How does the phenomenon of hollowing and surface microcracking occur in reinforced steel shot?

Hollowing and surface microcracking of reinforced steel shot are problems that may be encountered during production and use, which not only affect the performance of the shot, but may also reduce its service life. The following is a detailed discussion of the reasons for the phenomenon of hollow and surface micro-cracking of reinforced steel shot:

First, the reasons for the generation of hollow reinforced steel shot

1. Production process factors
   

• Gas is not exhausted: in the production process of reinforced steel shot, liquid steel through the injection control of die casting moulds, and the use of rapid cooling methods to solidify the formation of steel balls. If air and other gases are not completely removed during this process, it can lead to the creation of air pockets within the steel shot and the formation of a hollow structure.
  

• Uneven internal contraction: steel shot in the cooling process, due to internal temperature differences, uneven internal contraction and other factors, may also lead to internal cavities, thus forming a hollow. This is one of the main reasons for the hollow phenomenon.
  

2. Raw material problems
   

• Scrap and sludge extraction: Some of the reinforced steel shot is extracted from scrap and sludge, which may result in an elemental ratio that is not easy to control and large deviations in hardness. The instability of this raw material may also increase the chance of hollowing out.
  

3. Production equipment and process control
   

• Equipment failure or improper maintenance: If the production equipment failure or improper maintenance, such as grouting mould damage, unstable die casting pressure, etc., may lead to hollow steel shot in the production process.
  

• Improperly set process parameters: cooling time, temperature and other process parameters are set to have an important impact on the quality of steel shot. If the parameters are not set properly, such as the cooling rate is too fast or too slow, may trigger the hollow phenomenon.
  

Second, the causes of micro-cracks on the surface of reinforced steel shot

1. Casting process
   

• Uneven temperature: In the casting process, if the temperature control is not uniform, it may lead to too rapid cooling of the edge, which may produce microscopic defects, such as micro-cracks.
  

• Mould material and design: The material and design of the mould also have a significant impact on the quality of the steel shot. If the mould material is not wear-resistant or not well-designed, it may lead to excessive pressure or shear force on the steel shot during the die-casting process, thus producing micro-cracks.
  

2. Processing
   

• Improper heat treatment: Heat treatment is an important part of the production process of reinforced steel shot. If the heat treatment temperature, time and other parameters are not set properly, it may lead to residual stresses inside the steel shot, which in turn may cause micro-cracks.
  

• Cold working and drilling: In the process of cold working, drilling and other processes, if not properly handled, may also cause micro-cracks. Especially in high-speed cutting, the process will quickly generate heat, serious microstructure phase change, while causing material expansion and contraction, it is easy to cause the formation of micro-cracks.
  

3. Storage and Transport
   

• Uneven force: In the process of prolonged handling or stacking, if the force is uneven, it may also lead to micro-cracks on the surface of the steel shot.
  

• Environmental factors: Humidity, temperature and other environmental factors may also have an impact on the surface quality of steel shot. For example, high humidity may lead to surface corrosion of steel shot, which in turn triggers micro-cracks.
  

Third, preventive measures

In order to avoid the emergence of hollow and surface micro-cracking phenomenon of reinforced steel shot, the following preventive measures can be taken:

1. Optimise the production process: strengthen the control of the production process to ensure that the liquid steel in the die casting before the complete exclusion of air and other gases; strict control of the cooling time and temperature, to avoid uneven internal contraction leading to hollow phenomenon.
   

2. Improve the quality of raw materials: choose raw materials with stable quality to avoid problems caused by unstable elemental ratio of steel pills extracted from scrap steel and iron sludge.
   

3. Strengthen the maintenance of equipment: regular inspection and maintenance of production equipment to ensure that the grouting mould, die-casting machine and other equipment in good condition.
   

4. Optimise the heat treatment process: set the heat treatment parameters reasonably to avoid the generation of residual stress.
   

5. Pay attention to storage and transport: in the storage and transport process, to avoid excessive pressure or shear force on the steel shot; maintain appropriate humidity and temperature environment.
   

In summary, the hollow and surface micro-cracking phenomenon of reinforced steel shot is the result of a combination of factors. By optimising the production process, improving the quality of raw materials, strengthening equipment maintenance and paying attention to storage and transport and other preventive measures, can effectively reduce the incidence of these phenomena.