THE HIGH TEMPERATURE STRENGTH OF LOW ALLOY STEELS

Abstract

Room and high temperature strength of some typical low alloy steels (Cr-Mo-V, Ni-Cr-Mo Ni-Mo-V, 1 Cr-Mo and 2.5 Cr-Mo steel) in steam turbine rotor shaft materials were studied.
The results were summerized as follows: (1) The impact transition temperature in Ni-Mo-V and 1 Cr--Mo steel having a comparatively small hardenability lie on to moderately higher side. (2) Generally the higher the room-temperature tensile strength, the higher the tensile strength at high temperature for short time, but it is not apparent that this difference is small. (3) In 500-550°C range 1 Cr-Mo-V steel have the strongest creep-resisting strength and Ni-Mo-V, 1 Cr-Mo, Ni-Cr-Mo and 2.5 Cr-Mo steel beomes weaker in the aforementioned order. (4) 2.5 Cr-Mo steel have the most remarkable elongation and Ni-Cr-Mo, Ni-Mo-V, 1 Cr-Mo and 1 Cr-1 Mo-V steel is a little elongation in their order during the creep rupture test. 1 Cr-1 Mo steel have an elongation of 12-13 per cent and the others have an elongation of over 20 per cent after the creep rupture test. (5) Design curve and master rupture curve at 500°C in each steels have been obtained. (6) Carbide corgulation and spheroidization was not observed in the specimens after no loaded heating test but it was observed after creep rupture test. (7) The tensile test results at high temperature for short time were not always agree with test results of long-time creep rupture and therefore creep resisting properties could not be judged from the former.