① is not allowed for forgings of any type or use.
Any burnt forgings must be scrapped.
② for overheating and decarburization forgings, it should distinguish between their use and type, make corresponding provisions.
According to the use of forgings and working conditions can be divided into: the first category (security) Category II (important), category III (General category) The following are introduced separately: The first category: When working, subjected to frequent and complex alternating stress role, once the forgings damaged, may cause significant personal casualties, such as the car's front axle, axle, steering and braking system forgings. The finished products of such forgings are generally not allowed to have overheating tissue. When there is mild overheating, its mechanical properties, especially the impact toughness should not be lower than the same material and hardness range of values. The processing surface allows the decarburization layer depth according to-like surface defects treatment, that is, not more than half of the actual processing allowance.
Non-machined surface of the allowable depth of the middle, small pieces (below 6kg) No more than 0.5mm, larger pieces not more than 0.8mm. The second type: This kind of forgings often withstand the complex alternating stress function, transmits the big torque or makes the 卨 speed movement, for example: the internal combustion engine crank, the connecting rod, the automobile Direction festival again, the cross axle and so on. Once the parts are damaged, may cause the vehicle, the mechanical equipment accident, but generally does not cause the personal safety accident, this kind of item overheating degree should be limited; the grain size or the permissible degree of the organization of the structure of the carbon steel, the grade of the Bainite and the degree of sulfide precipitation of the alloy structural steel are stipulated. When making the metallographic standard of overheating, the mechanical properties of forgings should be ensured, especially the impact toughness has no obvious reduction. When the condition permits, the fatigue strength test of solid forgings is made, and the overheating standard is worked out according to the test results.
The decarburization depth on the machined surface is still treated as a general surface defect. But not processing surface, to medium, small pieces (below 6kg), not exceeding 0.6mm, bulky not exceeding 1mm, to some special forgings, such as the rod part of the middle and small-sized connecting rod, the bar of the decarburization layer depth shall not exceed 0.4mm. Category III: General Gear parts, connectors, handles and so on, such pieces usually have sufficient strength, generally not easy to damage, the overheating of such forgings and decarbonization can not be specified.