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The nitrogen content of Alloy 317LMN acts as a strengthener, giving it a higher yield strength than SS 317L, while also improving the alloy's resistance to pitting and crevice corrosion.
Decoding the Nomenclature: L vs. M vs. N
To understand the core differences between these two alloys, it helps to break down the suffixes used in their designations:
- "L" (Low Carbon): Both grades restrict carbon to a maximum of 0.03%. This prevents chromium carbide precipitation along the grain boundaries during welding, allowing both alloys to be utilized in the as-welded condition without risking intergranular corrosion.
- "M" (Molybdenum Increase): While 317L contains 3.0% to 4.0% Molybdenum, the "M" indicates that 317LMN pushes its composition to the absolute upper end of that range or higher (typically 4.0% to 5.0%), providing enhanced protection against general corrosion.
- "N" (Nitrogen Controlled): The defining difference is the deliberate addition of Nitrogen (0.10% to 0.22%) to 317LMN. Nitrogen acts as a highly effective interstitial strengthening agent and structural stabilizer.
Alloy 317L VS 317LMN Stainless Steel
1. Chemical Composition:
| Element (Wt %) | Grade 317L (UNS S31703) | Grade 317LMN (UNS S31726) |
| Carbon (C) | 0.030% Max | 0.030% Max |
| Chromium (Cr) | 18.00% – 20.00% | 17.00% – 20.00% |
| Nickel (Ni) | 11.00% – 15.00% | 13.50% – 17.50% |
| Molybdenum (Mo) | 3.00% – 4.00% | 4.00% – 5.00% |
| Nitrogen (N) | 0.10% Max | 0.10% – 0.22% |
| Manganese (Mn) | 2.00% Max | 2.00% Max |
2. Corrosion Resistance:
- Alloy 317L: Includes acids, alkaline solutions, and chloride-containing environments. Its low carbon content helps mitigate the risk of sensitization and intergranular corrosion.
- Alloy 317LMN: The addition of nitrogen improves the alloy's resistance to pitting and crevice corrosion, while also increasing its strength and toughness.
3. Mechanical Properties:
- Higher Yield Strength: The interstitial nitrogen in 317LMN significantly increases its resistance to plastic deformation, providing a higher yield strength than 317L without compromising ductility.
- Elevated Temperature Performance: 317LMN offers superior creep strength, stress-to-rupture limits, and higher overall tensile performance when subjected to sustained, elevated thermal conditions.
- Structural Stability: Nitrogen additions help stabilize the purely austenitic structure, retarding the precipitation of brittle intermetallic sigma phases during hot forming, fabrication, or welding processes.
4. Weldability
Both AISI 317L and 317LMN can be welded using common welding techniques such as TIG (tungsten inert gas) welding, MIG (metal inert gas) welding, and shielded metal arc welding.
5. Price
317LMN may cost slightly more than 317L.
7. Typical Industrial Applications
- Specify 317L For: Standard chemical processing plants, pulp and paper bleaching lines, textile equipment, and food processing systems dealing with mild organic or dilute inorganic acids.
- Specify 317LMN For: Flue Gas Desulfurization (FGD) scrubbers in power plants, severe marine piping networks, air pollution control systems, and petrochemical installations handling highly concentrated hot chemical process streams.
Global Supply of 317L and 317LMN Products
As an established industrial piping component manufacturer, HT Pipeline supplies premium 317L and 317LMN seamless pipes, welded tubes, fittings, and flanges. All components undergo thorough quality checks, arrive solution-annealed, and include full EN 10204 3.1 Mill Test Certification (MTC).
Contact HT Pipeline's Engineering Team to obtain a custom technical quote for your project.
