Q: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.

Time：25/05/2026 17:27:15

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.

Time：21/05/2026 16:38:26