Papers by Author: Yong Deuk Lee

Abstract: A study was made to investigate the precipitation behavior of sigma phase via various heat treatments and corresponding mechanical properties of super duplex stainless steels. Isothermal heat treatment was performed at temperature range of 600~1000°C to draw TTT diagram for sigma phase. Tensile and Charpy impact tests were performed at room temperature and the results were analyzed in relation with the microstructure. The effect of lattice misfit strains due to the precipitation of sigma phase on the mechanical properties was also discussed.

Abstract: Sticking phenomenon occurring during hot rolling of ferritic stainless steels, STS 430J1L and STS 436L, was investigated in this study. The simulation test results at 900 oC and 1000 oC revealed that STS 430J1L had a smaller number of sticking nucleation sites than the STS 436L. When the test temperature was 1070 oC, the sticking hardly occurred in both stainless steels as Fe- Cr oxide layers were formed on the surface of the rolled materials. These findings suggested that the improvement of high-temperature properties of stainless steels and the appropriate rolling conditions for readily forming oxide layers on the rolled material surface were required in order to prevent or minimize the sticking.

Abstract: In order to investigate the effect of the reduction degree per rolling pass on the evolution of recrystallization textures and microstructures, the hot band of 17.5 Cr-1.1 Mo ferritic stainless steel sheets were cold rolled with lubrication according to two processing routes, by which different reduction degrees per pass were introduced. Rolling with a large number of passes led to the formation of fairly homogeneous rolling textures at all through-thickness positions. In contrast, cold rolling with large draughts resulted in pronounced texture gradients along the thickness direction. After recrystallization annealing, the texture maximum was obtained at {334}<483> in all samples regardless of the rolling routes and thickness layers. During subsequent annealing, recrystallization was observed to be faster in those grains with {111} orientations, while it was retarded in grains having orientations close to {001}<110>.