JIS S40C Alloy Steel Bar S40C Round Bars S40C Rods

Product Description

JIS S40C is a high-quality medium-carbon steel grade specified under the Japanese Industrial Standard JIS G4051. Positioned between the more common S35C and S45C, S40C is a "precision" structural steel that provides a predictable mechanical response for components requiring moderate strength and high wear resistance.

1. Chemical Composition

As an unalloyed carbon steel, S40C relies on a tightly controlled carbon range (0.37%–0.43%) to ensure consistent results during heat treatment, particularly induction hardening.

2. Mechanical Properties

The performance of S40C is highly dependent on its heat treatment state. While often used in the normalized state, its full potential is reached when Quenched and Tempered (+QT).

3. Key Technical Characteristics

• Induction Hardening: S40C is optimized for high-frequency induction hardening. It can reach a surface hardness of 50–55 HRC, making it ideal for parts that require a hard, wear-resistant "skin" while maintaining a tough, shock-absorbing core.

• Machinability: Excellent. It is widely used in high-speed CNC turning and milling. It offers better surface finish and chip control than lower carbon steels like S20C.

• Weldability: Limited/Poor. Due to the 0.40% carbon content, it is prone to hydrogen cracking. If welding is necessary, preheating to 200°C–300°C and slow cooling are mandatory.

• Forging: It possesses excellent hot-workability, typically forged at temperatures between 850°C and 1100°C.

4. Global Equivalents

If you are sourcing internationally, JIS S40C is virtually identical to these common global grades:

5. Common Applications

S40C round bars and rods are a standard choice for "moving parts" in automotive and industrial machinery:

• Automotive: Connecting rods, crankshafts, steering knuckles, and axle shafts.

• Power Transmission: Medium-load gears, splined shafts, and transmission pinions.

• Machinery Components: Machine tool spindles, guide rods, and heavy-duty spacers.

• Fasteners: High-tensile bolts and studs (typically Property Class 8.8).

Available Stock & Conditions

• Round Bars: Range from 5mm to 500mm in diameter.

• Rods: Commonly supplied as Cold Drawn or Centerless Ground (h9/h11 tolerances) for precision manufacturing.

• Delivery State: Usually stocked in Normalized or Annealed condition to facilitate easier machining before the final hardening process.