MATERIALS ILECTURE COURSE 6

UNALLOYED STEELSFOUNDRY CAST IRONS

UNALLOYED STEELS

Influence of the carbon content on the properties of untreated unalloyed steels

Iron-base alloys with a less than 2% carbon content, together with other elements, in a small amount (accompanying elements):

Si, Mn, P, S, O, N, H

UNALLOYED STEELSACCOMPANYING ELEMENTS IN STEELS

P : max. 0.05% (generally)Comes from oresOccurrence: dissolved in ferrite

Fe3P, Fe2PCauses cold embrittlement;Generates the fibrous structure in steels:

increase of strength on the hot forming direction

S : max. 0.05% (generally)Comes from ores, coke, burning gasesMakes an Fe – FeS eutectic (985°C melting)

→ hot brittleness

Sulphides

CLASSIFICATION AND SYMBOLIZATION OF STEELSA. According to the structure hypo-eutectoid F + P

eutectoid Phyper-eutectoid P + C’’

B. According to the route for making semiproducts castformed

C. According to the destination generalspecialty (tubes, machine-tools, boilers, …)

SR EN symbolization for steelsSR EN 10027-1:2006 Systems for the symbolization of steels. Part 1: alphanumerical symbols;SR EN 10027-2:1996 Systems for the symbolization of steels. Part 2: numerical symbols;

CLASSIFICATION AND SYMBOLIZATION OF UNALLOYED STEELS

ALPHANUMERICAL SYMBOLIZATION

(G)annnn ananan… +an+an+an…↓ ↓ ↓

principal additional additional symbolssymbols symbols for the steel products

for steel

CLASSIFICATION AND SYMBOLIZATION OF UNALLOYED STEELS

Unalloyed steels for general usage: Type + strength (Rp0.2) + additional symbols

Unalloyed structural steels SR EN 10025 : 2004- Structural steels S + Rp0.2 [MPa] + (JR, J0, J2, K0, K2) + G1,2,3,4

- Engineering steels E + Rp0.2 [MPa] + (JR, J0, J2, K0, K2) + G1,2,3,4

Additional symbols:J = fracture energy (minimum 27 J); K = fracture energy (minimum 40J); L = fracture energy (minimum 60J) + R (20˚C); Q (0˚C); 2 (-20˚C);G = deoxidizing degree :1 (non-deoxidized) – 4 (completely deoxidized)

Ex. S355 J2G4, E360 JRG3

CLASSIFICATION AND SYMBOLIZATION OF UNALLOYED STEELSSteels with specified destination:

P – pressure vessels; L – pipes for lines; B – for reinforcing of concrete; Y – for pre-compressed concrete; R – rails;…

Ex. R1100

CLASSIFICATION AND SYMBOLIZATION OF UNALLOYED STEELSHigh – grade steels: chemical composition in the symbol

unalloyed steels, C content (in hundredths of %)

Steels for quenching and tempering SR EN 10083:2000Unalloyed – part of the standard

C + %C x 100 + E, R [+ H;HH;HL + T + heat treatment state]E – S max. = 0.035%; R – S max. = 0.02-0.04%

Ex. C45E HH-TA

H – normal hardenability prescriptions; HH – higher hardenability band; HL – lower hardenability band;Heat treatment state:TS – improved machinability; TA – soft annealing;TN – normalized; TQ+T – quenched and tempered;

CLASSIFICATION AND SYMBOLIZATION OF UNALLOYED STEELSTool steels SR EN ISO 4957:2002Unalloyed – part of the standard

C45U, C70U, C80U, C90U, C105U, C120U

+ Steels for cast partsSR EN 10293:2005 Cast steels for general usageG + symbol of steel (alphanumerical symbolization)

CLASSIFICATION AND SYMBOLIZATION OF UNALLOYED STEELS

NUMERICAL SYMBOLIZATION

1 . XX YY (ZZ)

all steel grades order nr. [extensionyy = 00…99 of symbol]

the number of the group of the steel, refering to the chemical compositionand to some mechanical and technologicalcharacteristicsXX = 00…99

Ex. 1.0420 = GE 200

Foundry cast irons: Fe – C alloys with more than 2% C destined to cast parts and containing graphite in the structure;

The graphite amount determined by the Si (graphitizing) / Mn (anti- graphitizing) ratio

Si (+ high carbon content) – ferrite + graphite structures are favouredMn – favours the formation of cementite (pearlite included)

opposite to graphite

Classification according to the shape of graphite:

Grey cast irons – lamellar graphite; [+ vermicular, coral]Malleable cast irons – temper graphite;Ductile cast irons - spheroidal graphite;

