UNS S20910 vs S21800 Stainless Steel – Key Differences

1. Introduction

NOUS S20910 (commonly marketed as Nitronique 50 ou XM-19) and UNS S21800 (commonly marketed as Nitronique 60 ou Alliage 218) are advanced austenitic aciers inoxydables engineered for demanding service.

Both deliver better performance than conventional 300-series grades, but they are optimized for different priorities:

• S20910 (Nitronique 50) est un résistant à la corrosion, nitrogen-strengthened austenitic stainless optimized for high corrosion resistance (including sour service), bonne force, Excellente ténacité (including cryogenic), et bonne soudabilité.
  It is often specified where resistance to pitting, SCC and low-temperature toughness are required together with reasonable strength.
• S21800 (Nitronique 60) is formulated primarily for wear and galling resistance while retaining corrosion resistance typical of austenitics.
  It contains high silicon and manganese for tribological performance and is selected where sliding contact, exaspérant, and high wear are the dominant failure modes.

This article compares composition, mechanical and corrosion behaviour, fabrication, and real-world application trade-offs so you can select the right alloy for a specific component or environment.

2. What Is UNS S20910 (Nitronique 50)

NOUS S20910, communément appelé Nitronique 50 ou XM-19, est un high-performance nitrogen-strengthened austenitic stainless steel.

It is engineered to deliver a combination of Excellente résistance à la corrosion, forte résistance, ductilité, et la ténacité, including at cryogenic temperatures.

These attributes make it well-suited for demanding industrial applications such as chemical processing, environnements marins, and sour-service conditions.

Key material designations and specifications inclure:

• ASTM A276 / A479 (as XM-19)
• UNS S20910
• DEPUIS 1.3964

Primary characteristics of UNS S20910 (Nitronique 50):

• Résistance à la corrosion: Enhanced by increased chromium, molybdène, et contenu d'azote; highly resistant to pitting and crevice corrosion in chloride environments.
• Résistance mécanique: Stronger than conventional 300-series stainless steels, with excellent yield and tensile properties.
• Ductility and toughness: Maintains performance at both elevated and cryogenic temperatures.
• Fabrication and weldability: Can be machined, formé, and welded with conventional techniques; solution annealing restores ductility after cold working.
• Nitrogen-strengthened: Nitrogen addition increases yield strength and contributes to pitting resistance without compromising austenitic ductility.
• Application suitability: Listed in NACE MR0175 for sour service, suitable for marine hardware, équipement de processus chimique, composants de pression, and structural applications requiring corrosion resistance and mechanical performance.

3. What Is UNS S21800 (Nitronique 60)

NOUS S21800, communément appelé Nitronique 60 ou Alliage 218, est un high-performance austenitic stainless steel designed primarily for wear and galling resistance, while maintaining good corrosion performance typical of austenitics.

Its specialized composition makes it ideal for applications where sliding contact, usure d'adhésif, and high surface stress are primary concerns.

Key material designations and specifications include:

• ASTM A276 / A479 (for bars, tiges, and other wrought forms)
• UNS S21800

Primary characteristics of UNS S21800 (Nitronique 60):

• Wear and galling resistance: Elevated manganese and silicon content, combined with a nitrogen-strengthened austenitic matrix, provides superior resistance to exaspérant, usure d'adhésif, and surface seizure.
• Résistance à la corrosion: While not as corrosion-resistant as Nitronic 50 in highly aggressive chloride environments, il offre Bonne résistance à la corrosion générale suitable for moderate chemical and marine exposures.
• Résistance mécanique: Exhibits high strength in both annealed and cold-worked conditions, with excellent surface hardness after work hardening.
• Fabrication and welding: Can be welded and fabricated using standard methods, though its higher silicon and manganese content may require adjustments in welding filler selection and machining parameters.
• Application suitability: Couramment utilisé pour tiges de soupape, attaches, arbres de pompe, bearing surfaces, and other components subjected to repeated sliding contact or wear-intensive service.

4. Typical Chemical Compositions and Alloying Differences

A critical factor distinguishing UNS S20910 (Nitronique 50) and UNS S21800 (Nitronique 60) is their alloying strategy, which directly influences corrosion resistance, résistance mécanique, wear behavior, and fabrication characteristics.

While both are nitrogen-strengthened austenitic stainless steels, they are optimized for different service priorities.

Representative Chemical Compositions (WT%) and Performance Role

Interpretation: S20910 emphasizes Croisement + Dans + MO + N (classic austenitic corrosion alloying with nitrogen strengthening and Mo for pitting resistance).

S21800 trades some chromium and nickel for elevated silicon and manganese, which improve hardness, wear and galling resistance.

4. Mechanical Properties and Temperature Behaviour

NOUS S20910 (Nitronique 50) and UNS S21800 (Nitronique 60) exhibit distinct mechanical profiles reflecting their alloying strategies.

Propriétés mécaniques clés

Temperature Behaviour

• Cryogenic Performance:
  S20910 retains ~90% of impact energy at liquid helium temperatures, making it suitable for LNG storage, cryogenic piping, et applications aérospatiales.
  S21800 retains reasonable toughness but is not optimized for extreme low temperatures.
• Performance à température élevée:
  Both alloys maintain dimensional stability and strength at moderate elevated temperatures.
  Nitronic 50’s Mo content provides additional resistance to high-temperature corrosion, while Nitronic 60’s high Si content improves oxidation resistance in sliding-contact applications.
• Travail en durcissant:
  Both alloys are austenitic and work-hardening, meaning mechanical properties, especially hardness and yield strength, can be increased via cold working.
  S21800 benefits most due to high Mn and Si, improving wear and galling performance.

