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Composition and Properties of 18CrMnBH Gear Steel
18CrMnBH gear steel is a specialized steel grade designed for the transmission gears of heavy-duty trucks. It is produced using a process involving a 100-ton DC electric arc furnace, LF (VD) refining, 300mm square continuous casting, and continuous rolling to yield 18CrMnBH steel bars with diameters ranging from φ80mm to φ120mm. Following vacuum degassing, a combined addition of Aluminum (Al) and Titanium (Ti) is employed to ensure the steel achieves a grain size within the range of Grade 5 to Grade 8. All performance indicators meet or exceed the standards typically associated with ingot-cast steel.
Chemical Composition of 18CrMnBH Steel:
Carbon (C): 0.15–0.20
Silicon (Si): 0.15–0.37
Manganese (Mn): 1.00–1.30
Sulfur (S): 0.015–0.035 (Residual limit: ≤0.035)
Phosphorus (P): ≤0.030 (Residual limit)
Chromium (Cr): 0.90–1.30
Nickel (Ni): ≤0.030 (Residual limit)
Copper (Cu): ≤0.030 (Residual limit)
Boron (B): 0.001–0.003
18CrMnBH steel is commonly used in the manufacture of automotive components, machinery parts, and similar applications. Its typical heat treatment process is outlined below:
1. Annealing: The steel undergoes annealing at a temperature of 800–850°C, with a holding time of 1–2 hours. The objective is to soften the steel, relieve internal stresses and structural defects, and enhance its plasticity and toughness.
2. Quenching: The steel is heated to a temperature of 850–880°C and subsequently cooled rapidly in either water or oil. The purpose of this step is to induce the formation of a hard martensitic structure on the steel's surface, thereby increasing its hardness and strength.
3. Tempering: The martensitic structure formed on the steel's surface after quenching is inherently brittle; therefore, a tempering process is required to reduce hardness while simultaneously improving toughness and machinability. The tempering temperature typically ranges from 150°C to 500°C, with the holding time adjusted according to specific requirements.
Chemical Composition of 18CrMnBH Steel:
Carbon (C): 0.15–0.20
Silicon (Si): 0.15–0.37
Manganese (Mn): 1.00–1.30
Sulfur (S): 0.015–0.035 (Residual limit: ≤0.035)
Phosphorus (P): ≤0.030 (Residual limit)
Chromium (Cr): 0.90–1.30
Nickel (Ni): ≤0.030 (Residual limit)
Copper (Cu): ≤0.030 (Residual limit)
Boron (B): 0.001–0.003
18CrMnBH steel is commonly used in the manufacture of automotive components, machinery parts, and similar applications. Its typical heat treatment process is outlined below:
1. Annealing: The steel undergoes annealing at a temperature of 800–850°C, with a holding time of 1–2 hours. The objective is to soften the steel, relieve internal stresses and structural defects, and enhance its plasticity and toughness.
2. Quenching: The steel is heated to a temperature of 850–880°C and subsequently cooled rapidly in either water or oil. The purpose of this step is to induce the formation of a hard martensitic structure on the steel's surface, thereby increasing its hardness and strength.
3. Tempering: The martensitic structure formed on the steel's surface after quenching is inherently brittle; therefore, a tempering process is required to reduce hardness while simultaneously improving toughness and machinability. The tempering temperature typically ranges from 150°C to 500°C, with the holding time adjusted according to specific requirements.
