圣戈班新版样本册
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A ferrous product classification can be established in terms of the carbon content of the basic metal:–iron: 0 to 0.1% C,–steel: 0.1 to 1.7% C,–cast iron: 1.7 to 5% C.Below 1.7 % carbon, solidification produces an austenitic single phase material, with the carbon present inthe structure in solid solution.
Above 1.7% carbon, the carbon cannot all be dissolved in the iron structure and consequently solidifies in theform of a secondary phase, either as graphite (pure C), or iron carbide (Fe3C). Iron is a multi-phase material,of complex structure: the most common constituents are ferrite (Feα) and pearlite (Feα+ Fe3C).
Other elements present in iron in very low proportions have an effect on the structure, mechanical propertiesand casting of the metal. Silicon (usually 1 to 3 %) plays a particular part and makes the iron in reality aternary alloy: iron, carbon, silicon.
■Different types of cast ironThe term “Cast iron” covers a wide variety of Fe-C-Si alloys. It is usual to class them in groups according tothe graphite condition, making an additional differentiation based on the structure of the metal matrix(ferritic, pearlitic).
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DUCTILE IRONDuctile iron is distinguished from ordinary grey iron by its remarkablemechanical properties (elasticity, impact strength, elongation...). Theseare due to the spheroidal nature of the graphite particles.
DUCTILE IRON3162
DefinitionofironsIn so called “grey irons” the graphite is present in the form of flakes,hence their metallurgical name: flake graphite irons (sometimes calledlamellar graphite irons). By concentrating abnormal stresses at certainpoints, each of these flakes may initiate cracking.
Metallurgists have therefore sought to diminish, or eliminate, this effectby changing the size or distribution of the flakes.
In a first stage, the adoption of the centrifugal process to cast flakegraphite iron pipes (so called “grey iron pipes”), led to an appreciableimprovement, by producing very fine graphite flakes.
A decisive advance was then made in 1948, when research in both theU.S.A. and Great Britain led to the discovery of spheroidal graphiteiron, more commonly known as ductile iron.
The graphite no longer exists in flake form but precipitates in a sphericalform. The possibility of crack propagation lines is therefore eliminated.
Graphite precipitation in spheroidal form is obtained by the controlledaddition of a small amount of magnesium to the previously desulfurizedbase iron.
Ductile iron owes its remarkable mechanical properties to the sphe-roidal shape of its graphite:–tensile strength,–impact resistance,–high elastic limit (yield stress),–good elongation.
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DUCTILE IRONEffectofgraphiteshape
S.G. ironpropertiesThese properties are further enhanced by control of the chemical anal-ysis and heat treatment of the metal matrix.
Ductile iron maintains the traditional qualities of cast irons, resultingfrom the high carbon content:–compression strength,–castability,–abrasion resistance,–machinability,–fatigue strength.
All SAINT-GOBAIN PAM pipes and fittings are manufacturedfrom S.G. iron complying with Standards ISO 2531 and EN 545.
Note 1:By agreement between the manufacturer and the customer, the conven-tional elastic limit at 0.2 % (Rp0.2) can be measured. It should not be lessthan:– 270 MPa when A ≥ 12 % for DN 40 to 1000 or ≥ 10 % for DN > 1 000;– 300 MPa in all other cases.
The Brinell hardness should not exceed 230 HB for pipes and 250 HB for fittings and accessories. Forwelded components, a higher Brinell hardness is admissible in the area affected by heat adjacent to the weld.
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DUCTILE IRONPipes centrifugally cast420107Pipes not centrifugally cast fittings and accessories42055
Type of productMinimum tensilestrengthRm MPaDN 40 to 2 000DN 40 to 1 000DN 1 100 to 2 000Minimum elongationat failureA (in %)
SAINT-GOBAINPAMductile iron
Comparison of properties of different typesof cast iron for spun pipes31
MANUFACTUREThree stages are involved in the manufacture of pipes and fittings:–metal preparation: blast furnace, cupola, metal treatment,–pipe spinning/foundry casting,–finishing/coatings.
MANUFACTURE284240
