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. 4 09599 Freiberg Tel.: 03731 / 39-4000 www.gi.tu-freiberg.de Dr.-Ing. Claudia Dommaschk South Africa 2017
Introduction In Ductile Iron the strength increases with the increase of the pearlite content, promoted by Mn,Cu,Sn pearlitic EN GJS-600-3 EN GJS-600-10 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
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
Basics conventional Ductile iron: control of properties by Ferrite Pearlite ratio GJS 400 18 GJS 500 7 GJS 600 3 high Si- Ductile iron: control of properties by Si-Content GJS 450 18 Si~3.2% GJS 500 14 Si~3.8% GJS 600 10 Si~4,3% 4
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
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] min. Rp 0,2 [N/mm²] min. A [%] 450 450 500 500 600 600 310 350 320 400 370 470 10 18 7 14 3 10 6
0.2 % Yield Strength [MPa] Comparison of the properties Conventional Ductile Iron High silicon Ductile iron Elongation [%] 7
Tensile Strength [MPa] 4,3 %Si Results The Influence of the silicon content [M 700 600 500 400 300 200 100 0 Y-2 samples Y-4 samples 2 3 4 5 6 % Si The tensile strength has the maximum at 4.3 % silicon Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 8
0.2 % yield strength [MPa] 4,3 %Si The Influence of the silicon content [M 700 600 500 400 300 200 100 0 Y-2 samples Y-4 samples 2 3 4 5 6 % Si The 0.2 % yield strength has the maximum later than the tensile strength Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 9
Elongation [%] 4,3 %Si The Influence of the silicon content Y-2 samples Y-4 samples [M 2 3 4 5 6 % Si With silicon contents higher than 4.3 % the elongation is dramatically reduced Quelle: Projekt SIRON ;AiF-Nr.: 41 EN 10
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
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
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
[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
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
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
Impact strength (J) Fibrous Fracture Fibrous Fracture Brittle Fracture 120 100 80 Fibrous and Brittle Fracture 60 40 Brittle Fracture 20 0 GJS 400-18 (ferritic) GJS 500-7 (ferritic/pearlitic) GJS 450-18 (ferritic, Si: 3.08%) RT -20 C GJS 500-14 (ferritic, Si: 3.62%) GJS 600-10 (ferritic, Si: 4.12%) Quelle: Knothe, Vortrag VDI Konferenz 2016 18-17 -
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 2012 19
K IC (Mpa*m 1/2 ) Results Fracture mechanics 120 100 80 60 40 20 0 1 1,5 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. 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
K IC (Mpa*m 1/2 ) Results Fracture mechanics 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: Pusch, G. u.a.: CAEF, Continuous Casting Section, Prüfbericht: TU Bergakademie Freiberg, Januar 2012 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
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
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
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
Results on a real casting GJS-600-3 GJS-600-10 1 1 2 2 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 25 25
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
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