EN31 52100 Bearing Steel: Properties, Uses & Manufacturing Guide

What are the core properties of EN31 52100?

EN31 52100 is a high-carbon chromium bearing steel. Its chemistry and heat treatment are tailored to deliver the hardness and toughness needed for rolling or sliding components. Tight chemical controls ensure consistent performance.

Chemical composition

The elements work together to provide high hardness after heat treatment and excellent fatigue strength.

Physical properties

These traits are essential for design and manufacturing calculations.

• Density: 7.81 g/cm³
• Melting point: 1,420–1,460°C
• Thermal conductivity: 42 W/(m·K) at 20°C
• Thermal expansion: 11.5 × 10⁻⁶/°C (20–100°C)
• Electrical resistivity: 0.20 Ω·mm²/m at 20°C

Mechanical properties

EN31 52100’s mechanical performance shines after quenching and tempering. Here’s how it compares to a common carbon steel.

A bearing manufacturer switched from 1045 steel to EN31 52100 for electric motor ball bearings. The EN31 bearings lasted 5 times longer—from 2,000 to 10,000 operating hours—and reduced friction-related energy loss by 8%.

Other key properties

• Wear resistance: Excellent. High hardness makes it 3–4 times more wear-resistant than 1045 steel.
• Fatigue strength: Outperforms carbon steel by 80–130%. Components last longer under repeated stress.
• Corrosion resistance: Better than plain carbon steel. Chromium adds a thin oxide layer that slows rusting.
• High-temperature strength: Maintains hardness and strength up to 200°C.
• Weldability: Moderate. Requires preheating to 200–300°C to avoid cracking. Post-weld heat treatment is recommended.
• Formability: Best shaped via forging or cold rolling. Hot forming is easier than cold forming due to high carbon content.

Where is EN31 52100 used?

EN31 52100’s combination of wear resistance and fatigue strength makes it indispensable across industries.

Bearings (primary application)

It’s the gold standard for bearing components where low friction and long life are critical.

• Ball bearings: Inner and outer rings and balls for electric motors, pumps, and automotive wheels
• Roller bearings: Cylinders or tapered rollers for heavy-duty machinery like construction equipment
• Thrust bearings: Plates and rollers handling axial loads in gearboxes or turbines

Automotive

Automotive relies on it for high-stress, high-wear components.

• Engine components: Camshafts, valve lifters, and timing gears resist wear from metal-to-metal contact
• Transmission components: Gear teeth and shafts handle torque and repeated shifting
• Steering components: Tie rod ends and steering knuckles withstand road vibrations

Industrial machinery

Industrial equipment uses it for durable, low-maintenance parts.

• Gears: High-precision gear teeth in conveyors, mixers, and machine tools
• Shafts: Drive shafts and spindle shafts resist bending and wear
• Machine parts: Guide rails and sliding blocks for CNC machines or presses

Aerospace and railway

• Aerospace: Aircraft engine bearings and landing gear components withstand extreme stress and temperature changes
• Railway: Freight train axles handle heavy loads and vibration

A railway manufacturer used EN31 52100 for freight train axles. The axles lasted 3 times longer than HSLA steel—from 500,000 to 1.5 million km—and reduced maintenance costs by 40%.

How is EN31 52100 manufactured?

EN31 52100 requires precise manufacturing and heat treatment to unlock its full potential.

Steelmaking and heat treatment

• Steelmaking: Electric arc furnace (EAF) is most common. Ensures tight control over impurities critical for bearing performance.
• Quenching and tempering: Heat to 830–860°C, quench in oil or water, then temper at 150–200°C. Achieves 58–62 HRC hardness while reducing brittleness.
• Carburizing (optional): For parts needing hard surface and tough core like gear teeth. Creates 0.5–1 mm hard surface layer at 60+ HRC with tough core.
• Nitriding (optional): Enhances surface hardness and corrosion resistance. Forms thin hard layer of 5–15 μm at 70+ HRC.

