P. Lenk et B. Melzer, STRUCTURE OPTIMIZATION AND DAMAGE BEHAVIOR OF HEAT-RESISTANT CRMOV TUBE STEELS, International journal of pressure vessels and piping, 58(3), 1994, pp. 361-371
The heat treatment of a heat-resistant tube steel 12 CrMoV 4 3 has bee
n optimized in relation to its long-term creep resistance. The influen
ce of initial structure and of stress, time and strain on the formatio
n of creep cavities has been determined. Cooling rates from the austen
itizing temperature and tempering conditions were varied during heat t
reatment. It has been demonstrated that, with an increasing cooling ra
te down from the austenitizing temperature, the structure tends toward
s a more finely dispersed precipitation of VCN with formation of grain
boundary carbides as well as a higher dislocation density. The optimu
m tempering conditions are for 2 h at 725-degrees-C. Longer times or h
igher temperatures lead to degradation of the structure. Creep rupture
tests show that a clear influence of the structure on the secondary c
reep rate and rupture time exists. Both pore size distribution and por
e density in the specimen surface are strain- and time-dependent. An i
nfluence of stress could not be detected. Pore density in the surface
approaches, with increasing strain, a saturation value. This saturatio
n value depends on the initial structure and is related to rupture str
ain.