If you need the toughest stuff available for your next metal project, 52100 steel might fill the bill.

One of the best-known of the "bearing steels," 52100 offers high hardness and toughness suitable for some of the most demanding application environments, including high-end knives.

Maxing out the hardness without sacrificing corrosion resistance requires careful heat treating. So, let's get right into it with this guide to heat treating 52100 steel.

What Is 52100 Steel?

52100 steel is a high-carbon, chromium alloy steel. Developed in the early 1900s for ball bearings and other high-stress and -pressure applications, today it's just as popular for making tough blades.

Important Properties

• High hardness: Up to Rockwell C 60-67 after proper heat treating.
• Wear resistance: Able to withstand repeated impact forces without losing shape.
• Low corrosion resistance: Lower chromium concentration than other tool steels such as D2.
• Low machinability: Due to high hardness, it’s difficult to machine without specialized equipment.

Composition

The following concentrations are approximate and will vary by vendor. Check with your supplier on the exact composition of your 52100 steel.

Trace amounts of sulfur and phosphorus are also often present but with negligible impact on properties.

Common Applications

52100 steel is great for making a wide range of parts requiring high strength and wear resistance, including:

• Ball and roller bearings
• Knives and other cutting tools
• Heavy machinery gears in agriculture, mining, transportation, and other demanding industries
• Automotive and aircraft components

52100 Steel Heat Treatments

Optimizing the hardness of your 52100 steel takes paying attention to the heat treating details.

Here's an overview of the key processes. The right parameters for your project depend on your exact material, application, and other factors. So be sure to consult with a metals expert to determine your recipes.

Annealing

Some experts recommend annealing to refine the grain size of the steel, which helps maximize hardness and toughness.

Consider a specialized process called DET (Divorced Eutectoid Transformation ... don't ask) annealing. It involves several cycles of heating and cooling:

1. Heat the furnace to 1700°F.
2. Insert your workpiece and allow it to equalize at temperature. Hold for 20 minutes.
3. Remove from the furnace and air cool. The metal should be black and magnetic before the next cycle.
4. Reheat in the furnace to 1460°F.
5. Hold for 30 minutes.
6. Remove from the furnace and air cool.
7. Repeat steps 4 and 5.
8. Turn off the furnace and allow the metal to cool slowly inside to 1250 °F.
9. Finally, cool in ambient air to room temperature.

Hardening

Hardening 52100 will optimize its wear resistance. This process is also referred to as austenitizing.

1. Heat your furnace to 1500°F.
2. Protect your metal with foil to reduce surface scaling. Insert into the furnace and let it heat up to the target temperature. Monitor with a thermocouple or watch for a bright red color evenly distributed across the metal.
3. Soak at temperature for 15 minutes.
4. Quench immediately in an industrial fast quench oil, such as Parks AAA. Oil quenching produces slightly lower hardness but helps minimize cracking.
5. Move promptly to tempering.

Tempering

Reduce internal stresses caused by the hardening/austenitizing process.

1. Heat your furnace back up to 300-600°F. The lower the temperature, the higher the resulting hardness. The higher end will improve toughness.
2. Insert your workpiece and soak for 30 minutes.
3. Remove from the furnace and air cool.

If you need maximum strength, consider a cryogenic tempering treatment.

Cryo subjects the metal to temperatures as low as -320°F for several hours or more. This process can further increase hardness by Rockwell C 0.5.

Key Considerations & Best Practices

52100 steel isn't the simplest metal to work with where heat treating is concerned. There are a few things to keep in mind for the best results.

Prepare your surface. Proper surface preparation is critical for achieving consistent results. Make sure your workpiece is free of rust, scale, and other contaminants before heat treating.

Mind your quench. Most experts recommend a fast or medium oil quench. Your quenching rate should be rapid enough to achieve full hardness but not so rapid that the steel cracks. Water cooling isn't recommended due to 52100's low corrosion resistance.

Temper with patience. Tempering temperature and time can greatly affect the final properties of 52100 steel. The right temp for your project depends on your desired combination of hardness, toughness, and ductility. You may need to do several cycles. Consult with a metals expert, and don't skimp on this process if you want a long-lasting product.

Ensure even heating and cooling. Uniform heating and cooling are essential to optimal hardening and avoid internal stresses that can lead to frustrating cracks and other imperfections in your metal. Choose a heat treating furnace with precise temperature control, such as a Hot Shot knife and metallurgy oven. With convenient, precision control options and a range of sizes in stock and ready to ship, you're sure to find a solution that suits your needs.

Still have questions about heat treating 52100 steel? Contact our experts anytime. Meanwhile, enjoy working with this strong, blade-friendly material!