Acciaio inossidabile UNS S20910 vs S21800 – Differenze chiave

1. Introduzione

NOI S20910 (commonly marketed as Nitronico 50 O XM-19) and UNS S21800 (commonly marketed as Nitronico 60 O Lega 218) are advanced austenitic acciai inossidabile engineered for demanding service.

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

• S20910 (Nitronico 50) è un resistente alla corrosione, nitrogen-strengthened austenitic stainless optimized for high corrosion resistance (including sour service), buona forza, Eccellente tenacia (including cryogenic), e buona saldabilità.
  It is often specified where resistance to pitting, SCC and low-temperature toughness are required together with reasonable strength.
• S21800 (Nitronico 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, malvagio, and high wear are the dominant failure modes.

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

2. What Is UNS S20910 (Nitronico 50)

NOI S20910, comunemente noto come Nitronico 50 O XM-19, è un high-performance nitrogen-strengthened austenitic stainless steel.

It is engineered to deliver a combination of Eccellente resistenza alla corrosione, alta resistenza, duttilità, e tenacità, including at cryogenic temperatures.

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

Key material designations and specifications includere:

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

Primary characteristics of UNS S20910 (Nitronico 50):

• Resistenza alla corrosione: Enhanced by increased chromium, molibdeno, e contenuto di azoto; highly resistant to pitting and crevice corrosion in chloride environments.
• Resistenza meccanica: 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, formato, 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, Equipaggiamento di processo chimico, componenti di pressione, and structural applications requiring corrosion resistance and mechanical performance.

3. What Is UNS S21800 (Nitronico 60)

NOI S21800, comunemente indicato come Nitronico 60 O Lega 218, è 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, usura adesiva, and high surface stress are primary concerns.

Key material designations and specifications include:

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

Primary characteristics of UNS S21800 (Nitronico 60):

• Wear and galling resistance: Elevated manganese and silicon content, combined with a nitrogen-strengthened austenitic matrix, provides superior resistance to malvagio, usura adesiva, and surface seizure.
• Resistenza alla corrosione: While not as corrosion-resistant as Nitronic 50 in highly aggressive chloride environments, Offre buona resistenza alla corrosione generale suitable for moderate chemical and marine exposures.
• Resistenza meccanica: 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: Comunemente usato per steli valvole, dispositivi di fissaggio, alberi di pompa, 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 (Nitronico 50) and UNS S21800 (Nitronico 60) is their alloying strategy, which directly influences corrosion resistance, resistenza meccanica, 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 Cr + In + 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

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

Proprietà meccaniche chiave

Temperature Behaviour

• Cryogenic Performance:
  S20910 retains ~90% of impact energy at liquid helium temperatures, making it suitable for LNG storage, cryogenic piping, e applicazioni aerospaziali.
  S21800 retains reasonable toughness but is not optimized for extreme low temperatures.
• Prestazioni a temperatura elevata:
  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.
• Il lavoro indurimento:
  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 (Legna)

Numero equivalente alla resistenza alla resistenza (Legna) 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).

• Nitronico 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).
• Nitronico 60 (S21800) — because Mo is typically absent and Cr is lower, PREN is inferiore (typical mid-20s or less depending on exact chemistry).
  While S21800 resists general corrosion reasonably well, è non chosen primarily for pitting resistance; Invece, it is used where galling and wear are primary concerns.

6. Indossare, galling and tribological performance

• Nitronico 60 (S21800) è progettato per 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, sedili, dispositivi di fissaggio, and pump components where repeated sliding contact occurs.
• Nitronico 50 (S20910) offerte Buona resistenza all'usura, 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. Fabbricazione, welding and heat-treatment considerations

Saldabilità

• Both alloys are saldabile by standard processes (TIG, ME, Smaw).
• 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 sostenuto il lavoro 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.

Trattamento termico

• 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, Proprietà meccaniche, and corrosion/wear characteristics of UNS S20910 (Nitronico 50) E UNS S21800 (Nitronico 60) define their suitability across different industrial applications.

Applications of UNS S20910 (Nitronico 50)

UNS S20910 is engineered for elevata resistenza alla corrosione, Eccellente tenacia, e buona saldabilità, making it ideal for environments where both corrosion and mechanical performance sono critici.

Applications of UNS S21800 (Nitronico 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, saldabilità, and low-temperature performance are required.
• Choose UNS S21800 when malvagio, Indossare, 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 rivestimenti, nitriding, or PVD treatments can further extend service life when combined with these alloys.

9. Direct Comparison Table: UNS S20910 vs UNS S21800

10. Conclusione

NOI S20910 vs 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?

SÌ, 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 lavoro freddo e lega; conventional quench/temper treatments are not used to significantly increase strength. Solution annealing restores ductility/corrosion resistance.