S355 vs S460 – Composition, Heat Treatment, Properties, and Applications
Share
Table Of Content
Table Of Content
Introduction
S355 and S460 are two widely used structural steels in EN 10025-series specifications. Engineers, procurement managers, and manufacturing planners frequently face the selection dilemma between lower-cost, readily fabricated steels and higher-strength materials that permit lighter structures or reduced section sizes. Typical trade-offs include weldability versus strength, fabrication ease versus weight savings, and available toughness at design temperatures.
The principal technical distinction is that S460 provides a higher minimum yield strength than S355, achieved through composition control and thermo-mechanical processing or microalloying. Because their chemical basis and processing options overlap, these grades are commonly compared when optimizing structural efficiency, weld procedures, and whole-life costs.
1. Standards and Designations
- EN: Both S355 and S460 are specified in EN 10025 (e.g., EN 10025‑2 for non-alloy structural steels). Variants include suffixes for impact properties (JR, J0, J2) and for processing (M = thermo‑mechanically rolled, N = normalized).
- ISO: Equivalent designations may appear in ISO structural steel lists, but EN names are most common in Europe.
- ASTM/ASME: These steels are not direct one-to-one matches to ASTM grades (ASTM uses different chemistries and nomenclature); selection between EN and ASTM steels requires property comparison rather than direct name substitution.
- JIS/GB: Japanese (JIS) and Chinese (GB) standards have their own structural steel grades; cross-referencing tables are used for interchangeability.
- Classification: Both S355 and S460 are HSLA-type (high-strength low-alloy) structural steels—non-stainless carbon-manganese steels that may include microalloying elements (Nb, V, Ti) for strength and toughness. They are not alloy tool steels or stainless steels.
2. Chemical Composition and Alloying Strategy
| Element | Typical S355 (EN 10025 variants) | Typical S460 (EN 10025 variants) |
|---|---|---|
| C (max) | ~0.20–0.24 wt% (varies by variant) | ~0.16–0.22 wt% (varies by variant) |
| Mn (typ.) | ≤1.60 wt% | ≤1.60 wt% |
| 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 | trace to low (not mandatory) | trace to low |
| Ni | trace to low | trace to low |
| Mo | trace to low | trace to low |
| V (microalloy) | may be present in microalloyed variants | frequently used in microalloyed grades |
| Nb (microalloy) | may be present | commonly used in S460M/N variants |
| Ti (microalloy) | sometimes present | sometimes present |
| B (ppm level) | possible in microalloy variants | possible in microalloy variants |
| N (controlled) | controlled for toughness | controlled for toughness |
Notes: - Values are indicative ranges. Exact limits depend on the EN 10025 sub‑grade (e.g., S355JR, S355J0, S355J2, S460M, S460N) and manufacturer certifications. - S460 commonly achieves higher yield strength through thermo‑mechanical rolling (TMCP) and microalloying (Nb, V, Ti) rather than a large increase in carbon. - Alloying strategy: maintain low carbon and controlled phosphorus/sulfur for weldability and toughness; add microalloy elements to refine grain size and promote precipitation strengthening without compromising weldability.
How alloying affects properties: - Carbon: increases strength and hardenability but reduces weldability and toughness if excessive. - Manganese: promotes strength and hardenability; in controlled amounts it supports deoxidation and toughness. - Si: deoxidizer; moderate levels help strength but can affect toughness. - Nb, V, Ti: microalloying elements that enable higher strength via grain refinement and precipitation hardening with minimal negative effect on weldability when kept at low concentrations. - Mo, Cr, Ni: not primary in these grades but can affect hardenability and corrosion resistance if present.
3. Microstructure and Heat Treatment Response
Typical microstructures: - S355 (as-rolled/normalized): ferrite–pearlite microstructure with relatively coarse grains in plain-rolled conditions; toughness improved by normalization. - S460 (TMCP or normalized): finer-grained ferrite with a controlled amount of bainite/tempered martensite in some thermo‑mechanically rolled products; microalloy precipitates refine grain size and add strength.
Effect of processing routes: - Normalizing: reheating and air cooling refines grain size and improves toughness for both grades; S460 variants with “N” are normalized to guarantee consistent properties. - Thermo‑mechanical control processing (TMCP): used widely for S460M to achieve higher strength at lower carbon equivalents — produces a fine, high-strength ferrite/matrix with improved toughness. - Quenching & tempering: not typical for standard structural S355/S460 grades (these are delivered as rolled or normalized); quench and temper is a different route used for higher-strength, quenched alloy steels and would materially change properties beyond EN grade specifications.
4. Mechanical Properties
| Property | S355 (typical) | S460 (typical) |
|---|---|---|
| Minimum Yield Strength (Rp0.2) | ~355 MPa (flat products per EN 10025) | ~460 MPa |
| Tensile Strength (Rm) | ~470–630 MPa (variant and thickness dependent) | ~510–680 MPa (variant and thickness dependent) |
| Elongation (A, % min) | ~20–22% (thickness dependent; lower with increasing thickness) | ~14–20% (thickness and variant dependent) |
| Impact Toughness (Charpy V) | Specified by variant (e.g., 27 J at +20°C / 0°C / −20°C depending on JR/J0/J2) | Often specified for lower temperatures (variants ensure equivalent or improved toughness at design temperature) |
| Hardness (typical, non-HT) | Low–moderate (structure dependent; typically in the lower hardness range for structural steels) | Moderate (higher strength commonly yields somewhat higher hardness) |
Interpretation: - S460 is the stronger grade in terms of yield and often tensile strength; strength increase is obtained mainly via microalloying and TMCP, not by a significant carbon increase. - S355 tends to be slightly more ductile (higher elongation) in many product/variant comparisons because of its lower proof stress requirement. - Toughness is variant-dependent; both grades can be specified with impact requirements appropriate to low-temperature service. S460 is engineered to retain toughness at higher strength levels through controlled processing.
