18-8 ステンレス鋼の連鋳スラブにおけるδフェライトのオーステナイトへの溶け込みについて

概要

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Dissolution of δ-ferrite into austenite in the annealing temperature range of 1050 to 1250℃ for 18-8 (SUS304) stainless steel continuously cast slabs has been studied experimentally together with numerical calculation of diffusion model. (1) Secondary dendrite arm spacing (S_II) increased approximately linearly with the distance from slab surface. δ content as cast did not increase linearly. At 1/4 thickness of slabs, it had minimum point which may be caused by reheating in the slab making process. (2) At the early stage of annealing, δ content increased. It was explained by diffusion model. (3) The logarithm of dissolution rate decreased approximately linearly with decreasing δ content except the initial and final stages of annealing. Apparent activation energy was about 60kcal/mol, which was nearly the same as the activation energy for diffusion in γ-phase. (4) The relation between δ content and log(t/S^2_<II>), where t is virtual annealing time which is compensated by addition of modified reheating time in the slab making process, is nearly the same at any S_<II> on the same temperature. The calculated result agrees with these relations except the final stage of annealing, where the dissolution rate of the experiment is slower than the calculation.
社団法人日本鉄鋼協会の論文
1979-07-01