If you’ve ever used 1.2311 (P20) mold steel and encountered problems like cracking during machining or poor polishing results, you’re not alone. These are among the most common complaints from mold manufacturers and end users worldwide.

But here’s the key point:

👉 1.2311 itself is not a “bad steel” — most problems come from quality variation and process control.

Let’s break this down clearly and practically so you can identify the real cause and avoid costly mistakes.

1. Internal Steel Quality Issues (The #1 Root Cause)

Problem: Inclusions, porosity, and segregation

Low-quality 1.2311 often contains:

  • Non-metallic inclusions

  • Gas porosity

  • Chemical segregation

These defects act like “weak points” inside the steel.

Impact

  • Cracking during machining or EDM

  • Poor polishing (orange peel, pinholes)

  • Reduced mold life

Why It Happens

  • Poor melting process (no LF/VD refining)

  • No ESR (Electro-Slag Remelting)

  • Low-cost production shortcuts

Solution

✔ Choose steel with:

  • EAF + LF + VD process (minimum requirement)

  • ESR grade for high-end molds

  • UT testing (EN 10228-3 or equivalent)

👉 ESR is the most effective way to improve cleanliness and polishability.

2. Improper Forging Ratio (Structure Not Dense Enough)

Problem

If the forging reduction ratio is too low, the internal structure remains:

  • Coarse

  • Non-uniform

Impact

  • Uneven hardness

  • Weak mechanical properties

  • Higher cracking risk

Typical Scenario

Large blocks cut from insufficiently forged ingots.

Solution

✔ Ensure:

  • Proper forging ratio (≥3:1 recommended)

  • Homogeneous microstructure

3. Residual Stress Inside the Steel

Problem

Residual stress is often left inside the material due to:

  • Improper heat treatment

  • Fast cooling after forging

Impact

  • Cracking during machining

  • Deformation after rough machining

Especially Risky During

  • CNC machining

  • Deep cavity machining

  • EDM processing

Solution

✔ Require:

  • Stress-relief annealing before delivery

  • Optional stress relief after rough machining

4. Poor Pre-Hardening Heat Treatment

Problem

1.2311 is supplied pre-hardened (28–34 HRC), but poor heat treatment can cause:

  • Hardness variation

  • Brittle structure

Impact

  • Cracking during processing

  • Inconsistent machining performance

Common Issues

  • Uneven cooling

  • Incorrect tempering

Solution

✔ Ask supplier for:

  • Hardness uniformity report

  • Heat treatment process details

5. Chemical Composition Deviation

Problem

If alloy elements are not well controlled:

  • Too high carbon → brittle → cracking

  • Too low alloy content → poor hardness → poor wear resistance

Impact

  • Reduced toughness

  • Poor polishing performance

Solution

✔ Always check:

  • Mill Test Certificate (MTC)

  • Composition within standard range

6. Low Cleanliness → Poor Polishing Performance

Problem

Polishing defects like:

  • Pinholes

  • Black spots

  • “Orange peel” surface

are often caused by:

👉 Non-metallic inclusions inside steel

Impact

  • Cannot achieve mirror finish

  • Surface defects in plastic parts

Solution

✔ For high polish requirements:

  • Choose ESR 1.2311 or upgrade to:

    • 1.2738

    • 1.2316 (for mirror finish)

Final Conclusion

If your 1.2311 steel is:

  • Cracking easily ❌

  • Difficult to machine ❌

  • Poor in polishing ❌

👉 The root cause is usually quality, not the material itself.

Key Takeaways

✔ Choose the right process (at least LF + VD)
✔ Ensure proper forging and heat treatment
✔ Match material with application
✔ Work with a reliable supplier

Need Reliable 1.2311 Steel?

At  Otai Special Steel, we help customers avoid exactly these problems.

✔ Stable quality control
✔ ESR grade available
✔ Strict UT inspection
✔ Export experience worldwide

📩 Contact us today: