MATERIALS SCIENCE AND ENGINEERING I

Transcription

1 MATERIALS SCIENCE AND ENGINEERING I LECTURE COURSE 6 UNALLOYED STEELS FOUNDRY CAST IRONS

2 UNALLOYED STEELS UNALLOYED (CARBON) 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 Influence of the carbon content on the properties of untreated unalloyed steels

3 UNALLOYED STEELS ACCOMPANYING ELEMENTS IN STEELS P : max. 0.05% (generally) Comes from ores Occurrence: dissolved in ferrite Fe 3 P, Fe 2 P Causes 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 gases Makes an Fe FeS eutectic (985 C melting) hot brittleness Sulphides

4 CLASSIFICATION AND SYMBOLIZATION OF STEELS A. According to the structure hypo-eutectoid F + P eutectoid P hyper-eutectoid P + C B. According to the route for making semiproducts cast formed C. According to the destination general specialty (tubes, machine-tools, boilers, ) SR EN symbolization for steels SR EN :2006 Systems for the symbolization of steels. Part 1: alphanumerical symbols; SR EN :1996 Systems for the symbolization of steels. Part 2: numerical symbols;

5 CLASSIFICATION AND SYMBOLIZATION OF UNALLOYED STEELS ALPHANUMERICAL SYMBOLIZATION (G)annnn ananan +an+an+an principal additional additional symbols symbols symbols for the steel products for steel

6 CLASSIFICATION AND SYMBOLIZATION OF UNALLOYED STEELS Unalloyed steels for general usage: Type + strength (Rp0.2) + additional symbols Unalloyed structural steels SR EN : 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

7 CLASSIFICATION AND SYMBOLIZATION OF UNALLOYED STEELS High grade steels: chemical composition in the symbol unalloyed steels, C content (in hundredths of %) Steels for quenching and tempering SR EN 10083:2000 Unalloyed part of the standard C + %C x E, R [+ H;HH;HL + T + heat treatment state] E S max. = 0.035%; R S max. = % 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;

8 CLASSIFICATION AND SYMBOLIZATION OF UNALLOYED STEELS Tool steels SR EN ISO 4957:2002 Unalloyed part of the standard C45U, C70U, C80U, C90U, C105U, C120U + Steels for cast parts SR EN 10293:2005 Cast steels for general usage G + symbol of steel (alphanumerical symbolization)

9 CLASSIFICATION AND SYMBOLIZATION OF UNALLOYED STEELS NUMERICAL SYMBOLIZATION 1. XX YY (ZZ) all steel grades order nr. [extension yy = of symbol] Ex = GE 200 the number of the group of the steel, refering to the chemical composition and to some mechanical and technological characteristics XX = 00 99

10 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 favoured Mn 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;

11 GREY CAST IRONS Composition: % C (generally); % Si; 0.1 1% P; % 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 irons d, e hyper-eutectic cast irons; only heterogeneous nucleation;

12 GREY CAST IRONS Size 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: MPa Ductility: very low (brittle) A = % Hardness: HB

13 GREY CAST IRONS

14 GREY CAST IRONS Cast 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: SiO 2, Al 2 O 3, CaO heterogeneous nuclei

15 MALLEABLE CAST IRONS Contain 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 fracture Black heart cast irons F + GM (b.); P + GM (a.) White heart cast irons F + P + GM (c.)

16 MALLEABLE CAST IRONS

17 MALLEABLE CAST IRONS White heart cast irons malleabilization performed in oxidizing environment for the decomposition of free cementite (secondary + ledeburitic) Rm = MPa; A = 3 16%; HB Black heart cast irons malleabilization in neutral environment for the complete decomposition of cementite The most used cost of heat treatment, favourable compromise Rm / A Rm = MPa; A = 2 10%; HB Pearlitic malleable cast irons - variant of black heart malleable cast irons Strongest malleable cast irons Rm = MPa; A = 1 4%

18 SPHEROIDAL GRAPHITE (DUCTILE) CAST IRONS Cast irons containing ~3.5% C, with graphite nodules obtained through inoculation Inoculants: Mg, Ce,... generate films on the graphite surface Most favourable shape of graphite (minimum stress concentration effect) Rm = MPa; A = 2 22%; HB

19 STANDARDISATION OF FOUNDRY CAST IRONS EN-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 1562:1999 I 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 II. EN-GJMB- Rm [MPa] A [%] Ex. EN-GJMB-300-6; EN-GJMB Standardization of ductile cast irons SR EN 1563:1999 EN-GJS- Rm [MPa] A [%] Ex. EN-GJS

20 Glossary Oţel 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;

21 Glossary Fontă 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;