ASTM A240 N08904 904l Stainless Steel Sheet , SS Sheet Metal Cold Rolled

ASTM A240 N08904 904L cold rolled stainless steel plate

UNS N08904 Plate

UNS N08904 is a high-alloy austenitic stainless steel intended for use under severe corrosion conditions within the process industry. The grade is characterized by:

• Very good resistance to attacks in acidic environments, e.g. sulphuric, phosphoric and acetic acid
• Very good resistance to pitting in neutral chloride-bearing solutions
• Much better resistance to crevice corrosion than steels of the ASTM 304 and ASTM 316 types
• Very good resistance to stress corrosion cracking
• Good weldability

Standards

• ASTM 904L
• UNS N08904
• ISO 4539-089-04-I
• EN number 1.4539
• EN name X1NiCrMoCu25-20-5

Product standards

Approvals
Approved for use in ASME Boiler and Pressure Vessel Code section VIII, div. 1 construction
NGS 685 (Nordic rules for application of SS 2562)
VdTÜV-Werkstoffblatt 421 (Austenitischer Walz-und Schmiedestahl)

Chemical composition (nominal) %

Finishes and dimensions

Seamless tube and pipe are supplied in dimension up to 230 mm outside diameter in the solution annealed and white-pickled condition or in the bright-annealed condition.

Tubes can be bent according to customer drawings and, on request, annealed after bending.

Fittings

90 deg. bends are manufactured as standard in UNS N08904 according to ANSI B16.9 and, where applicable, ASTM A403. Flanges are made as standard to ANSI B16.5 in the form of slip-on flanges (class 150) and weld neck flanges (class 300), and to relevant sections of ASTM A182. Fittings can be manufactured to other standards by agreement. Other types of fittings such as reducers, tees and couplings can also be supplied on request.

Packages comprising of different product forms can be supplied. Examples of product forms are:

• Forged tube-sheets

Mechanical properties

At 20°C (68°F)

The following figures apply to material in the solution annealed condition. Tube and pipe with thickness above 20 mm (0.79 in.) may have slightly lower values.

1 MPa = 1 N/mm²
a) R_p0.2 and R_p1.0 correspond to 0.2% offset and 1.0% offset yield strength, respectively.
b) Based on L₀ = 5.65 √S₀ where L₀ is the original gauge length and S₀the original cross-section area.
c) NFA 49–217 with min 40% can be fulfilled.

Impact strength

Due to its austenitic microstructure, UNS N08904 has very good impact strength both at room temperature and at cryogenic temperatures.

Tests have demonstrated that the steel fulfils the requirements (60 J (44 ft-lb) at -196 ^oC (-320 ^oF)) according to the European standards prEN 13445-2 (UFPV-2) and prEN 10216-5.

At high temperatures

The steel should not be exposed to temperatures above about 550 °C (1020 °F) for prolonged periods, since this leads to precipitation of intermetallic phases, which can have an adverse effect on both the mechanical properties and the corrosion resistance of the steel.

Physical properties

Density: 8.0 g/cm³, 0.29 lb/in³

1) Mean values in temperature ranges (x10^-6)

1) (x10³)

Corrosion resistance

General corrosion

The steel was originally developed for use in sulphuric acid. Its good resistance is achieved by virtue of a high molybdenum content and alloying with copper. Figure 1 is an isocorrosion diagram for UNS N08904, UNS N08028 and ASTM 316L in deaerated sulphuric acid.

Figure 1. Isocorrosion diagram for UNS N08904, UNS N08028 and ASTM 316L in deaerated sulphuric acid at a corrosion rate of 0.1 mm/year (4 mpy) in stagnant solution.

Figure 2 shows the isocorrosion diagram for the above steels but in naturally aerated sulphuric acid.

Figure 2. Isocorrosion diagram 0.1 mm/year (4 mpy) for UNS N08904 and ASTM 316L in naturally aerated sulphuric acid of chemical purity.

Technical phosphoric acidmanufactured by means of the "wet" method contains varying amounts of impurities from the starting material, the phosphate rock. The most dangerous of these impurities are chlorides, Cl^- , and fluorides in free form, F^- . UNS N08904 has been used with success in many applications in phosphoric acid plants and for the handling of technical acid. However, for the severest corrosion conditions, UNS N08028, which was developed especially for phosphoric acid applications, provides superior corrosion resistance.

In pure acetic acid, both UNS N08904 and AISI 316L are completely resistant at all temperatures and concentra-tions at atmospheric pressure. At elevated temperatures and pressures, however, AISI 316L will corrode while UNS N08904 will remain resistant. Experience from acetic acid production has shown that acetic acid contaminated with formic acid is always corrosive. In acid of this kind, UNS N08904 is far more resistant than AISI 316L, see table 1 below. Practical operating experience has confirmed the superiority of UNS N08904 to AISI 317L as well.

