A515 Grade 70 is a carbon steel plate specified in ASTM A515/ASME SA515, primarily used for moderate- to high-temperature pressure vessel applications; the "Grade 70" indicates a minimum tensile strength of 70 ksi (about 485 MPa), and it is valued for its good weldability, strength, and heat resistance in industries such as oil and gas, power generation, and petrochemical processing.
Chemical Composition of ASTM A515 Grade 70
|
Element |
Product Analysis Max (%) |
Ladle Analysis Max (%) |
|---|---|---|
|
Carbon (C) |
0.30-0.35 |
0.30-0.35 |
|
Manganese (Mn) |
1.30 |
1.20 |
|
Phosphorus (P) |
0.035 |
0.035 |
|
Sulfur (S) |
0.035 |
0.035 |
|
Silicon (Si) |
0.13-0.45 |
0.15-0.40 |
Mechanical Properties of ASTM A515 Grade 70
|
Thickness (mm) |
Yield Strength (Min Mpa) |
Tensile Strength (Mpa) |
Elongation (Min %) |
|---|---|---|---|
|
≤ 200 |
260 |
485-620 |
17 |
|
≤ 50 |
260 |
485-620 |
21 |
applications
ASTM A515 GR.70 is widely used in industries requiring robust materials for high-temperature and high-pressure environments. Common applications include:
Boilers and Pressure Vessels:
Ideal for fabricating boilers and pressure vessels due to its high tensile strength and heat resistance.
Heat Exchangers:
Used in heat exchangers for efficient heat transfer under elevated temperatures.
Power Generation:
Employed in power plants for components exposed to high temperatures.
Petrochemical Industry:
Suitable for storage tanks and processing equipment in petrochemical plants.
Processing Treatment
1. Heat Treatment
The standard requirements for heat treatment depend on the plate thickness:
Thickness ≤ 2 in. (50 mm): Usually supplied in the as-rolled condition but can be ordered normalized, stress-relieved, or both.
Thickness > 2 in. (50 mm): Must be normalized to refine the grain structure and improve mechanical properties.
Additional Processes: Depending on customer requirements, technology such as annealing, normalizing plus tempering, or quenching and tempering (to increase hardness and toughness) may be applied.
2. Welding Process
ASTM A515 Gr. 70 has good weldability and can be processed using standard methods:
Common Methods: SMAW (stick), GTAW/TIG, GMAW/MIG, and SAW (submerged arc).
Consumables: Low-hydrogen electrodes like E-7018 are recommended.
Preheat & Post-Weld Heat Treatment (PWHT): For heavy sections, pre-heating and PWHT (stress relieving) are advised to prevent cracking and manage hardness.
3. Forming and Machining
Cold Forming: Readily bent or cold-formed using conventional means due to its good ductility.
Hot Working: Can be hot-worked; forging is typically performed between 1800°F and 2350°F.
Machinability: Comparable to plain carbon steels (e.g., AISI 1330).
4. Surface Treatment
Plates are typically delivered with a hot-rolled oxide or scale.
Optional treatments include shot blasting, pickling, and painting/coating to prevent corrosion.
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What is the purpose of LF furnace refining in A515 Grade 70 production?
LF (ladle furnace) refining improves steel cleanliness by slag refining, adjusts chemical composition precisely, and maintains molten steel temperature stability.
Why is VD vacuum degassing used in some A515 Grade 70 production?
VD (vacuum degassing) reduces gas content (e.g., hydrogen, oxygen) in molten steel, minimizing internal defects and enhancing the steel's internal purity and mechanical stability.
What surface defects are removed during A515 Grade 70 slab cleaning?
Surface defects such as oxide scale, cracks, scratches, and segregation layers are removed by scarfing, grinding, or shot blasting.
What inspection methods are used for A515 Grade 70 finished plates?
Common methods include dimensional inspection, visual inspection, ultrasonic testing (UT) for internal defects, tensile testing, impact testing, and hardness testing.
What is the maximum thickness of A515 Grade 70 plates per ASTM A515?
It can be supplied up to 8 inches (203 mm) thick, with specific mechanical property requirements adjusted for thicker sections.
Can A515 Grade 70 be welded?
Yes. It is designed for welded structures and has good weldability when proper welding procedures (e.g., preheating, post-heat treatment) are followed.
What is the difference between A515 Grade 70 and A516 Grade 70?
A515 is for boiler and pressure vessel plates used at moderate/elevated temperatures, while A516 has stricter impact toughness requirements and is suitable for lower-temperature service.
What manufacturing process is commonly used for A515 Grade 70 plates?
Answer: The typical process includes melting (BOF), refining (LF/VD), continuous casting, reheating, controlled rolling, heat treatment (if required), descaling, and inspection.