S1 Tool Steel: High Toughness for Impact Applications

S1 tool steel is a shock-resisting material. Its primary characteristic is exceptional toughness, which makes it highly resistant to impact loading. Understanding its properties helps determine if it fits your manufacturing needs correctly.

1. Chemical Composition and Microstructure

The typical chemical composition (weight %) for S1 steel falls within these ranges:

• Carbon (C):40% – 0.55%
• Silicon (Si):15% – 1.20%
• Manganese (Mn):10% – 0.40%
• Chromium (Cr):00% – 1.80%
• Tungsten (W):50% – 3.00%
• Molybdenum (Mo):up to 0.50%
• Vanadium (V):15% – 0.30%

The medium carbon content is key. When properly hardened, it helps create a microstructure (low-carbon martensite matrix with finely dispersed carbides) that delivers S1’s signature high toughness, excellent fracture resistance, good strength, and adequate wear resistance, particularly under impact conditions.

2. Heat Treatment and Hardness

S1 is an oil-hardening tool steel. The heat treatment process is critical to achieving its desired properties.

2.1 Austenitizing and Quenching

The steel is heated to a specific austenitizing temperature (e.g., 925 °C) and then quenched in oil to achieve hardening. Alloying elements like chromium and tungsten provide good hardenability, superior to water-hardening grades, allowing for effective hardening even in medium sections.

2.2 Tempering

Tempering after hardening is crucial. This step adjusts the final hardness and significantly increases toughness, achieving the necessary balance for performance.

2.3 Hardness

The typical hardness range for S1 after proper heat treatment is 40-60 HRC (Rockwell C Hardness). The exact hardness depends on the specific austenitizing and tempering parameters used.

2.4 Stress Relief

We recommend stress-relief tempering for components undergoing significant machining or welding to minimize residual stresses and prevent potential distortion or cracking.

3. Key Properties and Performance

S1’s standout feature is its excellent shock resistance. Key performance aspects include:

• Toughness: Very high, ranking among the highest in tool steels.
• Wear Resistance: Generally low to medium compared to high-wear grades like the O or D series tool steels.
• Compression Strength: S1 (along with S5) offers a good combination of compression strength and shock resistance, which can be advantageous in cold forming operations compared to S7.

4. Applications

Due to its high toughness and impact resistance, S1 tool steel is commonly used for:

• Chipping chisels, Hand chisels
• Circular pipe cutters
• Drift pins, Knock-out pins
• Grippers
• Mandrels
• Punches
• Rivet sets
• Screwdriver blades
• Shear blades
• Stamps
• Track tools

It is also suitable for small-to-medium-sized molds where toughness is the primary requirement and for some hot punching or shearing applications needing moderate heat resistance.

S1 steel can undergo carburizing to improve wear resistance for specific applications. This process adds carbon to the surface layer, creating a harder outer case while maintaining the tough core.

5. Considerations and Alternatives

It’s important to note that S1 tool steel is less common in the market today than other shock-resisting grades like S7. Exploring alternative materials might be necessary depending on availability and your specific application requirements. However, understanding S1’s technical profile provides a solid benchmark for evaluation.