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NF709 (20Cr-25Ni-Mo-Nb-Ti-N-B) high-pressure boiler tube

Nippon Steel is in the conventional austenitic stainless steel, based on strict control of impurities on components made further refined and improved composite - Diverse developed from strengthening means, is dedicated to a new supercritical unit boiler austenitic stainless steel.

In this steel, the Ni increased to about 25%, Cr up to about 20%, was added 1.50%, of Mo, 0.30% of Nb, 0.10% of Ti, was added N (0.006%) and a trace amount of B (0.003%) . Formed with Cr, Ni increased austenite stability, a composite solid-solution strengthening of N-Mo, Nb-Ti carbonitride precipitation strengthening and dispersion strengthening grain boundaries B, to improve its high temperature creep rupture strength; and Cr, Ni increasing the amount of increase its resistance to steam oxidation resistance, Cr to improve its resistance to ash corrosion; Cr, Ni prevents the formation of intermetallic compounds, Nb-Ti weaken the intergranular precipitation to improve the impact toughness of the material. Because of the role of these elements, its enduring strength of 105 hours at 700 ℃ up to 88MPa; resistance to oxidation and corrosion resistance is three times 17-14CuMo steel; welding performance with conventional 18-8 stainless steel, such as TP347H and TP310S same; persistent strength of the weld head is also the same as the base material.

The main parameters used in the manufacture of large-scale supercritical pressure power boiler or circulating fluidized bed boiler superheater, reheater high temperature, high temperature section and various high temperature, high pressure pipe corrosion or platen superheater and so on. Due to its overall performance is much better than 18-8 stainless steel, the future will be able to be widely applied.




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