5. Weldability
Weldability considerations hinge on carbon content, carbon equivalent, and microalloying. Common predictive formulas include:
-
IIW carbon equivalent: $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$
-
More global parameter ($P_{cm}$) for weld cracking susceptibility: $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Qualitative interpretation: - Both S355 and S460 are generally considered weldable with appropriate preheat, interpass temperature control, and matching filler materials. S460, because of higher hardenability from microalloying and slightly higher strength, may require more controlled welding procedures (lower heat input limits, higher preheat or post‑weld heat treatment in some cases) than S355 to avoid cold cracking. - Carbon equivalents for typical EN S355 and S460 variants are generally low to moderate compared to quenched alloy steels, but S460M/N variants can have higher CE due to Nb/V additions. Always calculate CE or $P_{cm}$ for the manufacturer's chemistry and thickness to define preheat and consumable selection.
6. Corrosion and Surface Protection
- Neither S355 nor S460 are stainless steels; they lack significant chromium or nickel for passive film formation. Corrosion protection is therefore by coatings and design:
- Hot-dip galvanizing, zinc-rich primer plus paint systems, metallizing, or corrosion-resistant linings are common.
- Design for drainage, avoid crevices, and use sacrificial coatings where appropriate.
- PREN (Pitting Resistance Equivalent Number) is not applicable to non-stainless structural steels, but for reference: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$ This index is relevant for stainless alloys and is not meaningful for S355/S460.
7. Fabrication, Machinability, and Formability
- Cutting: Plasma, oxy‑fuel, laser, and waterjet cutting are standard for both grades. Higher-strength S460 may show slightly higher tool wear and springback in burn cutting due to higher hardness.
- Bending/forming: S355 is easier to cold-form and bend because of lower yield stress; S460 requires higher forming forces and tighter springback control. Forming limits depend on thickness, heat treatment, and variant.
- Machinability: Both are standard carbon/microalloy steels; machinability is generally moderate. S460's higher strength and microalloy precipitates can slightly reduce machinability and increase wear on cutting tools.
- Finishing: Surface treatments (shot blasting, painting, galvanizing) are similar for both grades; preheating and stress-relief considerations for welded assemblies differ per grade.
8. Typical Applications
| S355 — Typical Uses | S460 — Typical Uses |
|---|---|
| Building structures (beams, columns) where standard strength suffices | Bridges and long-span structures where higher strength reduces section size |
| General structural components, frames, and platforms | Heavy machinery frames with weight-saving requirements |
| Welded steel buildings and secondary steelwork | High‑performance structural elements in offshore/onshore steelwork where strength-to-weight is critical |
| Fabricated sections, plates, and profiles for moderate loading | Crane girders, large welded fabrications, and structures where reduction in material thickness is desirable |
Selection rationale: - Choose S355 when cost, ease of fabrication, and standard structural performance are primary. It is often the default for building structures and general fabrication. - Choose S460 when the design benefits from higher yield strength — e.g., to reduce member size, meet tighter deflection or buckling requirements, or save weight in transportation-limited systems — provided welding and fabrication controls are implemented.
9. Cost and Availability
- Relative cost: S460 is generally more expensive per tonne than S355 due to tighter processing controls (TMCP/normalizing), potential microalloy content, and lower production volumes. Price premium varies by market, product form, and thickness.
- Availability: S355 has broader availability in plates, hot-rolled sections, and structural shapes. S460 is widely available for plate and structural sections but may have longer lead times for specific thicknesses, treatment levels, or impact variants.
- Product form effect: Plates and coils with certified S460M/N properties may be more limited in supply than standard S355; procurement should consider lead time and supplier qualification.
10. Summary and Recommendation
| Criterion | S355 | S460 |
|---|---|---|
| Weldability | Good (standard procedures) | Good-to-moderate (may require tighter controls) |
| Strength–Toughness balance | Moderate strength with good ductility | Higher strength with engineered toughness via TMCP |
| Cost | Lower | Higher (premium for higher strength/processing) |
Choose S355 if: - Fabrication simplicity, broad availability, and lower material cost are priorities. - Design loads and weight constraints can be met without high-strength sections. - Standard welding procedures and routine preheat/interpass control are desired.
Choose S460 if: - Structural efficiency and weight reduction are critical (e.g., long spans, crane girders, constrained transport). - The project can support tighter welding/fabrication controls and possibly higher material costs to realize lifecycle or performance benefits. - Specified impact toughness and higher proof stress values are required by design.
Concluding remark: Both S355 and S460 are engineered to deliver reliable structural performance; the choice is governed by required yield strength, fabrication constraints, design temperature/toughness requirements, and total cost of ownership. Always verify the exact chemical and mechanical limits from the supplier’s mill certificate and perform carbon equivalent and weld procedure qualification for critical fabrications.