Casting Materials. Prof. Juhani Orkas

Transcription

1 Casting Materials Prof. Juhani Orkas

2 Overview Iron based Grey iron Nodular iron White iron Cast steel Nonferrous cast materials Aluminium alloy Magnesium alloy Titanium alloy Copper alloy Nickel-base alloy

3 Iron-carbon diagram Cast iron C > 2,06 % Grey cast iron Stable system Fe-C Iron-graphite Si, Ti, Al White cast iron Metastable system Fe-Fe 3 C Iron-cementite Mn, Cr, Mo

4 Classification of iron based materials Iron based materials Grey cast iron White cast iron Cast steel Lamellar graphite iron Vermicular graphite iron Spheroidal graphite iron Alloyed cast iron Malleable iron Chilled iron GS GJL GJV GJS ADI Whiteheart melleable iron Blackheart malleable iron GJN GJMW GJMB

5 Cast iron Carbon cut out as Graphite Grey color at the fracture surface Silicon Graphite stabilizing Compressive strength higher than tensile strength (~2:1) No bond between Iron and Carbon Good machinability Carbon interrupts the metal micro-structure Carbon lubricates the cutting tools Designation system: GJ(Symbol) - R m

6 Wikipedia: Datei:GGV-GGG.jpg Cast iron - Overview Lamellar graphite iron (GJL) Pressure and wear-resistant Corrosion-resistant Good damping characteristics Low tensile strength and elongation at fracture Low costs Vermicular graphite iron (GJV) Between GJL and GJS Low thermal expansion Spheroidal graphite iron (GJS) Ductile High tensile strength and elongation at fracture

7 Cast iron - Overview Un-etched photomicrograph SEM image

8 Lamellar graphite iron GJL Ferritic-pearlitic structure R m 400 MPa Poor toughness Good compressive strength Cooling conditions affects microstructure Tensile strength depends on wall-thickness Higher strength in thin walls Very good damping capacity (Vibration) GJL : GJS : Steel 1 : 1,8 : 4,3 Notch-sensitive High tension gradient at graphite flakes Good friction properties Very good pouring properties EN GJL-250

9 Surface hardening Thermophysical hardening Martensitic hardening HRC Ledeburitic hardening Better wear resistance Thermochemical hardening

10 Lamellar graphite iron GJL Bed for machine tools EN GJL-250 /-300 Up to 12,8 m Gearbox for a printing machine EN GJL-250

11 Spheroidal graphite iron GJS Add magnesium or cerium Spheriodal graphite Ferritic-pearlitic structure R m 800 MPa Moderate toughness Less Notch-sensitive than GJL Average tension gradient at graphite spheres Moderate damping capacity For mechanical stresses parts EN GJS-400 EN GJS-700

12 Spheroidal graphite iron GJS High C- and Si-level Low strength and Brinell hardness High elongation at fracture

13 Spheroidal graphite iron GJS Cylinder block for marine diesel engine EN GJS U 9 x 2.84 x 3.35 m kg Rotor hub (1.5MW) EN GJS U-LT x 2.7 x 2.1 m kg

14 Austempered ductile iron ADI Multi-step heat treatment of GJS Bainitic-similar structure Acicular ferrite and carbon-enriched austenite (without carbide precipitation!) R m 1400 MPa Steely characteristics Very good wear resistance Even greater with added hard carbides (CADI) Lower specific weigh than steel (~10%) Comparable mechanical properties ADI 800/ EN GJS-800-8

15 Austempered ductile iron ADI Relative weight Relative costs

16 Multi-step heat treatment ADI Austenizing Heating above AC1 temperature ( C) Completely austenitic microstructure Quenching Avoid formation of perlite Austempering Salt / oil bath or oven ( C) Isothermal transformation Ferrite needles and austenite (Ausferrite) Too short holding metastable residual austenite Too long holding: real bainite (ferrite with carbide precipitation)

17 Multi-step heat treatment ADI Austenitised at 950 C, Austenitised at 950 C, austempered at 400 C for 53 min austempered at 250 C for 50 min low strength at higher elongation high strength with high hardness at fracture and high wear resistance but imited ductility

18 Austempered ductile iron ADI enguss.htm ADI crankshaft TVR sportscar ADI gears Hymi Kymmene Engineering, Finland

19 Vermicular graphite iron GJV Deliberately insufficent treatment to build Spheriodal graphite Three-dimensional worms Properties between GJL and GJS Ferritic-pearlitic structure R m 600 MPa Especial suitable for thermal and mechanical stressed parts EN GJV-400

