52100

52100 is a high-carbon chromium alloy steel designated in the SAE/AISI system for bearing applications. It is widely used for bearing rings, balls, and races due to its combination of hardness, wear resistance, and toughness. In Japanese standards it is known as SUJ2, and in European standards it corresponds to EN 100Cr6, a common bearing steel grade.

Composition and designation figures typically place carbon around 0.98 to 1.10 percent and chromium around 1.3 to 1.65 percent, with smaller amounts of manganese, silicon, and very low phosphorus and sulfur. This composition enables through-hardening and popular heat-treatment responses that yield high surface and core hardness.

Properties and behavior: 52100 is valued for its ability to be hardened throughout the cross-section, producing high wear resistance and fatigue strength after appropriate heat treatment. It is not stainless steel; while chromium improves hardenability and some corrosion resistance, the steel remains susceptible to rust without lubrication or protective measures. Machinability is moderate and improved with proper tooling and coolants.

Heat treatment commonly involves austenitizing around 830–900°C, followed by oil quenching and tempering at roughly 150–200°C to achieve final hardness typically in the range of HRC 60–66, depending on size and desired properties. For enhanced surface wear resistance, surface hardening or nitriding can be employed post-hardening.

Applications and standards: beyond ball and roller bearing components, 52100 is selected where a balance of hardness, toughness, and resistance to wear is required. It remains one of the most widely used bearing steels globally, with equivalents in other standards such as JIS SUJ2 and EN 100Cr6.