> SNCM220 is a nickel-chromium-molybdenum case hardening steel under JIS G4053. The nickel addition gives it better toughness and hardenability than the SCM series, making it the signature material for automotive transmission and differential gears. This guide presents strength and hardness data
SNCM220 is a nickel-chromium-molybdenum case hardening steel under JIS G4053. The nickel addition gives it better toughness and hardenability than the SCM series, making it the signature material for automotive transmission and differential gears. This guide presents strength and hardness data in tables and compares SNCM220 with SCM420.
What is SNCM220?
SNCM220 is a Ni-Cr-Mo case hardening steel (JIS G4053). Nickel improves core toughness and hardenability, making parts far more resistant to brittle failure under impact loading, while carburizing still delivers an HRC 58–62 wear-resistant case. Typical applications include automotive and motorcycle transmission gears, differential gears, and drive shafts subject to high impact loads.
Chemical Composition (JIS G4053)
| Element | C | Si | Mn | P | S | Ni | Cr | Mo |
|---|---|---|---|---|---|---|---|---|
| Content (%) | 0.17–0.23 | 0.15–0.35 | 0.60–0.90 | ≤0.030 | ≤0.030 | 0.40–0.70 | 0.40–0.65 | 0.15–0.30 |
Mechanical Properties of SNCM220 by Heat Treatment
1. Normalized / Annealed State (As-Machined)
| Property | Value |
|---|---|
| Tensile Strength | Approx. 550–700 MPa |
| Brinell Hardness | Approx. HB 150–200 |
| Elongation | Approx. 17–23% |
Features: Good machinability. Complete major forming operations before carburizing.
2. After Carburizing, Quenching & Tempering
| Zone | Reference Value | Notes |
|---|---|---|
| Surface Hardness | HRC 58–62 | Wear and pitting resistant |
| Core Tensile Strength | ≥ 830 MPa (JIS G4053 reference) | Nickel enhances core toughness |
| Core Hardness | Approx. HRC 25–38 | Depends on size and hardenability |
| Effective Case Depth | Typically 0.5–1.5 mm | Specify on the drawing |
Features: Core impact toughness exceeds equivalent SCM carburizing grades — ideal for gears under shock and variable loading.
Toughness, Fatigue Life, and Practical Notes
- Nickel toughening: Ni at 0.40–0.70% improves low-temperature toughness and impact resistance — gears resist tooth breakage under start-stop and gear-shift shocks.
- Hardenability: The combined Ni-Cr-Mo addition gives excellent hardenability, with stable core properties in larger sections.
- Fatigue: Residual compressive case stress plus a tough core delivers excellent bending and contact fatigue life — key to long-life automotive gears.
- Cost: Nickel raises material cost above the SCM series; for general industrial parts without impact demands, SCM420 is usually sufficient.
SNCM220 vs SCM420: Material Selection
| Criteria | SNCM220 | SCM420 |
|---|---|---|
| Alloy System | Ni-Cr-Mo | Cr-Mo |
| Core Tensile Strength | ≥ 830 MPa | ≥ 930 MPa |
| Core Impact Toughness | Better (with Ni) | Standard |
| Material Cost | Higher | Lower |
| Typical Uses | Automotive transmission / differential gears | General industrial gears, shafts |
Choose SNCM220 for high-impact, high-reliability automotive drive components; SCM420 covers general industrial drive parts at a better cost.
SNCM220 Frequently Asked Questions (FAQ)
Q1: How do I choose between SNCM220 and SCM420?
A: Surface hardness after carburizing is equivalent (HRC 58–62). SNCM220's nickel content gives better core impact toughness and hardenability, suiting automotive transmissions and differentials with frequent shift shocks; SCM420 offers a higher reference core strength (≥ 930 MPa) at lower cost, and covers most general industrial gears and shafts. Rule of thumb: heavy impact and high reliability → SNCM220; general loading → SCM420.
Q2: Why do automotive gears often specify SNCM220?
A: Automotive drivetrain gears endure constant start-stop and gear-shift impacts. Nickel provides core toughness that reduces tooth breakage risk, while the Ni-Cr-Mo hardenability keeps mass-production heat treatment quality consistent. The carburized case ensures tooth-face wear and pitting resistance. This combination of life and reliability is why OEMs commonly specify it.
Q3: What bar forms and mill certificates are available for SNCM220?
A: SNCM220 round bars are supplied as black bars or ground/polished bars. Request a Mill Test Report confirming Ni 0.40–0.70%, Cr 0.40–0.65%, and Mo 0.15–0.30% per JIS G4053. Double Steel Corp. stocks SNCM220 round bars and can help you weigh it against the SCM series for your application — contact us for a quote!