Cr12 steel technical overview

Cr12 steel technical overview: At Aobo Steel, we have extensive experience with tool steels, and Cr12 is a significant material in the cold work category. It’s a high-carbon, high-chromium ledeburitic steel, known primarily for its high hardness and excellent wear resistance.

1. Chemical Composition:

The specific composition can vary slightly, but typically, you’ll find:

• Carbon (C): 2.00%  – 2.30%
• Chromium (Cr): 11.50 % – 13.00%
• Silicon (Si): ≤ 0.40%
• Manganese (Mn): ≤ 0.40%
• Phosphorus (P): ≤ 0.030%
• Sulfur (S): ≤ 0.030%

The high carbon content contributes significantly to its hardness but also results in lower impact toughness and a tendency toward brittleness compared to lower-carbon grades. The high chromium content is key, forming hard (CrFe)7C3 carbides.

2. Microstructure and Properties:

Cr12 solidifies with a network of eutectic carbides, making up about 20% of the volume. These carbides are hard and brittle. While forging and hot rolling – processes we have over 20 years of experience with at Aobo Steel – help break down and distribute these carbides, they often remain segregated, especially in larger diameter bars. This non-uniformity is a core characteristic of Cr12 and presents challenges that require careful processing. Heat treatment alone generally cannot eliminate this segregation entirely.

Beyond its hardness and wear resistance, Cr12 exhibits:

• Relatively poor impact toughness.
• Lower thermal conductivity.
• Limited high-temperature plasticity.

3. Heat Treatment:

Proper heat treatment is critical to achieving the desired properties in Cr12.

3.1 Hardening

Typically involves quenching from 930-980°C (1706-1796°F) in oil or air. The Ac1 point is around 810°C (1490°F), and the Ms temperature is about 180°C (356°F). Adjusting the quenching temperature controls alloy dissolution and retained austenite levels, influencing final dimensions.

3.2 Tempering

Performed after quenching to achieve target hardness and relieve stress. Common tempering ranges and resulting hardness (approximate HRC) are:

• 100°C (212°F): ~64 HRC
• 200°C (392°F): ~62 HRC (Recommended for stress relief/stabilization, 2-hour soak)
• 300°C (572°F): ~59 HRC
• 320-350°C (608-662°F): ~57-58 HRC (For stress relief and hardness reduction, 2-hour soak)
• 400°C (752°F): ~57 HRC

3.3 Refining Treatments

To improve toughness, specialized treatments like high-temperature solution (1100–1150°C / 2012-2102°F) followed by specific quenching/tempering cycles (double refining) can refine carbides and grain structure. These processes can significantly improve the service life of Cr12 tools.

Important Note: The non-uniform carbide structure increases the risk of cracking during or after quenching if not managed carefully.

4. Applications:

Cr12 is best suited for cold work applications demanding high wear resistance where impact loading is not severe. Common uses include:

• Wear-resistant stamping dies (e.g., for silicon steel sheets).
• Drawing dies (hardness target: 62-64 HRC).
• Coining dies.
• Thread rolling plates and dies.
• Cold extrusion dies and punches (e.g., for aluminum parts, target hardness 60-62 HRC).
• Gauges, drill sleeves.
• Complex punches, inserts in bending dies.
• High-wear-resistance plastic molds.

5. International Equivalents:

You’ll find Cr12 under different designations globally:

• ASTM/UNS: D3 / T30403
• ISO:210Cr12
• EN/DIN: X210Cr12 (1.2080)
• JIS/KS: SKD1 / STD1
• GOST:Х12
• BS: BD3
• AFNOR: Z200Cr12

6. Handling and Processing Considerations:

• Cooling/Annealing: Ingots require controlled cooling and prompt annealing after solidification (transfer hot or use controlled heating rates for cold ingots) to prevent cracking and relieve stress. Avoid excessive heating/cooling rates.
• Grinding: Surface defects should be handled carefully. If grinding is necessary, use soft wheels and light pressure and avoid localized overheating (bluing), which can cause micro-cracks that propagate during subsequent heating.

7. Comparison with Similar Grades:

• Cr12MoV: Contains Molybdenum (Mo) and Vanadium (V) with slightly lower carbon. This improves toughness, hot workability, and carbide distribution compared to Cr12.
• Cr12Mo1V1 (D2):  Due to its higher Mo and V content, Cr12Mo1V1 offers further improvements over Cr12MoV. It often provides significantly longer tool life in demanding applications, making it a frequent replacement choice.

8. Summary:

Cr12 is a high-carbon, high-chromium tool steel defined by its hardness and wear resistance. Its primary limitation is lower toughness due to the inherent eutectic carbide network. Success with Cr12 depends on careful heat treatment and processing, making it a reliable choice for specific cold work tooling applications where wear is the main concern.