Suitable Forms

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316 grades are available in virtually every stainless steel product form, including coils, sheets, plates, strips, tubes, pipes, fasteners, rods, bars, angle products, wires, castings, and other shapes. Furthermore, 316 stainless steel is produced in a full range of surface finishes—from standard to custom textures.

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Applications

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The typical applications of 316 stainless steel can be summarized as follows: it is used in yacht fittings and structural components, particularly in maritime architectural structures, in harsh or industrial environments, in equipment for food and beverage processing, in hot water systems, as well as in chemical, petrochemical, mineral processing, photographic, and various other industrial applications.

Often described as “marine grade,” 316 is considered a level above 304 base quality.

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Alternatives

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In certain applications and service environments, alternative grades to 316 should be considered:

• Strong Reducing Acid Environments: Consider alternatives such as 904L, 2205, or super duplex grades.

• Environments Above 50–60 °C with Chloride Content: Opt for grades like 2205, super duplex, or super austenitic steels that offer superior resistance to stress corrosion cracking and pitting.

• High Demands Such as Heavy Welding (316L), Additional Processing (an enhanced form of 316 with improved machinability), or Requirements for High Strength or Hardness (martensitic or precipitation-hardened grades).

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Low-Nickel Austenitic Stainless Steels

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304 and 316 grades—popular for their excellent corrosion resistance (stemming from their austenitic microstructure), combined with favorable mechanical, physical, and manufacturing properties—are among the most recognized stainless steels. The austenitic structure is formed with an approximate addition of 8–10% nickel. However, nickel is not the sole element responsible for creating the austenitic structure; manganese, nitrogen, carbon, and copper are also employed for this purpose.

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Cost of Nickel and Its Addition to Stainless Steel

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Generally, the cost of stainless steel is determined by the prices of its alloying components. Although chromium—the primary element responsible for forming the protective chromium oxide layer that prevents corrosion—is not expensive, the addition of elements that enhance corrosion resistance (especially molybdenum) or improve manufacturability (particularly nickel) significantly increases the cost. For example, nickel’s price was approximately $5,000–$6,000 per ton in 2001, but by the end of May 2007, it had risen to $50,000 per ton. Similarly, the price of molybdenum increased from about $8,000 per ton in 2001 to approximately $40,000 per ton today.

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These cost increases have directly impacted the following two grades: 304 (18% Cr, 8% Ni) and 316 (18% Cr, 10% Ni, 2% Mo)—with 316 being the most affected. Additionally, other stainless steels with high alloying content such as the 2205 duplex grade (22% Cr, 5% Ni, 3% Mo) have also been influenced. The role of the alloying elements is primarily to modify the microstructure in ways that affect corrosion resistance as well as the mechanical and manufacturing properties. One widely used approach to quantify corrosion resistance is the Pitting Resistance Equivalent (PRE) ratio, defined as:

PRE = %Cr + 3.3×%Mo + 16×%N

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The PRE ratio is used to rank materials based on their resistance to pitting corrosion, although it does not account for every factor influencing overall corrosion behavior. As seen, in addition to chromium, both molybdenum and nitrogen play significant roles in providing resistance to this type of corrosion.

 

The Role of Nitrogen Relative to Molybdenum and Nickel

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Although nitrogen is much less expensive than molybdenum and nickel, its solubility in steel is limited to approximately 0.2%, which in turn limits its impact on corrosion resistance. The steel’s microstructure is governed by the balance between ferrite-forming and austenite-forming elements. In forming the austenitic structure, elements such as carbon, manganese, nitrogen, and copper serve as viable alternatives to nickel. All these elements are less costly than nickel. As observed in the PRE formulation, each element influences corrosion resistance differently, and it is not feasible to completely eliminate nickel from austenitic grades.

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Even though manganese is not as potent as nickel, it is a key stabilizer of the austenitic structure. In fact, Cr-Mn steels exhibit a higher degree of cold-work hardening compared to Cr-Ni steels. While the PRE equation does not explicitly account for manganese, nickel tends to have a more beneficial effect in environments where corrosion aggression is more severe. Moreover, there is a synergistic relationship among alloying elements: nitrogen significantly stabilizes the austenitic structure, and as manganese aids in stabilization, it concurrently enhances the solubility of nitrogen in the steel.

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The Rise of 200 Series Stainless Steels

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Manganese has evolved into an important alternative to nickel—from a minor additive to a major constituent. The development of high-manganese austenitic steels began roughly 60 years ago, during periods of sharply rising nickel prices. In those times, Cr-Mn-Ni grades such as 201 (17% Cr, 4% Ni, 6% Mn) and 202 (18% Cr, 4% Ni, 8% Mn) emerged as alternatives to traditional Cr-Ni grades like 301 and 302 under the AISI classification, and they continue to be produced and utilized today. However, their consumption has declined in recent times compared to their Cr-Ni counterparts. The lower demand for these grades can be attributed to several factors:

• High Cold-Work Hardening: Although this may be an advantage in some applications, it can also be a drawback in others.

