What is the standard S355 Jr?

The term "S355 Jr" (often seen with a space) refers to the same steel grade as S355JR - it is simply a common stylistic variation in writing the name. The standard that defines it is unequivocally:

EN 10025-2:2019

"Hot rolled products of structural steels - Part 2: Technical delivery conditions for non-alloy structural steels"

This is the current, harmonized European standard that fully specifies S355JR.

Here is a detailed breakdown of the standard and what it mandates for S355JR:

1. Scope of EN 10025-2

This standard covers hot-rolled flat and long products (plates, sheets, sections, bars) made from non-alloy structural steels. These steels are intended for use in welded, bolted, and riveted structures.

2. Key Specifications for S355JR in EN 10025-2

The standard dictates every critical aspect of the material.

a) Mechanical Properties (for nominal thickness ≤ 16 mm)

Minimum Yield Strength (ReH): 355 MPa

Tensile Strength (Rm): 470 MPa to 630 MPa

Minimum Elongation (A): 21% (for longitudinal strip test pieces)

Impact Toughness (Charpy V-notch):

Test Temperature: +20°C (This is the key for "JR")

Minimum Average Energy: 27 Joules

b) Chemical Composition (Maximum Values, % by weight)
The limits vary slightly by product thickness. For common thicknesses up to 30mm:

Carbon (C): 0.24%

Manganese (Mn): 1.60%

Silicon (Si): 0.55%

Phosphorus (P): 0.045%

Sulfur (S): 0.045%

Nitrogen (N): 0.009% (if sufficient Al is present)

Aluminum (Alt): ≥ 0.020% (if specified for deoxidation)

c) Mandatory Carbon Equivalent (CEV) Formula
To ensure weldability, EN 10025-2 enforces a maximum Carbon Equivalent Value, calculated as:
CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

For S355JR with thickness ≤ 30 mm: Max CEV = 0.40%

This is a critical difference from older or simpler standards and is a key reason for its excellent weldability.

3. Delivery Conditions & Testing

Condition: The steel is supplied in the as-rolled condition (signified by the "R" in JR).

Deoxidation Practice: It is typically "Fine Grain Steel" and can be killed (with Aluminium) or semi-killed.

Mandatory Testing: The standard requires the manufacturer to perform and certify:

Tensile Test

Impact Test (Charpy V-notch at +20°C)

Chemical Analysis

4. Associated Standards & Documentation

Inspection Standard: EN 10204 defines the type of inspection document. For S355JR, a Type 3.1 Certificate or 3.2 Certificate is common, providing a declaration of compliance with the order and a report of the actual test results.

Material Identification: Markings on the product or bundle must include the grade (S355JR), heat number, manufacturer's mark, and size.

5. Important Note on Superseded Standards

EN 10025-2 replaced several older national and European standards. You may encounter references to these in older drawings or literature, but they are obsolete:

BS 4360 Grade 50B (British Standard - historical equivalent)

DIN 17100 St 52-3 (German Standard - historical equivalent)

Euronorm 25 Fe 510 D (Older European standard)

Any reference to "S355JR" or "S355 Jr" in a modern technical drawing, contract, or purchase order is implicitly a call-up to the full requirements of EN 10025-2.

Summary Table: The "S355 Jr" Standard at a Glance

Therefore, when you ask for "S355 Jr", you are requesting a material that must conform to all the chemical, mechanical, and testing requirements detailed in the pan-European standard EN 10025-2.