In formic acid, high-alloy UNS N08904 shows better resistance than conventional steels of the AISI 316L type, see figure 3. In oxalic acid UNS N08904 shows better performance than 316L, see figure 4. UNS N08904 is resistant (corrosion rate <0.1 mm/year) in lactic acid at all concentrations at temperatures up to or slightly below the boiling point at atmospheric pressure. This means a corrosion resistance similar to or slightly better than of 316L in lactic acid. Due to its molybdenum content, UNS N08904 is less resistant to nitric acid than steels of the AISI 304L and AISI 310L types, which are commonly used in these environments.

Figure 3. Isocorrosion diagram 0.1 mm/year (4mpy) ior UNS N08904 and AISI 316L in formic acid.

Figure 4. Isocorrosion diagram 0.1 mm/year (4mpy) ior UNS N08904 and AISI 316L in oxalic acid.

Figure 5. Isocorrosion diagram 0.1 mm/year (4 mpy) ior UNS N08904 and AISI 316L in hydrochloric acid.

Figure 6. Isocorrosion diagram 0.1 mm/year (4mpy) ior UNS N08904 and AISI 316L in hydrofluroic acid.

High molybdenum content is an advantage in hydrochloric acid, and UNS N08904, with its 4.5% Mo is consequently far more resistant than, for example, AISI 316L. UNS N08904 is therefore suitable for use in chemical process solutions containing small amounts of hydrochloric acid. The isocorrosion diagram is presented in figure 5. The risk of pitting should, however, be kept in mind. Also in hydrofluoric acid UNS N08904 benefits from its high molybdenum content, although hydrofluoric acid is an even more aggressive acid compared to hydrochloric acid, see isocorrosion diagram in figure 6.

Table 1. results of laboratory tests lasting 1+3+3 days in boiling mixtures of acetic and formic acid.

Due to its high chromium and nickel contents, UNS N08904 possesses much better resistance in sodium hydroxide than AISI 304 and AISI 316, see figure 7.

Figure 7. Isocorrosion diagram 0.1 mm/year (4mpy) ior UNS N08904, 304L and AISI 316L in sodium hydrooxide of chemical purity.

As can be seen the risk of stress corrosion cracking (SCC) increases at high temperatures. This risk is enhanced if chlorides are present. The alloy UNS N08028, see data sheet S-1885-ENG, provides better resistance against SCC and also general corrosion than is the case for UNS N08904.

Pitting

The high chromium and molybdenum contents of this steel make it very resistant to pitting. This has been verified by extensive practical experience of service involving chloride-bearing process solutions and seawater cooling.

Figure 8. Mean values of critical pitting temperature (CPT) at 400 mV SCE and different Cl^- concentrations (NaCl solutions), pH ~ 6 (1.8%Cl^- corresponds to the chloride content of seawater).

As can be seen in figure 8, the mean critical pitting temperature (CPT) for UNS N08904 is around 75°C (165°F) at a potential of 400 mV SCE in a neutral solution (pH = 6) with the same chloride content as seawater. This value is 50°C (120°F) higher than for AISI 316 and 20°C (68°F) higher than for Alloy 825 (21Cr42Ni3Mo).

Stress corrosion cracking

Ordinary austenitic steels of the AISI 304 and AISI 316 types are susceptible to stress corrosion cracking in chloride-bearing solutions at temperatures above about 60°C (140^oF). At high temperatures, above about 100^oC, chloride contents as low as in the ppm-range (10^-4 %) are sufficient to cause stress corrosion cracking in these steels. A nickel content of 25% is sufficient to provide very good resistance under practical conditions.

Laboratory tests in calcium chloride confirm the superiority of UNS N08904 in resisting stress corrosion cracking compared to AISI 304 and AISI 316. As is shown by figure 9, the threshold stress (the stress necessary to induce fracture within the maximum testing time) is considerably higher for UNS N08904 than for AISI 304 and AISI 316. UNS N08904 is resistant up to at least 0.9 times the tensile strength.

Autoclave tests at different chloride contents and temperatures provide valuable data for material selection. Also this type of testing demonstrates the good SCC-resistance of UNS N08904, far better than 304 and 316 types of steels, see figure 10.

It is important to be aware of the fact that the residual stresses around a weld that has not been heat treated often equal the proof strength of the material. These stresses correspond to applied stress/tensile strength ratios of only 0.3-0.5, which is sufficient to exceed the threshold stress and thereby cause stress corrosion cracking in AISI 304 and AISI 316.

Figure 9. Results of stress corrosion cracking tests on different steel grades in 40% CaCl₂ at 100°C (210°F), pH = 6.5.

Figure 10. SCC resistance of UNS N08904 in comparision to AISI 304 and AISI 316 types of steels in neutral aerated chloride environments.

Crevice corrosion

Both laboratory tests and practical experience have shown that UNS N08904 is substantially more resistant to crevice corrosion than AISI 316L. This is illustrated in Table 2. Crevices should nevertheless be avoided as far as possible, especially in chloride-bearing solutions.