20 Vermicular graphite iron GJV Advantages to GJL Better tensile strength and elongation at fracture Higher fracture toughness Properties are less dependent on wall thickness Advantages to GJS Lower coefficient of thermal expansion Higher heat conductivity Lower modulus of elasticity Better thermoshock resistance and lower tendency to distortion Better damping capacity Better pouring properties

21 Vermicular graphite iron GJV Audi V12 TDI crankcase EN GJV PS / Nm More rigid and fatigue-resistant Thinner walls and less weigh MAN TG-A cylinder block EN GJV PS

22 Austenitic cast iron materials GJSA > 20% nickel (Ni-Resist) Austenitic structure Extremely corrosion resistant Sea water & alkaline media High heat resistance Adjustable thermal coefficient of expansion Nickel contend Max at ~20% Min at ~35% Laminar and spheroidal graphite possible Non-magnetizable Good running properties EN GJSA-XNiCr20-2

23 Austenitic cast iron materials GJSA x Cylinder block for LNG 35% Nickel Huge temperature difference between suction and pressure valve Housing of turbocharger K16 BorgWarner Temperatures around 1000 C

24 White cast iron Google Books: Gefüge Der Gusseisenlegierungen White cast iron Malleable iron Chilled iron Whiteheart melleable iron Blackheart malleable iron GJN GJMW GJMB

25 Google Books: Gefüge Der Gusseisenlegierungen White cast iron x Carbide stabilizing elements (Mn, S) Graphite-free solidified Fe 3 C Perlit and ledeburit (hypoeutectic) White color at the fracture surface Hard and brittle Less applications Intermediate product in steel production Heat treatment for malleable iron Cementite decompose to temper carbon (equiaxed nodular graphite) Temper carbon interrupts matrix less then carbon in grey iron Better mechanical properties

26 Whiteheart malleable cast iron GJMW Malleablizing in oxygen containing atmosphere 60 to 120 h at 1000 C Cementite decompose to Fe and C Fe 3 C 3Fe + C Carbon diffuses outwards Converts in the surface to CO and CO 2 C + O 2 CO 2 Decarburization depends on wallthickness Max. 8mm for complete decarburization Residual carbon as Temper carbon

27 Functionally graded Surface Graphite-free, ferritic structrue High ductility Excellent machinability Suitability for welding Suitability for surface treatment Transition Ferritic-perlitic structrue with temper carbon Core Perlitic structure with temper carbon High stiffness

28 Weldability Residual carbon content < 0.3% at weld area No preparation and postprocessing All welding methods No hardness increaseing Suitable for connecting complex casted parts with semi-finished products

29 Cold forming

30 Blackheart malleable cast iron GJMB Malleablizing in neutral atmosphere Inert gas 1 st level of graphitization approx. 20 h at C Cementite decompose to Fe and C Fe 3 C 3Fe + C Temper carbon in a austenitic matrix 2 nd level of graphitization Cooling to C Eutectoid transformation γ α + C Carbon from austenite diffused to existing temper carbon Cooling rate affects the final matrix

31 Matrix of GJMB Ferritic structure Slow cooling to C Stable eutectoid transformation Temper carbon evenly distributed Perlitic structure Fast cooling Metastable solidification to perlite Martensitic structure Very fast cooling Suppressed diffusion Martensite Mixed structure

32 Chilled iron GJN x High S and Mn or rapid cooling Surface White iron Graphite-free cementite Ledeburiteutecticum Up to 20 mm Extreme hard and wear resistant Core Grey iron Perlitic structure with laminar graphite

33 Chilled iron GJN Extrealmy wear-resistant Rolls Milling disks Ore crusher Crawler elements Armor plates

34 Cast steel GS Advantages Mechanical properties of steel together with the castability Malleable Wide range of materials Adjusable strengt properties Heat treatment necessary Disadvantages Higher melting point > 1400 C High demands on technology Bad mould-filling capacity More viscouse than cast iron hypoeutectic High shrinkage ~2% Castings without heat treatment unusable Brittle Coarse grain Dendritic

35 Cast steel GS Pelton wheel High strengt Shunting switch G-X120Mn12

36 Classification of nonferrous cast materials Nonferrous cast materials Light metal cast Heavy metal cast Precious metal cast Aluminum casting Magnesium casting Titanium casting Copper casting Pewter casting Lead casting Zinc casting Gold casting Silver casting Platinum casting G-Al G-Mg G-Ti G-Cu G-Sn G-Pb G-Zn G-Au G-Ag G-Pt

37 Aluminum alloy Suitable for complex thin-walled parts High dimensional accuracy Low weight with high rigidity Good strength-weight ratio Smooth surfaces and edges Good machinability High thermal conductivity Good electrical conductivity Corrosion and weathering resistance Several surface treatments possible