Forming and surface treatment

• Hot rolling: Heats to 1,100–1,200°C and rolls into bars, rods, or sheets for bearing blanks.
• Forging: Heats and hammers into complex shapes like landing gear components.
• Chromium plating: Adds corrosion resistance and reduces friction for bearings.
• Titanium nitride coating: Harder than steel for cutting tools or high-wear gears.
• Shot peening: Creates compressive stress, improving fatigue resistance.

How to write a spec that gets priced correctly

A drawing is a contract. If it leaves a number open, the shop fills that number in with its own default. The default is rarely the one you had in mind. Put these five lines on every RFQ and most of the back-and-forth disappears before it starts.

• Alloy designation and the standard behind it
• Temper or heat treatment condition
• Mechanical properties you actually need
• Mill certificate and traceability requirement
• Finish and the faces it applies to

The point is not paperwork. Each line removes a decision the shop would otherwise make for you. A complete RFQ comes back priced. An incomplete one comes back guessed.

What actually drives the price

Buyers usually push on material because it is the line they can see. In practice the material is rarely the biggest number on a quote. These five lines decide most of it:

• alloy grade and mill availability
• stock size versus finished size
• heat treatment and testing
• machinability
• certification

Ask for the quote split by line. A supplier who cannot break it down is guessing, and you will pay for the guess. The line you can usually renegotiate is the tolerance band, not the raw material.

Problems you will meet, and the fix

Every process has a failure mode it prefers. The same four show up again and again on this kind of work, and none of them are mysteries once you know what to look for.

• Substituting a similar grade without telling anyone
• Hardness that varies across a single bar
• Corrosion in a weld heat-affected zone
• Distortion after heat treatment on a thin part

Catch the fault on the first part, not the hundredth. A first-article check costs an hour. A bad batch costs the whole order. Write the check into the purchase order so nobody has to remember it.

What to check on the first article

The first article is the cheapest inspection you will ever buy. Use it properly and the rest of the run becomes boring, which is exactly what you want.

• Every dimension on the drawing, with the measured value written beside it.
• The material certificate, matched to the heat or lot number on the parts.
• The finish against the sample you approved, under the same light.
• Fit against the mating part, assembled rather than measured.
• Packaging, because parts that arrive damaged were never in tolerance.

Check in this order: datums, then mating features, then cosmetic faces. If the datums are wrong, every number after them is noise. Keep the report on file. When a problem shows up in month six, that document is the only thing that tells you what changed.

How to compare two quotes fairly

Two numbers are not comparable unless the scope matches. Line them up before you decide, because a low number with three gaps is not a low number.

Same drawing, same material, same finish, same inspection. Anything else is a different job wearing the same part number. Then look at what each quote leaves out. Freight, packaging, certificates and tooling are the usual gaps.

Ask each supplier to state their assumptions in writing. The one who does is usually the one who has run the process before.

Scaling from one part to a batch

The first part teaches you the process. The hundredth teaches you the process cost.

Watch three things as volume grows: setup amortisation, tool wear, and how much hand work the finish still needs. If the unit price barely moves between ten and a hundred, the cost sits in material or in hand work, not in setup. Ask which, because only one of them is negotiable.

Lead time behaves the same way. A one-off is scheduled around other jobs. A repeat order is scheduled around your forecast. Give the shop a forecast and the lead time gets shorter, not longer.

How to read a supplier's quote

A quote is a short document with a long shadow. Four things in it decide whether the job runs smoothly, and only one of them is the price.

• The scope line. It should name the process, the material and the finish, not just the part.
• The tolerance basis. General tolerance or the drawing, and which standard it follows.
• The exclusions. Tooling, freight, certificates and inspection are the usual omissions.
• The validity date. Material prices move, and an open-ended quote is a promise nobody can keep.

Read the exclusions before you read the total. A quote that leaves out tooling is not cheaper. It is a quote for a different job.

