45Cr round steel (GB/T 699) has a composition of 0.42–0.50% carbon (C), 0.17–0.37% silicon (Si), 0.50–0.80% manganese (Mn), 0.80–1.10% chromium (Cr), ≤0.035% P, ≤0.035% S.
Compared to 45# steel (no intentional Cr), chromium (0.80–1.10%) improves wear resistance via carbide formation-a chemical process that creates hard, wear-resistant particles in the matrix:
Chromium carbide formation: Chromium reacts with carbon to form chromium carbides (Cr₇C₃ and Cr₂₃C₆) during heat treatment. These carbides have a hardness of 1500–1800 HV, far harder than the iron carbides (Fe₃C, ~800 HV) in 45# steel. The harder carbides resist abrasive wear by acting as "miniature armor" on the steel surface.
Uniform carbide distribution: Cr carbides are more uniformly dispersed than Fe₃C in 45# steel. In 45#, Fe₃C forms coarse lamellae that can flake off during wear, exposing fresh steel to damage. Cr carbides remain embedded in the martensitic matrix, providing continuous wear protection.
This makes 45Cr's wear resistance ~50% higher than 45# steel, as measured by weight loss in abrasive wear tests-all while maintaining similar ductility (elongation ≥12%).