Study on Reduction Annealing Behavior of Oxide Scale of Hot‐Rolled High‐Strength Steel

The study investigated the reduction behavior of oxide scale on hot‐rolled high‐strength steel through simulated annealing tests in 30% H 2 –N 2 at 500°C–1100°C. The research delved into the kinetics of reduction, internal oxidation, and associated mechanisms. Findings revealed that at 500°C and 600°C, the reduction product was porous iron, transitioning to dense iron between 800°C and 1100°C. The shift from porous to dense structures occurred, with the slowest reduction rate observed at 700°C. Internal oxidation, featuring silicon and manganese oxides, occurred from 800°C to 1100°C, with minimal depth changes despite increasing reduction temperatures. Equilibrium oxygen partial pressure at the oxide scale/substrate interface predominantly controlled internal oxidation, where oxygen atoms from oxide scale reduction drove the nucleation and growth of internal oxides. The reduction process involved hydrogen diffusion through the gas boundary layer, internal diffusion of hydrogen within solid products, chemical reactions at the outer gas/oxide scale interface, outward diffusion of water vapor, and the formation of internal oxides. Comparing the reduction rate progression to the reduced iron growth rate at the gas/oxide scale interface, key reduction products were identified as porous and dense iron.