Seamless stainless steel tubes in heat resistant grade

Grade 1.4845 is an austenitic chrome-nickel type 25/20 stainless steel suitable for high-temperature applications. The grade has good resistance to carburizing, sulfidation and oxidation combined with moderate creep strength and structural stability.

1.4845 has very good resistance to oxidation and sulfidation. It can be used in:

-Air: up to 1100°C (2010°F)

-Sulfur-containing atmospheres: up to 650-1050°C (1200-1920°F), depending on operating conditions. Factors to consider in this situation include whether the atmosphere is oxidizing or reducing, and whether impurities such as sodium and vanadium are present.

Good overall resistance to high-temperature corrosion makes this steel suitable for a wide range of applications, such as:

-Furnace tubes

-Recuperators

-Muffle tubes in continuous wire annealing furnaces

-Thermocouple protection tubes

-Pipe hangers in oil and steam boilers

-Burners

This grade of steel is characterized by:

-extremely good resistance to sulfur gas reduction

-very good resistance to oxidation in air

-good resistance to oil and ash corrosion

-good resistance to molten copper, lead and tin

This steel can be used at temperatures up to 1150°C (2102 °F). However, the low creep strength at the highest temperatures must be taken into account to avoid deformation due to the weight of the steel.

Since H25T steel has very high creep elongation, often exceeding 100%, and low creep resistance, it is necessary to allow significant creep deformation long before cracking occurs. At normal operating temperatures, i.e. above 700 °C (1290 °F), even the pipe's own weight can cause stresses leading to large deformations.

For this reason, special attention should be paid to how the tubes are supported. H25T, like other ferritic chromium steels, is less strong than austenitic stainless steels as delivered. The transition temperature for H25T is about 100-150 °C (210-300 °F). After a certain period of service, the strength at room temperature may decrease further. For this reason, high impact stresses and the like should be avoided during repairs.

In the EN standard, the equivalent grade of H25T (15Cr25Ti) is steel grade 1.4749, whose stabilizing additive, in place of titanium, is aluminum.

Steel 15X25T (15Cr25Ti, H25T) is sometimes used as an alternative to materials in grade 1.4749. The stabilizing element in this case is Titanium, instead of Aluminum (Al).

Comparison of the chemical composition of 15X25T and 1.4749

Recommendations for grade 1.4749:

For construction parts, which should be resistant to scaling up to about 1100°C and extensively inured to the effects of sulphurous gases. The inclination to carbonisation in reduced gases is very low.