5CrNiMo Tool Steel Properties

5CrNiMo tool steel is a reliable low-alloy tool steel widely used for hot work applications, particularly in forging dies. At Aobo Steel, with our extensive experience in tool steel forging, we understand the properties and processing requirements necessary to achieve optimal performance from this grade.

1. 5CrNiMo tool steel Chemical Composition

The typical chemical composition range for 5CrNiMo steel is:

• Carbon (C): 0.50% – 0.60%
• Silicon (Si): ≤ 0.40%
• Manganese (Mn): 0.50% – 0.80%
• Chromium (Cr): 0.50% – 0.80%
• Nickel (Ni): 1.40% – 1.80%
• Molybdenum (Mo): 0.15% – 0.30%

This combination of alloying elements provides a good balance of essential properties for demanding tooling applications.

2. 5CrNiMo tool steel Properties

2.1 Mechanical Properties

• Balance: 5CrNiMo offers a solid combination of strength, toughness, and wear resistance, making it versatile for both hot and cold work applications.
• Plasticity and Toughness: The steel exhibits good ductility and impact resistance.
• Temperature Performance: It maintains relatively stable mechanical properties at room temperature and up to 500-600°C.
• Hardness: Achievable hardness depends directly on the quenching and tempering parameters used. Quenching from 850 °C to 1000 °C, followed by appropriate tempering, typically yields hardness values ranging from the low 30s HRC to the low 50s HRC. Higher quenching temperatures generally increase as-quenched hardness, while higher tempering temperatures reduce hardness but improve toughness.
• Impact Toughness: Heat treatment has a significant influence on impact toughness. While higher quench temperatures might initially lower it, correct tempering enhances this property. The desired plate martensite microstructure achieved after quenching contributes to better toughness.

2.2 Physical Properties

• Thermal Expansion: The coefficient of linear expansion increases with temperature, from around 12.55×10−6°C−1 (100-250°C) to 15.0×10−6°C−1 (600-700°C). This is important for applications involving temperature changes.
• Elastic Modulus: Decreases as temperature rises, from approx. 209,720 MPa (room temp) to 186,200 MPa (500°C).
• Shear Modulus: Also decreases with temperature, from 83,300 MPa (room temp) to 73,500 MPa (500°C).
• Thermal Conductivity: Reduces slightly at higher temperatures, from ~0.44 W/(m·K) (room temp/100°C) to ~0.35 W/(m·K) (500°C).

2.3 High-Temperature Performance

• Strength: While maintaining a usable hardness of ~300 HBW at 500°C, its strength decreases significantly compared to room temperature, potentially halving by 500 °C. It has lower hot stability and a weaker secondary hardening response compared to higher-alloy hot work steels due to its composition.
• Hardness: High-temperature hardness drops notably above 600°C.

3. 5CrNiMo tool steel Applications

Given its property profile, 5CrNiMo is frequently used for:

• Forging Dies: Suitable for large and medium-sized hammer and press forging dies, especially those with complex shapes or subject to impact loads.
• Hot Work Tooling: Used for hot cutting and trimming dies.
• Plastic Molds: Its good polishing characteristics make it suitable for some plastic mold components. Modified grades (like 5CrNiMnMoVSCa) are used for precision injection molds.
• Extrusion Dies: Can be employed for hot extrusion processes.
• Die Components: Often used as the main body for composite dies that incorporate more wear-resistant inserts.
• Forging Equipment Parts: Components like hammer heads and guide rods.
• Cold Work Dies: Applicable in certain cold work scenarios.

4. 5CrNiMo tool steel Heat Treatment

Correct heat treatment is essential for the performance of 5CrNiMo. Aobo Steel’s experience ensures proper handling through these stages:

4.1 Annealing

• Typically performed after forging to soften the steel for machining.
• Common methods: Conventional annealing (760-780°C) or Isothermal annealing (850-870°C, hold ~680°C).
• Cooling: Furnace cool to <500°C, then air cool. Target hardness: 197-241 HBW.

4.2 Quenching

• Standard range: 830-860°C. Staged preheating (e.g., 600-650°C) is recommended.
• Method: Oil quenching is common. Delayed quenching (cooling to 750-780°C in air before oiling) can reduce distortion. Ensure rapid cooling through critical transformation ranges for a martensitic structure, especially in larger sections.
• High-temperature quenching (~900-950°C) can yield lath martensite for improved toughness, but it is essential to avoid excessive grain growth.

4.3 Tempering

• Perform immediately after quenching.
• Forging Dies: Temper between 490-580°C to achieve a hardness of 34-47 HRC, depending on size and use.
• Die Shanks: Temper higher (620-660°C) for increased toughness (30-37 HRC).
• Note: Avoid tempering between 300 °C and 450°C due to the risk of temper embrittlement. Double tempering is often beneficial.

4.4 Surface Treatments

• Nitriding, boronizing, or composite treatments can be applied to enhance surface hardness, wear resistance, and fatigue life.

5. Comparison with Other Tool Steels

• vs. 5CrMnMo: 5CrNiMo generally offers better hardenability and high-temperature properties, making it suitable for larger dies. 5CrMnMo might be chosen for smaller dies that require higher strength and wear resistance over toughness.
• vs. Newer Grades (e.g., 4CrMnSiMoV, 5Cr2NiMoVSi): These grades were developed to address the limitations of 5CrNiMo, offering improved high-temperature strength and fatigue resistance.
• vs. High-Alloy Grades (e.g., H13/4Cr5MoSiV1, 3Cr2W8V): 5CrNiMo has lower hot strength and wear resistance. H13 and similar grades are preferred for very high temperatures or abrasive conditions.

6. Quality and Forging Considerations

The final performance heavily relies on the steel’s metallurgical quality, including inclusion control and homogeneity, as well as proper forging practices.

• Quality Control: Processes such as vacuum refining enhance steel cleanliness.
• Forging: Controlled reduction and slow cooling after forging are crucial to prevent internal defects, to which 5CrNiMo is susceptible. Aobo Steel’s 20+ years of forging expertise ensure these factors are managed correctly.

7. Summary

5CrNiMo is a versatile and economical low-alloy tool steel providing a good balance of toughness, strength, and wear resistance for many hot work forging die applications and some cold work uses. Achieving optimal results depends critically on precise heat treatment and quality starting material. While newer alloys exist, 5CrNiMo remains a standard choice for numerous tooling requirements.