5. Corrosion Resistance and Pitting Resistance (Bois)

Nombre équivalent de résistance aux piqûres (Bois) is a useful indicator of resistance to chloride pitting; it’s calculated from Cr, Mo and N content (simplified form: PREN ≈ Cr + 3.3× mo + 16× n).

• Nitronique 50 (S20910) — higher Cr, Mo and N yield PREN values in the low-to-mid 30s (typical engineering figure ≈ ~34).
  That places it well above 316L (PREN ≈ 20–25) and makes it suitable for many chloride-bearing environments, including some marine and sour service (it is commonly accepted for NACE MR0175 qualifying in many conditions—verify certificate).
• Nitronique 60 (S21800) — because Mo is typically absent and Cr is lower, PREN is inférieur (typical mid-20s or less depending on exact chemistry).
  While S21800 resists general corrosion reasonably well, c'est pas chosen primarily for pitting resistance; plutôt, it is used where galling and wear are primary concerns.

6. Porter, galling and tribological performance

• Nitronique 60 (S21800) est conçu pour galling resistance and sliding wear.
  High silicon and manganese, combined with work-hardening capacity, produce a surface that resists adhesive wear and metal-to-metal seizure.
  Typical uses include valve stems, sièges, attaches, and pump components where repeated sliding contact occurs.
• Nitronique 50 (S20910) offres Bonne résistance à l'usure, but its primary strengths are corrosion resistance and toughness rather than optimized galling resistance.
  It is sometimes used in wear applications where corrosion control is also required, but for extreme galling environments S21800 usually outperforms it.

7. Fabrication, welding and heat-treatment considerations

Soudabilité

• Both alloys are soudable by standard processes (Tig, MOI, Sombrer).
• S20910 (higher Ni/N) is highly weldable and retains corrosion resistance after welding when proper procedures and filler metals are used.
  Low carbon and stabilized practices can minimize sensitization risk.
• S21800 requires attention to heat input and filler selection because its high Si and Mn can influence weld metal composition; preheat/post-weld heat treatment practices depend on component size and code requirements.

Forming and machining

• Both are durcissement austenitics; S21800’s higher Si/Mn can make cutting more challenging—tooling and speeds need adjustment.
  S20910 in solution-annealed condition is generally easier to machine/form.

Traitement thermique

• These are austentic alloys—strength is primarily from cold working and alloying; full hardening by quench/tempering is not applicable.
  Solution annealing can restore ductility and corrosion resistance (typical anneal ~1000–1100 °C followed by rapid cooling).

Hydrogen/sour service

• S20910’s chemistry and listing in some sour-service guidance make it suitable for H₂S environments (verify NACE/ISO certifications).
  For sour service weld procedures and hardness limits (HRC thresholds) are normally enforced.

8. Applications of UNS S20910 vs UNS S21800 Austenitic Stainless Steel

The distinct alloying strategies, propriétés mécaniques, and corrosion/wear characteristics of UNS S20910 (Nitronique 50) et UNS S21800 (Nitronique 60) define their suitability across different industrial applications.

Applications of UNS S20910 (Nitronique 50)

UNS S20910 is engineered for résistance élevée à la corrosion, Excellente ténacité, et bonne soudabilité, making it ideal for environments where both corrosion and mechanical performance sont critiques.

Applications of UNS S21800 (Nitronique 60)

UNS S21800 is optimized for galling and wear resistance while maintaining reasonable corrosion performance.

It is ideal for mechanical components subjected to sliding, adhesive contact, or high surface stress.

Application Guidance

• Choose UNS S20910 when the primary concern is corrosion resistance in aggressive or sour environments, especially when toughness, soudabilité, and low-temperature performance are required.
• Choose UNS S21800 when exaspérant, porter, and sliding contact dominate failure modes, even if corrosion resistance is less critical.
• In complex assemblies, hybrid designs can leverage both alloys—using S20910 for corrosion-critical parts and S21800 for high-wear mating surfaces.
  Surface engineering such as revêtements, nitrative, or PVD treatments can further extend service life when combined with these alloys.

9. Direct Comparison Table: UNS S20910 vs UNS S21800

10. Conclusion

NOUS S20910 contre S21800 are complementary alloys within the Nitronic family.

Pick S20910 where corrosion resistance (especially pitting/crevice and sour service) plus toughness and weldability are paramount.

Pick S21800 where galling and wear dominate and corrosion is a secondary concern.

In many real applications the optimum solution is a combination—design the system so each part sees the alloy best suited to its dominant failure mode, or apply surface engineering to extend service life.

 

FAQ

Can I weld S21800 with standard stainless fillers?

Oui, but select fillers and procedures to accommodate S21800’s high Si/Mn chemistry—consult welding procedure specifications and filler supplier guidance.

Which alloy resists sulfide stress cracking (Ssc)?

S20910 is commonly accepted for many SSC environments and is used in NACE-subject applications; verify specific NACE/ISO certification and hardness limits.

Is Nitronic 60 (S21800) suitable for seawater?

It has reasonable general corrosion resistance in seawater but lacks the pitting resistance of Nitronic 50 or Mo-bearing grades; if seawater pitting is critical, choose S20910 or a higher PREN alloy.

Can either alloy be heat-treated to increase strength?

These austenitic alloys gain strength mainly by travail froid Et l'alliage; conventional quench/temper treatments are not used to significantly increase strength. Solution annealing restores ductility/corrosion resistance.