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Korosi umum:Karena kandungan kromium yang tinggi dan komposisi yang seimbang, Sandvik SAF 2304® memiliki ketahanan korosi yang sangat baik di lingkungan asam. Tabel di bawah memberikan laju korosi pada asam yang berbeda dan Gambar 4-6 menunjukkan diagram isokorosi untuk Sandvik SAF 2304® dalam asam sulfat, format, dan nitrat. | Conc. | Suhu | Sandvik |
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| Berat-% | °C (°F) | SAF 2304 | ASTM 304L | ASTM 316L | | asam asetat CH3COOH | | | | | | 20 | B | 0.01 (0.4) | | 0.01 (0.4) | | 50 | B | 0 | 0.04 (1.6) | 0 | | 70 | B | 0 | | | | 90 | B | 0.01 (0.4) | | | | Asam format, HCOOH | | | | | | 5 | 60 (140) | 0 | | | | 10 | B | 0.04 (1.6) | 0,80 (32) | 0,19 (7.6) | | 30 | 60 (140) | 0 | | | | 30 | 90 (194) | 0 | | | | 80 | 90 (194) | 0 | | 0.50 (20) | | 90 | 60 (140) | 0 | | | | Hydrochloric acid, HCI | | | | | | 0.5 | 40 (104) | 0 | | 0 | | 1 | 40 (104) | 0.30 (12) | | 0.70 (28) | | Nitric acid, HNO3 (5x2 days) | | | | | | 65 | B | 0.16 (6.4) | 0.16 (6.4) | 0.30 (12) | | Phosphoric acid, H3PO4 | | | | | | 30 | B | 0.10 (4) | 0.20 (8) | 0.07 (2.8) | | 50 | 100 (212) | 0.04 (1.6) | 0.09 (3.6) | 0.21 (8.4) | | 60 | 90 (194) | 0.01 (0.4) | 0.2 (0.8) | 0.02 (0.8) | | 80 | 80 (176) | 0.01 (0.4) | 0.01(0.4) | 0.06 (2.4) | | Sulphuric acid, H2SO4 | | | | | | 5 | 60 (140) | 0 | | | | 5 | 90 (194) | 0.06 (2.4) | 3.6 (144) | | | 10 | 60 (140) | 0.10 (4) | | 0.66 (26.4) | | 10 | 70 (158) | 0.14 (5.6) | | 1.7 (68) | | 10 | 80 (176) | 0.20 (8) | | 7.9 (316) | | 15 | 50 (122) | 0.17 (6.8) | | 0.47 (18.8) | | 20 | 30 (86) | 0.20 (8) | | 0.02 (0.8) | | B =Boiling |
Corrosion rates in acid-water mixtures, mm/year (mpy). Activated specimens, 1+3+3 days, average of the last two periods for two specimens.
Pitting:The pitting resistance of a steel is determined primarily by its chromium and molybdenum contents, but the nitrogen content also has an effect. Praktek manufaktur dan fabrikasi, mis. welding, are also of vital importance for the actual performance in service.
A parameter for comparing the pitting resistance of different steels is the PRE-number (Pitting Resistance Equivalent).
PRE didefinisikan sebagai, dalam berat-%
PRE =% Cr + 3.3 %x Mo + 16 x % N
As the table shows, the PRE number for Sandvik SAF 2304® is considerably higher than the number for ASTM 304L and comparable to the number for ASTM 316L. Potentiostatic tests in solutions with different chloride contents (pH =6) are reported in Figure 7. Each curve is based on at least 4 measuring points, each of which is derived from a minimum of three separate measurements. Variation in the measurement results is within the range +/-5°C (+/-9°F). The test results for ASTM 316L have been compared with results obtained under practical conditions of service, and the correlation is good. As is evident from Figure 7, the critical temperature for pitting for Sandvik SAF 2304® is higher than that for ASTM 304L and comparable to that for ASTM 316L. The test results correspond with the PRE ranking.
Stress corrosion cracking:Because of its two-phase structure and its well balanced composition, Sandvik SAF 2304® possesses very good resistance to stress corrosion cracking (SCC). This is evident from the results of tests in both concentrated chloride solutions and oxygen-containing dilute chloride environments.
Figure 8 shows the results of tests carried out in 40% CaCl₂ solution at 100°C (210°F). In this environment, the stress that is required to cause fracture due to SCC (known as the threshold stress) is much higher for Sandvik SAF 2304® than for ASTM 304/304L and ASTM 316/316L. This demonstrates the superior resistance of Sandvik SAF 2304®.
Welding of Sandvik SAF 2304® does not appreciably reduce the resistance to SCC, provided that the welding recommendations are followed (see Welding). The threshold stress of material that has been TIG-welded with Sandvik 22.8.3.L or MMA-welded with Sandvik 22.9.3.LR is on a level with that of the parent metal.
The results of SCC testing of Sandvik SAF 2304 in chloride solutions at high temperatures and pressures are presented in Figure 9. The curve for Sandvik SAF 2304® is based on tests performed in various chloride contents and at different temperatures. Usually, six separate measurements were taken at each measuring point. The testing method involved spring-loaded specimens stressed to the proof strength (Rp0.2) at the testing temperature or U-bends in which the stress at the apex is at least equal to the proof strength of the solution annealed material. The oxygen content of the inlet water (refreshed autoclaves were used) was 4.6 to 10 ppm and the pH 4.5 to 7. The curve for ASTM 304/304L and ASTM 316/316L is based on published test results and on practical experience.
The results in Figure 9 indicate that Sandvik SAF 2304® can be used in dilute oxygen-bearing chloride solutions up to about 125°C (260°F) without any risk of SCC. This is much higher than for ASTM 304/ 304L and ASTM 316/316L, which should not be used above 60°C (140°F) in such environments. At temperatures above 125°C (260°F), Sandvik SAF 2304® should not be used in oxygen-bearing solutions in environments with more than about 10 ppm Cl-. For such conditions, we recommend Sandvik SAF 2205™, Sandvik SAF 2507® or Sanicro® 28. At low oxygen contents, which are common in the process and power industries, considerably higher chloride contents and temperatures can be tolerated by Sandvik SAF 2304® without any risk of SCC.
Intergranular corrosion:Sandvik SAF 2304® is a member of the family of modern duplex stainless steels whose chemical manner that the reformation of austenite in the heat-affected zone adjacent to the weld takes place quickly. This results in a microstructure that gives corrosion properties and toughness similar to that of the parent metal. Welded joints in Sandvik SAF 2304® easily pass Strauss' intergranular corrosion testing according to SS-EN ISO 3651-2 Method A.
Crevice corrosion:In the same way as the resistance to pitting can be related to the chromium, molybdenum and nitrogen contents of the steel so can the resistance to crevice corrosion. Sandvik SAF 2304® possesses better resistance to crevice corrosion than steels of the ASTM 304/304L type and is comparable with ASTM 316/316L.
Erosion corrosion:Steels of the ASTM 304/304L and ASTM 316/316L type can be attacked by erosion corrosion if exposed to flowing media containing highly abrasive solid particles, e.g. sand, or media with very high flow rates. Under such conditions, Sandvik SAF 2304® displays very good resistance because of its combination of high mechanical strength and good corrosion resistance.
Corrosion fatigue:Sandvik SAF 2304® possesses higher strength and better corrosion resistance than ordinary austenitic stainless steels. Consequently, Sandvik SAF 2304® has considerably better fatigue strength under corrosive conditions than such steels. | 
