> SCM415 is a low-carbon chromium-molybdenum case hardening steel under JIS G4053. After carburizing and quenching, its surface reaches HRC 58–62 while the core stays tough — the classic "hard case, tough core" material for small gears, shafts, and piston pins. This guide presents strength and h
SCM415 is a low-carbon chromium-molybdenum case hardening steel under JIS G4053. After carburizing and quenching, its surface reaches HRC 58–62 while the core stays tough — the classic "hard case, tough core" material for small gears, shafts, and piston pins. This guide presents strength and hardness data in tables for the normalized and carburized states, and compares SCM415 with SCM420.
What is SCM415?
SCM415 is a low-carbon Cr-Mo steel (JIS G4053) with only 0.13–0.18% carbon. Rather than through-hardening, it gains its performance from carburizing: carbon is diffused into the surface layer, which is then quenched to form a hard, wear-resistant case over a tough low-carbon core. Typical applications include small gears, cams, piston pins, shafts, and wear parts.
Chemical Composition (JIS G4053)
| Element | C | Si | Mn | P | S | Cr | Mo |
|---|---|---|---|---|---|---|---|
| Content (%) | 0.13–0.18 | 0.15–0.35 | 0.60–0.85 | ≤0.030 | ≤0.030 | 0.90–1.20 | 0.15–0.30 |
Mechanical Properties of SCM415 by Heat Treatment
1. Normalized / Annealed State (As-Machined)
The low carbon content keeps SCM415 soft and ductile before carburizing — excellent for cutting and cold working.
| Property | Value |
|---|---|
| Tensile Strength | Approx. 500–650 MPa |
| Brinell Hardness | Approx. HB 140–190 |
| Elongation | Approx. 18–25% |
Features: Excellent machinability. Gear teeth, holes, and other major features should be machined before carburizing, leaving only a grinding allowance afterward.
2. After Carburizing, Quenching & Tempering
This is the final service condition, with distinctly different case and core properties.
| Zone | Reference Value | Notes |
|---|---|---|
| Surface Hardness | HRC 58–62 | High-carbon martensite case; wear and pitting resistant |
| Core Tensile Strength | ≥ 830 MPa (JIS G4053 reference) | Tough low-carbon core |
| Core Hardness | Approx. HRC 25–35 | Depends on size and hardenability |
| Effective Case Depth | Typically 0.5–1.5 mm | Specify on the drawing |
Features: Wear-resistant surface with an impact-tolerant core — ideal for gear teeth under combined contact and bending stress.
Toughness, Fatigue Life, and Practical Notes
- Process sequence: Rough machining → carburizing, quenching & tempering → finish grinding. Allow grinding stock for distortion.
- Case specification: State the effective case depth (e.g., 0.8–1.2 mm) and surface hardness range on the drawing to avoid inconsistent interpretation between heat treaters.
- Core strength: Core properties depend on hardenability and section size. For higher-load gears, consider upgrading to SCM420.
- Fatigue: Residual compressive stress in the carburized case improves bending and contact fatigue life — a key advantage for gear applications.
SCM415 vs SCM420: Material Selection
| Criteria | SCM415 | SCM420 |
|---|---|---|
| Carbon Content (%) | 0.13–0.18 | 0.18–0.23 |
| Core Tensile Strength (carburized) | ≥ 830 MPa | ≥ 930 MPa |
| Core Toughness | Better | Slightly lower, but stronger |
| Typical Uses | Small gears, piston pins, cams | Medium-load gears, shafts |
Surface hardness is equivalent (HRC 58–62); the difference is core strength. Choose SCM420 for higher-load gears and shafts, SCM415 for small parts or when core toughness matters most.
SCM415 Frequently Asked Questions (FAQ)
Q1: What are the surface and core hardness of SCM415 after carburizing?
A: After carburizing, quenching, and tempering, the surface reaches HRC 58–62 for excellent wear resistance. The low-carbon core stays around HRC 25–35, with a reference core tensile strength of ≥ 830 MPa (JIS G4053), retaining good toughness and impact resistance. Actual values depend on part size and carburizing conditions — refer to the heat treatment report.
Q2: What is the difference between SCM415 and SCM420, and how do I choose?
A: The main difference is carbon content and post-carburizing core strength: SCM415 (C 0.13–0.18%) offers a core tensile strength of ≥ 830 MPa, while SCM420 (C 0.18–0.23%) reaches ≥ 930 MPa. Surface hardness is the same. Use SCM420 for higher-load gears and shafts; SCM415 suits smaller parts or applications prioritizing core toughness, at a slightly lower material cost.
Q3: How should carburizing depth be specified?
A: Specify the effective case depth and surface hardness range on the drawing — for example, "effective case depth 0.8–1.2 mm, surface hardness HRC 58–62." Typical depths are 0.5–1.5 mm; for gears, estimate roughly 0.15–0.2 times the module. Double Steel Corp. stocks SCM415 round bars and can advise on machining and heat treatment sequencing — contact us for a quote!