and a ferritic structure, the

strength increases by solid-solution hardening of the ferrite

In Ductile Iron the strength increases with the increase of the pearlite

content, promoted by Mn,Cu,Sn

EN GJS-600-10

EN GJS-600-3

2

pearlitic

high silicon

Ductile Iron with homogenous ferritic Matrix

The radii of the Si- and Fe- Atoms are different

Stress in the lattice

solid-solution hardening of the ferrite

rSi = 117 pm

rFe = 124 pm

3

Basics

body-centered cubic

lattice

„conventional“ Ductile iron: control of properties by Ferrite – Pearlite – ratio

Basics

GJS – 400 – 18 GJS – 500 – 7 GJS – 600 – 3

GJS – 450 – 18

Si~3.2%

GJS – 500 – 14

Si~3.8%

GJS – 600 – 10

Si~4,3%

„high Si-“ Ductile iron: control of properties by Si-Content

4

2,4 % Si 4,8 % Si

The effects of Silicon

• Movement of the eutectic point to lower Carbon-contents

• Increase of the eutectoid temperature The formation of ferrite is promoted

• Increase of the eutectoid interval

• Decrease of the austenite area5

In 2011 the DIN EN 1563 was modified.

Three high silicon materials were registered:

EN-GJS-450-18

EN-GJS-500-14

EN-GJS-600-10

EN-GJS 450-10 450-18 500-7 500-14 600-3 600-10

min. Rm

[N/mm²]

450 450 500 500 600 600

min. Rp0,2

[N/mm²]

310 350 320 400 370 470

min. A

[%]

10 18 7 14 3 10

6

Comparison of the properties –

„Conventional“ Ductile Iron – High silicon Ductile iron

7

Elongation [%]

0.2

% Y

ield

Str

ength

[MP

a]

2 3 4 5 6

% Si

The tensile strength has the maximum at 4.3 % silicon

[M

4,3

%S

i

Y-2 samples

Y-4 samples

700

600

500

400

300

200

100

0Te

nsile

Str

en

gth

[MP

a]

The Influence of the silicon content

Results

8Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

The Influence of the silicon content

2 3 4 5 6

% Si

The 0.2 % yield strength has the maximum later than the tensile strength

[M

4,3

%S

i

Y-2 samples

Y-4 samples

0.2

% y

ield

str

en

gth

[MP

a]

700

600

500

400

300

200

100

0

9Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

2 3 4 5 6

% Si

With silicon contents higher than 4.3 % the elongation is dramatically reduced

The Influence of the silicon content

[M

Y-2 samples

Y-4 samples

Elo

ng

atio

n [%

]

4,3

%S

i

10Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

With increasing the Si content, the hardness increases continuously

The Influence of the silicon content

4,3

%S

i

Bri

ne

llH

ard

ne

ss

% Si

11Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

The mechanical properties depends on

the temperature.

The difference of the Tensile strength

and Yield Strength between „new“ and

„conventionel“ Dutile Iron is minimal at

temperatures above 400 °C

12Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

4,3

%S

i

The influence of pearlitic and carbidic elements

Tensile

str

ength

[MP

a]

The tensile strength is not influenced by different alloying or trace elements

13Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

4,3

%S

i

[MP

a]

The influence of pearlitic and carbidic elements

The Yield stress is not influenced by different alloying or trace elements

14Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

4,3

%S

i

Elo

ngation [%

]

The influence of pearlitic and carbidic elements

The elongation is not influenced by different alloying or trace elements

15Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

4,03% Si; 3,01 %C; 1,0 % Mn; 0,003 % Cr

Rm: 581 MPa; Rp0,2: 486 MPa; A: 19,8 %

Structure Y2-sample

4,16% Si; 3,04 %C; 1,0 % Mn; 0,3 % Cr

Rm: 618 MPa; Rp0,2: 481 MPa; A: 18,6 %

0 % Pearlite 0,5 % Pearlite

16Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

- 17 -

0

20

40

60

80

100

120

GJS 400-18(ferritic)

GJS 500-7(ferritic/pearlitic)

GJS 450-18(ferritic, Si: 3.08%)

GJS 500-14(ferritic, Si: 3.62%)

GJS 600-10(ferritic, Si: 4.12%)

RT -20°C

Impact

str

ength

(J)

Fibrous Fracture

Fibrous Fracture

Fibrous and Brittle Fracture

Brittle Fracture

Brittle Fracture

Quelle: Knothe, Vortrag VDI Konferenz 2016 18

Influence of the Silicon content to the Notched bar impact strength

Notc

hed

bar

impactstr

ength

(J)

Temperature (°C)

ferritic

ferritic (Si: 3,2%)

ferritic (Si: 3,8%)

ferritic/pearlitic

• Conventional ferritic Ductile iron has the best impact strength.

