52100 Bearing Steel | 1.3505 | 100Cr6

2. Properties of 52100 Bearing Steel

This section details the critical characteristics of AISI/SAE 52100 steel that make it a preferred material in numerous industries.

Hardness Potential and Heat Treatment Response

One of the standout 52100 bearing steel properties is its exceptional hardness capability.

• Achievable Hardness: With appropriate heat treatment, 52100 steel consistently achieves a hardness of 60 to 64 HRC throughout its section. For example, a 1-inch-thick piece can reach approximately 60 HRC when tempered around 204°C (400°F).
• Bearing Applications: For critical ball bearing components, a minimum hardness of 62 HRC is typically specified and achieved after hardening and tempering.
• Hot Hardness: It’s important to consider that the hot hardness of 52100 steel decreases notably as operating temperatures rise.

2.1 Microstructure Characteristics

The microstructure of 52100 steel after correct heat treatment is fundamental to its performance:

• Typical Structure: It primarily consists of high-carbon martensite with finely dispersed primary (undissolved) spherical carbides. A retained austenite content of 5 to 10% is also typical.
• Wear Resistance Contribution: For bearing applications, 52100 steel is intentionally austenitized below its Acm temperature. This process encourages the formation of cementite carbide arrays within the final martensitic structure, significantly enhancing wear resistance.
• Cleanliness: A clean microstructure, free from excessive inclusions, is vital, especially for applications requiring highly polished surfaces, such as dies.

2.2 Core Mechanical Strengths of 52100 Steel

52100 alloy steel is engineered for high load-bearing capacity and resilience.

2.3 Fatigue Performance

High fatigue life is a critical property of 52100 bearing steel, especially for components like journal bearings subjected to cyclic loading. The fatigue resistance can be influenced by factors such as inclusion content and the precision of heat treatment. Quality control, including fatigue testing, is paramount.

2.4 Wear Resistance

52100 steel demonstrates good wear resistance. This is significantly enhanced by the presence of very small, hard cementite particles that are uniformly distributed within the microstructure after optimal heat treatment. Specialized treatments, like duplex processes, can further improve wear characteristics compared to standard chromizing or other alloy steels like 8620 in certain conditions.

2.5 Hardenability

Thanks to its chromium content, 52100 steel possesses good hardenability. This allows it to achieve consistent hardness through its cross-section in parts up to approximately 1 inch thick. Its hardenability is comparable to that of 5280 steel.

2.6 Machinability

For the best machining outcomes and to ensure a uniform response during subsequent hardening processes, a spheroidized microstructure is highly recommended for 52100 steel. This condition improves tool life and surface finish.

2.7 Material Cleanliness and Quality

High-quality 52100 bearing steel is produced with a strong emphasis on internal soundness, cleanliness, and uniform chemical composition.

• Inclusion Control: For critical applications like ball bearings, very low levels of non-metallic inclusions (e.g., Type A, B, C, D) and minimal oxygen content are essential.
• Melting Processes: Advanced melting techniques such as consumable-electrode vacuum melting (CEVM) or electroslag remelting (ESR) can provide the exceptionally clean microstructure required for demanding applications like polished dies.
• Casting Considerations: When producing 52100 steel via modern continuous casting, insufficient homogenizing cycles can lead to segregation and undesirable carbide distributions, negatively impacting its properties and heat treatment response.
• Standards: ASTM A 535 covers special quality alloy steel billets, bars, tube rounds, rods, and tubes intended for manufacturing antifriction bearings.

2.8 Dimensional Stability

Achieving very high dimensional stability in 52100 steel components requires precise control over heat treatment. It can be sensitive to distortion, and tempering to a lower hardness might be necessary compared to some advanced steels if ultimate stability is the primary goal. Incorrect austenitizing temperatures or tempering practices can lead to cracking.

2.9Weldability

It is important to note that 52100 bearing steel is generally considered nonweldable due to its high carbon content, which makes it prone to cracking during and after welding.

2.10 Toughness

When correctly oil quenched from around 850°C (1560°F) to achieve a microstructure of dispersed spherical carbides in tempered martensite, 52100 steel exhibits good toughness. This can be assessed using standard tests like Charpy V-notch impact energy and plane-strain fracture toughness (KIc). Studies have shown that 52100 bainite can offer higher impact toughness compared to some powder-forged steels.