Effects of Nonmetallic Inclusions on the Hot Torsional Deformability of Rimmed Steels

Abstract

The effects of nonmetallic inclusions on the hot torsional deformability were investigated on the specimens cut from the slubs of rimmed steels (12t). The kinds and cleanliness of nonmetallic inclusions were examined in the test part of each test piece. The hot torsional tests were carried out at 1000 and 1200°C at the strain rates of 15·2, 1·67×10^-2 and 5·81×10^-4sec^-1.
The results obtained were as follows:
(1) The effect of MnS on the hot torsional deformability was most remarkable. The relation between the cleanliness of MnS and the number of twist to failure was changed in the form of hyperbola. When the cleanliness was more than about 0·075%, the number of twist to failure was small, and it decreased slowly with increasing cleanliness. When the cleanliness was less then 0·075%, the number of twist to failure remarkably, increased by decreasing the cleanliness. The number of twist to failure did not depend on the strain rate, but on the strain. The cleanliness is so defined as to increase when the density of inclusions increases.
(2) In case of the oxide-type inclusions which were hardly deformed during the hot torsional deformation, the initiation of the cracks from them depended on their shapes and sizes, the deformability of matrix, and the strain rate.