Chances and limits of High silicon ductile iron. Metal Casting Conference South Africa 2017

Transcription

1 Chances and limits of High silicon ductile iron Dr.-Ing. Claudia Dommaschk TU Bergakademie Freiberg, Foundry Department Metal Casting Conference South Africa 2017 TU Bergakademie Freiberg Foundry Department Bernhard-von-Cotta-Str Freiberg Tel.: / Dr.-Ing. Claudia Dommaschk South Africa 2017

2 Introduction In Ductile Iron the strength increases with the increase of the pearlite content, promoted by Mn,Cu,Sn pearlitic EN GJS EN GJS high silicon By using Si-contents between 3 and 4.3 % and a ferritic structure, the strength increases by solid-solution hardening of the ferrite 2

3 Basics 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 r Si = 117 pm r Fe = 124 pm body-centered cubic lattice 3

4 Basics conventional Ductile iron: control of properties by Ferrite Pearlite ratio GJS GJS GJS high Si- Ductile iron: control of properties by Si-Content GJS Si~3.2% GJS Si~3.8% GJS Si~4,3% 4

5 The effects of Silicon 2,4 % Si 4,8 % Si Movement of the eutectic point to lower Carbon-contents Increase of the eutectoid temperature Increase of the eutectoid interval Decrease of the austenite area The formation of ferrite is promoted 5

6 In 2011 the DIN EN 1563 was modified. Three high silicon materials were registered: EN-GJS EN-GJS EN-GJS EN-GJS min. Rm [N/mm²] min. Rp 0,2 [N/mm²] min. A [%]

7 0.2 % Yield Strength [MPa] Comparison of the properties Conventional Ductile Iron High silicon Ductile iron Elongation [%] 7

8 Tensile Strength [MPa] 4,3 %Si Results The Influence of the silicon content [M Y-2 samples Y-4 samples % Si The tensile strength has the maximum at 4.3 % silicon Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 8

9 0.2 % yield strength [MPa] 4,3 %Si The Influence of the silicon content [M Y-2 samples Y-4 samples % Si The 0.2 % yield strength has the maximum later than the tensile strength Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 9

10 Elongation [%] 4,3 %Si The Influence of the silicon content Y-2 samples Y-4 samples [M % Si With silicon contents higher than 4.3 % the elongation is dramatically reduced Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 10

11 Brinell Hardness 4,3 %Si The Influence of the silicon content % Si With increasing the Si content, the hardness increases continuously Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 11

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

13 Tensile strength [MPa] 4,3%Si The influence of pearlitic and carbidic elements The tensile strength is not influenced by different alloying or trace elements Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 13

14 [MPa] 4,3%Si The influence of pearlitic and carbidic elements The Yield stress is not influenced by different alloying or trace elements Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 14

15 Elongation [%] 4,3%Si The influence of pearlitic and carbidic elements The elongation is not influenced by different alloying or trace elements Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 15

16 Structure Y2-sample 4,03% Si; 3,01 %C; 1,0 % Mn; 0,003 % Cr Rm: 581 MPa; Rp0,2: 486 MPa; A: 19,8 % 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 Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 16

17 Impact strength (J) Fibrous Fracture Fibrous Fracture Brittle Fracture Fibrous and Brittle Fracture Brittle Fracture 20 0 GJS (ferritic) GJS (ferritic/pearlitic) GJS (ferritic, Si: 3.08%) RT -20 C GJS (ferritic, Si: 3.62%) GJS (ferritic, Si: 4.12%) Quelle: Knothe, Vortrag VDI Konferenz

18 Notched bar impact strength (J) Influence of the Silicon content to the Notched bar impact strength ferritic ferritic (Si: 3,2%) ferritic (Si: 3,8%) ferritic/pearlitic Temperature ( C) 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

19 K IC (Mpa*m 1/2 ) Results Fracture mechanics ,5 2 2,5 3 3,5 4 Si (%) 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 [5] Komatsu, S. u. a: AFS Transactions, 102, 1994, pp [6] Pusch, G. u.a.: CAEF, Continuous Casting Section, Prüfbericht: TU Bergakademie Freiberg, Januar

20 K IC (Mpa*m 1/2 ) Results Fracture mechanics GJS GJS GJS (ferritic) (ferritic, high-si) (pearlitic) The Fracture toughness of the ferritic High Si- Ductile Iron and the pearlitic Ductile Iron are similarly low. Quelle: Pusch, G. u.a.: CAEF, Continuous Casting Section, Prüfbericht: TU Bergakademie Freiberg, Januar

21 Content of Nodular graphite particels (shape V and VI) Inoculation technology % Inoculants Wall Thickness (mm) The degree of nodularity depends on the type of inoculant Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 21

22 Content of Nodular graphite particels (shape V and VI) Example Inoculant 1: The content of nodular graphite particels with shape V and VI decreases with increasing the Si-content % Inoculant 1 (73-78 % Si; max 0,1 % Ca; 0,6-1 % Sr; max. 0,5 % Al) Wall Thickness (mm) Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 22

23 Content of Nodular graphite particels (shape V and VI) Example Inoculant 2: The content of nodular graphite particels with shape V and VI increases with increasing the Si-content to ~4.4% % Inoculant 2 (62-38 % Si; 1 % Al; 1,8-2,4% Ca; 0,8-1,2% Re; 0,8-1,2 % Bi) Wall Thickness (mm) Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 23

24 Content of Nodular graphite particels (shape V and VI) Structure and inoculation technology % Low Si Good inoculation Different inoculants High Si Poor inoculation Wall Thickness (mm) Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 24

25 Results on a real casting GJS GJS Material do Rm Rp0.2 A Pos. [mm] [Mpa] [Mpa] [%] 1 GJS GJS GJS GJS

26 Summary Benefits of HighSi- ferritic Ductil Iron against ferritic/pearlitic Ductile Iron 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. 26

27 Summary Problems - 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. 27