GREY CAST IRONSComposition: 2.8 – 3.5% C (generally); 0.5 – 3.5% Si; 0.1 – 1% P; 0.02 – 0.15% S

Classification of graphite: according to

size shape distribution

Lamellar graphite in grey cast irons

a, b, d – differ by the germination capacity (different cooling rate, particles for heterogeneous nucleation) c – for hyper-eutectic cast ironsd, e – hyper-eutectic cast irons; only heterogeneous nucleation;

GREY CAST IRONSSize of graphite – essential for strength (and toughness):

fine graphite → tougher cast iron

Metallic matrix (for standardized marks): F + P, P, [+ steadite]Steadite = ternary eutectic Feα – C - P;

favours castability but brittleness also

Increase of the pearlite amount – increase in strength

Strength of grey cast irons: 100 – 300 MPaDuctility: very low (brittle) A = 0.2 – 0.5%Hardness: 100 – 300 HB

GREY CAST IRONS

GREY CAST IRONSCast irons with inter-dendritic graphite (high strength) – inoculated

Inoculation = altering of the characteristics of the as-cast structure by inserting of small amounts of inoculants (less than 1%)

Inoculants for grey cast irons: SiO2, Al2O3, CaOheterogeneous nuclei

MALLEABLE CAST IRONSContain graphite in irregular agglomerates

TEMPER GRAPHITE (GM)

Graphite is obtained through heat treatments MALLEABILIZATION ANNEALING – applied to white cast irons

Classification – according to the aspect of the fractureBlack heart cast irons – F + GM (b.); P + GM (a.)White heart cast irons – F + P + GM (c.)

MALLEABLE CAST IRONS

MALLEABLE CAST IRONSWhite heart cast irons malleabilization performed in oxidizing environment for the decomposition of free cementite (secondary + ledeburitic)Rm = 270 – 570 MPa; A = 3 – 16%; 200 – 250 HB

Black heart cast irons malleabilization in neutral environment for the complete decomposition of cementiteThe most used – cost of heat treatment, favourable compromise Rm / ARm = 300 – 550 MPa; A = 2 – 10%; 150 – 320 HB

Pearlitic malleable cast irons - variant of black heart malleable cast ironsStrongest malleable cast ironsRm = 450 – 650 MPa; A = 1– 4%

SPHEROIDAL GRAPHITE (DUCTILE) CAST IRONSCast irons containing ~3.5% C, with graphite nodules obtained through

inoculationInoculants: Mg, Ce, ... – generate films on the graphite surface

Most favourable shape of graphite (minimum stress concentration effect)

Rm = 370 – 900 MPa; A = 2 – 22%; 140 – 300 HB

STANDARDISATION OF FOUNDRY CAST IRONSEN-GJ… for all standard classes

Grey cast irons SR EN 1561:1999 (lamellar graphite cast irons) EN-GJL- Rm [MPa]

Ex. EN-GJL-100

Malleable cast irons SR EN 1562:1999I – decarburised cast irons (white heart)II – non- decarburised cast irons (black heart + pearlitic)

I. EN-GJMW- Rm [MPa] – A [%]Ex. EN-GJMW-350-4, EN-GJMW-550-4

II. EN-GJMB- Rm [MPa] – A [%]Ex. EN-GJMB-300-6; EN-GJMB-500-5

Standardization of ductile cast irons SR EN 1563:1999 EN-GJS- Rm [MPa] – A [%]

Ex. EN-GJS-350-22

GlossaryOţel carbon = unalloyed (non-alloy) steel;Dezoxidare = deoxidizing;Incluziuni nemetalice = non-metallic inclusions;Desulfurare = desulphurizing;Fragilizare = embrittlement;Fibraj = fibrous structure (fibrousness);(semifabricat) Deformat = formed / wrought (semiproduct);Oţeluri pentru construcţii (în general) = structural steels;Oţeluri pentru construcţii mecanice = engineering steels;Călire = quenching / hardening;Revenire = tempering;Oţel de calitate = high-grade steel;Carburare = carburizing;Oţel de scule = tool steel;

GlossaryFontă de turnătorie = foundry cast iron;Element grafitizant / antigrafitizant = graphitizing / anti- graphitizing element;Fontă cenuşie = grey cast iron;Grafit lamelar = lamellar / flake graphite;Eutectic fosforos = steadite;Modificare = inoculation;Fontă maleabilă = malleable cast iron;Recoacere de maleabilizare = malleabilization annealing; Grafit in cuiburi = temper graphite;Fontă maleabilă cu miez alb / negru = white heart / black heart cast iron;Fontă cu grafit nodular = spheroidal graphite / ductile cast iron;