STEELS AND CAST IRONS

STEELS

Fe-Fe3C Phase Diagram

Steel Alloys can be divided into five groups1- Carbon Steels2- Low Alloy Steels3- Quenched and Tempered Steels4- Heat Treatable Low Alloy Steels5- Chromium-Molybdenum Steels

1-Carbon Steels

10xx Plain Carbon

11xx Resulfurized

12xx Resulfurized and rephosphorized

Manganese steels  

13xx Mn 1.75

Nickel steels  

23xx Ni 3.5

25xx Ni 5.0

51xx Cr 0.80 – 1.05

STEELS

2-Nickel Chromium Steels

31xx Ni 1.25 Cr 0.65-0.80

32xx Ni 1.75 Cr 1.07

33xx Ni 3.50 Cr 1.50-1.57

34xx Ni 3.00 Cr 0.77

3- Chromium Molybdenum steels

41xx Cr 0.50-0.95 Mo 0.12-0.30

6-Nickel Chromium Molybdenum steels

 

43xx Ni 1.82 Cr 0.50-0.80 Mo 0.25

47xx Ni 1.05 Cr 0.45 Mo 0.20 – 0.35

86xx Ni 0.55 Cr 0.50 Mo 0.20

4- Nickel Molybdenum steels

46xx Ni 0.85-1.82 Mo 0.20

48xx Ni 3.50 Mo 0.25

5-Chromium steels

50xx Cr 0.27- 0.65

STEELS

Alloy steel - Tool steels

AISI-SAE

Types

Classification of Tools Steels

COMPOSITION %

C Cr V W Mo Other

W1 Water hardening 0.60 - - - - -

S5 Shock resisting 0.55 - - - 0.40 0.80 Mn-

2.00 Si

O1 Oil hardening 0.90 0.50 - 0.5 - -

A2 Cold work 1.00 5.00 - - 1.00 -

A4 Medium alloy air

hardening 1.00 1.00 - - 1.00 2.00 Mn

D2 Cold work High carbon

High chromium 1.50 12.0 - - 1.00 -

M1 Cold work 0.80 4.00 1.00 1.5 8.00 -

M2 Molybdenum 0.85 4.00 2.00 6.0 5.00 -

H11 Hot work 0.35 5.00 0.40 - 1.50 -

H12 Chromium 0.35 5.00 0.40 1.5 1.50 -

P20 Die casting mold 0.35 1.25 - - 0.40 -

Stainless steels usually contain less than 30% Cr and more than 50% Fe. They attain their stainless characteristics because of the formation of an invisible and adherent chromium-rich oxide surface film. Other alloying elements added to enhance characteristics include Ni, Mo, Cu, Ti, Al, Si, Nb, and N. Carbon is usually present in amounts ranging from 0.03% to 1.0%. Addition of Mo improves the corrosion resistance in salt water (316). Reduced carbon content from 0.08 wt% to 0.03 wt% further improve corrosion resistance in chloride solutions (316L type).

 Stainless steels are commonly divided into five groups:• Martensitic stainless steels• Ferritic stainless steels• Austenitic stainless steels• Duplex (ferritic-austenitic) stainless steels• Precipitation-hardening stainless steels.

Stainless steels

Stainless Steel Properties and Selections

Type ConditionUltimate Tensile Strength [MPa]

Yield Strength [MPa]

Elongation [%]

316 Annealed 515 205 40

Cold-finished 620 310 35

Cold-worked 860 690 12

316L Annealed 505 195 40

Cold-finished 605 295 34

Cold-worked 860 690 12

Corrosion resistance Resistance to oxidation and sulfidation

Toughness Cryogenic strength

Resistance to abrasion and erosion Resistance to galling and seizing

Surface finish Magnetic properties

Retention of cutting edge

Ambient strength Ductility

Elevated temperature strength Suitability for intended cleaning

procedures Stability of properties in service

Thermal conductivity Electrical resistivity

Suitability for intended fabrication

Cast Iron

Classification of Cast IronCast iron has higher carbon and silicon contents than steel. The carbon content of cast iron is 2.1 % or more. Carbon exists as free graphite in all types of cast iron except in white cast iron (as intermetallic compound Fe3C called cementite).

