SA516 Gr60 vs Q345R – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
SA516 (ASTM A516/A542 family) Grade 60 and Chinese Q345R are two commonly specified pressure‑vessel and structural steels that engineers and procurement professionals frequently weigh against one another. The selection dilemma typically centers on balancing strength and cost (higher yield for lighter structures) against fracture toughness and code compliance (material behaviour in pressure‑containing, low‑temperature, or cyclic environments). Decisions are commonly driven by required yield/tensile levels, required Charpy impact performance, welding constraints, and regional availability.
The principal technical difference between the two is their design intent and nominal strength tier: Q345R is specified as a higher‑yield, low‑alloy structural/pressure‑vessel steel (higher nominal yield), whereas SA516 Gr60 is a pressure‑vessel carbon steel grade formulated to deliver a balance of strength and low‑temperature toughness appropriate to many boiler and pressure applications. They therefore appear together in tradeoffs between strength-per-thickness and toughness/weldability/specification fit.
1. Standards and Designations
- SA516 Grade 60: Governed by ASTM A516/A516M (commonly referenced in ASME Section II for boiler and pressure vessel plates). It is a carbon steel plate produced for moderate- to high‑temperature service in pressure vessels. Classified as a carbon pressure‑vessel steel (non‑stainless, non‑tool).
- Q345R: Defined in Chinese standard GB/T 713 (pressure vessel and boiler steel plates) as a low‑alloy structural/pressure vessel steel. Q345 denotes a nominal minimum yield of 345 MPa; the “R” suffix indicates the plate is intended for pressure vessel use. Classified as a low‑alloy/HSLA pressure‑vessel steel.
Other related standards (contextual, for cross‑reference and equivalents): - EN: EN 10028 series covers pressure vessel steels (e.g., P265GH, P355GH), which play similar roles in European practice. - JIS: JIS G3115 and related standards for pressure vessel steels. - GB: Chinese GB/T 713 for Q345R is the direct national standard.
2. Chemical Composition and Alloying Strategy
The following table shows representative element ranges for each grade. These are indicative, not normative limits — always consult the controlling standard or mill certificate for procurement or design.
| Element (wt%) | SA516 Gr60 (representative) | Q345R (representative) |
|---|---|---|
| C | ~0.20–0.28 (low‑to‑moderate) | ≤ ~0.18–0.22 (controlled low) |
| Mn | ~0.60–1.10 | ~0.80–1.60 |
| Si | ~0.10–0.35 | ~0.15–0.50 |
| P | ≤ 0.035 (max) | ≤ 0.035 (max) |
| S | ≤ 0.035 (max) | ≤ 0.035 (max) |
| Cr | trace–small (often ≤0.30) | trace–small (≤0.30) |
| Ni | trace (usually ≤0.30) | trace (usually ≤0.30) |
| Mo | typically ≤0.08 | typically ≤0.08 |
| V, Nb, Ti | typically none or microalloying in some heats | may contain microalloying (Nb, V, Ti) in some batches |
| B, N | ppm levels if controlled | ppm levels if controlled |
How alloying affects performance: - Carbon (C) raises strength and hardenability but reduces weldability and toughness if over‑alloyed. Both grades keep C moderate for balance. - Manganese (Mn) increases hardenability and strength; Q345R often has higher Mn to reach its higher yield target. - Silicon (Si) is a deoxidizer and can slightly increase strength. - Microalloying elements (Nb, V, Ti) are used in Q345R variants to raise yield without sacrificing toughness via grain refinement and precipitation strengthening. - Chromium, nickel, and molybdenum, if present in small amounts, increase hardenability and elevated‑temperature strength.
3. Microstructure and Heat Treatment Response
Typical microstructures: - SA516 Gr60: Typically produced as a normalized or as-rolled plate resulting in a ferrite–pearlite matrix with controlled grain size. The microstructure emphasizes good toughness (refined ferrite and evenly distributed pearlite). Not normally supplied in quenched‑and‑tempered condition. - Q345R: Manufactured with controlled rolling and, in many cases, microalloying and thermomechanical processing (TMCP) to produce fine ferritic or bainitic‑ferritic microstructures depending on cooling rates. This results in higher yield strength while retaining good toughness.
Heat treatment responses: - Normalizing: Both steels respond to normalizing (heating then air cooling) with grain refinement and improved toughness, but Q345R's TMCP route often obviates separate normalization. - Quench & temper: Not typical for either grade in standard supply form; quench & temper can raise strength considerably but will change toughness and require post‑weld heat treatment considerations. SA516 is usually used in as‑rolled or normalized condition for pressure vessels. - Thermo‑mechanical rolling (TMCP): Common for Q345R (and other HSLA steels) to achieve high yield with good toughness; this gives a refined microstructure and higher yield for a given thickness.
4. Mechanical Properties
Representative mechanical behaviour (indicative ranges; verify with supplier test certificates):
| Property | SA516 Gr60 (typical) | Q345R (typical) |
|---|---|---|
| Tensile Strength (MPa) | Moderate; typical range ~410–520 MPa | Moderate‑high; typical range ~470–630 MPa |
| Yield Strength (MPa) | Moderate; generally lower than Q345R (depends on thickness) | Higher; nominal target ~345 MPa (as per grade designation) |
| Elongation (A%) | Good ductility; often ≥20% (depending on thickness) | Good ductility; often ≥17–22% (thickness dependent) |
| Impact Toughness (Charpy V‑notch) | Designed for good impact energy at specified temperatures (pressure‑vessel performance) | Good toughness, often ensured at specified CVN temperatures, but depends on processing |
| Hardness (HBW) | Moderate (suitable for forming/welding) | Moderate to slightly higher (depending on heat treatment and microalloying) |
Explanation: - Q345R targets a higher yield level (by its naming convention and design intent) which typically allows lighter sections for the same load, but higher yield can mean less margin for ductility-sensitive designs if not verified. - SA516 Gr60 is formulated and often certified for pressure‑vessel service at specified impact temperatures, giving confidence in fracture toughness for thin‑ to moderate‑thickness plates used in boilers and low‑temperature vessels. - Actual values vary with plate thickness, rolling schedule, and heat treatment. Always use mill certificates and material tests for final design.