• With increasing Si content, the notched impact strength decreases.

• The steep front of the impact strength is displaced to higher temperatures.

Quelle: Pusch, G. u.a.: CAEF, Continuous Casting Section, Prüfbericht: TU Bergakademie Freiberg, Januar 2012 19

Results – Fracture mechanics

The Fracture toughness decreases dramatically with increasing Si content.

Quellen: [4] Wolfensberger, S. u. a.: Teil II: Gusseisen mit Kugelgraphit, Giessereiforschung 39 (1987) 2, S. 71-80

[5] Komatsu, S. u. a: AFS Transactions, 102, 1994, pp 121-125

[6] Pusch, G. u.a.: CAEF, Continuous Casting Section, Prüfbericht: TU Bergakademie Freiberg, Januar 2012 20

0

20

40

60

80

100

120

1 1,5 2 2,5 3 3,5 4

KIC

(Mp

a*m

1/2

)

Si (%)

Quelle: Pusch, G. u.a.: CAEF, Continuous Casting Section, Prüfbericht: TU Bergakademie Freiberg, Januar 2012 21

Results – Fracture mechanics

KIC

(Mpa*m

1/2)

GJS 400-18 GJS 450-18 GJS 700-2

(ferritic) (ferritic, high-Si) (pearlitic)

The Fracture toughness of the ferritic High Si- Ductile Iron and the pearlitic

Ductile Iron are similarly low.

Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

Inoculation technology

Conte

nt

ofN

odula

rgra

phite

part

icels

(shape

V a

nd

VI)

Wall Thickness (mm)

% Inoculants

21

The degree of nodularity depends on the type of inoculant

Wall Thickness (mm)

Inoculant 1%

Conte

nt

of

Nodula

rgra

phite

part

icels

(shape

V a

nd

VI)

(73-78 % Si; max 0,1 % Ca; 0,6-1

% Sr; max. 0,5 % Al)

22Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

Example Inoculant 1:

The content of nodular graphite particels with shape V and VI decreases

with increasing the Si-content

Wall Thickness (mm)

Inoculant 2%

Conte

nt

ofN

odula

rgra

phite

part

icels

(shape

V a

nd

VI)

(62-38 % Si; 1 % Al; 1,8-2,4%

Ca; 0,8-1,2% Re; 0,8-1,2 % Bi)

23Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

Example Inoculant 2:

The content of nodular graphite particels with shape V and VI increases

with increasing the Si-content to ~4.4%

Structure and inoculation technology

Co

nte

nt o

fN

od

ula

rg

rap

hite

pa

rtic

els

(sh

ap

eV

an

dV

I)

%

Good inoculation

Poor inoculationHigh Si

Low Si

Different

inoculants

Wall Thickness (mm)

24Quelle: Projekt „SIRON“;AiF-Nr.: 41 EN

25

Results on a real casting

GJS-600-3

Material do Rm Rp0.2 A

Pos. [mm] [Mpa] [Mpa] [%]

1 GJS-600-3 6 675 372 7.9

2 GJS-600-3 12 646 375 4.4

1 GJS-600-10 6 638 503 18.0

2 GJS-600-10 12 633 508 14.7

1

2

GJS-600-10

2

1

25

Because of the combination of a high tensile strength, high 0.2 yield

strength and good elongation it is possible to decrease the wall thickness

(Light weight construction)

The hardness and tensile strength is homogenous over the wall thickness

It is not necessary to chance the pattern

Higher contents of carbidic elements in the charge materials are not a problem.

Benefits of HighSi- ferritic Ductil Iron

against ferritic/pearlitic Ductile Iron

26

Summary

27

Summary

- An optimal process technology is absolutly necessary.

- The Si-content is limited to 4.3 %.

- The solid solution hardening leads to a massive embrittlement of the ferrite.

The properties are not comparable to the conventional α- ferrite.

- The fracture behavior changes from the fibrous fracture to the brittle fracture

- With Increasing the Si- content will decrease the impact strength will decrease

- The Fracture toughness of the ferritic High Si- Ductile Iron and the pearlitic

Ductile Iron are similarly low.

Problems