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Analysis of Machining Characteristics and Application Properties of Cr-Ni-Mo Steel SNCM420H
Applicable Standards and Specifications:
SNCM420H belongs to the alloy structural steel series developed by Nippon Special Steel (Hitachi Metals); it primarily complies with the requirements for hot-rolled steel bars specified in the NSHA130 and NSHA131 standards. Internationally recognized equivalent materials include the European DIN 17440 grade 1.3425 (17CrNi4-6) and the American SAE J1391 grade AISI 5140. The applicable standards explicitly define key parameters such as dimensional tolerances (±1.5 mm), surface quality (minor scratches permitted), and ultrasonic testing grades (Class II acceptance); additionally, hardness (50–52 HRC) and tensile strength (≥1200 MPa) must meet the requirements of the ASTM A864-19 mechanical testing standard.
Chemical composition range of SNCM420H:
Carbon (C): 0.38–0.42%
Chromium (Cr): 1.35–1.45%
Nickel (Ni): 1.40–1.60%
Molybdenum (Mo): 0.65–0.85%
Phosphorus (P) ≤ 0.025%
Sulfur (S) ≤ 0.020%
Additional elements: Vanadium ≤ 0.20%, Titanium ≤ 0.10%
Differences in SNCM420H Processing:
Initial Forming Stage:
Grain growth behavior during hot rolling (800–850°C) differs significantly from that of 1.3425 steel; the controlled rolling process requires maintaining a refining temperature of 650–680°C to refine the grain size (D50 ≤ 4 μm).
Heat Treatment Process:
Carburizing and Quenching:
Carburized case depth: 0.8–1.2 mm (using atmospheric carburizing agents)
Quenching temperature: 920 ± 15°C; cooling medium: oil (30–50°C)
Tempering: 460°C × 1 h + 520°C × 1.5 h (air cooling)
Compared to 1.3425 steel, SNCM420H exhibits a 15% increase in hardenability (Jominy index) and a carbon content reduced to the 0.30–0.35% range, while impact toughness (at -40°C) improves to over 25 J.
Cold Working Characteristics:
For cold-rolled sheets cut via bandsaw, surface roughness (Ra) must be controlled within the 1.6–3.2 μm range. Deep-drawing tests show that at an indentation depth of 15 mm, the material retains over 72% of its elongation at fracture, outperforming AISI 5140 steel (which retains 65%).
SNCM420H belongs to the alloy structural steel series developed by Nippon Special Steel (Hitachi Metals); it primarily complies with the requirements for hot-rolled steel bars specified in the NSHA130 and NSHA131 standards. Internationally recognized equivalent materials include the European DIN 17440 grade 1.3425 (17CrNi4-6) and the American SAE J1391 grade AISI 5140. The applicable standards explicitly define key parameters such as dimensional tolerances (±1.5 mm), surface quality (minor scratches permitted), and ultrasonic testing grades (Class II acceptance); additionally, hardness (50–52 HRC) and tensile strength (≥1200 MPa) must meet the requirements of the ASTM A864-19 mechanical testing standard.
Chemical composition range of SNCM420H:
Carbon (C): 0.38–0.42%
Chromium (Cr): 1.35–1.45%
Nickel (Ni): 1.40–1.60%
Molybdenum (Mo): 0.65–0.85%
Phosphorus (P) ≤ 0.025%
Sulfur (S) ≤ 0.020%
Additional elements: Vanadium ≤ 0.20%, Titanium ≤ 0.10%
Differences in SNCM420H Processing:
Initial Forming Stage:
Grain growth behavior during hot rolling (800–850°C) differs significantly from that of 1.3425 steel; the controlled rolling process requires maintaining a refining temperature of 650–680°C to refine the grain size (D50 ≤ 4 μm).
Heat Treatment Process:
Carburizing and Quenching:
Carburized case depth: 0.8–1.2 mm (using atmospheric carburizing agents)
Quenching temperature: 920 ± 15°C; cooling medium: oil (30–50°C)
Tempering: 460°C × 1 h + 520°C × 1.5 h (air cooling)
Compared to 1.3425 steel, SNCM420H exhibits a 15% increase in hardenability (Jominy index) and a carbon content reduced to the 0.30–0.35% range, while impact toughness (at -40°C) improves to over 25 J.
Cold Working Characteristics:
For cold-rolled sheets cut via bandsaw, surface roughness (Ra) must be controlled within the 1.6–3.2 μm range. Deep-drawing tests show that at an indentation depth of 15 mm, the material retains over 72% of its elongation at fracture, outperforming AISI 5140 steel (which retains 65%).