What to send with the first order

The first order sets the pattern for every order after it. Send a complete package once and the shop files it, and the second order takes a fraction of the time.

• A STEP or native model plus a PDF drawing carrying the same revision letter.
• The material callout by standard number, not by trade name.
• The finish and the exact faces it applies to.
• Any test the part must pass: fit, seal, drop, salt spray, dielectric.
• A contact who can answer a question inside one working day.

Then write down what was agreed. An email that confirms the material, the finish and the date is worth more than a longer purchase order that leaves them open.

When this is the wrong choice

A good supplier tells you when the process does not fit. These are the cases where we say so.

• The volume is so low that setup costs more than the parts are worth.
• The tolerance is tighter than the process can hold without a second operation.
• The geometry cannot be made without a tool feature that will not pay back.
• The material you need is not available in the form the process requires.
• The schedule is shorter than the tooling or setup time, and nobody has said so yet.

None of these are refusals. They are reasons to look at a different route, and the earlier that conversation happens the cheaper it is. The most expensive mistake in manufacturing is a process chosen before the question was understood.

Planning the ramp from prototype to production

The gap between one good part and a thousand identical ones is a plan, not a machine. Three decisions close it.

First, freeze the design. Every change after tooling starts is a re-cut, and re-cuts are where schedules go. Second, decide the inspection level. A prototype is checked by eye; a production part is checked against a report. Third, agree the change process in writing, including who pays for it.

Write the ramp down as dates and owners, not as intentions. A ramp plan with three names and three dates is worth more than a page of good intentions.

What documentation to expect

Paperwork is not bureaucracy when a part fails at the customer. It is the only record of what was agreed. A normal shipment should carry four documents.

• A dimensional report covering every callout on the drawing.
• A material certificate traceable to the heat or lot number.
• A finish or coating certificate where the specification requires one.
• A packing list that matches the carton labels.

If a supplier cannot produce these on request, they are not running a controlled process. Ask for one sample set before you place the first order and you will know exactly what you are buying.

How to handle a change after the order

Changes happen. What matters is whether the change is priced, scheduled and recorded, or absorbed quietly and discovered later.

Send the change as a new revision, not as a note in an email. Ask for three answers in writing: what it costs, what it does to the date, and what happens to material or tooling already committed. Then decide.

A change without a revision number is a rumour. The shop will build what it has on file, and both sides will be right and unhappy at the same time.

How does EN31 52100 compare to other materials?

Choosing EN31 52100 means understanding its advantages over alternatives.

Key takeaways:

• EN31 52100 offers superior wear resistance and fatigue strength compared to carbon and stainless steels
• It’s more cost-effective than specialty alloys for wear-focused applications
• Its high hardness makes it ideal for bearings, gears, and high-stress components

EN31 52100 bearing steel delivers exceptional wear resistance and fatigue strength for high-stress, high-wear applications. Its high carbon and chromium content, combined with precise heat treatment, provides hardness up to 62 HRC and fatigue resistance up to 700 MPa. For bearings, automotive transmission parts, and industrial gears where component life matters, it offers proven reliability and long service life.

Our solution for EN31 52100 Bearing Steel: Properties

YiguProto runs metal sourcing and machining in house, from a single prototype to a production batch. We quote the process, the material and the finish as separate lines, so you can see where the money goes instead of arguing with one number.

Send a STEP file or a drawing and you get a DFM report in one to two business days. It flags the features that add cost and the features that will not hold tolerance on the process you picked.

Every order ships with an inspection report on the features you call out. If a part misses, we make it again. Ready to price a part? Start with a free quote and DFM review, or read more about our metal sourcing and machining. You can also talk to an engineer before you commit to a drawing.

FAQ about EN31 52100 Bearing Steel: Properties

The short version

EN31 52100 Bearing Steel: Properties rewards the buyer who reads the data sheet and the drawing together. Pick the option for the property that matters, not for the price per kilo.

Tighten only what mates. Test a sample before the run. Then let the process do the rest.