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And application of various cast irons .






Depending on crystallization conditions and consequent treatment the carbon in cast iron can be as cementite or graphite. In accordance with these conditions and treatment cast irons can be divided on two groups - white and gray.

White cast iron by the structure can consist of:

- perlite and ledeburite (hypoeutectic cast iron with the carbon content up to 4, 3%);

- ledeburite (eutectic white cast iron);

- ledeburite and cementite (hypereutectic white cast iron, containing more than 4, 3% of carbon).

In white cast iron there is a lot of cementite, therefore they are hard and are brittle. They are not used for articles manufacturing. Sometimes on some zones of articles made of cast iron (necks of shaft, rolls for rolling) specially bleached surface stratum is made to increase the hardness and wear resistance.

Grey cast iron contains large part of carbon as graphite. According to the graphite impurities gray cast iron can be divided on gray cast iron, malleable cast iron and high-strength cast iron. The graphite presence in a free state causes to decreasing of strength, friction factor and amplitude of resonance oscillations.

The gray cast iron is marked by the following letters СЧ: C - gray, Ч - pig-iron. In gray pig-iron ledeburite is absent, and the carbon partially or completely is lamellar graphite. The main metal matrix of gray cast iron can consist of ferrite, mixture of ferrite and perlite or perlite. That is why cast iron are frequently called ferrite cast iron, ferrite-perlite cast iron, perlite cast iron. Grey ferrite-perlite cast iron is used for manufacturing of articles, which are loaded by average dynamic loads (blocks of cylinders of engines, hydropumps cases) and which work in conditions of friction (sleeve of cylinders, tripping drums).

Perlite gray cast iron is apply for manufacturing of articles, which work at high dynamic loads and in conditions of friction (gears, chain-wheels, ratchets, spindles, piston rings).

In malleable cast iron the carbon is in a free condition in the form of flaky graphite. Malleable cast is manufactured by means of special annealing of white cast iron. Depending on annealing mode the base metal matrix can be ferrite, of ferrite-perlite or perlite. The created graphite zones looks like large spotty impurities of irregular shape with the deeply cut up boundaries.

Ferrite-perlite and perlite malleable cast iron is applied for manufacturing of articles which work at high static and dynamic loads and in hard wear conditions (couplings, chain-wheels, links of driving chains, braking shoes, crankshafts, blades of centrifugal shot throw drums).

In high-strength cast iron the carbon is in free condition of spherical graphite. Adding of magnesium, zirconium, germanium and other elements in liquid cast iron before pouring makes this cast iron. During this process the condition of cast iron varies. The graphite has almost regular spherical shape with the precisely outlined boundaries. The basic structure is usually perlite. Sometimes around graphite the ferrite shell can be observed.

High-strength cast iron is applied for manufacturing of responsible articles, which are loaded with alternative dynamic loads (crankshafts of engines, brackets, gears, brake disks, rolls for rolling).



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