Austenitic SS 321

Austenitic SS 321

Austenitic 321 stainless steel, also named niobium nitrogen alloy is a highly stabilized chromium-titanium steel with extra-ordinary oxidation resistance properties and creep strength. AISI 321 stainless steel is a stabilized version of SS 304 but with titanium. 

The titanium content in SS 321 Stainless Steel helps it prevent carbide precipitation while welding in temperatures ranging between 800 – 1500°F. It also allows the alloy to barely elevated temperatures.

Grade 321 stainless steel is highly resistant to oxidation & corrosion and it possesses good creep strength. It is properly used in continuous and intermittent process temperatures in the carbide precipitation ranging between 800 – 1500°F.

321 Stainless steel is ready to form and draw, when compared to carbon and ferritic stainless steel, SS321 requires higher pressure. 321 Stainless steel may also require annealing after severe forming as its work hardens quickly as compared to austenitic stainless steels of other types.

At moderate temperatures, Alloy 321 can be used in almost every diluted organic acid and at lower temperatures, in pure phosphoric acid. At elevated temperatures, it can be used in 10% diluted solutions. In hydrocarbon service, alloy 321 resist polythionic acid stress corrosion cracking. Alloy 321 can also be used in chloride or fluoride-free caustic solutions in moderate temperatures.

321 stainless steel supplier would suggest you to use it in higher temperature service as it comes with extraordinary mechanical properties. SS 321 material offers higher creep and stress rupture properties when compared to type SS 304. The maximum working temperature for SS321 is between the range of 1500°F whereas SS 304 and SS 304L are limited to 800°F.

Austenitic SS 321 material or UNS 321000 grade can be utilized with continuous and intermittent service around the range of 430°- 820° C. The grade offers exceptional mechanical properties at elevated temperatures. Below 950° C, austenitic SS321 is the first choice as it can retain strength, is phase stable, and can resist scaling. 

Alloy AISI 321 stainless steel presents better general corrosion resistance and can be compared to SS 304. SS321 was specially developed for applications where chromium carbide precipitation range is between 1800° – 1500°F (427 – 816°C); on the other hand, alloys like SS 304 can be at the risk of intergranular attack.

321 Stainless Steel Properties

Better than 321, some of the AISI 321 stainless steel supplier say austenitic SS321H comes with a higher carbon content that provides improved high-temperature strength. 321H Stainless stee is used for general purposes and it is more stable against carbide precipitation and developed to work within the carbide precipitation temperature range 427 to 816°C (800 to 1500°F). 

Here are some of the technical 321 stainless steel physical properties
Grade Density
Melting Point Elastic Modulus
Mean Co-eff of Thermal Expansion (μm/m/°C) Thermal Conductivity (W/m.K) Specific Heat
Electrical Resistivity
SS 321 8 1400-1450°C 190-210 0-100°C 0-315°C 0-538°C at 100°C ( J/Kg.K) 720
16.6 17.2 18.6 16.1 500
General Specification
SS 321 S32100 321S21 58B, 58C 1.4541 X6CrNiTi 8-10 2337 SUS 321
SS 321H S32109 321S51 1.4878 X10CrNiTi 8-10 SUS 321H

Alloy 321 is good when used in applications where oxidation resistance is required especially in intermittent service up to 900 °C and in continuous service to 925 °C. SS321H has higher hot strength and is suitable for structural applications where high temperature is expected. These grades work well in the 425-900 °C range, and especially in subsequent aqueous corrosive conditions.  

321 Stainless Steel Composition

The titanium content in SS 321 stainless steel or UNS 321000 reacts with carbon content in the steel and prevents precipitation of chromium carbides at the grain boundaries. This preserves corrosion-resistant properties as it prevents depletion of chromium near the grain boundaries during exposure in the critical temperature range.

Here’s a detailed 321 Stainless steel chemical composition for your understanding.
Cr Ni C Mn P Si Ti Fe S N
SS 321 MIN % 17 9 5x(C+N)
MAX % 19 12 0.08 2 0.045 0.75 0.7 BALANCE 0.03 0.1

Applications, where type 321 stainless steel  is used, are Aircraft piston engine manifolds and exhaust stacks, expansion joints, thermal oxidizers, refinery equipment, high-temperature chemical process equipment, exhaust systems, pressure vessels, etc.