En355 alloy steel

Introduction

We manufacture forging ingots, billets, and blooms in alloy steel specifically for En355, tailored for extremely heavy-duty case hardening applications.

En355 is a low carbon nickel–chromium–molybdenum alloy steel designed for components requiring an exceptionally hard, wear-resistant surface combined with a very strong and shock-resistant core. It is intended for the most demanding service conditions involving very high loads, impact, and continuous cyclic stress.

The very high nickel content provides outstanding core toughness and fatigue resistance, chromium improves hardenability and wear resistance, and molybdenum enhances deep hardening, strength, and resistance to temper brittleness. En355 offers good machinability in the annealed condition and maintains dimensional stability after heat treatment, making it suitable for forging and precision machining processes.

This steel delivers maximum strength, durability, and long-term reliability for critical industrial applications.

Chemical composition

Element	Content (%)	Function / effect
Carbon (c)	0.10 – 0.20	Ensures tough and ductile core
Manganese (mn)	0.40 – 0.70	Improves hardenability and strength
Silicon (si)	Max 0.35	Increases strength
Nickel (ni)	3.50 – 4.00	Improves toughness and fatigue resistance
Chromium (cr)	1.30 – 1.70	Improves hardenability and wear resistance
Molybdenum (mo)	0.25 – 0.40	Improves deep hardening and core strength
Phosphorus (p)	Max 0.035	Impurity; controlled for toughness
Sulphur (s)	Max 0.035	Impurity; controlled for machinability

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

• Core tensile strength: 900 – 1100 MPa
• Core yield strength: 650 – 850 MPa
• Surface hardness (carburized): 58 – 62 HRC
• Core hardness: 240 – 280 HB
• Impact toughness: Extremely high
• Fatigue resistance: Excellent

Heat treatment

• annealing: improves machinability before carburizing.
• carburizing: introduces carbon at high temperature to obtain an extremely hard, wear-resistant surface.
• quenching: rapid cooling to achieve a hard martensitic case with deep penetration.
• tempering: relieves internal stresses while maintaining surface hardness and core toughness.

The heat treatment cycle can be optimized for very heavy-duty service requirements.

Key features and benefits

• excellent case hardening response with deep and uniform case depth
• extremely high core strength and toughness
• superior resistance to wear, shock, and fatigue
• good machinability in annealed condition
• dimensional stability after heat treatment
• suitable for forging and precision machining

Typical applications

• extremely heavy-duty gears and pinions
• planetary and reduction gear systems
• mining, cement, and steel plant machinery
• power transmission and windmill components
• critical automotive and industrial engineering parts

Equivalent steel grades

• En355 has limited direct international equivalents. Comparable grades include:
• en36e – close equivalent (application-based)
• din ni-cr-mo case hardening steels (approximate)
• 18CrNimo7-6 – lower alloy alternative

Why choose En355 for your application?

En355 offers the highest combination of surface hardness, core strength, and fatigue resistance within the en35x series. Its enhanced ni-cr-mo chemistry makes it ideal for the most severe service conditions where failure is not acceptable.

Comparison table for similar grades

Grade	Carbon (%)	Key applications	Heat treatment	Comments
En355	0.10 – 0.20	Extreme-duty gears, mining parts	Carburizing + q&t	Highest ni-cr-mo strength
En354	0.10 – 0.20	Heavy gears, planetary systems	Carburizing + q&t	Very high strength
En353	0.10 – 0.20	Heavy-duty gears	Carburizing + q&t	High ni-cr
En36	0.12 – 0.18	Heavy gears	Carburizing	Widely used ni-cr steel

Summary

En355 is a premium nickel–chromium–molybdenum low carbon alloy steel optimized for extreme-duty case hardening applications. It provides an exceptionally hard surface, a very strong and tough core, and outstanding long-term performance for critical components.