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Keywords:Aging treatment,Heat Treatment,

Aging treatment
  To eliminate the measuring precision molds or parts used in the long dimensions , shape changes , often at a low temperature tempering ( tempering temperature 150-250 ℃) before finishing the workpiece reheated to 100-150 ℃, holding 5 -20 hours, such as stable quality precision parts processing , called aging . In the steel member or dynamic loading conditions of low temperature aging treatment to eliminate residual stress, tissue stability and size of steel , is particularly important.
  Aging treatment: solution treatment refers alloy workpiece , plastic deformation or cold casting, forging , the place at room temperature or higher temperatures to maintain its performance , shape, size change over time heat treatment process. The use of the workpiece is heated to a higher temperature and aging time than the aging treatment process , known as the aging treatment works , if the workpiece is placed at room temperature or under conditions of prolonged storage of natural aging phenomenon occurs is called the natural aging treatment . The purpose of the aging process , to eliminate the internal stress of the workpiece, the size of the organization and stability , improved mechanical properties.
  Cold rolled sheet in order to ensure the stability of its performance , it does not occur within the warranty period limitation as to cause hardening of steel must overaged strip in a continuous annealing furnace overaged segment , the first occurrence of the aging effect , this allows rapid cooling after the dispersion of the carbon in the steel precipitates , this process generates a hardening of the steel sheet , with the precipitation of carbides grow , the hardness of the steel sheet reached a peak , the peak over the hardness begins to decrease , carbides grow again , the strip began over aging effects. In short , the over-aging is to make the carbides precipitated at grain within a uniform distribution of solute carbon in the steel to reduce the reduce the timeliness of the steel sheet product . Therefore, the overaging temperature is important for producing high temperature, causes the over-aging treatment after ferritic steels are still a large number of solid solution carbon , overaging poor low temperature , will reduce the carbon activity , not easy to spread.
  Overaged steel will happen after the aging , but timeliness weakened, because even after over-aging treatment , cooling to room temperature ferritic matrix is still a part of a solid solution of carbon and nitrogen , over time , will change as the equilibrium slowly precipitated probably happen again kind of strain aging , I will not detail on strain aging say . In addition, to diminish the role of the carbon and nitrogen , the latter must also flat strip annealing process , the yield point of the upper and lower plates to eliminate , reduce or steel wire to slip in tensile strain marks stamping process, but over time the upper and lower yield point after still again, so there is a certain cold-rolled plate shelf life , usually six months, so the use of the unit to buy cold-rolled plate , to go through faster to use, can not place a long time

  In order to further reduce the dissolved carbon , using a rapid cooling to below the over- aging temperature, then heated to the overaging temperature and overaging treatment implement the so-called tilt "R-OA" process . The purpose is to quickly cool the high concentration of carbon at high temperature to dissolve the ferrite crystal lattice , and to maintain a lower temperature ( about 250 ℃), the ferrite crystal serious distortion , which is conducive to the iron Fe3C internal ferrite crystal nucleation . After nucleation Fe3C grow after the thermal diffusion process depends , obviously the higher the temperature the greater the diffusion coefficient through the aging time can be shortened, the rapid cooling to about 250 ℃, also heated to about 400 ℃ temperature overaging facilitate the supersaturated solid solution carbon precipitates quickly. However, to reduce the temperature of the solid solution carbon can not be fixed over time at 400 ℃, because with the aging process at a temperature of 400 ℃ , carbon in ferrite supersaturation smaller , close to its final equilibrium concentration , that is close to Fe2 Fe3C phase diagram PQ line. If the temperature decreases slowly over time , i.e., over time , then the inclination , the equilibrium concentration of carbon as the temperature decreases along the line PQ is reduced , further favor the precipitation of the dissolved carbon , so that the final residual carbon content in solid solution reduced the areas can reduce the solid solution hardening , more important is to reduce the amount of carbon dissolved movable dislocation pinning blockade or make anti- aging properties, stamping significantly improve the performance of the material . You can go to understand from the FE-C C- curve....

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