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Inspection Procedures For Heat Treatment Of Mechanical Castings

Author : Date : 2017-6-9 11:02:41
    Inspection procedures for heat treatment of mechanical castings

  First, the mechanical casting heat treatment inspection procedures

  Taking into account the shape of the valve casting complex, easy to deformation and cracking, carbon steel casting heat treatment is usually used annealing.

  The inspection focuses on whether the supplier is conducting the following heat treatment specifications and inspecting the hardness values of the castings.

  1. Attention to heat treatment of mechanical castings

  1.1 furnace temperature rose to 650 ℃ ~ 800 ℃, whether the slow warming

  Because in the heating process, especially the shape of the complex mechanical castings, when the furnace temperature rose to 650 ℃ ~ 800 ℃, it should be slowly warming, or at this temperature for a period of time. Since the phase change occurs in the carbon steel at this temperature zone, the phase change stress is generated with the change of the volume. If the temperature is rapidly heated, the temperature difference between the thin-walled portion of the casting and the thick-walled portion and the surface layer and the center layer is liable to be increased So that the thermal stress of the casting increases, easily lead to casting cracking.

  1.2 Is the holding time sufficient?

  In order to make the casting inside and outside the temperature uniform, and have enough time to completely change the organization, thick-walled castings holding time longer than the thin-walled castings.

  1.3 carbon steel casting annealing, the general cooling with the furnace.

  Second, the mechanical casting heat treatment inspection procedures

   Mechanical casting heat treatment is usually treated with solid solution and stabilization, so that it has the best corrosion resistance.

  The inspection focuses on whether the supplier is subject to the following heat treatment specifications.

  1. Solidification of stainless steel

  The purpose of the solid solution is to completely melt the carbide in the steel and obtain the single phase structure by heating the casting to 950 ° C to 1175 ° C. The heating method is preferably preheated at a low temperature and then heated to a solidification temperature Process to reduce the heating process of mechanical casting surface and the heart of the temperature difference, the solid melting insulation time is determined by the mechanical casting wall thickness, generally by wall thickness per mm insulation 2.5 ~ 3min calculation to ensure that all sections of the casting can be hot through, After the solid solution heat insulation into the water, oil or air, and to water for the common, air cooling is only applicable to thin-walled castings.

  2. Stabilized stainless steel castings

  In order to prevent the "sensitization" phenomenon of stainless steel castings, titanium, niobium and other alloying elements are added to the steel, and then solidified, and then stabilized, that is, the casting is heated to 850 ℃ ~ 930 ℃, In the carbon and titanium, niobium combined to form a stable carbide.