BILBAINA DE TRATAMIENTOS
The temple is to harden, giving tenecidad and increase resistance of steels. Strong> For this, we heat the material to a temperature above the critical (AC3), then cooling them quickly.
By heating the material above Ac3 critical point modifies the crystalline structure that had a room temperature, leaving the formed steel at that temperature for austenite crystals.
If the steel is rapidly cooled from the austenite region, the carbon can not be detached, as it is impossible to stop the transformation of gamma to alpha iron iron with carbon dissolution capabilities quite different, there is a supersaturated solid solution of carbon in alpha iron is known as martensite.
The hardness of martensite is greater, the more amount of carbon is dissolved in it, and explains the phenomenon that the crystal lattice is highly distorted by the carbon atoms. This makes the basic crystal lattice of the martensite but we is cubic tetragonal. Which in turn hinders their plastic deformation.
The cooling to the annealing process can be performed at different speeds, according to the ends sought, and the type of steel (amount of carbon and other alloying elements) the most used are: Water. Oil. Molten salts. Saline solutions, and even the air for certain alloy steel.
Martensite structure is unstable, with a high hardness and fragility significant so that the entire process must always be accompanied by one or more tempering they freed voltage hardening steel, providing it with greater toughness and slightly decreasing hardness steel.
There are three types of annealing:
Tempering of low temperatures (between 180 and 220oC); With it reduces internal stresses but martesítica structure is preserved. Tempering used cutting tools, which must be maintained hardness and wear resistance.
Tempering at medium temperatures (300-400 ° C) At these temperatures the martensite is modified and becomes what is known as Troostite and applied to the springs or matrices.
Tempering high temperatures (500-550 oC) At these temperatures the Troostite becomes another form called sorbitol, mainly applies for steel construction. The Troostite and sorbitol obtained during the tempering of martensite, outweigh their tenacity, similar structures are obtained directly on cooling from austenite.
METALLURGICAL DEFINITIONS OF INTEREST strong>
Ferrite is alpha iron or nearly pure iron, in solution which may contain small amounts of silicon, phosphorus, and other alloyed steels impurezas.En usually form solid solution with the nickel ferrite, manganese, copper, silicon, aluminum, etc. . crystallization in elementary cube consists of eight atoms located at the edges and one in the middle. Has a strength of about 28 kg/mm2, 35% elongation and a hardness of Brinell 90. It is softer and ductile of all constituents of the steel
Cementite is iron carbide, Fe3C. It is harder and brittle constituent of carbon steels and hardness exceed 68 HRc.
Eutectoid is a constituent formed of alternating layers of ferrite and cementite. Is constant and defined chemical composition, the ferrite contains six parts by cementite. Has a resistance of 80 kg/mm2 and an elongation of 15%. A faster cooling rate are more compact layers, a lower speed the perlira be thicker.
Is a solid solution of carbon in iron gamma. May contain from 0 to 1.7% carbon and is, therefore, one constituent of varying composition. All steels are formed when austenite crystals calientana critical temperature above Ac3. Although generally a constituent unstable, can be obtained at temteratura esaestructura quenching temperature for the steels of high carbon or high alloy.
Constituent is typical of hardened steel, is formed by a carbon sobresturada solution alpha iron, and obtiane by rapid cooling of the steel from high temperature. Their physical properties vary with composition, increasing its strength and fragility hardness with carbon content. After carbides and cementite, is the hardest constituent of steel, with a resistance of 170/250 kg/mm2, a hardness of 50-70 HRC and elongation of 2.5 to 0.5%.