CrNi 18-10 Stainless Steel (1.4301 / 304): Composition and Properties
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What the Designation CrNi 18-10 Means
CrNi 18-10 is shorthand for an austenitic stainless steel containing about 18 % chromium and 10 % nickel. In the European system the grade is X5CrNi18-10 with the material number 1.4301; in the American system it is AISI 304 / UNS S30400; in Japan it is SUS304; and in China it is 06Cr19Ni10 under GB/T 20878. The nickname 18-8 is still used in trade for the same family.
The composition range behind the nickname is tighter than the nickname suggests. EN 10088-2 specifies 17.5 - 19.5 % chromium and 8.0 - 10.5 % nickel for 1.4301, so a heat at the bottom of both ranges is a different material from one at the top, particularly in resistance to stress corrosion cracking and to pitting in chloride-bearing water.
Composition and Mechanical Properties
Table 1 gives the limits most often quoted on enquiry, taken from EN 10088-2 for 1.4301 and from ASTM A240/A240M for UNS S30400. The two standards are not identical: EN limits carbon to 0.07 % and silicon to 1.00 %, while ASTM limits carbon to 0.08 % and silicon to 0.75 % for the same grade.
| Element / property | EN 10088-2, 1.4301 | ASTM A240/A240M, S30400 |
|---|---|---|
| Carbon, % max | 0.07 | 0.08 |
| Silicon, % max | 1.00 | 0.75 |
| Manganese, % max | 2.00 | 2.00 |
| Phosphorus, % max | 0.045 | 0.045 |
| Sulfur, % max | 0.015 | 0.030 |
| Chromium, % | 17.5 - 19.5 | 18.0 - 20.0 |
| Nickel, % | 8.0 - 10.5 | 8.0 - 10.5 |
| Nitrogen, % max | 0.10 | Not specified |
| Tensile strength Rm | 540 - 750 MPa | 515 MPa min |
| 0.2 % proof stress Rp0.2 | 230 MPa min | 205 MPa min |
| Elongation | 45 % min (A80) | 40 % min |
| Hardness | Not specified | 201 HBW or 92 HRB max |
Physical Properties and Heat Treatment
EN 10088-1 gives the physical properties of 1.4301 at room temperature as a density of 7900 kg/m3, a modulus of elasticity of 200 GPa, a thermal conductivity of about 15 W/(m K), an electrical resistivity of 0.73 micro-ohm metre and a specific heat of about 500 J/(kg K). The low thermal conductivity and relatively high expansion coefficient explain why distortion and heat tint must be managed when welding thin sections.
Solution annealing is carried out in the 1000 - 1100 C range followed by rapid cooling in water or air, which dissolves the carbides and restores the softest, most corrosion-resistant condition. For forging, the material is heated slowly to about 1150 - 1180 C and forged between roughly 1180 C and 950 C, after which it is cooled in water or air. Cold forming by bending, flanging, deep drawing and spinning is straightforward, but the grade work hardens quickly, so intermediate anneals are needed for severe draws.
Welding and Intergranular Corrosion
1.4301 can be welded by all the usual processes except oxy-fuel gas welding, and normally without filler metal on thin sections. The limitation is thermal: in the 425 - 815 C band, chromium carbides precipitate at the grain boundaries and deplete the adjacent metal of chromium. The heat-affected zone of a weld passes through that band as it cools, so a welded 1.4301 component that is not subsequently solution annealed is not resistant to intergranular corrosion in aggressive media. Two established answers are used in practice: switch to the low-carbon grade 1.4307 (304L), or use the stabilised grade 1.4541 (321) when elevated-temperature strength is also required.
Where CrNi 18-10 Is Used
Typical service includes pressure equipment such as reactors and vessels, where the grade is covered by EN 10028-7 for flat products and by EN 13445 for the vessel design; food contact equipment including tanks, pipes and fittings; pharmaceutical and medical equipment; architectural and sanitary components; and general chemical plant in mildly corrosive duty. It is not the appropriate choice for chloride pitting service, where a molybdenum-bearing grade is required.
Frequently Asked Questions
Q: Is CrNi 18-10 the same as 304 stainless steel?
A: Yes. CrNi 18-10 is the trade nickname for X5CrNi18-10 / 1.4301, which is AISI 304 / UNS S30400 and corresponds to the Chinese grade 06Cr19Ni10.
Q: What are the chromium and nickel contents of CrNi 18-10?
A: EN 10088-2 specifies 17.5 - 19.5 % chromium and 8.0 - 10.5 % nickel for 1.4301, with carbon at 0.07 % maximum.
Q: Can CrNi 18-10 be welded?
A: Yes, by every common process except oxy-fuel gas welding, generally without filler metal, but the welded joint is not resistant to intergranular corrosion unless the assembly is solution annealed afterwards.
Q: What is the density and modulus of 1.4301?
A: EN 10088-1 gives 7900 kg/m3 for density and 200 GPa for the modulus of elasticity at room temperature.
Q: Why would 304L be chosen instead of CrNi 18-10?
A: Because the carbon content of the low-carbon variant is limited to 0.030 %, which prevents chromium carbide precipitation in the heat-affected zone of a weld and preserves resistance to intergranular corrosion.
Q: Is CrNi 18-10 suitable for marine or chloride service?
A: Not for chloride pitting or crevice corrosion service. A molybdenum-bearing austenitic grade is required where chlorides are present.
