Study on the composition, microstructure and properties of new W-Al alloyed ethylene cracking furnace tube under 1100 celcius carburising test conditions

The carburising tests were carried out at 1100 celcius for 50 h, 100 h, 150 h and 200 h for a new type of tungsten-aluminium alloyed ethylene cracking furnace tube. The composition, microstructure transformation and performance of furnace tubes were analysed. The results showed that the average carbon content within 1 mm of the inner wall increased with the prolongation of carburising time. The thickness of carburised layer increased from 0.3 mm to 1.5 mm. The carbides in as cast structure were mainly massive (Cr, Fe, W)(23)C-6 on the outside and fishbone (Cr, Fe, W)(7)C-3 on the inside. During carburising process, the external (Cr, Fe, W)(23)C-6 carbides coarsened and transformed into (Cr, Fe)(7)C-3, and then gradually transformed into (Cr, Fe, W)(7)C-3. Carbide coarsening mainly occurred in internal (Cr, Fe, W)(7)C-3 during carburising. The carbide precipitation and transformation also led to Vickers hardness value of furnace tube increased.