SAE 4340 alloy steel

Introduction

we manufacture forging ingots, billets, and blooms in alloy steel specifically for SAE 4340, designed for ultra-high strength and critical engineering applications where exceptional toughness, fatigue resistance, and reliability are required. SAE 4340 is a medium carbon nickel-chromium-molybdenum alloy steel renowned for its outstanding strength, very high toughness, and excellent fatigue and impact resistance. It is engineered to perform under extreme mechanical loads, shock, and cyclic stress, making it a preferred choice for aerospace, automotive, defense, and heavy-duty engineering applications. The addition of nickel significantly enhances toughness and impact strength, while chromium improves hardenability and wear resistance. Molybdenum contributes to high-temperature strength, fatigue resistance, and tempering stability. SAE 4340 offers excellent response to quenching and tempering and maintains good dimensional stability after heat treatment. This grade provides an exceptional combination of strength, durability, and service life for the most demanding industrial applications.

Chemical composition

Element Content (%) Function / effect
Carbon (c) 0.38 – 0.43 Provides high strength and hardness
Manganese (mn) 0.60 – 0.80 Improves hardenability and toughness
Silicon (si) 0.15 – 0.35 Increases strength and elasticity
Nickel (ni) 1.65 – 2.00 Greatly improves toughness and impact resistance
Chromium (cr) 0.70 – 0.90 Enhances hardenability and wear resistance
Molybdenum (mo) 0.20 – 0.30 Improves fatigue strength and tempering stability
Phosphorus (p) Max 0.035 Impurity; controlled to maintain toughness
Sulphur (s) Max 0.040 Impurity; controlled for machinability

Mechanical Properties

  • Tensile strength: 900 – 1200 MPa
  • Yield strength: 700 – 1000 MPa
  • Hardness: 28 – 40 HRC (customizable)
  • Impact toughness: Very high
  • Fatigue resistance: Excellent

(Typical – quenched & tempered; properties may vary depending on section size and heat treatment conditions)

Heat Treatment

  • Annealing: Used to soften the steel and improve machinability before final processing
  • Normalizing: Refines grain structure and enhances mechanical uniformity
  • Quenching: Heating to approximately 830 – 860°C followed by oil quenching to achieve a hard martensitic structure
  • Tempering: Reheating to a controlled temperature to reduce internal stresses and achieve the required balance of strength and toughness
  • Heat treatment parameters can be precisely adjusted to meet specific performance requirements.

Key Features and Benefits

  • Ultra-high strength and toughness
  • Excellent fatigue and impact resistance
  • Deep hardenability for large sections
  • Good machinability in annealed condition
  • Dimensional stability after heat treatment
  • Ideal for critical and safety-related components

Typical Applications

  • Aircraft landing gear and structural parts
  • Heavy-duty gears and shafts
  • Crankshafts and axles
  • High-strength bolts and fasteners
  • Defense and aerospace components
  • Forged parts subjected to extreme loads

Equivalent Steel Grades

SAE 4340 has several international equivalents, including:

  • EN34NiCrMo6 – European standard
  • DIN 34NiCrMo6 – German standard
  • IS 1570 (Part 3) – 34NiCrMo6 type – Indian standard

Why choose SAE 4340 for your application?

SAE 4340 is the ideal choice for applications demanding the highest levels of strength, toughness, and fatigue resistance. Its superior hardenability and excellent response to heat treatment make it suitable for large and critical components operating under extreme stress conditions. The addition of nickel ensures exceptional impact performance and long service life.

Comparison table for similar grades

Grade Carbon (%) Key applications Heat treatment Comments
SAE 4340 0.38 – 0.43 Aerospace, gears, shafts Quenching & tempering Very high strength and toughness
SAE 4140 0.38 – 0.43 Automotive and machinery parts Quenching & tempering Good strength, lower toughness
SAE 4330 0.28 – 0.33 Aircraft and structural parts Quenching & tempering Better toughness, lower strength

Summary

SAE 4340 is a premium nickel-chromium-molybdenum alloy steel designed for the most demanding engineering applications. It delivers consistent performance, extended service life, and excellent reliability in automotive, aerospace, defense, and heavy machinery industries.