65Si7 spring steel

Introduction

We manufacture forging ingots, billets, and blooms in alloy steel specifically for 65Si7, designed for high-strength spring applications where excellent elasticity, toughness, and fatigue resistance are essential.

65Si7 is a high carbon silicon spring steel renowned for its outstanding resilience, high yield strength, and excellent fatigue life. The presence of silicon significantly improves elastic limit and spring performance, making this grade ideal for dynamic and cyclic loading conditions in automotive, agricultural, and industrial spring applications.

This steel grade shows excellent response to quenching and tempering, providing a reliable combination of hardness, toughness, and long service life in demanding spring and high-stress components.

Chemical composition

Element	Content (%)	Function / effect
Carbon (c)	0.60 – 0.70	Provides high strength, hardness, and fatigue resistance
Silicon (si)	1.50 – 2.00	Increases elastic limit and spring performance
Manganese (mn)	0.70 – 1.00	Improves hardenability and toughness
Phosphorus (p)	Max 0.035	Controlled to maintain toughness
Sulphur (s)	Max 0.035	Controlled to prevent brittleness

Mechanical properties (typical – quenched & tempered)

• Tensile strength: 1400 – 1600 MPa
• Yield strength: Very high
• Hardness: 48 – 56 HRC
• Elongation: Moderate
• Fatigue resistance: Excellent

(properties may vary depending on section size and heat treatment conditions)

Heat treatment

• Annealing – softens the steel to improve machinability before final processing
• Quenching – heating to approximately 830 – 870°c followed by rapid cooling (oil quench)
• Tempering – reheating to a controlled temperature to improve toughness while maintaining required hardness
• Stress relieving – used after forming or machining to reduce residual stresses

Key features and benefits

• Excellent elasticity and high yield strength
• Superior fatigue resistance for long service life
• High wear resistance and toughness
• Good hardenability and dimensional stability
• Reliable performance under cyclic and impact loading
• Suitable for heavy-duty spring applications

Typical applications

• Leaf springs and coil springs for automotive and agricultural vehicles
• Valve springs
• Heavy-duty industrial springs
• High-stress mechanical components subjected to cyclic loading
• Suspension parts

Equivalent steel grades

• En 10089 – 65Si7
• Din 65Si7
• Is 3195 – 65Si7 type
• Jis sup9 (approximate equivalent)

Why Choose 65si7 For Your Application?

65si7 Is An Ideal Material For Applications Involving High Loads And Continuous StreSS Cycles. Its Higher Carbon Content Provides Enhanced Strength And Wear Resistance, While Silicon Ensures Excellent Elasticity And Fatigue Life. This Makes It A Reliable Choice For Demanding Spring And Suspension Systems.

Comparison table for similar grades

Grade	Carbon (%)	Silicon (%)	Key applications	Comments
55Si7	0.52 – 0.60	1.50 – 2.00	Light to medium springs	Lower strength than 65Si7
60si7	0.56 – 0.64	1.50 – 2.00	Medium to heavy springs	Intermediate strength
65Si7	0.60 – 0.70	1.50 – 2.00	Heavy-duty springs	Highest strength and fatigue resistance
51crv4	0.47 – 0.55	0.15 – 0.40	High-strength springs	Better hardenability
Sup9	0.52 – 0.60	1.50 – 2.00	Automotive springs	Japanese equivalent

Summary

65Si7 is a high-carbon silicon spring steel that delivers excellent elasticity, high fatigue resistance, and superior wear properties. It is the preferred grade for heavy-duty spring applications in automotive, agricultural, and industrial sectors, providing long service life and reliable performance under cyclic and impact loading conditions.