38 Aluminum alloy designation system

39 Aluminum alloy

40 Aluminum alloy xxx Casting alloys Most common 4xxx For die casting 4xxx 5xxx 7xxx For gravity die casting 2xxx 4xxx 5xxx 7xxx

41 Aluminum alloy Al Si (4xxx) Near eutectic (12% Si) Low melting point (576 C) Good fluidity Less shrinkage High strength Hypereutectoid (up to 25% Si) Used as piston alloy Worse fluidity Primary solidification of Si Higher wear resistance due to Si crystals Lower coefficient of expansion

42 Aluminum alloy Hypoeutectic Eutectic Hypereutectic

43 Aluminum alloy - Treatments F Without treatment O Solution annealed Dead soft, low strength T Heat treated H Strain hardened i.e. for non age hardening alloys

44 Precipitation hardening Before Treatment Precipitates along grain boundaries Solution Heat Treatment Heat above solvus temperature Dissolve any precipitates Alloying elements in solid solution Quench No time to diffuse Supersaturated solid solution

45 Precipitation hardening Hardening Below solvus temperature Alloying elements diffuses to coherent precipitate clusters Increases strength and hardness Natural ageing Room temperatur Stops after several hours Artificial ageing Precipitation heat treatment Higher hardness then with natural ageing

46 Precipitation hardening Overageing First partially coherent precipitations Later incoherent precipitations Reduced tensile strength Remember for designing parts with a higher operation temperature! AlCu 2014-T6

47 Precipitation hardening Differential housing from KSM Castings GmbH Cast-on rivets Connect housing cover with housing bell Clinch rivets directly after quench Artificial ageing for final strength and hardness

48 Aluminum alloy Daimler valve body AlSi9Cu3 Wall-thickness: 2-6mm Drafts: 1 (valve core 5 ) BMW integral cross member EN AC - AlMg5Si2Mn Weldable without pre-treatment

49 Magnesium alloy Lightest of all structural metals ~ 1800 kg/m 3 Excellent strength-weight ratio Hexagonal lattice High strength High electrical and thermal conductivity Without Al and Zn Brittle Notch-sensitive Excellent machinability Good damping coefficient Better vibration reduction than Al or GJx

50 Roos, Maile: Werkstoffkunde für Ingenieure Magnesium alloy Al and Zn Avoid problems with brittleness and notch-sensitivity Mg Increases corrosion resistance Ce and Th Increases high temperature strength Zr Grain refinement Increases strength and formability

51 Magnesium alloy designation system Two letters for the major alloying elements Two digits for the approximate percentage of the elements May an additional letter for the different alloy modifications Example: AZ91C Approx. 9% Al; approx. 1% Zn; the 3th modification

52 xx Titanium alloy Very high tensile strength and toughness even at extreme temperatures Light weight Properties depending on phase α phase α+β phase β phase Extreme corrosion resistance Very dense TiO2 layer Biocompatibility Expensive

53 Titanium alloy α phase Good fracture toughness Good creep resistance Not heat-treatable α+β phase High mechanical strength Up to 1000 MPa Heat-treatable Ti6Al4V (50% of world usage) β phase Heat-treatable Very high strength up to 1400 MPa

54 xx Copper alloy Properties Corrosion resistance Good bearing qualities Attractive appearance Bronze CuSn Brass CuZn Red brass (gunmetal) CuZnSn Aluminium bronze CuAl CuSn11 (50:1) CuAl20 (500:1)

55 Bronze (CuSn) Up to 20% Sn 9 12% for casting alloys Nonmagnetic High thermal and electrical conductivity High corrosion resistance Seawater resistance Good wear resistance Good damping coefficient Red brass (CuZnSn) Cheaper due to cheap Zn Similar properties

56 Brass (CuZn) to 45 % Zn Tensile strength up to 750 MPa No cryogenic embrittlement Good corrosion resistance Depends on alloying element Antimicrobial Used at public places Specialbrass CuZn + other element Impeller for a pump CuZn37Mn3Al2PbSi Multi Cone Synchro System Depends on the application

57 Aluminium bronze (CuAl) 9 14% Al High corrosion resistance Seawater resistance Good wear resistance Good cavitation resistance Applications Ship propeller Sliding elements Bearings Chemical industries Gear wheels World largest ship propeller (MMG) CuAl9Ni6Fe5Ma Container ship with 120,000 PS 9,6 m; 131 t

58 Nickel-base alloy Pure nickel Ductile and tough face-centered cube crystal structure up to its melting point High resistance against Corrosion environments High temperatures ( 1100 C) High stresses Base for developing specialized alloys Intermetallic phases very high strength alloys low- and high-temperature