A285 GrC vs A516 Gr60 – Composition, Heat Treatment, Properties, and Applications

Introduction

ASTM A285 Grade C and ASTM A516 Grade 60 are two common carbon-steel plate grades encountered in pressure-vessel, tank, and general structural applications. Engineers and procurement managers frequently weigh trade-offs among strength, toughness, weldability, surface protection, and cost when selecting between them. Typical decision contexts include low-cost storage tanks where ductility and local formability are critical versus pressure vessels where defined toughness at temperature and stricter mechanical-property control are required.

The principal practical distinction between the two lies in their metallurgical balance: one is formulated and specified primarily as a low-cost, general-purpose carbon plate with relatively higher carbon and simpler property control, while the other is a pressure-vessel quality plate engineered for improved toughness and controlled mechanical properties. Those differences drive choices in fabrication, preheating, inspection, and final service environment.

1. Standards and Designations

• ASTM/ASME:
• A285 — “Pressure Vessel Plates, Low and Intermediate Tensile Strength” (Grades A, B, C; Grade C is the highest strength/carbon among them).
• A516 — “Pressure Vessel Plates, Carbon Steel, for Moderate- and Lower-Temperature Service” (Grades 55, 60, 65, 70; Grade 60 is a common mid-range option).
• EN: Equivalents are not one-to-one; EN 10028 series (e.g., P235, P265, P355) covers similar functions but require specific mapping by mechanical and toughness requirements.
• JIS/GB: Local standards (e.g., JIS G3115, GB/T 1591) use different classifications; conversion requires comparing chemical and mechanical requirements and impact testing conditions.
• Material family: Both A285 GrC and A516 Gr60 are plain carbon steels (not stainless, not alloy/HSLA in the strict sense). A516 grades are produced to tighter property and toughness criteria than general A285 grades.

2. Chemical Composition and Alloying Strategy

The full ASTM standards list permitted elements and limits. Instead of quoting single numeric limits, the table below summarizes the typical relative presence of common elements for design and selection purposes.

How alloying affects performance: - Raising carbon and elements that increase hardenability (Mn, Cr, Mo) increases strength and the tendency to form martensite in rapid cooling—this can compromise weldability and toughness unless compensated by processing. - Microalloying elements (Nb, V, Ti) in small amounts help grain refinement and precipitation strengthening, improving yield strength and toughness without large carbon increases; these are more common in controlled-pressure-vessel steels than in low-cost general plate.

3. Microstructure and Heat Treatment Response

Typical as-rolled or normalized products for these grades exhibit predominantly ferrite–pearlite microstructures.

• A285 Grade C:
• Manufacturing intent is general-purpose plate produced by conventional hot rolling and either as-rolled or stress-relieved condition. Microstructure tends toward ferrite with banded pearlite; grain size and inclusion cleanliness are not as rigorously controlled as for pressure-vessel grades.

• Normalizing will refine grains and modestly improve toughness; aggressive quench & temper cycles are not standard practice for A285 and may produce higher hardness and require post-weld heat treatment to avoid embrittlement.

• A516 Grade 60:

• Produced to tighter control for fracture toughness, often with more attention to deoxidation practice and thermal history. Microstructure is ferrite–pearlite with less banding and finer grain size compared with generic A285.
• Normalizing and controlled rolling improve toughness. These plates are not typically supplied in quenched-and-tempered conditions for the grade as specified; heat treatments aim to produce uniform mechanical properties and achieve required impact toughness at specified temperatures.

Effect of processing routes: - Normalizing: beneficial to both grades for refining grain size and improving toughness—more impactful for A285 to bring properties closer to those of A516. - Quench & temper: not typical for standard A516/A285 grades; would convert microstructure to martensite–tempered martensite and require re-specification of the material grade. - Thermo-mechanical control processing (TMCP): used in modern pressure-vessel steels to improve strength–toughness balance; more sophisticated TMCP variants are more likely for steels specified with tight toughness requirements than for generic A285.

4. Mechanical Properties

Below is a qualitative comparison of commonly relevant mechanical properties. For project work, always use the actual mill test report and the governing standard for numeric acceptance criteria.

Which is stronger/tougher/ductile and why: - A516 Grade 60 is designed and often supplied with more consistent toughness and ductility at the specified test temperatures because of tighter control on composition, deoxidation, and thermal processing. - A285 Grade C can have slightly higher carbon and less stringent toughness controls, which may yield acceptable strength but lower and less predictable toughness—particularly at low service temperatures.

