Duplex Stainless Steel
Expanite surface hardening can be applied to a variety of alloy materials and all main categories of stainless steel including Duplex.
These grades are referred to as duplex (or austenitic-ferritic) alloys due to their unique metallurgical structure, which comprises two phases: austenite with a face-centered cubic lattice and ferrite with a body-centered cubic lattice, occurring in approximately equal proportions. They are engineered to offer superior corrosion resistance, particularly against chloride-induced stress corrosion and chloride pitting corrosion, as well as greater strength compared to standard austenitic stainless steels like Type 304 or 316.
The primary distinctions in composition, when contrasted with austenitic stainless steel, are the higher chromium content (20–28%), increased molybdenum levels (up to 5%), reduced nickel content (up to 9%), and the presence of 0.05–0.50% nitrogen. The combination of lower nickel content and enhanced strength, allowing for the use of thinner sections, leads to significant cost advantages. Consequently, they find extensive application in the offshore oil and gas industry for various components like pipework systems, manifolds, and risers, as well as in the petrochemical sector for pipelines and pressure vessels. Beyond the improved corrosion resistance relative to the 300 series, duplex stainless steels also boast higher overall strength.
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UNS S31803 / S32205 / AISI 318LN / 1.4462 / Alloy 2205
Alloy 2205 offers an excellent combination of strength and corrosion resistance due to its chemical composition and duplex microstructure consisting of austenite and ferrite phases. Duplex stainless steel has twice the annealed yield strength of typical austenitic stainless steels. In the hot rolled unannealed condition, a yield strength of 75 ksi (518 MPa) or higher can be achieved for bar diameters up to 1.375 in. (34.925mm). Duplex possesses good resistance to general corrosion in many acid environments and, has excellent resistance to chloride stress corrosion cracking, pitting and crevice corrosion
UNS S32750 / AISI F53 / 1.4410 / Alloy 2507
Alloy 2507 is a super-duplex stainless steel with a microstructure consisting of austenite and ferrite phases in approximately equal amounts. The chemical composition and microstructure impart a good combination of strength, corrosion resistance and toughness with an annealed yield strength twice that of typical austenitic stainless steels possessing comparable impact strength. AISI F53 exhibits good resistance to general corrosion in many acid environments with exceptional resistance to chloride stress corrosion cracking, pitting and crevice corrosion.
| EN designation |
EN |
AISI |
| X2CrNiN22-2 |
1.4062 |
S32202 |
| X2CrCuNiN23-2-2 |
1.4669 |
|
| X2CrNiMoSi18-5-3 |
1.4424 |
S31500 |
| X2CrNiN23-4 |
1.4362 |
S32304 |
| X2CrMnNiN21-5-1 |
1.4162 |
S32101 |
| X2CrMnNiMoN21-5-3 |
1.4482 |
|
| X2CrNiMoN22-5-3 |
1.4462 |
S31803 |
| X2CrNiMnMoCuN24-4-3-2 |
1.4662 |
S32205 |
| X2CrNiMoCuN25-6-3 |
1.4507 |
S32520 |
| X3CrNiMoN27-5-2 |
1.4460 |
S31200 |
| X2CrNiMoN25-7-4 |
1.4410 |
S32750 |
| X2CrNiMoCuWN25-7-4 |
1.4501 |
S32760 |
| X2CrNiMoN29-7-2 |
1.4477 |
S32906 |
| X2CrNiMoCoN28-8-5-1 |
1.4658 |
S32707 |
| X2CrNiCuN23-4 |
1.4655 |
S32304 |
The purpose of the process:
ExpaniteHigh-T
The purpose of this process is to dissolve nitrogen in the surface of stainless steel to a depth in the range of 0.2-2 mm. Peak hardness ranges from 280HV on austenitic grades to 950HV on martensitic/ferritic grades.
ExpaniteLow-T
The purpose of this process is to dissolve nitrogen and carbon in the surface of stainless steel to a depth in the range of 5 - 30µm. Peak hardness ranges from 1100-1300HV.
SuperExpanite
The purpose of this process is to combine ExpaniteHigh-T and ExpaniteLow-T processes to achieve higher load bearing and corrosion properties. Firstly, the ExpaniteHigh-T process is applied to create a deep case depth with moderate nitrogen content. Secondly, the ExpaniteLow-T process is applied to create a high-hardness surface on top of the ExpaniteHigh-T zone. The Expanite process does not result in a coating, but a diffusion zone with an increased carbon and nitrogen content. We call this zone expanded austenite, expanded martensite or simply: Expanite.
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