There are four basic types of cast iron:

– 1- White cast iron ( hard, brittle, and not weldable)

– 2- Grey cast iron (relatively soft, easily machined and welded. Main applications: engine cylinder blocks, pipe, and machine tool structures

– 3- Malleable cast iron (ductile, weldable, machinable and offers good strength and shock resistance)

– 4- Nodular or Ductile cast iron (ductile, malleable and weldable)

Cast Iron

White cast iron is very hard, brittle and non-machinable. Exhibits a white, crystalline fracture surface because fracture occurs along the iron carbide plates.

Hypo-eutectic white cast iron, (x 100)

Hyper-eutectic white cast iron (x 100).

Cast Iron

The factors mainly influencing the character of the carbon are:

The rate of cooling.

The chemical composition.

The presence of nuclei of graphite and other substances.

A high rate of cooling tends to prevent the formation of graphite, hence maintains the iron in a hard, unmachinable condition (white C.I).

If the casting consists of varying sections then the thin ones will cool at a much greater rate than the thick. Consequently, the slowly cooled sections will be grey C.I and the rapidly cooled material will be chilled White C.I.

Cast Iron

Carbon: lowers the melting-point of iron and produces more graphite. Silicon (graphite former) it will be noted that either a high carbon and low silicon or low carbon and high silicon content give grey iron.

Sulphur and manganese: Sulphur can exist in iron, as iron sulphide, FeS, or manganese sulphide, MnS. The first effect of the manganese is, therefore, to cause the formation of graphite due to its effect on the sulphur.

Phosphorus: has a little effect on the graphite-cementite ratio; but renders the metal very fluid.

Cast Iron

Grey cast irons usually contain 2.5 to 4% C, 1 to 3% Si, and additions of manganese, depending on the desired microstructure (as low as 0.1% Mn in ferritic grey irons and as high as 1.2% in pearlitics).

For common cast iron, the main elements of the chemical composition are carbon and silicon. The combined influence of carbon and silicon on the structure is usually taken into account by the carbon equivalent (CE):

CE = %C + 0.3x(%Si) + 0.33x(%P) - 0.027x(%Mn) + 0.4x(%S)

Cast Iron

Silicon and aluminum increase the graphitization potential for both the eutectic and eutectoid transformations and increase the number of graphite particles.

Nickel, copper, and tin increase the graphitization potential during the eutectic transformation, but decrease it during the eutectoid transformation.

Chromium, molybdenum, tungsten, and vanadium decrease the graphitization potential at both stages. Thus, they increase the amount of carbides and pearlite.

Cast Iron

Combined use of cerium and magnesium followed by ferro-silicon as an inoculent is used to produce ductile or spheroidal graphite iron.

The most important heat treatments and their purposes are:

Stress relieving - a low-temperature treatment, to reduce or relieve internal stresses remaining after casting Annealing - to improve ductility and toughness, to reduce hardness and to remove carbides Normalizing - to improve strength with some ductility Hardening and tempering - to increase hardness or to give improved strength and higher proof stress ratio Austempering - to yield bainitic structures of high strength, with some ductility and good wear resistance Surface hardening - by induction, flame, or laser to produce a local wear-resistant hard surface

Cast Iron

Malleable cast iron is a heat-treated iron-carbon alloy, which solidifies in the as-cast condition with a graphite-free structure, i.e. the total carbon content is present in the cementite form (Fe3C).

Malleable iron, like ductile iron, possesses considerable ductility and toughness because of its combination of nodular graphite and low-carbon metallic matrix. Because of the way in which graphite is formed in malleable iron, however, the nodules are not truly spherical as they are in ductile iron but are irregularly shaped aggregates.

Malleable iron and ductile iron are used for some of the applications in which ductility and toughness are important.

