S235JR vs S275JR – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
S235JR and S275JR are two of the most commonly specified European structural carbon steels used in plate, sheet, and rolled sections. Engineers, procurement managers, and manufacturing planners routinely face a selection dilemma between the two: balancing cost and ease of fabrication against the need for higher strength and design margins. Typical decision contexts include choosing the steel for welded loadbearing structures, economy-grade fabrication where forming and painting are primary protections, or when marginal increases in strength can reduce section size and weight.
The principal technical difference between these grades is the specified minimum yield strength (the numeric grade identifier), which drives different design choices: S275JR delivers higher minimum yield strength than S235JR while maintaining similar chemistry and basic processing routes. Because they share the same family of low-alloy, non-stainless steels under EN 10025, they are commonly compared in structural design and manufacturing for their trade-offs in strength, toughness, weldability, and cost.
1. Standards and Designations
- EN: Both S235JR and S275JR are defined in EN 10025-2 (non-alloy structural steels).
- ISO: Corresponding ISO/EN identifiers are often cross-referenced; ISO equivalent descriptions reflect minimum yield strength classes.
- ASTM/ASME: These grades do not have direct one-to-one ASTM names; similar low-carbon structural steels in ASTM practice are available but specification language and acceptance criteria differ.
- JIS/GB: Japanese (JIS) and Chinese (GB) standards provide comparable structural carbon steels, but direct equivalents require checking mechanical and chemical acceptance criteria.
- Classification: Both S235JR and S275JR are plain carbon/low-alloy structural steels (not stainless, not tool steels, not high-strength low-alloy (HSLA) with significant microalloying), typically grouped as structural carbon steels.
2. Chemical Composition and Alloying Strategy
Table: Typical chemical composition (approximate ranges; consult EN 10025 and supplier mill certificates for exact values—values vary with thickness and delivery conditions)
| Element | S235JR (typical, wt%) | S275JR (typical, wt%) |
|---|---|---|
| C (Carbon) | ≤ ~0.17–0.20 (low) | ≤ ~0.20–0.22 (low–moderate) |
| Mn (Manganese) | ~0.8–1.6 (moderate) | ~1.0–1.6 (moderate) |
| Si (Silicon) | ≤ ~0.3 (deoxidizer) | ≤ ~0.3 (deoxidizer) |
| P (Phosphorus) | ≤ 0.035 (impurity control) | ≤ 0.035 (impurity control) |
| S (Sulfur) | ≤ 0.035 (impurity control) | ≤ 0.035 (impurity control) |
| Cr (Chromium) | typically ≤ trace | typically ≤ trace |
| Ni (Nickel) | typically ≤ trace | typically ≤ trace |
| Mo (Molybdenum) | typically ≤ trace | typically ≤ trace |
| V, Nb, Ti, B (microalloys) | generally not present in significant amounts | generally not present in significant amounts |
| N (Nitrogen) | low (residual) | low (residual) |
Notes: - These steels are intentionally low in carbon and low-alloy content to preserve weldability and formability. Exact maximums depend on thickness and the specific EN table; suppliers issue mill test certificates (MTCs) that record measured values. - Alloying strategy: both grades use a "low-carbon" approach with controlled manganese and silicon for deoxidation. They avoid significant additions of Cr, Mo, Ni or microalloying elements in the standard versions, keeping hardenability and carbon equivalent low.
How alloying affects properties: - Carbon increases strength and hardenability but reduces weldability and toughness when elevated; both grades keep carbon low to preserve toughness and ease of welding. - Manganese contributes to hardenability and tensile strength and is limited to maintain toughness. - Silicon functions as a deoxidizer and slightly increases strength. - Phosphorus and sulfur are controlled to minimize embrittlement and hot-shortness; their maximums are allowed only at low levels.
3. Microstructure and Heat Treatment Response
Typical microstructure: - As-produced (normalized/rolled) S235JR and S275JR microstructures are composed primarily of ferrite and pearlite. The relative fraction of pearlite increases slightly with higher carbon and manganese, which is why S275JR (marginally higher carbon/manganese) can exhibit slightly higher strength. - Neither grade is intended for quench-and-temper treatments in standard supply conditions; they are supplied in the hot-rolled, normalized, or annealed condition depending on the mill’s process and order.
Response to common heat treatments: - Normalizing: Refines grain size, slightly increases toughness and strength; both grades respond similarly and normalizing can be used when improved mechanical uniformity or cleanliness is desired. - Annealing: Softens the steel and improves formability; used when increased ductility is required prior to forming operations. - Quenching and tempering: Possible but not typical—because these grades lack significant hardenability alloying, quench-and-temper will not develop high strength without risk of poor toughness unless chemical composition and section thickness are tightly controlled. - Thermo-mechanical processing (controlled rolling): Not a standard feature of S235JR or S275JR but where applied can increase yield strength and toughness—moving the product toward HSLA behavior. Such products are usually designated differently.
4. Mechanical Properties
Table: Typical mechanical properties (indicative ranges—verify with standards or MTCs)
| Property | S235JR (typical) | S275JR (typical) |
|---|---|---|
| Minimum Yield Strength (Rp0.2) | 235 MPa | 275 MPa |
| Tensile Strength (Rm) | 360–510 MPa | 410–560 MPa |
| Elongation (A) | ≥ ~22–26% (depends on section/thickness) | ≥ ~20–23% (depends on section/thickness) |
| Charpy Impact (JR) | 27 J at 20°C (JR grade requirement) | 27 J at 20°C (JR grade requirement) |
| Hardness | Typical ranges ~110–150 HB (varies with condition) | Typical ranges ~120–160 HB (varies with condition) |
Interpretation: - Strength: S275JR is the stronger of the two by specification—its higher minimum yield and typically higher tensile strength allow reduced section sizes for the same loads. - Ductility and toughness: S235JR generally displays slightly higher elongation due to lower yield strength, which can translate to marginally better formability. Both grades require impact toughness verification (JR = 27 J at +20°C), ensuring basic notch toughness in common environments. - Why differences exist: The slightly higher permitted carbon and manganese (on average) in S275JR increase strength through more pearlite/ferrite balance and strain-hardening potential.