5. Weldability
Weldability considerations hinge on carbon content, hardenability (Mn, Cr, Mo), and microalloying. Two useful empirical indices are the IIW carbon equivalent and the Pcm formula:
$$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$
$$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Interpretation (qualitative): - Lower $CE_{IIW}$ and $P_{cm}$ imply easier weldability with lower pre‑heat requirements. Both SA516 Gr60 and Q345R are intended to be weldable using common processes (SMAW, GMAW, SAW), but parameters differ. - SA516 Gr60: Moderate carbon and controlled alloying make it readily weldable for conventional vessel fabrication; attention to preheating and PWHT is required for thicker sections or low‑temperature service to avoid hydrogen cracking and preserve toughness. - Q345R: Slightly higher Mn and possible microalloying increase hardenability somewhat; preheat and controlled interpass temperatures may be needed for thicker sections. Q345R typically is weldable but must follow GB/T welding recommendations and qualification procedures. - In both cases, use qualified weld procedures (WPS/PQR) and perform post‑weld nondestructive testing and impact tests per design code.
6. Corrosion and Surface Protection
- These are non‑stainless steels; intrinsic corrosion resistance is limited.
- Standard protections: coatings (epoxy, polyurethane), primers, painting systems, and hot‑dip galvanizing (where appropriate) are commonly used. Selection depends on service environment (atmospheric, marine splash, chemical exposure).
- Stainless indices like PREN are not applicable to SA516 Gr60 or Q345R because they are carbon/low‑alloy steels without stainless chromium levels. For stainless materials the index would be:
$$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$
but this is not relevant for these grades.
7. Fabrication, Machinability, and Formability
- Cutting: Both grades machine and cut with standard thermal (plasma, oxy‑fuel) and mechanical (sawing) methods. Slag adherence and HAZ properties require usual post‑cut treatment.
- Bending/Forming: SA516 Gr60 typically has good formability because of its ferrite–pearlite structure and is widely cold‑formed into shells. Q345R, as a higher‑yield material, can be less forgiving for tight bends — springback and required bend radii must be adjusted to the higher yield and work‑hardening behaviour.
- Machinability: Both have machinability similar to typical carbon steels; Q345R may be slightly more abrasive depending on alloying. Use appropriate tooling and feeds; preheating for heavy fabrication, if specified, must be considered.
- Surface finishing: Welding, grinding, and post‑weld cleaning follow standard vessel fabrication practice; scale removal prior to coating is essential.
8. Typical Applications
| SA516 Gr60 | Q345R |
|---|---|
| Pressure vessel shells and heads for boilers, moderate‑pressure vessels, tanks where low‑temperature toughness is required | Pressure vessel plates where higher yield and lower weight are desired; large structural welded pressure vessels in regional practice |
| Storage and transport tanks requiring code compliance with ASME/ASTM specifications | Boilers and vessels per GB/T practice; structural components where higher yield reduces section sizes |
| Low‑temperature and cyclic service requiring demonstrated CVN performance | General structural and pressure applications where TMCP and HSLA benefits are used |
Selection rationale: - Choose SA516 Gr60 when the design emphasizes validated pressure‑vessel performance, specified Charpy impact levels, and widespread acceptance in ASME/ASTM jurisdictions. - Choose Q345R when the project is specified to Chinese standards or when designers want higher yield per thickness and favorable availability in regions where GB/T standards dominate.
9. Cost and Availability
- Relative cost: Q345R is often cost‑competitive or lower in regions where GB/T products are produced in high volume; higher yield can reduce weight and total material cost. SA516 Gr60 may carry a premium in regions where ASME‑certified plate and documentation are required.
- Availability: SA516 Gr60 is widely available worldwide where ASME code compliance is demanded; Q345R is widely available in China and in supply chains oriented to GB/T standards. Product form (coils, plates, cut‑to‑length) and thickness availability vary by mill and region.
10. Summary and Recommendation
Summary table (qualitative):
| Attribute | SA516 Gr60 | Q345R |
|---|---|---|
| Weldability | Good (designed for vessel fabrication) | Good, but slightly higher hardenability potential — follow WPS |
| Strength–Toughness balance | Optimized for vessel toughness and ductility | Higher yield; good toughness when TMCP/microalloyed |
| Cost / Availability | Common in ASME markets; moderate cost | Often lower cost in GB/T markets; high availability regionally |
Recommendations: - Choose SA516 Gr60 if you require ASME/ASTM pressure‑vessel plate with documented Charpy impact performance, proven behaviour in low‑temperature service, and broad code acceptance for boilers and vessels. - Choose Q345R if your project follows GB/T standards or you need higher nominal yield (345 MPa) to reduce section thickness/cost and you can qualify weld procedures and toughness for the intended service environment.
Closing note: Both materials are mature, well‑understood steels. Final material selection should be driven by the controlling design code, required mechanical and impact properties at operating temperature, welding and fabrication constraints, and supply chain considerations. Always verify chemical and mechanical data from the mill certificate and, where necessary, require specific testing (tension, CVN, PWHT validation) to ensure fitness for service.