SAE 8640 alloy steel

Introduction

We manufacture forging ingots, billets, and blooms in alloy steel specifically for SAE 8640, tailored for high-performance engineering and through hardening applications.

SAE 8640 is a medium carbon nickel-chromium-molybdenum alloy steel known for its excellent strength, toughness, and fatigue resistance. It is widely used in applications requiring high mechanical reliability, wear resistance, and resistance to shock loading.

The addition of nickel improves impact strength and toughness, chromium enhances wear resistance and hardenability, while molybdenum contributes to high-temperature strength and resistance to tempering softening. SAE 8640 offers good machinability in the annealed condition and provides excellent dimensional stability after heat treatment, making it suitable for forging, machining, and heavy-duty engineering components.

This steel offers an excellent balance of strength, durability, and performance for demanding industrial and automotive applications.

Chemical composition

Element Content (%) Function / effect
Carbon (c) 0.38 – 0.43 Provides hardness and strength
Manganese (mn) 0.75 – 1.00 Improves strength and hardenability
Silicon (si) 0.15 – 0.35 Enhances strength and elasticity
Nickel (ni) 0.40 – 0.70 Improves toughness and impact resistance
Chromium (cr) 0.40 – 0.60 Improves wear resistance and hardenability
Molybdenum (mo) 0.20 – 0.30 Improves strength and heat resistance
Phosphorus (p) Max 0.035 Impurity; lower content improves toughness
Sulphur (s) Max 0.040 Improves machinability in controlled amounts

Mechanical properties (typical, depending on condition & heat treatment)

  • Tensile strength: 900 – 1100 MPa
  • Yield strength: 650 – 850 MPa
  • Hardness: 28 – 36 hrc (quenched & tempered condition)
  • Impact toughness: high
  • Fatigue resistance: excellent

Heat treatment

  • annealing: applied to soften the steel and improve machinability before final processing.
  • normalizing: heating and air cooling to refine grain structure and improve uniformity.
  • quenching: heating to approximately 830 – 870°c followed by rapid cooling to obtain a hardened martensitic structure.
  • tempering: reheating to a controlled temperature to relieve internal stresses and improve toughness while maintaining hardness.

The heat treatment process can be adjusted to achieve the required Mechanical properties depending on application requirements.

Key features and benefits

  • excellent through hardening capability
  • high strength and toughness
  • good wear resistance
  • high fatigue strength under cyclic loading
  • superior impact resistance due to nickel addition
  • good machinability in annealed condition
  • excellent dimensional stability after heat treatment
  • suitable for forging and heavy-duty machining applications

Typical applications

  • heavy duty shafts and axles
  • gears and pinions
  • automotive drivetrain components
  • crankshafts and connecting rods
  • forged machine parts
  • industrial load-bearing components
  • oil and gas engineering components

Equivalent steel grades

SAE 8640 has several international equivalents, including:

  • En24 – nickel chromium molybdenum alloy steel
  • 40nicrmo7 – european alloy steel equivalent
  • din 1.6565 – approximate equivalent

Why choose SAE 8640 for your application?

SAE 8640 offers an outstanding combination of strength, toughness, and fatigue resistance, making it suitable for heavily loaded engineering components. The nickel-chromium-molybdenum alloy system provides excellent hardenability and mechanical stability. Its reliable heat treatment response and dimensional stability help improve component durability and manufacturing efficiency.

Comparison table for similar grades

Grade Carbon (%) Key applications Heat treatment Comments
SAE 8640 0.38-0.43 Shafts, gears, heavy-duty components Quenching & tempering High strength alloy steel
En24 0.36-0.44 Aerospace and automotive components Quenching & tempering Widely used high strength steel
40nicrmo7 Similar Heavy duty engineering parts Quenching & tempering European equivalent
SAE 4340 0.38-0.43 Aerospace and high load parts Quenching & tempering Higher nickel content

Summary

SAE 8640 is a medium carbon nickel-chromium-molybdenum alloy steel optimized for through hardened engineering components requiring high strength, toughness, and wear resistance. It provides dependable performance, long service life, and excellent mechanical reliability for automotive and heavy industrial applications.