Sandvik 253 MA (Plate and sheet)

Chemical composition (nominal) %

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

Forms of supply-finishes and dimensions

Plate and sheet are delivered in the solution annealed and pickled/unpickled condition.

Mechanical properties

At 20°C (68°F)

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 ÖS₀ where L₀ is the original gauge length and S₀ the original cross-section area

At high temperatures

Creep strength

The creep and creep-rupture strength values correspond to values evaluated by the Swedish Institute for Metals Research to be included in Swedish Standard. The evaluation is based on data submitted by AB Sandvik Steel and Avesta Sheffield AB and tests made by the Swedish Institute for Metals Research. The values apply to tube and pipe, sheet and plate and bar steel. The somewhat higher values given in parentheses apply to Sandvik seamless tube and pipe only. The basic values have been determined by testing at intervals of 100 degrees Celsius, as well as at 750°C (1380°F), under uniaxial stress and with a constant load. The mean values in the tables below have been evaluated from the test results with the aid of linear regression of the logarithmic relation between stress and time. This evaluation has also provided the basis of interpolation and extrapolation of temperatures and times. The temperature above which the calculation is based on creep-rupture strength instead of R p0.2 proof strength can be read off from Fig. 1. For Sandvik 253 MA this temperature is about 550°C (1020°F). Fig. 2 shows the relation between nominal stress and minimum creep rate, measured during testing under constant load.

Fig. 1. Proof strength Rp0.2 and creep-rupture strength at 10 000 and 100 000 h.

Fig. 2 Relation between nominal stress and minimum creep rate at 600 –1100°C (1110–2010°F).

Physical properties

Density: 7.8 g/cm³, 0.28 lb/in³

Relative magnetic permeability

(typical value) 1.003

1) Mean values in temperature ranges (x10⁶)

1) x10³

Corrosion resistance

Air

Sandvik 253 MA has very high resistance to oxidation, especially at cyclically varied temperatures; see Figs. 3 and 4. The service temperature in air should not exceed about 1150°C (2100°F).

Isothermal

Oxidation at 1150°C (2100°F) for 100 h results in a corrosion rate of about 0.3 mm/year (13 mpy), and exposure at the same temperature for 1000 h causes about 0.2 mm/year(9 mpy).

Cyclic

Oxidation at 1150°C (2100°F) for 5 x 24 h with cooling to room temperature every 24 hours gives a corrosion rate of less than 1.1 mm/year (43 mpy), which isinsignificantly greater than the corrosion rate at 1000°C (1830°F).

Cyclic oxidation testing for 1000 h (15 min. at the testing and 5 min. at room temperature, making a total of 3000 cycles) places heavy demands on the elasticity and adhesive capacity of the oxide. The test results in Fig. 4 show the resistance of Sandvik 253 MA in such difficult conditions is superior to that of both ASTM 310 and W.-Nr. 1.4828 (ASTM 309). The very good properties of this grade in cyclic conditions have been achieved by adding rare earth metals and silicon.

Figure 3. Oxidation in air during cyclic testing 5x24 h with cooling to room temperature every 24 h. Comparison of Sandvik 253 MA with four other high-temperature materials.<br /> 1 = W.-Nr. 1.4828 (ASTM 309)<br /> 2 = ASTM 446<br /> 3 = ASTM 310<br /> 4 = Sandvik 253 MA<br /> 5 = Alloy 800 H

Figure 4. Oxidation in air during 1000 h cyclic exposure. The cycles comprise 15 min. at the testing temperature and 5 min at room temperature. The curves represent averages.

Carburising atmosphere

Carburisation can occur when a material comes into contact with hot gases of high carbon activity, e.g. hydrocarbons. The degree of carburisation depends on the composition of the material and on the carbon and oxygen content of the gas.

Thanks to the relatively high chromium content and the addition of silicon and rare earth metals a protective oxide is easily formed on the surface of 253 MA. The carburisation resistance is therefore good. Fig. 6 shows carburisation after 500 h at different temperatures in a mixture of about 10% methane and about 90% argon containing 0.5% oxygen. As can be seen, 253 MA is less prone to carburisation at high temperatures in these conditions than AISI 310 and Alloy 800H.

In alternately oxidising and carburising atmospheres and carburising slags 253 MA is slightly more prone to carburisation than steels of higher chromium and/or nickel content.

Figure 5. Carburisation of a cylindrical test piece at 0.5 mm<br /> (0.02 in. )distance from the surface after testing for 500 h at different temperatures in about 10% CH₄ + about 90% Ar + 0.5% O₂ .

