On 2018-08-08 14:48:54
Defects of annealing normalizing heat treatment
Heat treatment is an important link in mechanical manufacturing, and heat treatment process refers to the heat-treatment method that the parts are heated to a certain temperature in the quenching medium of quenching agent, kept at this temperature for a period of time, and then cooled in a certain way to obtain a certain structure and performance.
Judgment of defects in annealing and normalizing heat treatment
1) The hardness of medium carbon steel is too high, which means the heating temperature is too high and the cooling rate is too fast. High carbon steel is mostly low isothermal temperature, insufficient holding time and so on. In case of the above problems, the hardness can be reduced by annealing according to the correct process parameters.
2) This kind of structure often appears in hypoeutectoid and hypereutectoid steel, in hypoeutectoid steel there is reticular ferrite, in hypereutectoid steel there is reticular carbide, because the heating temperature is too high and the cooling speed is too slow, which can be eliminated by normalizing. Inspection shall be carried out according to specified standards.
3) Decarburization is carried out in an air furnace when annealing or normalizing, and decarburization occurs due to oxidation on the metal surface when the workpiece is heated without gas protection.
4) Graphite carbon graphite carbon is obtained from the decomposition of carbide, which is mainly caused by too high heating temperature and too long holding time. When graphite carbon appears in steel, it will be found that the hardness of quenching is low, soft spot, strength is low, brittleness is large, fracture is gray black and so on.