What is the difference between E355 and S355 steel?

The distinction between E355 and S355 steel grades lies primarily in their governing standards, product forms, and application contexts, though both share similar mechanical properties. Here's a detailed breakdown:

1. Core Difference: Standards & Product Forms

Grade	Governing Standard	Typical Product Forms	Scope
S355	EN 10025 (Structural steels)	Plates, sheets, structural sections (I-beams, angles), bars	General structural applications (buildings, bridges)
E355	EN 10210-1/EN 10219-1 (Hot-finished/cold-formed hollow sections)	Hollow structural sections (HSS), pipes, tubes	Welded/cold-formed tubular structures

Key Insight:

S355 = Broad structural steel (open profiles).

E355 = Specific to tubular profiles

2. Mechanical Properties Comparison

Both grades share a minimum yield strength of 355 MPa, but differ in testing and certification:

Property	S355 (e.g., S355J2/NL)	E355 (e.g., E355+N/NL)
Yield Strength	≥355 MPa (thickness-dependent)	≥355 MPa
Tensile Strength	470–630 MPa	470–630 MPa
Impact Toughness	Tested (e.g., -20°C for J2, -50°C for NL)	Tested (e.g., -30°C for NL)
Mandatory Delivery	As-rolled/normalized (N/NL)	Always normalized (or thermo-mechanically rolled)

3. Chemical Composition

Similar but not identical:

Element	S355 (EN 10025)	E355 (EN 10210)
C	≤0.22%	≤0.20%
Mn	≤1.60%	≤1.50%
P	≤0.025%	≤0.025%
S	≤0.015%	≤0.015%
CEV	≤0.45–0.47%	≤0.45%

Critical: E355 has stricter carbon content (C) and manganese (Mn) limits for weldability in tubular sections.

4. Impact Toughness Designations

S355: Suffixes denote impact temperatures:

J2 = -20°C, K2 = -40°C, NL = -50°C.

E355: Suffixes vary by standard:

+N = Normalized, +NL = Normalized (-50°C impact).

5. Application Context

Grade	Typical Applications	Why Preferred
S355	Building frames, bridges, cranes, shipbuilding	High strength-to-weight ratio; wide availability
E355	Tubular trusses, offshore platforms, roll cages, architectural columns	Optimized for hollow section welding; uniform mechanical properties