Inspection procedure for heat treatment of cast steel

  date:2015-11-03 10:42:50

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

Inspection is to focus on the supervision of the supplier to the following heat treatment specifications, as well as the test of the hardness value of the casting.

1 points of attention during heat treatment of carbon steel castings

1.1 furnace temperature rise to 650 degrees ~800, whether slow heating
Because in the heating process, especially carbon steel castings with complex shape, when the furnace temperature is raised to 650 DEG C to 800 DEG C should be slow to warm up, or at this temperature insulation for a period of time. Because in this temperature range of carbon steel, with the volume changes, the phase transformation stress, if the rapid heating, easy to make the casting thin wall part and the temperature difference between the surface layer and the center layer, so that the thermal stress increases, easy to lead to casting cracking.

1.2 insulation time is enough
In order to make the temperature inside and outside the casting, and there is enough time to completely change the structure, the heat preservation time of thick walled casting is longer than that of thin wall castings.

1.3 carbon steel casting, generally with the furnace cooling.

2.Specification for heat treatment of austenitic stainless steel castings

Heat treatment of austenitic stainless steel castings is usually treated by solid fusion and stabilization, which has the best corrosion resistance.
Inspection is to focus on the supervision of the supplier is the following heat treatment specification.

1 austenitic stainless steel
Solid fusion processing of the purpose is to make the carbides in steel completely melting and single-phase structure. The method is casting heated to 950 DEG C ~1175 DEG C and heating mode should be the first low temperature preheating, heating and acceleration to solid melting temperature of the process, to reduce the temperature difference in the heating process of steel casting surface and the heart, the solid melt holding time decided to cast steel wall thickness, generally according to the wall thickness per mm of insulation calculation for 2.5~3min, ensure the casting section all the hot permeability can be, solid melting insulation after quenched in water, oil or air and water is commonly used, air cooling only for in thin-walled castings.

2.stabilization treatment of austenitic stainless steel castings
In order to prevent the phenomenon of sensitized austenitic stainless steel castings, in the steel adding titanium, niobium and other alloy elements, solid fusion processing, stable processing, re casting heating to 850 degrees Celsius ~930 DEG C, after heat preservation, the carbon steel fully with titanium and niobium compounds formed stable carbides.

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