Other gaseous atmospheres

In addition to its very good oxidation resistance in air, 253 MA is also highly resistant to other atmospheres. The highly protective oxide layer makes it possible for this steel to be used at high temperatures in atmospheres containing sulphur and other aggressive compounds. 253 MA is more resistant than the higher-alloyed 25Cr/20Ni steels to combustion gas attacks in cyclic conditions. It has an equivalent resistance, compared to the same grades, in conditions which are virtually isothermal. 253 MA can also be used in nitrogen-containing atmospheres provided that the gas contains enough oxygen to form a protective oxide layer. In gas shields containing little or no oxygen the resistance of 253 MA is inferior to that of

Alloy 800H and 25Cr/20Ni steels as illustrated in Fig. 6. Thus 243 MA is not recommended to be used in muffle tubes using cracked ammonia gas.

Figure 6. Testing for 400 h at 825°C (1515°F) in nitrogen containing 43 and 205 ppm O₂ , respectively

Salt and metal melts

Compared with ordinary austenitic stainless steels, Sandvik 253 MA has good resistance to cyanide melts and neutral salt melts and also to metal melts, e.g. lead, at high temperatures. Its resistance to metal melts is to a great extent determined by the oxygen content of the melt. As with other alloyed steels, corrosion is greatest at the surface of the metal bath.

Wet corrosion

Sandvik 253 MA is not generally used in conditions requiring great resistance to wet corrosion. The steel is, however, somewhat more resistant than ASTM 304 to stress corrosion cracking in chloride- bearing aqueous solutions. Its resistance is more or less the same as that of ASTM 316S.

Structural stability

Because Sandvik 253 MA contains less chromium, and because of the nitrogen addition, it is less prone to sigma phase embrittlement than 25Cr/20Ni steels, see Fig. 7.

Figure 7. Time-Temperature- Transformation (TTT) diagram showing incipient sigma phase formation curves. No sigma phase is formed in the steel to the left of the curves. The figures at the measuring points refer to sigma phase percentage by volume.

Heat treatment

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

Stress relieving

850-950°C (1560-1740°F), 10-15 minutes, cooling in air

Solution annealing

1050-1150°C (1920-2100°F), 5-20 minutes, rapid cooling in air or water.

Welding

The weldability of Sandvik 253 MA is good. Suitable welding methods are manual metal-arc welding with covered electrodes and gas shielded arc welding with the TIG and MIG methods 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 must be carried out with a 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. If, despite these precautions, it is foreseen that the residual stresses might impair the function of the weldment, we recommend that the entire structure be stress-relieved.

As filler metal for gas-shielded arc welding we recommend wire electrodes and rods Sandvik 22.12.HT. In manual metal-arc welding covered electrodes Sandvik 22.12.HTR 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.

Data concerning the creep strength of weld metal and welds are obtainable on request.

Bending

Annealing after cold bending is not normally necessary, but this point must be decided with regard to the degree of bending and the operating conditions. However, if cold bending has exceeded 10-20%, we recommend solution annealing for material that is to be used at temperatures above about 800°C (1450°F) and when the highest possible creep strength is required in the material.

Hot bending is carried out at 1100-850°C (2050-1560°F) and should be followed by solution annealing.

Applications

The high creep strength of Sandvik 253 MA, coupled with its excellent oxidation resistance and its good resistance to carburisation in constantly carburising gas, makes it a very suitable material for purposes for which 18/8 steels lack the necessary resistance to oxidation and carburisation. Stainless chromium steels have insufficient creep strength and structural stability. What is more, 253 MA can very well take the place of higher-alloyed materials such as 25Cr/20Ni steels and Alloy 800H, or even Alloy 600 in certain cases.

Sandvik 253 MA has come to be extensively used in the metallurgical industry and in the petrochemical and power industries. Applications include the following:

• In waste-heat recovery systems in metallurgical industry, e.g. recuperators
• In heat treatment furnaces, e.g. radiation tubes, thermocouple protection tubes, burner components, furnace rollers
• For injection of pulverised coal in blast furnaces
• For fluidised-bed combustion plants
• Furnace tubes for mud incineration plants
• Tubes for carbon black process gas coolers/air heaters
• Tubes for the glass and cement industries
• Styrene reactor tubes
• EDC cracking tubesConvection tubes in ethylene cracking
• Air preheater tubes in sulphuric acid gas converters

* 253 MA is a trademark owned by Outokumpu OY.