5. Weldability

Weldability depends primarily on carbon content, effective alloying (hardenability), and impurities. Two commonly used indices illustrate the qualitative effect:

• IIW carbon equivalent (widely used for welding assessment): $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$

• International Institute of Welding “Pcm” (more conservative): $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$

Interpretation (qualitative): - A285 GrC typically yields a higher carbon equivalent than a well-controlled A516 Gr60 of the same thickness, so it is generally more sensitive to hydrogen-assisted cold cracking and requires more preheat, controlled interpass temperatures, and perhaps post-weld heat treatment for thick sections or low-temperature service. - A516 Gr60, with somewhat lower carbon and tighter alloy control and often improved cleanliness, is easier to weld with standard filler metals and less severe preheat requirements for comparable thicknesses, and it is more commonly used where weldability plus impact toughness are important.

Practical welding notes: - For either grade, thickness, joint design, welding process, and service temperature dictate preheat/interpass requirements. Use the CE/Pcm formulas as screening tools; verify with procedure qualification (PQR/WPS) and hydrogen control measures in shop practice.

6. Corrosion and Surface Protection

• Neither A285 GrC nor A516 Gr60 are stainless steels; inherent corrosion resistance is low compared with stainless or weathering steels.
• Typical protection strategies:
• Barrier coatings: paint systems (epoxy, polyurethane), shop primer + finish coat.
• Metallic coatings: galvanizing is feasible for many plate thicknesses but consider weld removal and local continuity of coating.
• Cladding or lining: for severe chemical or abrasive environments, stainless cladding or internal linings are used.
• PREN (pitting resistance equivalent) is not applicable to plain carbon steels; PREN is relevant to stainless alloys: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$
• For A285/A516 applications where corrosion is a concern, selection is driven by coating/layering strategies, cathodic protection, or substitution to corrosion-resistant alloys rather than by small composition differences between these grades.

7. Fabrication, Machinability, and Formability

• Formability and bending:
• A516 Gr60 generally offers better guaranteed ductility and formability for pressure-vessel fabrications because of its toughness requirements. It is routinely used for forming into cylindrical shells and heads.
• A285 GrC may be less forgiving in tight-radius forming due to variable toughness; practitioners often recommend trial forming or specifying lower forming strains.
• Cutting and machining:
• Both grades machine similarly in as-rolled condition; machinability is influenced by sulfur content and heat treatment. A285 may be slightly easier if not constrained by low-carbon chemistry, but gains are modest.
• Surface finishing/weld preparation:
• Both accept the same welding preparations and surface finishes; cleanliness and removal of mill scale or rust will aid weld quality.

8. Typical Applications

Selection rationale: - Choose A285 when minimizing raw material cost for non-critical or ambient-temperature tanks and when toughness and tight mechanical control are not required by code. - Choose A516 Gr60 when code compliance, documented toughness, and consistent mechanical properties drive design decisions—especially for pressure-retaining equipment and lower-temperature service.

9. Cost and Availability

• Availability:
• A516 Grade 60 is a widely stocked pressure-vessel plate in many markets and available in a broad range of thicknesses and mill-certified lots.
• A285 Grade C is also available but may be less commonly stocked for large-diameter pressure applications because many buyers prefer the stricter A516 family.
• Relative cost:
• A285 is typically lower cost as it represents a less strictly controlled manufacturing route and fewer toughness guarantees.
• A516 Gr60 carries a premium for tighter control, inspection, and impact testing; however, the premium is justified by lower fabrication risk and easier code compliance.
• Product forms:
• Both are commonly supplied as hot-rolled plates; availability in thin gauge, cut-to-size, or specific mill cert levels varies by mill and region.

10. Summary and Recommendation

Concluding recommendations: - Choose A285 Grade C if you need a low-cost, general-purpose carbon plate for non-code, ambient-temperature tanks or structures where strict toughness and documented vessel properties are not required. - Choose A516 Grade 60 if you require a pressure-vessel plate with specified impact toughness, more consistent mechanical properties, and easier code compliance for welded vessels and equipment—especially where lower-temperature toughness and predictable weld behavior are critical.

For final material selection always consult the applicable code (ASME, EN, etc.), the mill test certificate, and perform procedure qualification for welding and fabrication conditions.