Effect of Mo and C on Toughness of 1/2 Mo Steel for Pressure Vessel

Abstract

Effects of Mo and C contents on the impact properties of 1/2Mo steels utilized in the pressure vessel of the petroleum refining equipments, were investigated to improve the toughness.
(1) Molibdenum addition suppresses the formation of ferrite in the steel resulting in the improvement in the toughness. On the other hand, if the microstructure of the specimens is constituted by the same volume fraction of ferrite, pearlite, and bainite, increasing Mo content decreases the upper shelf energy andincreases the vTrs.
(2) Increasing C content from 0.15 to 0.30% in 1/2Mo steels lowers the toughness.
(3) On the basis of the experimental results on the relation between vTrs and microstructure of steels with 0.15-0.75%Mo, it is found that good toughness is obtained and the variation of which was very small if steel plates had more than 40% bainite in volume. The above condition was realized by the appropriate cooling rate according to the plate thickness.