Abstract
For the purpose of obtaining some knowledge about the effects of alloying elements on the high temperature strength of 18Cr-12Ni-0.2C steels, the testing temperature and rupture time dependences of the strengthening by B, N and Mo additions upon tensile and creep rupture strength at 600 to 800°were investigated.Also, age-hardening response and microstructures of those steels were observed.
The improvement due to B addition increased at higher temperature and longer time, and that due to N addition increased at lower temperature and shorter time. This effect of B addition was ascribed mainly to the suppression of intergranular fracture, and the effect of N addition was ascribed principally to the decrease of creep rate due to the solid solution hardening of N. However, this strengthening effect caused by N addition deteriorated extremely with increasing test temperature, because N promoted the coagulation of carbide.
The improvement due to Mo addition was persisted in constant for all temperature and time range tested
However, B and N respectively, in combination with Mo, appeared to interact and produced a more improvement in creep rupture strength than the sum of the individual contributions. The contributions of those alloy interactions increased grenerally with increasing test temperature and rupture time.
