Duplex stainless steel introduction
Duplex stainless steel refers to the material whose microstructure is composed of ferrite and austenite, each of which accounts for about 50%. In actual use, one of them is more suitable between 40-60%.
According to the characteristics of the two structures, through the correct control of the chemical composition and heat treatment process, the excellent toughness and weldability of austenitic stainless steel are combined with the higher strength and resistance to chloride stress corrosion of ferritic stainless steel It makes duplex stainless steel a type of steel that combines excellent corrosion resistance, high strength and easy processing and manufacturing.
The physical properties of duplex stainless steel are between austenitic stainless steel and ferritic stainless steel, but are closer to ferritic stainless steel and carbon steel.
The corrosion resistance and crevice corrosion resistance of duplex stainless steel pipes are related to the content of chromium, molybdenum and nitrogen. The corrosion resistance and crevice corrosion resistance of duplex stainless steel pipes can be similar to 316 stainless steel pipes or higher than seawater stainless steel pipes such as 6% Stainless steel tube.
All duplex stainless steels are significantly more resistant to chloride stress corrosion cracking than 300 series austenitic stainless steels, and their strength is much higher than that of austenitic stainless steels. They also exhibit good plasticity and toughness.
Duplex stainless steel can be generally divided into four types: low alloy type, medium alloy type, high alloy type and super duplex stainless steel type.
Check our Super Duplex 2507 Pipe Stock List here.
The common duplex stainless steel grades and the approximate comparison of grades are as follows:
| Types/Countries | CHINA | USA | SWEFEN | GERMANY | FRANCE | JAPAN |
| low alloy type | 00Cr23Ni4N | UN23 | SS232 | W．Nr.1.4362 | UR35N | DP11 |
| (SAF2304) | (SAF2304) | |||||
| medium alloy type | 00Cr18Ni5Mo3Si2 | UNS S31500 | SS2376(3RE60) | W.Nr.1.4417 | UR45N | DP1 |
| 00Cr22Ni5Mo3N | UNS S31803 | SS2377(SAF2205) | W.Nr.1.4462 | DP8 | ||
| high alloy type | 0Cr25Ni5Mo2 | UNS S32900 | SS2324(10RE51) | W.Nr.1.4460 | 329J1 | |
| 00Cr25Ni7Mo3WCuN | UNS S31260 | W.Nr.1.4501 | 329J2L | |||
| super duplex stainless steel type | 00Cr25Ni7Mo4N | UNS S32750 | SS2328(SAF2507) | W.Nr.1.4410 | UR47N+ | |
| 00Cr25Ni6Mo3CuN | UNS S32550 | W.Nr.1.4507 | UR52N+ |
Performance of duplex stainless steels:
- 1. Chemical composition(%)
| Grades | C≤ | Mn≤ | Si≤ | S≤ | P≤ | Cr | Ni | Mo | Cu≤ | N |
| S32750(SAF2507) | 0.03 | 1.2 | 0.8 | 0.02 | 0.035 | 24.0 | 6.0 | 3.0 | 0.5 | 0.24 |
| 00Cr22Ni7Mo4N | 26 | 8 | 5 | 0.32 | ||||||
| S31803(SAF2205) | 0.03 | 2 | 1 | 0.02 | 0.03 | 21.0 | 4.50 | 2.50 | 0.08 | |
| 00Cr22Ni5Mo3N | 23 | 6.5 | 3.5 | 0.2 | ||||||
| S31500(3RE60) | 0.03 | 1.2 | 1. 4 | 0.03 | 0.03 | 18.0 | 4.25 | 2.50 | 0.05 | |
| 00Cr18Ni5Mo3Si2 | 2 | 2 | 19 | 5.25 | 2 | 0.1 |
- 2. Chemical composition(%)
| Heat treatment temperature℃ | Ab（MPa）≥ | As（MPa）≥ | ∮≥ | Brinell Hardness | Rockwell hardness | |
| S32750（SAF2507） | 1025-1125 | 800 | 550 | 15 | 310 | 32 |
| 00Cr22Ni5Mo3N | WATER | |||||
| S31803（SAF2205） | 1020-1100 | 620 | 450 | 25 | 290 | 30.5 |
| 00Cr22Ni5Mo3N | ||||||
| S31500（3RE60） | 980-1040 | 630 | 440 | 30 | 290 | 30.5 |
| 00Cr18Ni5Mo3Si2 |
- 3. The continuous use temperature range of duplex stainless steel is -50 ℃ -60 ℃. The hot working temperature should not be lower than 950 ℃.
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