what is 1.4547 stianless steel?
1.4547 stainless steel, also known as 254 SMO, UNS S31254, or F44, is a high-alloy super austenitic stainless steel with excellent corrosion resistance, particularly in highly corrosive, chloride-rich environments such as seawater. Compared to ordinary steels, it offers superior resistance to pitting corrosion, crevice corrosion, and stress corrosion cracking, making it ideal for demanding marine, chemical, and offshore applications.
What is the material equivalent of 1.4547?
Material 1.4547 (X1CrNiMoCuN20-18-7) is a super austenitic stainless steel, equivalent to UNS S31254, commonly known by the trade name 254 SMO, and designated as ASTM F44 (for forgings) or 6Mo alloy, offering excellent resistance to pitting, crevice corrosion, and stress corrosion cracking in chloride-rich environments like seawater.
| Material No. | UNS | Alloy | AFNOR | EN | JIS | SIS | GOST |
| 1.4547 | S31254 | 254 SMO | Z1 CNDU 20.18.06Az | X1CrNiMoCuN20-18-7 | – | 2378 | – |
What is the chemical composition of 1.4547?
1.4547 stainless steel (also known as 254 SMO, UNS S31254) is a super austenitic stainless steel containing high levels of chromium, molybdenum, nickel, and nitrogen, as well as copper. Its main components include approximately 20% chromium, 18% nickel, 6% molybdenum, and added nitrogen (approximately 0.2%) and copper (approximately 0.5%).
| Title | UNS | Werkstoff | C | Si | Mn | P | S | Cr | Ni | Mo | Cu | N |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 6mo | S31254 | 1.4547 | <0.02 | 0.7 | 1 | 0.03 | 0.01 | 20 | 18 | 6.1 | 0.75 | 0.2 |
1.4547 Physical Properties (Room Temperature)
| Specific Heat (0-100°C) | 500 | J.kg-1.°K-1 |
| Thermal Conductivity | 14 | W.m -1.°K-1 |
| Thermal Expansion | 16.5 | μm/μm/°C |
| Modulus Elasticity | 196 | GPa |
| Electrical Resistivity | 8.5 | Ohm-cm |
| Density | 8.0 | g/cm3 |
1.4547 Mechanical Properties
| Temper | Annealed | |
|---|---|---|
| Tensile Rm | 98 | ksi (min) |
| Tensile Rm | 675 | MPa (min) |
| R.p. 0.2% Yield | 45 | ksi (min) |
| R.p. 0.2% Yield | 310 | MPa (min) |
| Elongation (2" or 4D gl) |
35 | % (min) |
1.4547 Heat treatment:
| Forging | 1200 to 950 °C |
| Welding | weldable with all common welding processes |
| Annealing | Solution annealing at at least 1150 °C, followed by water quenching |
| Stress relieving annealing | at approx. 500°C |
| Hardening | no |
What is the difference between 1.4404 and 1.4547?
1.4404 (316L) is a general-purpose low-carbon austenitic stainless steel, while 1.4547 (254 SMO) is a high-alloy super austenitic stainless steel containing higher levels of molybdenum (Mo) and nitrogen (N), suitable for extreme chloride/acidic environments and offering superior resistance to pitting and crevice corrosion. However, 1.4404 is less expensive and easier to weld/form. In short, 1.4404 is a general-purpose material, while 1.4547 is a specialized material.
1.4547 vs 1.4462
1.4547 (254 SMO) and 1.4462 (Duplex 2205) are both high-alloy stainless steels with excellent corrosion resistance, but 1.4547 is a super austenitic steel, offering superior pitting/crevice resistance, especially in chloride-rich acidic environments (like seawater), while 1.4462 is a duplex steel (ferrite/austenite mix) known for high strength and good all-around resistance, often used in demanding conditions but slightly less specialized for extreme pitting than 1.4547.
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