Chemical composition (nominal) %

* The quantity of other rare earth metals should be added to cerium, because the addition takes the form of misch metal containing about 50 % Ce.

Forms of supply

Seamless tube and pipe

Seamless tube and pipe in Sandvik 353 MA is supplied in dimensions up to 200 mm outside diameter in the solution annealed and white pickled condition, or solution annealed by a brightannealing process.

Other forms of supply

• Bar steel, min. diameter 80 mm
• Welding wire and filler wire/rods
• Covered electrodes

Mechanical properties

At 20°C (68°F)

1 MPa = 1 N/mm²
a) A is based on an original gauge length of 5.65 √S₀.

At high temperatures

R_p0.2 and R_p1.0 correspond to 0.2 % offset and 1.0% offset yield strength, respectively.

Creep strength
Average values

Physical properties

Density: 7.9 g/cm³, 0.28 lb/in³

1) (x10^-6)

1) (x10³)

Corrosion resistance

Oxidation

Owing to the high silicon content and the addition of Rare Earth Metals (REM), Sandvik 353 MA has very high resistance to oxidation. The REM addition also contributes to improved scale adhesion during temperature cycling. Fig. 1, which shows the measured weight increase after 45h cyclic oxidation at different temperatures, illustrates how Sandvik 353 MA compares with some other high temperature grades. Weight increase after longer exposure at 1150°C (2100°F) is shown in Fig. 2. The weight increase shown in Fig. 1 and Fig. 2 includes the weight of any spalled oxide.

Figure 1. Weight increase for Sandvik 353 MA and other grades after 45h oxidation.

Figure 2. Weight increase versus time during oxidation at 1150°C (2000°F).

Carburizing and nitrogen pick-up

Corrosion attack by carburization or nitrogen pick-up usually follows a parabolic rate law: x²=k_p * t+C,
where x is the attack, expressed as penetration depth or weight increase, k_p a rate constant, t exposure time and C a constant accounting for the initial attack (which follows a different rate law).

Due to its ability to form a dense chromium oxide and its high nickel content, Sandvik 353 MA also has good resistance to carburization and nitrogen pick-up.

Fig. 3 shows the measured rate constants for carburization tests of various alloys at different temperatures. Cyclically carburizing-oxidizing conditions are often more detrimental, but, as Fig. 4 shows, Sandvik 353 MA is able to resist these conditions better than other alloys.

In nitrogen pick-up tests, Figure 5, Sandvik 353 MA showed similar resistance to Alloy 601.

Figure 3. Rate constant for total carburization; a_c=1; PO₂~0.

Figure 4. Rate constant for total carburization and carburization-oxidation. Carburization: 950°C(1740°F); a_c=1; PO₂~0. Oxidation: 1050°C(1920°F); a_c~0; PO₂=0.21atm.

Figure 5. Rate constant for nitrogen pick-up in cracked ammonia.

Sulphur attack

Alloys with high nickel content are generally sensitive to attack by sulphur at higher temperatures. However, under oxidizing conditions a protective oxide will be able to form, contributing to an improved resistance to sulphur attack. This is illustrated in Fig. 6, which shows the rate constant for different alloys in different sulphidizing-oxidizing conditions. Again, the dense oxide formed on Sandvik 353 MA is shown to be advantageous.

Figure 6. Rate constant for sulphidation-oxidation.

Heat treatment

Tubes are delivered in the heat treated condition. If another heat treatment is needed after further processing, the following is recommended:

Stress relieving

1000-1100°C(1830-2010°F), 10-15 minutes, cooling in air.

Solution annealing

1100-1200°C (2010-2190°F), 5-20 minutes, rapid cooling in air or water.

Welding

The weldability of Sandvik 353 MA is good. Suitable welding methods are manual metal-arc welding with covered electrodes and gas-shielded arc welding, with the TIG method as first choice. Preheating and post-weld heat treatment are not normally necessary.

Since the material has low thermal conductivity and high thermal expansion, welding should be carried out with low heat input and with welding plans well thought out in advance, so that the deformation of the welded joint can be kept under control.

As filler metal for gas-shielded arc welding, we recommend Sandvik 28.34.HT wire electrodes and rods. In manual metal-arc welding, Sandvik 28.34.HTBcovered electrodes are recommended. The composition of these filler metals is designed to yield a weld metal whose creep strength and oxidation resistance will correspond to those of the parent metal.

Bending

Due to its higher strength compared with conventional stainless steels, higher deformation forces are required for cold bending of Sandvik 353MA.

Annealing after cold bending is not normally necessary, but this decision should be made taking account of the degree of bending and the service conditions.

Applications

The excellent resistance of Sandvik 353 MA to oxidation and carburization, in constantly carburizing gas, makes it a very suitable grade for, above all, high temperature petrochemical furnaces. The high nitriding resistance is very beneficial for service in high temperature cracked ammonia gas. Examples of applications are:

• Ethylene furnace, radiant cracking tubes
• EDC cracking furnaces
• Tubes in wast heat recovery systems in the metallurgical industry, e.g. recuperators
• Tubes in heat treatment furnaces, e.g. muffle tubes, radiant tubes, thermocouple protection tubes, burner components, furnace rollers
• Recuperator tubes in chemical waste and sewage sludge incineration

* 353 MA is a trademark owned by Outokumpu OY.