Alloyed Cast Iron: Modification of the micro-structure and properties of cast iron can be brought about by:

1- The use of special melting and casting technique, 2- The addition of alloying elements, and 3- Heat-treatment, particularly of white iron.

Cast Iron

Pearlitic Irons: (0,5-2% nickel, chromium up to 0,8% and molybdenum up to 0,6%). The addition of tin in amounts up to 0,1% promotes a fully pearlitic matrix. High carbon Ni-Cr-Mo cast iron is useful for resisting thermal shock in applications such as die-casting moulds and brake-drums.

Acicular Irons: (Carbon 2,9-3,2, nickel 1,5-2,0, molybdenum 0,3-0,6%, Copper can replace nickel up to 1-5%). This rigid, high-strength, shock-resisting material is used for diesel crankshafts, gears and machine columns.

Martensitic Irons:(5-7% nickel with other elements. Very hard irons used for resisting abrasion e.g. metal working rolls.

Austenitic Irons: Non-magnetic(11-33% nickel but below 20% it is necessary to add about 6% copper or 6% manganese to maintain fully austenitic structures which have a good resistance to corrosion and heat) e.g. Ni-Resist.

Cast Iron

Chemical composition is by far the most widely used basis for classification and/or designation of steels. The most commonly used system of designation in the United States is that of the Society of Automotive Engineers (SAE) and the American Iron and Steel Institute (AISI). The Unified Numbering System (UNS) is also being used with increasing frequency.

Numbering Systems for Metals and Alloys1. American Iron and Steel Institute (AISI) 2. Society of Automotive Engineers (SAE) 3. American Society for Testing and Materials (ASTM) 4. American Society of Mechanical Engineers (ASME) 5. American Welding Society (AWS) 6. American National Standards Institute (ANSI) 7. Steel Founders Society of America 8. Aluminum Association 9. Copper Development Association10. U.S. Department of Defense (Military Specifications) 11. General Accounting Office (Federal Specifications)

STEELS SPECIFICATIONS

The Unified Numbering System (UNS) has been developed by ASTM and SAE and several other technical societies, trade associations, and United States government agencies. The UNS establishes 9 series of designations for ferrous metals and alloys. Each UNS designation consists of a single-letter prefix followed by five digits. In most cases the letter is suggestive of the family of metals identified: for example, F for cast irons, T for tool steel, S for stainless steels.

D00001-D99999 Steels with specified mechanical properties

D40450-D40900 Carbon Steels

D50400-D52101 Alloy Steels Casting

F00001-F99999 Cast irons

F 10001-F15501 Cast Iron, Gray

STEELS

F 10090-F10920 Cast Iron Welding Filler Metal

F 20000-F22400 Cast Iron, Malleable

F 22830-F26230 Cast Iron, Pearlitic Malleable

F 30000-F36200 Cast Iron, Ductile (Nodular)

F 41000-F41007 Cast Iron, Gray, Austenitic

F 43000- F43030 Cast Iron, Ductile (Nodular), Austenitic

F45000 F 45009 Cast Iron, White

F47001-F47006 Cast Iron, Corrosion

G00001-G99999 AISI and SAE carbon and alloy steels

G10050-G15900 Carbon Steel

G11080-G11510 Resulfurized Carbon Steel

G12110-G12150 Rephosphorized and Resulfurized Carbon Steel

G13300-G13450 Mn Alloy Steel

STEELS

G40120-G48200 Mo Alloy Steel, Cr-Mo Alloy Steel, Ni-Cr-Mo Alloy Steel, Ni-Mo Alloy Steel

G81150-G88220 Ni-Cr-Mo Alloy Steel

G50150-G52986 Cr Alloy Steel, Cr-B Alloy Steel

G61180-G61500 Cr-V Alloy Steel

G92540-G98500 Cr-Si Alloy Steel, Si-Mn Alloy Steel, Cr-S-Mn Alloy Steel, Ni-Cr-Mo Alloy Steel,

