16MnCr5 round steel (EN 10084; GB equivalent 20MnCr5) has a composition of 0.14–0.19% carbon (C), 0.15–0.40% silicon (Si), 1.00–1.30% manganese (Mn), 0.80–1.10% chromium (Cr), ≤0.035% phosphorus (P), 0.015–0.035% sulfur (S).
Compared to 20CrMnTi (0.17–0.23% C, 0.17–0.37% Si, 0.80–1.10% Mn, 1.00–1.30% Cr, 0.04–0.10% Ti, ≤0.035% S), 16MnCr5 has two chemical differences that improve machinability:
Higher sulfur (0.015–0.035% vs. ≤0.035%): While both grades have similar sulfur limits, 16MnCr5's sulfur is intentionally controlled to form fine, evenly distributed manganese sulfide (MnS) inclusions. These inclusions act as chip breakers during machining, causing metal chips to snap into small pieces instead of long strings that clog tools. In 20CrMnTi, titanium reacts with sulfur to form titanium sulfides (TiS), which are harder and less effective at chip breaking.
No titanium: 20CrMnTi's titanium (0.04–0.10%) forms hard titanium carbides (TiC) that increase tool wear during machining. Without titanium, 16MnCr5 has fewer hard inclusions, reducing friction between the cutting tool and steel surface-this extends tool life and allows faster cutting speeds.
Lower carbon (0.14–0.19% vs. 0.17–0.23%) in 16MnCr5 also contributes to machinability by reducing the steel's overall hardness, making it easier to cut without excessive tool force.