Answers

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  Differences between Cold-rolled round bar and Ordinary Round bar？

  1. Cold-drawn round steel (also called cold-drawn round steel, plain round steel) is a high-precision round steel. The material undergoes a "quenching and tempering" process and can be directly used to make shafts without further processing. Ordinary round steel is the common round steel used in construction. It is supplied in a "normalized" heat treatment state, and both its dimensional accuracy and material are of a standard level.
  
  2. Cold-drawn steel allows for local buckling of the cross-section, thus fully utilizing the load-bearing capacity after buckling; hot-rolled steel does not allow for local buckling of the cross-section.
  
  3. The causes of residual stress in hot-rolled and cold-rolled steel are different, resulting in significant differences in their cross-sectional distribution. The residual stress distribution in the cross-section of cold-formed thin-walled steel is bending-type, while the residual stress distribution in the cross-section of hot-rolled or welded steel is membrane-type.
  
  4. Hot-rolled steel has a higher free torsional stiffness than cold-rolled steel, so hot-rolled steel has better torsional resistance than cold-rolled steel.

  
  
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  What causes cold-drawn cracking of 45 steel round bar?

  Raw material defects. The steel contains severe non-metallic inclusions, shrinkage cavities, or has a substandard chemical composition. For example, abnormally high nitrogen content (exceeding 0.017%) significantly increases aging sensitivity and brittleness, or excessive arsenic content leads to elemental segregation at grain boundaries, causing cold brittleness.
  
  Inappropriate hardness matching. If the original hardness of the 45# round bar is too high (e.g., without annealing, hardness far exceeds 229HB) and its plasticity is poor, the material cannot withstand the enormous tensile stress during large diameter reduction processing using cold-drawing dies, resulting in brittle fracture.

  
  
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  In some applications, are there alternatives to galvanized steel sheets that are more corrosion-resistant and have a similar cost?

  Yes, zinc-aluminum-magnesium (Zn-Al-Mg) coated steel sheets are a major alternative to traditional galvanized steel sheets, offering better corrosion resistance at a similar cost.
  
  1. Zinc-aluminum-magnesium coatings (containing 1.5%~8% Al and 0.2%~2% Mg) offer 10–20 times the corrosion resistance of hot-dip galvanized steel sheets (especially in cut, humid, and salt spray environments), while typically costing only 5%–15% more.
  
  2. Aluminized zinc (55% Al-Zn) coatings offer superior corrosion resistance compared to ordinary galvanizing (especially in dry/high-temperature environments), but are slightly more expensive (approximately 10–20%), and have weaker weldability and cut protection compared to zinc-aluminum-magnesium coatings.

  
  

  In many outdoor applications, galvalume steel sheets are indeed a more cost-effective alternative to galvanized steel sheets. Their initial cost is only slightly higher, but their service life is significantly extended. For highly corrosive environments such as coastal areas and chemical plants, zinc-aluminum-magnesium steel sheets offer superior performance and are an ideal upgrade.
  
  Galvalume steel sheets possess a "dual protection" mechanism. The dense oxide film formed by the outer aluminum layer acts as a robust barrier, effectively preventing corrosion; even if the coating is damaged, the inner zinc layer actively "sacrifices" itself to protect the steel substrate. According to industry data, galvalume steel sheets can withstand salt spray for up to 25 years, while ordinary hot-dip galvanized steel sheets typically only last about 5 years.
  
  The biggest highlight of zinc-aluminum-magnesium steel sheets is their "self-healing" function. When the sheet is cut or scratched, the magnesium and aluminum in the coating form a movable protective film that actively covers the exposed cut edges, preventing the spread of rust.
  
  If your project environment isn't extremely harsh and you're looking for a long-lasting solution that balances cost and performance, galvalume steel sheet is currently the preferred choice. It offers a lifespan several times longer than a galvanized steel sheet with a controllable initial investment, eliminating the need for frequent maintenance.
  
  However, if your project is located in a coastal area or a heavily polluted industrial environment with stringent corrosion resistance requirements, then zinc-aluminum-magnesium steel sheet, with its self-healing capabilities and top-tier corrosion resistance, is a more reliable option.