サンドビック SAF 2304®

Sandvik SAF 2304® は、良好な機械的および物理的特性、応力腐食割れおよびその他の形態の腐食に対する優れた耐性、ならびに良好な溶接性を備えています。これらの特性により、ASTM 304、304L、316、316L、321、347 のオーステナイト鋼、ASTM 430 および 444 のフェライト系クロム鋼、ASTM 410 のマルテンサイト系クロム鋼などのステンレス鋼の技術的および経済的に優れた代替品となります。 420型。 Sandvik SAF 2304® は、低合金鋼よりも優れています。次の表に、Sandvik SAF 2304® が他の材料より優れている例を示します。

優れた機械的特性と腐食特性により、Sandvik SAF 2304® は、機器のライフサイクル コストを削減することにより、多くの用途で経済的な選択肢となっています。

3RE60 の高い強度と硬度により、この材料は、重い負荷や摩耗にさらされる構造において、オーステナイト鋼に代わる魅力的な代替品になります。

承認:

Sandvik SAF 2304® が 280°C (540°F) を超える温度に長時間さらされると、微細構造が変化し、衝撃強度が低下します。これは、動作温度での材料の挙動に必ずしも影響しません。たとえば、熱交換器のチューブは、より高い温度で問題なく使用できます。詳しくはサンドビックまでお問い合わせください。圧力容器用途の場合、VdTÜV-Wb 496 によると、最大で 280°C (540°F) が必要です。

曲げに必要な初期力は、ASTM 304/316 より Sandvik SAF 2304® の方がわずかに高くなります。 Sandvik SAF 2304® は、その後の熱処理を必要とせずに 25% の変形まで冷間曲げできます。応力腐食割れのリスクが増加し始める使用条件下、たとえば、約 100 ppm Cl⁻ の中性酸素含有環境で材料温度がほぼ 125°C (255°F) である場合、熱処理はその後でも推奨されます。適度な冷間曲げ。ドイツおよび北欧諸国での圧力容器用途では、VdTÜV-Wb 496 および NGS 1607 に従って、冷間変形後に熱処理が必要になる場合があります。熱処理は、溶体化焼鈍 (熱処理を参照) または抵抗焼鈍の形式で実行されます。

全体的な腐食:クロム含有量が高く、バランスの取れた組成であるため、Sandvik SAF 2304® は酸性環境で優れた耐食性を備えています。下の表は、さまざまな酸での腐食速度を示し、図 4 ～ 6 は、それぞれ硫酸、ギ酸、硝酸での Sandvik SAF 2304® の等腐食図を示しています。

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.製造および製作の慣行。 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 は、重量 % で定義されます

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.

Expanding

In comparison with austenitic stainless steels, Sandvik SAF 2304® has a higher proof strength. This must be borne in mind when expanding tubes into tube-sheets. Normal expanding methods can be used, but the expansion requires higher initial force and should be undertaken in one operation.

Contact us for detailed recommendations on expanding duplex stainless steels.

チューブは通常、熱処理された状態で出荷されます。さらなる処理のために追加の熱処理が必要な場合は、以下をお勧めします。

Solution annealing:930 -1050°C (1710 -1920°F), rapid cooling in air or water.

Hot bending is carried out at 1100-950°C (2010-1740°F) and should be followed by solution annealing.

Being a two-phase material (austenitic-ferritic) Sandvik SAF 2304® will present a different tool wear profile from that of single-phase steels of type ASTM 304L. The cutting speed must, therefore, be slightly lower than that recommended for ASTM 304L and as a first recommendation 25 % lower cutting speeds should be used compared to the speed for machining Sanmac 304/304L. It is, however, recommended that a tougher insert grade is used for semi-roughing operations, Sanmac® 304/304L.

供給形態:

Seamless tube and pipe in Sandvik SAF 2304® is supplied in dimensions up to 260mm outside diameter. The delivery condition is solution annealed and either white pickled or bright annealed.

For hydraulic tubing applications, Sandvik SAF 2304® is also marketed under the name PW 400.

Other forms of supply

The weldability of Sandvik SAF 2304® is good.溶接は予熱なしで行う必要があり、その後の熱処理は通常必要ありません。 Suitable methods of fusion welding are manual metal-arc welding (MMA/SMAW) and gas-shielded arc welding, with the TIG/GTAW method as first choice.

For Sandvik SAF 2304®, heat input of 0.5-2.5 kJ/mm and interpass temperature of <150°C (300°F) are recommended.

Recommended filler metals

• TIG/GTAW or MIG/GMAW welding
  • ISO 14343 S 23 7 N L (e.g. Exaton 23.7.L)
  • ISO 14343 S 22 9 3 N L / AWS A5.9 ER2209 (e.g. Exaton 22.8.3.L)
• MMA/SMAW welding
  • ISO 3581 E 23 7 N L R
  • ISO 3581 E 22 9 3 N L R / AWS A5.4 E2209-17 (e.g. Exaton 22.9.3.LR)