• Inferior Surface Quality: Their surface finish is significantly lower, making them less suitable for certain applications.

• Additional Production Costs: Increased production expenses and high refractory wear during melting.

• Reduced Corrosion Resistance: In some working environments, their corrosion resistance is not as high as that of Cr-Ni grades.

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Additionally, it is noteworthy that while Cr-Ni and Cr-Mn-Ni austenitic grades are inherently non-magnetic, scrap metal dealers typically determine the scrap value based on the approximate nickel content.

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Recent Developments

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Recently, we have witnessed significant progress in Cr-Mn-Ni austenitic grades. The most notable development is occurring in India, where their use in kitchenware and cooking equipment is on the rise. The suitability of low‑nickel, high‑manganese grades for high cold‐work hardening is acceptable for these applications, and copper additions are employed to mitigate this issue.

 

Due to local economic factors, India is achieving favorable results in both development and production for these applications. Likewise, other Asian countries have built a robust market for these grades and have ramped up production in recent times. In particular, production and usage of these grades are growing daily in the Chinese market.

 

They are also manufactured in countries such as Taiwan, Brazil, and Japan—with nickel contents ranging from 1% to 4% and manganese contents reaching up to 9%. None of these grades have yet been incorporated into ASTM or other international standards. The production of low‑nickel austenitic grades is increasing very rapidly. According to ISSF data from 2003, production of these grades reached 1.5 million tons, representing 7.5% of the world’s total stainless steel production. In 2004, they were estimated to account for about 25% of stainless steel production in China. Given the soaring nickel prices since 2006, their production rate is believed to be even higher today.

 

Carbon Content

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General austenitic stainless steels such as 304 and 316 are produced with controlled low and high carbon contents, designated as the “L” and “H” grades, respectively. Low‑carbon or “L” grades are used to reduce (or prevent) sensitization and corrosion at high temperatures. The critical temperature range—where welding or specific applications are problematic—is between 450 °C and 850 °C. “L” grades are typically found in thick flat products (usually above 5 mm in thickness).

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High‑carbon “H” grades are utilized in applications requiring higher strength. The interchangeability of “L” and “H” grades is frequently encountered in practice.

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What Are “L” Grades and Where Are They Used?

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“L” grades are employed in applications involving high temperatures, including scenarios where the welding of medium to large-sized materials is performed. Low carbon content helps prevent or delay intergranular carbide precipitation (commonly referred to as “sensitization”) in corrosive environments. There is an incubation period for carbide precipitation within the 450–850 °C range, and because the time for carbide formation is largely dependent on carbon content, a lower carbon level enhances resistance to this problem. Owing to their properties, “L” grades are typically available in the form of plates, sheets, pipes, and often round bars. When high‑temperature exposure or heavy welding is not required, “L” grades are generally interchangeable with standard grades.

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What Are “H” Grades and Where Are They Used?

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“H” grades are the high‑carbon versions of standard grades and offer enhanced strength—especially at elevated temperatures (typically above 500 °C). They exhibit high creep strength under long‑term loading conditions and are primarily produced in the form of plates and pipes. In addition to the common 304H and 316H grades, high‑carbon versions of grades 309, 310, 321, 347, and 348—as defined in ASTM A240/A240M—are also available. However, if maintained within the 450–850 °C temperature range, these grades are highly susceptible to carbide precipitation (referred to as “sensitization”). Should sensitization occur, their room‑temperature ductility and toughness decrease significantly, and their corrosion resistance is markedly compromised.

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What Is the Difference?

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The chemical compositions of 304 and 304L are identical aside from their carbon content. In theory, 304L permits up to a maximum of 12% nickel, compared to a maximum of 10.5% nickel in standard 304. However, due to high nickel prices, both grades are typically produced with a minimum nickel content of about 8.5%. Neither grade has a defined minimum carbon limit; a material with 0.02% carbon content satisfies the requirements for both 304 and 304L.

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For 304H, the carbon content is limited to between 0.04% and 0.10% (note that no minimum is specified), and unlike standard and “L” grades, 304H does not have a maximum nitrogen limit of 0.1%. Otherwise, its chemical composition is the same as that of standard 304. Additionally, all austenitic “H” grades must possess an ASTM grain size of No.7 or larger.

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The relationship among 316, 316L, and 316H is analogous to that of the 304 series—restrictions apply only regarding carbon content, nitrogen content, and grain size. (Refer to Table 1 for the carbon content of grades as specified in ASTM A240/A240M.) In certain product specifications, such as those for pipes and tubes, the maximum carbon content for 304L and 316L is limited to 0.035% or 0.040%, while all other specification parameters remain the same.