5CrNiMo Hot Work Mold Steel
5CrNiMo is a typical hot work mold steel widely used in the manufacturing of molds subjected to high temperatures, high pressures, and alternating thermal shocks. Its chemical composition and mechanical properties endow it with excellent hot strength, wear resistance, and toughness, making it particularly suitable for applications such as hot forging and hot extrusion molds.
I. Chemical Composition (Typical Range)
The chemical composition of 5CrNiMo is central to its performance, with common element content ranges as follows:
Element Content Range (Mass Fraction, %) Role
Carbon (C) 0.50~0.60 Enhances hardness and wear resistance, providing the strength foundation for molds.
Chromium (Cr) 0.50~0.80 Improves hardenability, oxidation resistance, and corrosion resistance; enhances stability at high temperatures.
Nickel (Ni) 1.30~1.80 Significantly improves toughness and impact performance, especially maintaining toughness at high temperatures.
Molybdenum (Mo) 0.20~0.50 Enhances hardenability, hot strength, and wear resistance; inhibits grain growth at high temperatures and reduces temper brittleness.
Silicon (Si) 0.25~0.60 Strengthens the steel, improves hardenability, and optimizes casting performance.
Manganese (Mn) 0.50~0.80 Enhances hardenability and strength, and refines grain structure.
Phosphorus (P) ≤0.030 A harmful impurity; controlled to avoid increased brittleness.
Sulfur (S) ≤0.030 A harmful impurity; excessive content reduces toughness and hot workability.
II. Mechanical Properties (After Heat Treatment)
5CrNiMo achieves optimal performance through proper heat treatment (quenching + tempering). Typical mechanical properties are as follows:
Hardness: After quenching + high-temperature tempering, hardness is usually 30~45 HRC (adjusted based on tempering temperature to meet different mold requirements).
Tensile Strength: ≥800 MPa.
Yield Strength: ≥600 MPa.
Impact Toughness (αk): ≥30 J/cm² (at room temperature, transverse specimen), maintaining high toughness even at elevated temperatures.
Heat Resistance Temperature: Can work continuously at 500~600°C, with excellent resistance to thermal fatigue.
III. Heat Treatment Process
Proper heat treatment is crucial to unleash the full potential of 5CrNiMo:
Annealing
Purpose: Soften the steel for machining and homogenize the microstructure.
Process: Heat to 830~850°C, hold for 3~4 hours, then cool slowly (≤30°C/hour) to 600°C, followed by air cooling. Results in a hardness of ≤241 HB.
Quenching
Temperature: 830~860°C.
Holding Time: 1~2 hours (depending on part thickness) to ensure uniform austenitization.
Cooling Medium: Oil quenching to achieve a martensitic structure, with as-quenched hardness of 50~55 HRC.
Tempering
Temperature Range: 500~650°C (adjusted based on desired hardness).
Holding Time: 2~3 hours (double tempering recommended to eliminate retained austenite and reduce internal stress).
Effect: Balances hardness and toughness; higher temperatures increase toughness while slightly reducing hardness.
IV. Processing Performance
Machinability: Good in the annealed state (≤241 HB), suitable for turning, milling, and drilling with high-speed steel or carbide tools.
Weldability: Moderate; requires preheating to 300~400°C and post-weld tempering to prevent cracking. Welding is primarily used for mold repair.
Forging Performance: Excellent; forged at 1100~1150°C, followed by slow cooling to avoid cracking.
V. Application Fields
5CrNiMo is widely used in hot work mold applications requiring resistance to thermal shock and high pressure:
Hot Forging Molds: Forging dies for steel parts (e.g., automotive crankshafts, connecting rods) and large mechanical components.
Hot Extrusion Molds: Dies for extruding non-ferrous metals (e.g., aluminum, copper alloys) and low-carbon steel.
Die Casting Molds: Molds for medium-sized aluminum or zinc alloy die castings.
Other Hot Work Tools: Hot shear blades, upsetting dies, and pressure casting molds.
In summary, 5CrNiMo hot work mold steel is valued for its balanced combination of hot strength, toughness, and thermal fatigue resistance, making it a reliable choice for demanding hot forming processes in automotive, machinery, and metallurgical industries.