Hitoshi Ishii1 and Yoshinori Fujimura1
1Department of Mechanical Engineering, Shizuoka University, Hamamatsu
To elucidate the brittleness observed in high Cr ferritic steels quenched from a high temperature, tensile behavior was studied on 11 kinds of specimens whose Cr contents ranged from 17 to 30% and were annealed at various temperatures between 700 and 1250°C for 1 hr, followed by water quenching or furnace cooling. Principal findings were as follows. (1) The specimens water-quenched from a temperature above 900°C showed an increase in tensile strength and a decrease in elongation as the annealing temperature increased, irrespective of the increase in grain diameter. This tendency was not so marked in specimens with very low (C+N) contents. Furthermore, in some of the specimens water-quenched from a temperature above 1100°C the tensile strength started decreasing as the annealing temperature increased, and there were cases where the above-mentioned two opposing tendencies were observed even in the same specimen. However, in the furnace-cooled specimens the change in tensile behavior due to annealing temperature was quite normal and the yield stress followed the Hall-Petch equation. (2) Water-quenched specimens showed larger yield stress increments to the same strain aging treatment and also a more pronounced P-L effect when deformed above room temperature than the furnace-cooled ones. (3) Tensile behavior of the water-quenched specimens came close to that of the furnace-cooled one when reheated at about 600°C. (4) Tensile behavior of high Cr steels can be interpreted in terms of solution hardening by C and N atoms.
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