5. Weldability
Weldability considerations: - Both grades are widely considered readily weldable using common processes (SMAW, GMAW/MIG, FCAW, TIG) because of low carbon content and low carbon equivalent. - Carbon equivalent indices assist welders and engineers in assessing preheat and consumable choice. Useful formulas include: - $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$ - Interpretation: Because both S235JR and S275JR have low C and low amounts of other alloying elements, their $CE_{IIW}$ and $P_{cm}$ values are low, indicating low hardenability and a low propensity for cold cracking. S275JR may be marginally less forgiving because its higher nominal carbon/manganese can raise the carbon equivalent slightly—this can warrant modest preheat in thick sections or restrained welds. - Practical advice: Use standard filler metals compatible with structural steels (matching or slightly higher strength than base metal for reduced distortion), control interpass temperature, and apply appropriate preheat based on thickness, restraint, and measured carbon equivalent rather than grade name alone.
6. Corrosion and Surface Protection
- These grades are non-stainless carbon steels; intrinsic corrosion resistance is limited. Selection should consider environmental exposure and intended protective systems.
- Typical surface protection options:
- Hot-dip galvanizing: common for structural steel where atmospheric corrosion resistance is required.
- Paint systems: primers, mid-coats, and topcoats provide tailored protection for atmospheric, industrial, or marine environments.
- Metallizing (zinc/Al coatings), powder coatings, or cladding where required.
- PREN: The pitting resistance equivalent number formula, $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$ is not applicable here because S235JR and S275JR are not stainless steels and do not contain significant Cr, Mo, or N to make localized corrosion indices meaningful.
- Practical guidance: Choose protective schemes based on exposure class (ISO 12944 or similar guidance), and prioritize coatings or galvanizing for long-term durability.
7. Fabrication, Machinability, and Formability
- Cutting: Plasma, flame, and oxy-fuel cutting processes are routinely used; machining using standard carbides and HSS tooling is straightforward due to relatively low hardness.
- Machinability: Moderate—typical carbon steel machinability; S235JR can be slightly easier to machine than S275JR because of lower yield strength and slightly lower work-hardening tendency.
- Formability and bending: Both grades form well in the delivered condition; S235JR is marginally more forgiving for tight bends and deep drawing because of higher elongation. Forming limits should be validated by bend tests or supplier guidelines for specific thicknesses.
- Surface finishing: Both respond well to conventional surface treatments (grinding, shot-blasting, painting). Post-weld heat treatments are rarely required for these grades unless specific residual stress relief or property changes are required by design.
8. Typical Applications
| S235JR — Typical Uses | S275JR — Typical Uses |
|---|---|
| General structural members where cost and formability matter: light frames, non-critical supporting structures, welded enclosures, and purlins | Structural members with higher design loads or where smaller cross-sections are desired: bridge components (non-critical), heavier beams, loadbearing frames, and crane rails (where specified) |
| Architectural steelwork and fences, where painting/galvanizing provides corrosion protection | Medium-weight structural components, connectors, and fabricated members requiring higher yield strength |
| General-purpose plate and profiles for fabrication, where bends and forming are frequent | Situations requiring improved strength-to-weight ratio, allowing reduced section thickness and weight |
Selection rationale: - Choose S235JR when maximum formability, lower material cost, and greater ductility are prioritized, and when the required yield strength is within its limits. - Choose S275JR when a higher minimum yield strength is needed to reduce section sizes or meet design loads while still retaining good weldability and toughness at ambient temperatures.
9. Cost and Availability
- Relative cost: S275JR is typically priced slightly higher than S235JR because of its higher strength specification and marginally tighter chemistry and mechanical requirements, though market pricing fluctuates with steel commodity cycles.
- Availability: Both grades are widely produced and available in many product forms (plates, sheets, coils, sections). S235JR tends to be more common in very low-end consumer structural markets, while S275JR is strongly stocked by structural steel suppliers and service centers.
- Product forms: Availability can vary by thickness and finish—consult suppliers for lead times on hot-rolled normalized plate, pickled & oiled sheets, or pre-galvanized options.
10. Summary and Recommendation
Table: Quick comparative summary
| Parameter | S235JR | S275JR |
|---|---|---|
| Weldability | Excellent | Excellent (slightly higher CE potential) |
| Strength–Toughness balance | Good (higher ductility) | Better strength with retained toughness |
| Cost | Lower (generally) | Moderate (generally higher than S235JR) |
Conclusions: - Choose S235JR if you prioritize maximum formability, slightly higher ductility, lower material cost, and the project’s yield strength requirements do not exceed 235 MPa. It is ideal for general structural fabrications, architectural components, and situations where ease of bending/forming is valuable. - Choose S275JR if you need higher minimum yield strength to reduce section sizes or meet higher design loads while still retaining good weldability and adequate impact toughness. It is suited to heavier structural applications where the strength-to-weight advantage and modest increase in allowable stress are important.
Final practical notes: - Always verify mechanical and chemical values against the supplier’s mill test certificate and the applicable standard (EN 10025 or the specified delivery standard). - Base preheat and consumable choices on measured carbon equivalent ($CE_{IIW}$ or $P_{cm}$) and part restraint, not on the grade name alone. - Consider protective coatings early in procurement to ensure compatibility with fabrication steps (e.g., welding through coatings, post-fabrication hot-dip galvanizing).