Answers

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  Can wire and coiled rebar be used interchangeably?

  While both wire and coiled rebar are common metal materials, they differ significantly in shape and application. Wire is typically straight with a smaller diameter, suitable for binding or securing, while coiled rebar is coiled into a disc with a larger diameter, commonly used in construction or machinery manufacturing. Their materials and strengths may also differ. In most cases, it is not recommended to mix wire and coiled rebar. If mixing is absolutely necessary, first confirm that their materials and strengths are compatible, and ensure that the operating environment will not affect performance. For critical components, it is recommended to use specially designed materials to ensure safety and reliability.

  
  
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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?

  Possible causes: Raw material defects, unreasonable process parameters, insufficient lubrication, and failure to promptly eliminate work hardening.
  1. Inherent defects in raw materials: Hot-rolled billets may contain subcutaneous bubbles, shrinkage cavities, cracks, or excessive inclusions. During cold drawing, stress concentrates at these defects, directly causing cracking.
  2. Excessive deformation per pass: A single deformation exceeding the plastic limit of 45# steel (recommended ≤20%), or excessive cumulative deformation across multiple passes (exceeding 60%~70%), causes internal stress in the steel to exceed its fracture strength.
  3. Poor lubrication: Failure to use a graphite + machine oil composite lubricant, or uneven lubrication application, leads to a significant increase in friction between the die and the steel surface, generating excessive tensile stress and causing surface or internal cracking.
  4. Failure to anneal in time: Failure to intersperse low-temperature annealing (600~650℃) during multi-pass drawing results in work hardening, causing a sharp decrease in the steel's plasticity, making it prone to brittle fracture during subsequent drawing.

  
  

  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.