S275JR vs S355JR – Composition, Heat Treatment, Properties, and Applications

Introduction

S275JR and S355JR are two of the most commonly specified European structural steels used across construction, heavy fabrication, and general engineering. Engineers, procurement managers, and manufacturing planners routinely choose between them when balancing cost, strength, weldability, and toughness for a given application. Typical decision contexts include whether higher yield strength (to reduce section size and weight) justifies the higher material cost and whether fabrication constraints (welding, forming) favor the lower-strength option.

The primary difference between the two lies in their guaranteed minimum yield strength and associated mechanical properties: S355JR is a higher-strength “upgrade” of the S275JR family and is specified where greater static capacity or reduced section thickness is required. Both grades share similar chemistry and good fabrication characteristics, which is why they are commonly compared in design and procurement.

1. Standards and Designations

• EN: EN 10025-2 (hot rolled structural steels) — official source for S275JR and S355JR designations.
• ASTM/ASME: No direct one-to-one equivalents; ASTM grades (e.g., A36, A572) differ in chemistry and testing requirements. Selection between EN and ASTM grades should be made by cross-referencing mechanical and chemical requirements rather than by name alone.
• JIS / GB: Japanese and Chinese standards have their own designation systems; engineers should map required mechanical and chemical properties rather than rely on nomenclature alone.

Classification: - Both S275JR and S355JR are carbon–manganese structural steels, not stainless, not tool steels. They are generally considered conventional structural steels (not high-alloy nor tool steels) and can be produced to behave similarly to low-alloy HSLA steels when particular microalloying elements are included.

2. Chemical Composition and Alloying Strategy

The EN 10025 standard specifies chemistry limits that are designed to deliver predictable yield and tensile properties plus adequate toughness. The two grades use similar low-carbon, low-alloy strategies: carbon for strength, manganese as a deoxidizer and strengthener, and silicon/phosphorus/sulfur limits for ductility and weldability. Microalloying elements (V, Nb, Ti) are usually present either as trace or controlled additions in some product ranges to improve grain control and toughness.

Table: Typical chemical limits (representative limits from EN 10025-2; actual mill certificates can vary by product form and thickness)

Element	S275JR (typical limits)	S355JR (typical limits)
C (max)	0.22 wt% (approx.)	0.24 wt% (approx.)
Mn (max)	1.50–1.60 wt%	1.60 wt% (approx.)
Si (max)	0.55 wt%	0.55 wt%
P (max)	0.035 wt%	0.035 wt%
S (max)	0.035 wt%	0.035 wt%
Cr	typically ≤0.30 wt% (trace)	typically ≤0.30 wt% (trace)
Ni	typically ≤0.30 wt% (trace)	typically ≤0.30 wt% (trace)
Mo	typically ≤0.10–0.15 wt% (trace)	typically ≤0.10–0.15 wt% (trace)
V	trace (if present)	trace (if present)
Nb	trace (if present)	trace (if present)
Ti	trace (if present)	trace (if present)
B	trace (if present)	trace (if present)
N (max)	~0.012 wt%	~0.012 wt%

Notes: - The table shows typical maximum values used in mill specifications. EN 10025 includes thickness-dependent requirements and product-specific variants; therefore always verify mill test certificates (MTC) for procurement acceptance. - S355 grades may include variants (e.g., S355J0, S355J2) with different impact requirements; JR indicates 27 J minimum impact energy at +20 °C.

How alloying affects performance: - Carbon and manganese primarily govern strength and hardenability. Higher carbon increases strength but reduces weldability and ductility. - Silicon and manganese act as deoxidizers; silicon also affects strength slightly. - Microalloying elements (Nb, V, Ti) refine grain size and can increase yield without large C increases, allowing favorable strength–toughness tradeoffs. - Low P and S limits preserve ductility and avoid embrittlement; controlled N is important for precipitation behavior and toughness.

3. Microstructure and Heat Treatment Response

Typical microstructures: - As-rolled and normalized microstructures for both grades are predominantly ferritic–pearlitic in conventionally processed plate and section products. When thermo-mechanically processed, a finer-grained ferritic structure with dispersed pearlite or bainitic constituents can be produced, improving strength and toughness.

Heat treatment responses: - Normalizing/refining: Normalizing (heating above AC3 and air cooling) can refine grain size and improve toughness, useful for heavy sections. Both grades respond similarly, but S355JR’s higher carbon equivalent makes achieving identical toughness slightly more demanding in heavy sections. - Quench and temper: Not typically applied to “as-rolled” EN structural steels for general structural use; when applied to similar chemistries, quench-and-temper will produce much higher strengths and different toughness profiles — product must then be specified to the required mechanical properties rather than grade name. - Thermo-mechanical control processing (TMCP): TMCP can be used to achieve higher yield strengths without large carbon increases. S355JR is commonly manufactured with TMCP to meet the higher yield requirement with good toughness.

Practical implication: - Both grades are primarily supplied in the delivered (as-rolled) condition for structural applications. If heat treatment beyond normalizing is needed, specify it and accept potential changes in certification and cost.