Ni-Cr-Mo-B Alloy Steel

H00001-H99999 AISI and SAE H-steels

H10380-H15621 H-Carbon Steel, C-Mn H-Alloy Steel, C-B H Carbon Steel, Mn H-Carbon Steel,

B- Mn H -Carbon Steel

H40270-H48200 C-Mo H-Alloy Steel, Cr-Mo H-Alloy Steel Ni-Mo H-Alloy Steel

H50401-H51601 C-Cr-B H-Alloy Steel, C-Cr H-Alloy Steel

H61180-H61500 Cr-V H-Alloy Steel

H81451-H94301 Ni-Cr-Mo H-Alloy Steel

J00001-J99999 Cast steels (except tool steels)

J01700-J05003 Carbon Steel Casting

J11442-J84090 Alloy Steel Casting

J91100-J92001 Austenitic Manganese Steel Casting, Alloy Steel Casting

STEELS

J92110-J93000 Alloy Steel Casting Precipitation Hardening, Alloy Steel Casting, Cast Cr-Ni-

Mo Stainless Steel, Cast Cr-Ni Stainless Steel, Cast Cr-Mn-Ni-Si-N Stainless Steel

J93001-J95705 Stainless Steel Casting, Cast Cr-Ni-Mo Stainless Steel, Alloy Steel Casting,

Maraging Cast Ferritic-Austenic Stainless Steel, Duplex Alloy Steel Casting, Alloy Steel Casting

K00001-K99999 Miscellaneous steels and ferrous alloys

K00040-K08500 Carbon Steel, Carbon Steel with Special Magnetic Properties, Steel Welding

Rod, Enameling Steel

K10614-K52440 Alloy Steel, Welding Wire, High-Strength Low-Alloy Steel

K90901-K95000

Alloy Steel, Superstrength; Ferritic Cr-Mo-V Steel; Manganese Steel, Nonmagnetic; Ni-Co Steel Welding Wire; Iron, Electrical Heating Element

Alloy; Iron Thermostat Alloy; Martensitic Age-Hardenable Alloy; Maraging Alloy; Fe-Co Soft Magnetic Alloy; Nickel Steel; Invar; Iron; etc.

S00001-S99999 Heat and corrosion resistant steels (stainless), valve steels, iron-base "super

alloys"

S13800-S17780 Precipitation Hardenable Cr-Ni-Al-Mo-(Cu, Ti) Stainless Steels

S20100-S39000

Austenitic Cr-Mn-Ni (Si,Mo,Cu,Al) Stainless Steel; Thermal Spray Wire; Austenitic Cr-Mn-Ni Stainless Steel and Welding Filler Metal; Austenitic Cr-

Ni Heat Resisting Steel and Welding Filler Metal; Precipitation Hardenable Cr-Ni-(Si, Ti, Mo, Al) Stainless Steel, etc.

STEELS

S40300-S46800 Martensitic Cr Stainless Steel; Ferritic Cr Stainless Steel with Ti or Ni or Mo; Martensitic Cr-Ni-Mo Stainless Steel; Hardenable Cr Stainless Steel

S50100-S50500 Cr Heat Resisting Steels and Filler Metal

S63005-S65007 Valve Steel

S65150-S67956 Iron Base Super alloy

T00001-T99999 Tool steels, wrought and cast

T11301-T12015 High-Speed Tool Steels

T20810-T20843 Hot-Work Tool Steels

T30102-T 30407 Cold Work Tool Steels

T31501-S31507 Oil-Hardening Steels

T41901-T41907 Shock-Resisting Tool Steels

T51602-T51621 Mold Steels

T60601-T60602 C-W Tool Steels

T61202-T61206 Low-Alloy Tool Steels

T72301-T72305 Water Hardening Tool Steels

T74000-T75008 Cr-Steels Solid Welding Wire for Machinable Surfaces and Tool and Die

Surfaces

T90102-T91907 Cast Tool Steels

STEELS