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ASTM, as one of the core specifications established by the American Society for Testing and Materials, carries the mission of unifying global quality requirements for stainless steel plates and strips.
The ASTM A240 standard establishes a comprehensive material evaluation system, serving as the standard specification for pressure vessels and general service chromium, chromium-nickel stainless steel, and heat-resisting steel plate, sheet, and strip. Material types encompass four major categories: austenitic, ferritic, martensitic, and duplex stainless steels, with austenitic stainless steel predominating.
ASTM A240 includes grades such as 304, 304L, 310S, 316L, 317L, 321, 321H, 347, 304L, etc. Here we introduce 304L and 316L. Both ASTM A240 304L and ASTM A240 316L belong to austenitic stainless steels and are among the most widely used and versatile stainless steel sheets. They are both non-magnetic and possess high toughness. In their chemical composition, chromium (Cr) content is ≥16%, enabling the formation of a Cr₂O₃ passivation film to resist corrosion from atmosphere, fresh water, and weak acids. Their shared low-carbon design ensures no solution treatment is required after welding, avoiding the risk of intergranular corrosion. Both exhibit excellent cold formability (elongation ≥40%), making them suitable for processes like stamping and deep drawing.
Although 304L and 316L stainless steel sheets share similar chemical properties, they exhibit significant differences. One key feature is the content of chromium and molybdenum. 304L has 18-20% Cr, while 316L has 16-18% Cr. Although 316L has lower chromium content, the addition of molybdenum (Mo) supplements and enhances the stability of the passivation film. The addition of 2-3% Mo in 316L is the core factor for its performance leap. Molybdenum forms molybdate oxyanions, effectively blocking chloride ion attack on the passivation film, increasing the critical pitting temperature from 20°C for 304L to 60°C. This is the main difference between the two stainless steel sheets. These seemingly minor compositional differences build fundamentally different corrosion resistance systems within the material. This makes 304L more suitable for conventional environments, while 316L is better suited for harsh corrosive conditions.
These subtle chemical composition differences also result in different mechanical properties. Leveraging nitrogen strengthening, 316L exhibits significantly higher tensile strength (≥620 MPa) compared to 304L (≥485 MPa). Furthermore, 304L is not suitable for many corrosive media, whereas the molybdenum in 316L forms protective molybdates, enabling it to withstand temperatures up to 500°C and mixed media like sulfuric and hydrochloric acids. Its service life in seawater pipelines can reach 20 years, over three times that of 304L. This makes 316L a more reliable choice when exposed to seawater, corrosion, and atmospheric environments. Both exhibit elongation ≥40%, but 304L offers excellent low-temperature performance and responds well to cold work hardening, making it more suitable for deep drawing processes (such as kitchen sink fabrication). Conversely, the molybdenum in 316L increases cold working difficulty, requiring specialized processing equipment.
Stainless steel is the natural choice for applications requiring low maintenance and corrosion resistance, finding widespread use across various fields. C&N Group strictly adheres to the ASTM A240 standard, providing full-specification stainless steel sheets and customized solutions tailored to requirements for corrosion protection, high temperature, high pressure, and other scenarios. If needed, please contact us.