S235JRH and S355J2H Structural Steel

Both S235JRH and S355J2H are fine-grained steels defined in the European standard (EN 10210) for manufacturing hot-formed welded structural hollow sections. S355J2H is typically delivered in the normalized (+N) condition to ensure its high strength and low-temperature toughness; while S235JRH is typically delivered in the stress-relieved annealed (+R) condition after cold forming. There are significant differences between the two in key properties such as yield strength and impact toughness.

Material Grade Explanation:

Name Composition: 

S235 + J + R + H 

S355 + J2 + H

Where,
The prefix "S": indicates structural steel.

The number "235" or "355": indicates the minimum yield strength (unit: MPa). This is the most fundamental difference.

Impact toughness designations (“J”, “J2”):
J: Indicates a minimum impact energy of 27 Joules in a Charpy V-notch impact test at 0°C.
J2: Indicates a minimum impact energy of 27 Joules in a Charpy V-notch impact test at -20°C.
Therefore, J2 has stricter low-temperature toughness requirements than J. Thus, S355J2H can be used in lower-temperature environments (such as outdoor structures in cold regions).

Suffix “+R” (only for S235JRH): Indicates a “stress-relieved annealed” condition after cold forming. This helps improve the material properties after cold working.
The standard delivery condition of S355J2H(+N) already guarantees its performance; the “R” condition is usually not required.

Suffix “H”: Indicates suitability for hot-formed hollow profiles.

Performance and Requirements Comparison:

1. Mechanical Properties

Yield Strength: S235JRH ≥ 235 MPa; S355J2H ≥ 355 MPa.
Tensile Strength: S235JRH 360-510 MPa; S355J2H 470-630 MPa.
Elongation: Roughly equivalent, specific values depend on thickness.

2. Impact Toughness

Test Temperature: S235JRH at 0°C; S355J2H at -20°C.
Minimum Impact Energy (KV): Both 27 J.
Significance: This ensures that S355J2H material has better resistance to brittle fracture at low temperatures, making it suitable for structures under dynamic loads or in low-temperature environments (such as wind and earthquakes).

3. Chemical Composition

Both are fine-grained steels, typically refined through the addition of trace amounts of microalloying elements such as niobium (Nb), vanadium (V), and titanium (Ti), thereby improving strength, toughness, and weldability.
S355J2H generally has a higher carbon equivalent (CEV) than S235JRH due to potentially higher alloying element or carbon content, resulting in higher strength. This means S355J2H may have slightly poorer weldability, requiring more attention to welding processes (such as preheating).

4. Delivery Condition

S235JRH: Typically delivered in cold-formed + stress-relieved annealed (+R) condition.
S355J2H: Typically delivered in normalized rolled or normalized (+N) condition to ensure its mechanical properties and impact toughness. Normalizing refines the grain and homogenizes the microstructure.

5. Processing and Application

S235JRH, due to its lower strength and carbon equivalent, has relatively simple cutting, bending, and welding processes, resulting in lower costs. It is commonly used in non-critical load-bearing structures such as light frames and small mechanical equipment.
S355J2H, on the other hand, with its high strength and excellent low-temperature toughness, is more suitable for core structures with high requirements for safety, durability, and environmental resistance, such as high-rise buildings, heavy-duty machinery, bridges, and offshore platforms.

6. Cost and Cost-Effectiveness

The material and processing costs of S355J2H are generally higher than those of S235JRH. However, in projects requiring high safety and long service life, choosing S355J2H can reduce material usage and overall structural weight, potentially offering better long-term cost-effectiveness. If the project budget is limited and load requirements are not high, S235JRH is a more economical choice.

S235JRH and S355J2H: How to Choose the Right One?

a. Strength is the primary consideration: If design calculations indicate that the strength of S235 is sufficient, choosing S235JRH is more economical. If the strength is insufficient, it must be upgraded to S355J2H or a higher grade.
b. Ambient temperature is critical: If the structure will be used in an environment below 0°C, especially under impact loads, S355J2H with a -20°C impact guarantee should be given priority to ensure safety.
c. Cost trade-offs: S355J2H has superior performance but is also more expensive. Reasonable material selection should be made to optimize costs while meeting safety and usage requirements.

d. Application selection:
S235JRH: Suitable for general load-bearing structures where strength and low-temperature toughness requirements are not high. Examples include: indoor shelving, light display racks, railings, furniture, and some architectural decorative structures.

S355J2H: Suitable for important structures subjected to high loads, dynamic loads, or in low-temperature environments. For example: large factory structures, bridge components, crane trusses, offshore platform modules, outdoor venues (stadiums, stations) in cold regions, and building structures with seismic resistance requirements.