Particularly complex shape of the casting, when the furnace temperature to rise to 650-800C, should be slowly heated, or kept at this temperature for a period of time. Because, in this temperature range, stainless phase change is accompanied by a volume change, resulting in phase transformation stress, rapid heating, is easy to make the temperature difference is increased between the casting thin-walled portion and the thick portion and the surface layer and middle, thereby the casting of the thermal stress increases, and likely to cause casting cracking.
2) to the casting temperature inside and outside, and there is enough time to make the organization completely transformed, longer than the thin-walled castings.
Holding time generally refers to the castings are hot inside and outside temperature or color (ie castings reach consensus). If not specified the soaking time, the soaking time is included in the holding time, the holding time of the thick-walled castings.
The holding time is calculated as follows:
(1) according to the same furnace castings maximum wall thickness, 25mm insulation 1h, apply to the wall thickness of less than 200mm castings.
② same furnace castings maximum wall thickness, 50mm insulation 1h, but not less than 2h. For the special Heavy castings. Per 100mm incubated 1h using this calculation method, the incubation time generally does not include a soaking time, including may be used.
③ calculate the the stockyard height (ie castings stacking height), the holding time of the general carbon steel castings 1m high heat 4h.
(4) Tempering time is generally longer than normalizing or annealing.
3) castings annealing or tempering, generally with furnace cooling. Heavy, castings of complex shape and residual stress, slow cooling in the furnace. Stainless steel castings when normalizing the food over in the furnace cold, requiring higher hardness of the castings in the gas stream or Removing from the trolley to cool.