Answers

• 
  What is the reason for the cracking of the end of round bar?

  The hardness of round steel is relatively high. Some round steel is difficult to cut when cutting, which easily causes the edge of the shearing tool to crack. After the sheared bar is placed for a period of time (more than 12 hours), a through crack appears on the end face, indicating that there is a large residual stress in the bar after shearing. Stress cracking, which includes temperature stress, structural stress and deformation stress. End cracking is generally the result of the combined action of various stresses, but one of the factors is the main reason and plays a dominant role, and shearing is the direct cause or inducement.
  
  In the case of insufficient heating, 20CrMnTi(H) has serious segregation in the microstructure, resulting in the formation of martensite and bainite in the segregation zone. When the round steel is sheared at low temperatures, the huge shear stress and shear deformation cause microcracks in the martensite and bainite in the segregation zone.

  
  
• 
  What is the difference between C-shaped steel and channel steel?

  1. Difference in cross-sectional shape
  The cross-sectional shape of C-shaped steel is similar to the letter "C". This design makes it have a higher advantage in load-bearing capacity and rigidity, and is suitable for building beam-column structures of large buildings.
  The cross-sectional shape of channel steel is "U"-shaped, with parallel flanges on both sides and a web extending up and down in the middle. This structure makes it have higher bending and shear resistance, and is suitable for bearing larger bending moments and shear forces.
  
  2. Differences in processing technology and output
  C-shaped steel is usually made by cold bending of thin steel plates, with a relatively regular shape, relatively simple processing technology, and high output; while channel steel is generally hot-rolled, and the two legs are tilted outward. The production process requires more complex processes, such as cold bending, welding, hot rolling, etc., so the production output is relatively low.
  
  3. Differences in uses and applicable fields
  Due to its light weight and high load-bearing capacity, C-shaped steel is often used in purlins, wall beams, roof trusses, brackets and other fields of steel structure buildings. Channel steel has a larger cross-sectional area, higher bending strength and shear resistance, and is often used in load-bearing components such as beams and columns in building structures.
  
  4. Stress characteristics and economy
  C-shaped steel has a smaller force and is suitable for non-load-bearing enclosure structures, while channel steel has a larger force and can be used as the main load-bearing components such as beams and columns. In terms of price, the production cost of channel steel is higher than that of C-shaped steel, so under the same specifications and quality, the price of channel steel is usually higher than that of C-shaped steel.

  
  
• 
  How to distinguish floating rust from rust on spiral pipes?

  Floating rust is a layer of rust that floats on the spiral pipe and can be removed with a towel or other things. Simply put, floating rust is considered to be no rust and is a normal state.
  The rust on spiral pipes refers to the serious rust phenomenon such as pits on the surface of the pipe body after being exposed to wind and sun for a long time (at least 1 year). This is the key feature to distinguish floating rust from rust.