Effect of Annealing Process on Dissolution Behavior of δ Ferrite in 301L Stainless Steel Casting Billet

The dissolution behavior of 301L stainless steel casting billet by heat treatment furnace before rolling was analyzed.The results show that the dissolution of δ ferrite in 301L billet is significantly affected by annealing time and temperature.At the beginning of dissolution, the content of δ ferrite decreases from 12wt% to less than 6wt%.With the increase of annealing time and temperature, the decrease of δ ferrite content in the solid state of 301L billet is significantly controlled by the diffusion of Cr and Ni.After diffusion annealing at 1300 ℃for 60 min, ferrite spheroidized and the grain size decreases to 2-3 μm.The spheroidization behavior of the equilibrium δ ferrite at the node reduces the additional stress at the γ/α interface and facilitates the rolling process.The effects of Cr and Ni on the microstructure are verified by the kinetic equation.When the annealing temperature is 1210 ℃, the dissolution parameter K^γ_Ni is 0.26, and the diffusion coefficient of Ni is D ^γ_NiNi=4.8×10^-10 cm²/s.The volume fraction of δ ferrite is proportional to the annealing time t^1/2.The research results can provide theoretical guidance for the microstructure control of 301L casting billet.