9Cr18Mo Steel Technical Overview

9Cr18Mo Steel Technical Overview: 9Cr18Mo is a high-carbon, high-chromium martensitic stainless steel. The deliberate addition of molybdenum enhances several key properties, making it a valuable material for specific applications. At Aobo Steel, we leverage our extensive forging experience to supply high-quality 9Cr18Mo tailored to customer requirements.

1. 9Cr18Mo Steel Chemical Composition (Weight %)

The typical chemical composition of 9Cr18Mo, according to standard GB/T 1220-2007, is:

• Carbon (C): 0.95 – 1.10%
• Silicon (Si): ≤ 0.80%
• Manganese (Mn): ≤ 0.80%
• Chromium (Cr): 16.00 – 18.00%
• Molybdenum (Mo): 0.40 – 0.70%
• Sulfur (S): ≤ 0.030%
• Phosphorus (P): ≤ 0.040%

Comparable international grades include JIS SUS 440C and ASTM 440C. A closely related Chinese grade is G102Cr18Mo (GB/T 3086-2008).

2. 9Cr18Mo Steel Key Properties and Characteristics

• High Hardness and Wear Resistance: Following appropriate heat treatment, 9Cr18Mo achieves high hardness levels, providing excellent resistance against wear and abrasion.

• Enhanced Tempering Resistance: The molybdenum content improves the steel’s ability to resist softening during tempering, allowing it to retain hardness better at elevated service temperatures.

• Good Corrosion Resistance: With 16-18% chromium, further supported by molybdenum, this grade offers good resistance to corrosion, particularly in specific environments.

• High-Temperature Dimensional Stability: 9Cr18Mo maintains relatively good dimensional stability when exposed to elevated temperatures.

• Microstructure Considerations: As a ledeburitic steel, 9Cr18Mo can be prone to uneven carbide segregation. Proper control during the hot working process ensures optimal material structure and performance. Aobo Steel’s forging expertise ensures careful management of this aspect.

3. 9Cr18Mo Steel Heat Treatment Guidelines

• Hardening: Achieving the desired martensitic structure and high hardness requires quenching from a suitable austenitizing temperature.

• Tempering: Tempering after hardening is necessary to achieve the desired balance of hardness and toughness for the intended application. Specific parameters depend on final property requirements.

• Sub-Zero Treatment (Optional): A sub-zero (cryogenic) treatment (e.g., -75°C to -80°C) can be employed after quenching to minimize retained austenite for applications demanding maximum hardness and dimensional stability.

4. 9Cr18Mo Steel Hot-Working Recommendations

Strict control over hot working parameters is essential for 9Cr18Mo due to its ledeburitic nature and tendency for carbide segregation. Recommended temperature ranges are:

• Steel Ingots:

  • Heating: 1130 – 1150°C
  • Start Forging: 1080 – 1095°C
  • End Forging: 850 – 900°C
  • Cooling: Sand cool after forging

• Steel Billets:

  • Heating: 1100 – 1120°C
  • Start Forging: 1050 – 1080°C
  • End Forging: 850 – 900°C
  • Cooling: Sand cool after forging

5. Applications

The combination of high hardness, wear resistance, corrosion resistance, and dimensional stability makes 9Cr18Mo suitable for:

• Plastic molds, especially those operating in corrosive environments or under high wear conditions.
• Rubber molds require good wear and corrosion resistance.
• Components that must maintain dimensional stability at elevated temperatures.
• Cutting tools and wear parts intended for use in corrosive media.