Answers

• 
  Differences between High-Frequency Welded H-Beams and Hot-Rolled H-Beams

  Hot-Rolled H-Beams: Formed in one pass by heating continuously cast billets or ingots in a four-roll universal mill. The process is complex, requiring high-end equipment, and is typically produced by large steel mills. Hot-rolled H-beams have a scientifically sound structure, good plasticity and flexibility, and high structural stability, making them suitable for building structures subjected to high vibration and impact loads. They also have strong resistance to natural disasters. They are easy to manufacture mechanically, allowing for intensive production, high precision, convenient installation, and easy quality assurance. They can be used to build actual house construction factories, bridge construction factories, and industrial plant construction factories. The development of steel structures has created and driven the development of hundreds of emerging industries.
  
  High-Frequency Welded H-Beams: Cut strip steel (or plate) of suitable thickness to a suitable width, and weld the edges (flanges) and web directly on a continuous welding unit using localized high-frequency current heating. The process is relatively simple, using assembly line operations, resulting in high production efficiency. H-beams can be processed, designed, and combined in any way according to engineering projects, and special specifications can be manufactured to meet the actual needs of specific projects. The specifications of H-beams are designed economically, and their section moment, section coefficient, pressure resistance, and load-bearing capacity are far superior to hot-rolled steel of the same unit weight.
  
  Product Performance Differences:
  Hot-rolled H-beams: Dense internal structure, excellent mechanical properties (strong bending, torsional, and compressive strength), high structural stability, good overall performance, low residual stress, and good surface quality.
  
  High-frequency welded H-beams: Due to the heat-affected zone created by welding, the mechanical properties are affected by the welding quality, and the overall mechanical properties are slightly inferior to hot-rolled steel. However, high-frequency welding results in a smaller heat-affected zone, thinner and more uniform cross-sectional walls, better cross-sectional characteristics, and higher local strength.

  
  
• 
  How to inspect and accept NM400 when purchasing it?

  Verify the quality certificate, check the surface quality and stamped markings, retest the Brinell hardness, and measure the dimensions and thickness tolerances.

  
  

  It is recommended to conduct acceptance from the following aspects:
  Verify the quality certificate: Carefully check the quality certificate provided by the steel mill to confirm whether the grade, specifications, chemical composition, mechanical properties, etc., meet the contract requirements.
  Surface quality inspection: The surface of the steel plate shall not have defects such as cracks, bubbles, scabs, folds, and inclusions, and shall not have delamination.
  Measure the external dimensions and hardness: Check the flatness and hardness of the steel plate by random sampling. This ensures that the wear-resistant steel plates you purchase meet the requirements. If you are still concerned, you can arrange for a third party to conduct an inspection, which guarantees the quality of the steel from the source.
  Our platform has third-party inspection services, providing you with comprehensive support from resource matching, quality inspection, to logistics transportation. Please contact us at any time if you have any needs.

  
  
• 
  What is the difference between anti-corrosion coatings and rust-preventive oils for steel?

  Rust-preventive oil: This is a temporary protection method. It works by applying an oil film to isolate the steel from air and moisture, primarily preventing rust during transportation and short-term storage. It needs to be cleaned upon arrival and does not alter the steel itself.
  Anti-corrosion coating (paint/coating): This provides permanent or long-term protection. It forms a strong coating (such as epoxy zinc-rich paint or polyurethane topcoat) through sandblasting, brushing, or spraying, providing weather resistance, salt spray resistance, etc., and is the primary means of corrosion protection for engineering structures.
  The two have different uses and cannot be substituted for each other.