15CrMo Alloy Steel
15CrMo alloy steel is a widely used low-alloy heat-resistant steel with excellent high-temperature mechanical properties and oxidation resistance. Here is a detailed introduction:
Basic Information
Definition: 15CrMo is a low-alloy structural steel containing chromium and molybdenum, known for its good heat resistance, corrosion resistance, and mechanical properties.
Corresponding Standards: Complies with Chinese standard GB/T 3077, approximately equivalent to AISI 4115 in the United States and 15CrMo4 in European standards.
Chemical Composition
Carbon (C): 0.12%-0.18%, providing moderate hardness and strength while maintaining good weldability.
Silicon (Si): 0.17%-0.37%, improving oxidation resistance and strength.
Manganese (Mn): 0.40%-0.70%, enhancing hardenability and mechanical properties.
Chromium (Cr): 0.80%-1.10%, improving high-temperature strength, oxidation, and corrosion resistance.
Molybdenum (Mo): 0.40%-0.55%, the key element that enhances heat resistance and creep resistance at high temperatures.
Phosphorus (P): ≤0.035%, a harmful element controlled to prevent brittleness.
Sulfur (S): ≤0.035%, strictly controlled to avoid reducing toughness and weldability.
Physical Properties
Density: Approximately 7.85 g/cm³.
Melting Point: Around 1450°C.
Thermal Conductivity: About 44 W/(m·K) at room temperature.
Coefficient of Thermal Expansion: Approximately 12×10⁻⁶/°C (20-100°C).
Mechanical Properties
Tensile Strength: ≥440 MPa after heat treatment.
Yield Strength: ≥295 MPa.
Elongation: ≥22% (after fracture).
Impact Toughness: ≥63 J/cm² at room temperature.
Hardness: ≤179 HB in the annealed state.
Good High-Temperature Performance: Maintains stable mechanical properties at temperatures up to 500-550°C, with excellent creep resistance.
Heat Treatment Process
Normalizing: Typically heated to 900-950°C, held for a period, then air-cooled to refine grains and uniformize structure.
Tempering: Usually performed at 600-650°C after normalization or quenching to eliminate internal stress and adjust mechanical properties.
Annealing: Conducted at 880-920°C followed by slow cooling to reduce hardness and improve machinability.
Processing Performance
Weldability: Generally good, but preheating (150-300°C) and post-weld heat treatment are recommended to prevent cold cracking.
Machinability: Good in the annealed state; higher hardness after heat treatment may increase cutting resistance.
Formability: Can be cold-worked using conventional methods when in the annealed condition.
Application Fields
Petrochemical Industry: Widely used in high-temperature and high-pressure pipelines, reactors, and heat exchangers.
Power Generation: Used in boiler components, steam pipes, and turbine parts operating under high temperatures.
Mechanical Manufacturing: Applied in the production of high-temperature bolts, nuts, and other fasteners.
Automotive Industry: Utilized for manufacturing exhaust system components and high-temperature bearings.
Aerospace: Employed in certain aircraft engine parts requiring heat resistance.
The combination of chromium and molybdenum in 15CrMo steel creates a synergetic effect that significantly improves its high-temperature strength and corrosion resistance, making it indispensable in various industrial applications involving elevated temperatures and pressures.