There are many kinds of cracks: raw material cracks, heat treatment cracks, forging cracks etc., which make people dizzy. How to identify them is a very important course, so that it is easy to find exactly where the crack occurs in the process, is conducive to the analysis of the cause of crack.
First of all, it is necessary to determine the concept of "raw material crack" and "forging crack", and the cracks that appear after forging should be regard as "forging crack". However, the main factors leading to forging crack can be divided into:
1. Forging cracks caused by raw material defects;
2. Forging cracks caused by improper forging process.
Generally, the transverse crack has nothing to do with the base material, while the longitudinal crack needs to be analyzed in combination with the crack morphology and forging process.
There is decarbonization on both sides of the crack, which must be generated in the forging process. As for whether it is caused by raw materials or forging technology, it needs to be analyzed according to the metallography and technological process.
For the same batch of the same type of workpiece, the forging crack is basically in the same position, the extension is relatively shallow under the microscope, and there is decarbonization on both sides. And the material crack does not necessarily appear in the same position repeatedly, under the microscope the depth is different. Read more analysis, there is a certain law.
Material cracks are mostly consistent with the longitudinal direction of the material. There are two kinds of forging cracks, one is caused by overheating and over-burning, and there is oxidative decarbonization near the crack. There is also a cold iron will also cause cracking, this kind of lattice destruction tear phenomenon. It can be distinguished from the metallography.
The purpose of forging:
1. Forming requirements;
2, improve the internal organization of the material, refine the grain, uniform element composition and organization;
3. Make the material more compact (shrinkage or loose of the original unexposed air inside the forged material, etc.), and the streamline distribution is more reasonable;
4. Serve the next process through reasonable post-forging heat treatment.
Therefore, certain defects in forging and forging raw materials are the responsibility. Large castings and forgings are often directly started by ingot forging, and there must be a large number of smelting defects in the ingot. Obviously, reasonable forging can be done by forging the so-called "defects". Therefore, the rationality of forging process is the main reason to determine whether the forging will crack.
Of course, relative to a certain stable forging process, if a clear control requirement of raw material defect level is put forward for the raw material before forging, when the cracking phenomenon occurs in the forging process under the original forging process because the raw material defect level exceeds the requirement, we can consider it as "forging crack caused by raw material defect".
Crack problem specific problem specific analysis, combined with the process analysis, including heating process has no protective atmosphere should be considered, forging should be the raw material crack forging close to the right. The oxide skin is usually dense and gray, and the dirty things caused by the sample preparation process are very loose and black in color. At high power, you can see that it is impossible to distinguish the direct energy spectrum.
