Structural Change with Annealing in Cold Rolled Low Carbon High Cr-Low Ni Two Phase and High Cr Single Phase Steels

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  • 冷延低炭素高Cr-低Ni2相，高Cr単相鋼の加熱に伴う組織変化
  • レイエン テイ タンソ コウ Cr テイ Ni 2ソウ コウ Cr タンソウ

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To clarify a recrystallization process in (α+γ) two-phase stainless steels, the structural change with annealing was studied on three kinds of two phase specimens with 25%Cr and different nickel contents and also on three kinds of single phase specimens with 20∼30%Cr, which were cold rolled 75% in reduction followed by heating mainly for 1 hr. The results obtained are as follows. (1) Shape of a hardness-temperature curve for the two-phase specimen was greatly different from that for the single phase specimen. That is, considerable hardening due to 475°C brittleness prior to softening and furthermore another hardening was observed in the midst of softening. (2) Recrystallization process as well as its temperature in each phase of the two-phase specimen was different from each other. That is, in the α phase small recrystallized grains were observed after subgrains had been formed by recovery, but in the γ phase subgrains were hardly observed below the temperature where the recrystallized grains began to appear. (3) In the α phase, there was little difference in the temperature where subgrains began to form and in the beginning and ending temperatures of recrystallization for both the two-phase and single phase specimens. (4) In the two-phase specimen σ and γ phases were formed from the recrystallized α phase. The temperature where these phases were again transformed into the α phase became higher as the nickel content increased and at higher nickel contents it was fairly higher than the ending temperature of recrystallization in the γ phase. (5) Structural change with annealing in cold rolled high Cr-low Ni two-phase specimens can be regarded as being started form the recovery, followed by the formation of the recrystallized structure in the α phase at the same temperature as in the high Cr single phase specimens, and then the appearance of fine recrystallized grains and a gradual progress of recrystallization in the γ phase follow. Besides, the σ and γ phases are easily formed in the recrystallized α phase, which makes the ending temperature of softening considerably higher than that of recrystallization in the γ phase.

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