Chemical Composition of 1.4541 / 321 Stainless Steel (X6CrNiTi18-10)
Leave a message
Scope of the 1.4541 Specification
1.4541 is the European material number for the titanium-stabilised austenitic stainless steel X6CrNiTi18-10, the grade known in the American system as AISI 321 or UNS S32100, in Japan as SUS321 and in China as 06Cr18Ni11Ti. It is an 18-8 austenitic steel in which titanium is deliberately added to combine with carbon, so the chromium stays in solid solution and the steel resists intergranular corrosion in the temperature range where an unstabilised grade would fail.
The composition that matters commercially is the one written in the standard quoted on the order. EN 10088-2 and EN 10088-3 define 1.4541 in Europe; ASTM A240/A240M defines UNS S32100 in North America; and GB/T 20878 defines the Chinese designation and composition.
Composition Limits
Table 1 compares the heat-analysis limits of the two most frequently cited specifications. The titanium requirement is written differently in each: EN states a minimum of five times the carbon content, while ASTM states a minimum of five times the sum of carbon and nitrogen together with an upper limit of 0.70 %. Silicon and sulfur also differ, so a certificate issued to one standard should not be presented as evidence of compliance with the other without checking each line.
| Element, % | EN 10088-3, 1.4541 | ASTM A240/A240M, S32100 |
|---|---|---|
| Carbon | 0.08 max | 0.08 max |
| Silicon | 1.00 max | 0.75 max |
| Manganese | 2.00 max | 2.00 max |
| Phosphorus | 0.045 max | 0.045 max |
| Sulfur | 0.015 max | 0.030 max |
| Chromium | 17.0 - 19.0 | 17.0 - 19.0 |
| Nickel | 9.0 - 12.0 | 9.0 - 12.0 |
| Titanium | 5 x C min | 5 x (C + N) min, 0.70 max |
| Iron | Balance | Balance |
Why Titanium Is Added
In an unstabilised 18-8 steel, carbon above the solubility limit precipitates as chromium carbide, mainly Cr23C6, along the grain boundaries during slow cooling or during service between about 425 C and 815 C. Each carbide particle takes chromium out of the adjacent matrix, and where the chromium content falls below roughly 12 % the local passive film can no longer reform, so the boundary corrodes preferentially. Titanium has a stronger affinity for carbon than chromium does, so the carbon is consumed as titanium carbide and the chromium gradient never develops.
The stabilisation ratio matters. A titanium content below five times the carbon content leaves carbon free to combine with chromium, and an excessive titanium addition is not desirable either, because coarse titanium nitride and carbide particles reduce ductility and surface quality. This is why both a minimum and, in the American specification, a maximum are specified.
Mechanical Properties and Elevated-Temperature Behaviour
In the solution-annealed condition ASTM A240/A240M lists a minimum tensile strength of 515 MPa, a minimum 0.2 % proof stress of 205 MPa and a minimum elongation of 40 % for S32100. The grade retains useful strength and oxidation resistance to about 800 C and is commonly quoted for continuous service in air up to about 900 C, above which a higher-alloyed or nickel-base grade becomes the appropriate choice.
1.4541 is welded with matching stabilised consumables, classified in AWS A5.9 as ER347 or ER321 wire. The niobium-stabilised ER347 grade is frequently selected for the hottest joints. Because titanium oxidises readily, root shielding and interpass cleanliness need closer control than on an unstabilised 304 joint, and a post-weld solution anneal is not normally required when the correct filler is used.
Related Grades and Selection Notes
The low-carbon unstabilised grade 1.4307 (304L) and the stabilised 1.4541 (321) overlap in corrosion performance; the deciding factors are service temperature and required strength. Above roughly 500 C in continuous service, 321 with its titanium stabilisation and higher creep resistance is the more usual selection, while 304L is sufficient for ambient-temperature welded plant. For strongly oxidising or high-temperature cyclic duty, a higher nickel grade with better scale adhesion may be needed.
Verification of composition is normally by the heat analysis reported on the inspection certificate for the cast, with product analysis permitted within the tolerances of the product specification. Where the titanium ratio is critical to the application, it should be stated explicitly in the purchase order rather than left to the general composition requirement.
Frequently Asked Questions
Q: What is the chemical composition of 1.4541?
A: EN 10088-3 specifies carbon 0.08 % max, silicon 1.00 % max, manganese 2.00 % max, phosphorus 0.045 % max, sulfur 0.015 % max, chromium 17.0 - 19.0 %, nickel 9.0 - 12.0 % and titanium 5 x C minimum.
Q: What is 1.4541 equivalent to?
A: X6CrNiTi18-10, equivalent to AISI 321 / UNS S32100, JIS SUS321 and the Chinese grade 06Cr18Ni11Ti.
Q: How much titanium should 321 stainless steel contain?
A: At least five times the carbon content in the European specification, and at least five times the sum of carbon and nitrogen with a 0.70 % maximum under ASTM A240/A240M.
Q: Why does the titanium content matter?
A: Titanium ties up carbon as titanium carbide, which prevents chromium carbide precipitation at the grain boundaries and therefore preserves resistance to intergranular corrosion between about 425 C and 815 C.
Q: What are the mechanical properties of 1.4541?
A: Solution-annealed product requires a minimum tensile strength of 515 MPa, a minimum 0.2 % proof stress of 205 MPa and a minimum elongation of 40 % in ASTM A240/A240M, with comparable values in EN 10088-2.
Q: How does the sulfur limit differ between the European and American specifications?
A: EN 10088-3 limits sulfur to 0.015 % for 1.4541 while ASTM A240/A240M permits 0.030 % for S32100, so the European limit is the tighter of the two.
