内部窒化法を利用した熱処理による粒径傾斜組織の形成と高温疲労寿命への影響
1992 年 78 巻 12 号 p. 1838-1845
詳細
1992 年 78 巻 12 号 p. 1838-1845
A process of producing a grain size-gradient structure was proposed for low alloy steels containing nitride formers such as Ti, V, Al and Zr. Using a 1Cr-1Mo-3/4V steel, the grain size-gradient structure which combines a fine grain surface region and a coarse grain interior was obtained by the process, and an effect of the structure on the fatigue bebavior was examined.
The producing process is as follows:(a) precipitation of VN in the surface region through heating at 1000°Cin N2, (b) grain refining by recrystallization at 1000°C, (c) grain coarsening in the interior through solution treatment at 1150°C.In the surface region, the fine grain swere maintained by the grain growth inhibitor of VN after the solution treatment.The obtained grain size-gradient structure is composed of a fine grain (<10μm)surface region(01mm depth), a traRsient grain size(1080μm)region(12mm depth), and a comparatively coarse grain(80μm)interior.
The specimens with the grain size-gradient structure were tested at 550°C in arotating-bending fatigue machine and found to display better fatigue behavior than non-gradient homogeneous grain specimens. It was thought that the fine grain surface region suppresses the fatigue crack initiation and increases the fatigue life.