Table 2. Results of crevice corrosion tests in aerated stagnant NaCl solution (1.8% Cl^- ) pH = 6, test period 58 days. The area ratio between creviced and non-creviced surface on the specimen is 1/12.

Heat treatment

Solution annealing

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

1080-1150°C (1975-2100°F), 5-30 minutes, rapid quenching in air or water.

Welding

UNS N08904 possesses good weldability. Welding should be undertaken without preheating. If welding is correctly performed, there is no need for subsequent heat treatment. The temperature between welding passes should not exceed 100 °C (212^oF). Suitable methods of fusion welding are manual metal-arc welding with covered electrodes and gas-shielded arc welding, especially the TIG and MIG methods.

Since the material is intended for use under severe corrosion conditions, welding must be carried out with care and a thorough cleaning must be performed after welding to ensure that the weld metal and the heat-affected zone will have corrosion properties close to those of the parent metal.

Welding should be undertaken with low heat input, maximum 1.0 kJ/mm. Furthermore, the diameter of electrodes used in manual metal-arc welding should be max. 2.5 mm (3/32") for stock thicknesses up to 6 mm (1/4") and max. 3.25 mm (1/8") for heavier stock gauges. A stringer bead welding technique is recommended.

Like all austenitic stainless steels, UNS N08904 has low thermal conductivity and high thermal expansion, so welding must be carefully planned in advance to ensure that distortion of the welded joint can be kept under control. If, despite such precautions, it is believed that residual stresses might impair the functioning of the structure, it is recommended that the entire structure will be solution annealed, see under Heat treatment.

Welding of fully austenitic steels often entails the risk of hot-cracking in the weld metal, particularly if the weldment is under constraint. UNS N08904, however, possesses very high purity, which reduces the risk of such cracking.

Bending

The good ductility of UNS N08904 permits bending in the cold state to the smallest bending radii attainable with modern methods and machines. Annealing is not necessary after cold bending. If, however, the tubes have been heavily cold-worked and are to be used under conditions where stress corrosion cracking is liable to occur, solution annealing is recommended (see under this heading).

For pressure vessel applications in Germany, heat treatment may be required after cold deformation in accordance with VdTÜV-Wb 421. Heat treatment should be carried out by solution annealing.

Applications

UNS N08904 is a multi-purpose material for use under severe corrosive conditions. This has been proven both by laboratory tests and by extensive operational experience with the steel.

Typical applications for UNS N08904 are found in oil refineries and within the chemical and petrochemical industry. UNS N08904 is also used within the pulp and paper industry, the mineral and metallurgical industry, the food industry, in seawater cooling and in many other fields.

The grade is an excellent alternative to standard austenitic stainless steels in heat exchangers using high temperature water with chloride contamination.

Production process

Suzhou Vanforge Metals Co., Ltd. was set up in April 1999 with a registered capital of 230 million Yuan in Zhangjiagang Bonded Area in Jiangsu Province of China. It has developed to be an important R&D and manufacture enterprise of high performance stainless steels and nickel alloys.

Vanforge is a high-tech enterprise with 70 national patents, it has its own Special Alloy Research Center, academician workstation and post doctorate innovation practice base. Vanforge has been certificated the national laboratory accreditation of ISO/IEC 17025, and ISO9001, ISO14001, OHSAS18001, API Q1, IATF16949, GB/T23331, TUV, CCS, DNV, LR, ABS.

Vanforge has the international advanced special smelting capacity, including the German ALD 6t vacuum induction furnace, 6t consumable electrode vacuum furnace, 18t drawing-ingot protective atmosphere electroslag furnace and 1t vacuum induction furnace, 3t electroslag furnace, 18t drawing-hollow ingot electroslag furnace, and 2# Purification Furnace/1# Purification Furnace/LF/AOD/VOD refining production line, 25MN/8MN fast forging machine, 450/320 rolling mill, etc.

The current annual production capacity of Vanforge is 120,000 tons, and the main products are high-grade special alloy materials, including high temperature alloy, corrosion resistant alloy, precision alloy, ultra high strength steel, special stainless steel, high-grade tool and mould steel, steam turbine blades steel, gas turbine steel, ultra-supercritical materials, etc., which are widely used in aviation, aerospace, ship, petrochemical, nuclear power, electronics, steam turbine, high-speed rail, machinery manufacturing, and other fields; besides, we can organize the research and development and production of new materials according to customer demand for new materials. Vanforge has now become a qualified supplier of domestic high-end equipment manufacturing enterprises, such as CASIC, CGN, CRRC, CFHI, Wujin Stainless, Zhejiang Jiuli Hi-Tech Metals Co., Ltd., Xinxing Ductile Iron Pipe Co., Ltd., etc.

We always adhere to the concept of quality first, integrity based, scientific and technological innovation, making progress, and wholeheartedly serving customer and devote ourselves to becoming the well-known supplier of key basic materials of world’s high-end equipment manufacturing industry.

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