|Stainless Steel – Grade SUS321, UNS S32100, 1.4541|
|Fe, <0.08% C, 17-19% Cr, 9-12% Ni, <2% Mn, <1% Si, 0.3-0.7% Ti, <0.045% P, <0.03% S|
|SUS321 and SUS347 are the basic austenitic 18/8 steel (SUS 304) stabilised by Titanium (SUS321) or Niobium (SUS347) additions. These grades are used because they are not sensitive to intergranular corrosion after heating within the carbide precipitation range of 425-850°C. Grade 321 is the grade of choice for applications in the temperature range of up to about 900°C, combining high strength, resistance to scaling and phase stability with resistance to subsequent aqueous corrosion.
SUS321H is a modification of SUS321 with a higher carbon content, to provide improved high temperature strength.
A limitation with SUS321 is that titanium does not transfer well across a high temperature arc, so is not recommended as a welding consumable. In this case grade SUS347 is preferred – the niobium performs the same carbide stabilisation task but can be transferred across a welding arc. SUS 347 is therefore the standard consumable for welding SUS 321. Grade 347 is only occasionally used as parent plate material.
Like other austenitic grades, SS321 and SS347 have excellent forming and welding characteristics, are readily brake or roll formed and have outstanding welding characteristics. Post-weld annealing is not required. They also have excellent toughness, even down to cryogenic temperatures. SUS321 does not polish well, so is not recommended for decorative applications.
Grade SUS304L is more readily available in most product forms, and so is generally used in preference to SUS321 if the requirement is simply for resistance to intergranular corrosion after welding. However SUS304L has lower hot strength than SUS321 and so is not the best choice if the requirement is resistance to an operating environment over about 500°C.
|Grade||Tensile Strength (MPa) min||Yield Strength 0.2% Proof (MPa) min||Elongation (% in 50mm) min||Hardness|
|Rockwell B (HR B) max||Brinell (HB) max|
|SUS 321H also has a requirement for a grain size of ASTM No 7 or coarser.|
|Grade||Density (kg/m3)||Elastic Modulus (GPa)||Mean Coefficient of Thermal Expansion (mm/m/°C)||Thermal Conductivity (W/m.K)||Specific Heat 0-100°C (J/kg.K)||Electrical Resistivity (nW.m)|
|0-100°C||0-315°C||0-538°C||at 100°C||at 500°C|
Grade Specification Comparison
|Grade||UNS No||Old British||Euronorm||Swedish SS||Japanese JIS|
|SS 321||S32100||321S31||58B, 58C||1.4541||X6CrNiTi18-10||2337||SUS 321|
|SS 321H||S32109||321S51||–||1.4878||X10CrNiTi18-10||–||SUS 321H|
|SS 347||S34700||347S31||58G||1.4550||X6CrNiNb18-10||2338||SUS 347|
|These comparisons are approximate only. The list is intended as a comparison of functionally similar materials not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted.|
Equivalent to Grade SUS304 in the annealed condition, and superior if a weldment in these grades has not been post-weld annealed or if the application involves service in the 425-900°C range. Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C. Considered resistant to potable water with up to about 200mg/L chlorides at ambient temperatures, reducing to about 150mg/L at 60°C.
Good oxidation resistance in intermittent service to 900°C and in continuous service to 925°C. These grades perform well in the 425-900°C range, and particularly where subsequent aqueous corrosive conditions are present. SUS321H has higher hot strength, and is particularly suitable for high temperature structural applications.
Solution Treatment (Annealing) – heat to 950-1120°C and cool rapidly for maximum corrosion resistance.
Stabilising – heat to 870-900°C for 1 hour per 25mm of thickness and air cool. Stabilisation is recommended for most severe service conditions (above 425°C) and particularly for material annealed at the upper side of the annealing temperature range.
Stress Relief – Heat to 700°C for 1 to 2 hours and air cool.
These grades cannot be hardened by thermal treatment.
Excellent weldability by all standard fusion methods, both with and without filler metals. AS 1554.6 pre-qualifies welding of SS321 and SS347 with Grade SS347 rods or electrodes; high silicon version of SS347 is also pre-qualified for welding of SS321.