4. Mechanical Properties

Table: Typical mechanical properties (representative values; confirm by MTC and thickness limits)

Property	S275JR	S355JR
Minimum yield strength (ReH)	275 MPa (guaranteed)	355 MPa (guaranteed)
Tensile strength (Rm)	~410–560 MPa (depending on thickness/form)	~470–630 MPa (depending on thickness/form)
Elongation (A)	Typical minimum ~20–26% (thickness dependent)	Typical minimum ~20–22% (thickness dependent)
Impact toughness (JR)	≥27 J at +20 °C (JR classification)	≥27 J at +20 °C (JR classification)
Typical hardness	~120–160 HB (as-rolled)	~140–190 HB (as-rolled, higher due to strength)

Interpretation: - S355JR is the stronger material in both yield and tensile strength, enabling lighter designs or higher load capacity for the same section.
- Ductility (elongation) can be slightly lower in S355JR because of the higher strength, though TMCP and controlled chemistry minimize the trade-off.
- Impact toughness for both JR variants is specified at ambient temperature (+20 °C); if low-temperature toughness is required, choose variants with J0 or J2 suffixes or change grade accordingly.

5. Weldability

Weldability factors: - Key influencers: carbon content, carbon equivalent (hardenability), and presence of microalloying elements which promote hardening at the heat-affected zone (HAZ). - Both S275JR and S355JR are regarded as good to very good for manual and mechanized welding when appropriate preheat and welding consumables are used. S355JR’s higher carbon equivalent can modestly increase HAZ hardenability and susceptibility to cold cracking, especially in thicker sections.

Useful predictive formulas (interpret qualitatively; calculate with actual chemical analyses when assessing a specific plate): - IIW carbon equivalent: $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - International Pcm: $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$

Qualitative interpretation: - Lower $CE_{IIW}$ and lower $P_{cm}$ indicate easier weldability and lower preheat requirements. Both S275JR and S355JR usually fall in ranges permitting standard welding procedures, but verify the actual C and Mn of the supplied plate and use the formulas to set preheat/interpass temperatures and post-weld heat treatment if required. - For thick sections, increased preheat and controlled interpass temperature are more commonly required for S355JR than for S275JR to avoid HAZ hardening and hydrogen-assisted cracking.

6. Corrosion and Surface Protection

• Neither S275JR nor S355JR is stainless. For atmospheric exposure and general structural use, surface protection is required depending on the environment: primers and paints, hot-dip galvanizing, or metallization (e.g., zinc spray) are common.
• For aggressive environments (marine, chemical), select protective systems or consider corrosion-resistant alloys rather than relying on surface coating alone.

PREN (pitting resistance equivalent number) is relevant only to stainless alloys: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$ - PREN is not applicable to S275JR or S355JR because they lack sufficient Cr, Mo, or N to provide stainless corrosion resistance.

7. Fabrication, Machinability, and Formability

• Cutting: Plasma, oxy-fuel, and laser cutting are routinely used. S355JR will require marginally more energy for cutting than S275JR due to higher strength and hardness.
• Forming and bending: Lower-yield materials (S275JR) are generally easier to cold-form; S355JR can be formed but may require larger bend radii or reduced bend angles to avoid cracking, depending on thickness and temper.
• Machinability: Both steels machine adequately with standard tooling; higher strength in S355JR results in slightly higher tool wear and cutting forces.
• Surface finishing: Both accept painting, galvanizing, and post-machining finishing. For galvanizing, check thickness-related hydrogen uptake and consider post-weld stress relief for critical welded fabrications.

8. Typical Applications

S275JR (common uses)	S355JR (common uses)
General construction sections (I-beams, channels), light structural frames, welded small bridges, railings, non-critical ground support	Heavy structural members, crane components, heavy-duty frames, long-span structures, high-load welded assemblies
Secondary structures, purlins, small machinery frames	Where reduced section thickness and lower weight are required for the same load (value engineering)
Components where forming and cold workability are emphasized	Where higher static and fatigue strength is a priority

Selection rationale: - Choose S275JR when cost, ease of fabrication, and adequate strength are primary drivers.
- Choose S355JR when higher load capacity per unit area is required, allowing thinner sections, or where a higher design factor is specified.

9. Cost and Availability

• Relative cost: S355JR is generally more expensive per tonne than S275JR due to the higher guaranteed strength and slightly tighter processing controls. The delta varies by region, mill, and product form.
• Availability: Both grades are widely available in plate, sheet, sections, and structural profiles. S275JR often has wider availability for lower-thickness product lines in some regions; S355JR is widely stocked for mainstream structural use.
• Forms: Availability and lead time can depend on plate thickness, width, and production route (TMCP vs conventional rolling).

10. Summary and Recommendation

Table: Quick comparison

Characteristic	S275JR	S355JR
Weldability	Very good (lower CE)	Very good to good (slightly higher CE)
Strength–Toughness balance	Good for general structural use	Higher strength for lighter sections; similar toughness when processed correctly
Relative cost	Lower	Higher

Conclude with practical guidance: - Choose S275JR if: you need an economical, easily fabricated structural steel for general construction where a 275 MPa yield is adequate, fabrication speed and formability are priorities, and surface protection systems will provide required corrosion resistance. - Choose S355JR if: structural efficiency (higher yield strength that reduces section size and weight) is required, the application demands higher static or fatigue capacity, or specifications call for the S355 minimum yield; be prepared for slightly higher material cost and to address thicker-section welding controls.

Final procurement tip: - Always request the mill test certificate (MTC) and specify product form, thickness, and required impact testing temperature in the purchase order. Use actual chemical analysis to compute $CE_{IIW}$ and $P_{cm}$ when establishing welding procedures and preheat requirements. This ensures the selected grade meets both design intent and fabrication practicality.