S31500 1.4417 1.4424 Duplex Stainless Steel

S31500 material is a duplex (austenitic-ferritic) stainless steel with characters as High resistance to stress corrosion cracking (SCC) in chloride, bearing environments, Good resistance to general corrosion and pitting, High mechanical strength, roughly twice the proof strength of austenitic grades, Good resistance to erosion corrosion and corrosion fatigue, Physical properties that present design advantages, Good weldability

characterized by the following properties:

l High resistance to stress corrosion cracking (SCC) in chloride-bearing environments

l Good resistance to general corrosion and pitting

l High mechanical strength – roughly twice the proof strength of austenitic grades

l Good resistance to erosion corrosion and corrosion fatigue

l Physical properties that present design advantages

l Good weldability

Applications:

>Oil refineries

>Pulp and Paper industry

>Chemical industry

>Food industry

>Petrochemical plants

>Safety panels

Standards

l UNS: S31500

l EN Number: 1.4424

l EN Name: X2CrNiMoSi18-5-3

l W.Nr.: 1.4417

l DIN: X 2 CrNiMoSi 19 5

l SS: 2376

l AFNOR: Z2 CND 18.05.03

Chemical Composition:

Mechanical Properties

Heat treatment

The tubes are normally delivered in heat treated condition. If additional heat treatment is needed after further processing the following is recommended.

Solution annealing

990-1130°C (1815-2065°F), rapid cooling in air or water.

General corrosion

In terms of resistance to general corrosion, S31500 is comparable or superior to AISI 316L in most media. The table below contains examples of corrosion data obtained from laboratory tests in formic and hydrochloric acid.

Pitting

The pitting resistance of a steel is improved by increasing the contents of chromium and molybdenum, for example. Compared to steel of the AISI 316 type, S31500 has a higher chromium content and therefore better resistance to pitting. Compared to steel of the AISI 304 type, which does not contain molybdenum, S31500 is clearly far superior. This is confirmed by potentiostatic measurements of the critical temperature for the initiation of pitting corrosion (CPT) performed in chloride-bearing aqueous solutions.

Stress corrosion cracking

The standard austenitic steels AISI 304L and AISI 316L are prone to stress corrosion cracking (SCC) in chloride-bearing solutions at temperatures exceeding about 60°C (140°F).

Intergranular corrosion

S31500 is a member of the family of modern duplex stainless steels whose composition has been balanced in such a manner that, when welded, the reformation of austenite in the heat-affected zone adjacent to the weld takes place quickly. This results in a micro-structure that gives corrosion properties and toughness roughly equal to that of the parent metal. The long experience with S31500 in welded structures has confirmed the steels high resistance to intergranular corrosion.

Crevice corrosion

In the same way as the resistance to pitting can be related to the chromium and molybdenum contents of the steel, so can the resistance to crevice corrosion. S31500 therefore possesses better resistance to crevice corrosion than steels of the AISI 316L type.

Erosion corrosion

Steels of the AISI 316L type are attacked by erosion corrosion if exposed to flowing media containing highly abrasive solid particles. Due to its high hardness, S31500 displays very good resistance under such conditions.

Corrosion fatigue

In certain applications, e.g. suction rolls in paper mills, the resistance of the material to corrosion fatigue has a crucial bearing on its service life.

Laboratory tests have shown that S31500 has far better fatigue strength under corrosive conditions than the AISI 316L type of steels. This applies to both quench-annealed and welded material. The difference between the two steel grades is explained by the superior mechanical strength of S31500.