One, eutectoid steel, inferior eutectoid steel, cross eutectoid steel
1.Eutectoid steel
Carbon is deliquescent solid solution is fashioned in the crystal lattice of iron, carbon is deliquescent the solid solution in α—— iron calls ferrite, deliquescent the solid solution in γ—— iron calls austenite. Ferrite and austenite have good plasticity. When the carbon in iron carbon alloy cannot all dissolve enters ferrite or when austenite is medium, the carbon that the rest comes out will form compound —— cementite with iron (Fe 3C) the crystal organization of this kind of compound calls cementite, its hardness is extremely tall, plasticity is almost 0.
The iron carbon balance that concerns between the temperature of the quantity containing carbon that organizes structure and steel from what mirror steel and steel is seen on state diagram, be equal to when content as it happens of carbon 0.77% when, the cementite in be equivalent to alloy namely (cementite) occupy 12% about, ferrite is occupied about 88% when, the photograph of this alloy changes come true below constant temperature. The cementite that falls in this kind of specific scale namely and ferrite, when happening to change, if disappear both disappear at the same time (when heating) , if appear both appear at the same time again, on this the photograph of this kind of organization and pure metal becomes similar. Be based on this reason, people regards this kind of two-phase structure that makes by specific scale as wait for in light of a kind of organization, and name be pearlite, this kind of steel calls eutectoid steel. Containing carbon to measure just in time namely is the steel of 0.77% calls eutectoid steel, its organization is pearlite.
2.Inferior eutectoid steel
Commonly used structure steel contains carbolic quantity to be in mostly 0.5% the following, because contain carbon to measure under 0.77% , the cementite quantity in be being organized so is little also at 12% , then ferrite eliminate should form pearlite with cementite partly outside, still can have redundant occurrence, so the organization of this kind of steel is ferrite pearlite. Carbolic content is less, proportion of the pearlite in steel organization is smaller also, the intensity of steel is lower also, but plasticity is better, a general designation of this kind of steel is inferior eutectoid steel.
