Bk. Choudhary et al., EFFECTS OF STRAIN-RATE AND TEMPERATURE ON TENSILE DEFORMATION AND FRACTURE-BEHAVIOR OF FORGED THICK-SECTION 9CR-1MO FERRITIC STEEL, International journal of pressure vessels and piping, 58(2), 1994, pp. 151-160
Tension tests have been conducted to evaluate the influence of strain
rate (6.3 x 10(-3) to 3.2 x 10(-5) s-1) and temperature (300-873 K) on
tensile deformation and fracture behaviour of 1000 mm diameter and 30
0 mm thick 9Cr-IMo tube plate forging in simulated post weld heat trea
tment condition. Yield strength and ultimate tensile strength decrease
d gradually up to around 723 K. Beyond 723 K a rapid fall in both the
strength values was observed. In the intermediate temperature range (5
23-673 K), the alloy exhibited higher yield and tensile strength value
s with decreasing strain rate, indicating negative strain rate sensiti
vity. In contrast, at temperatures of 723 K and above, the strength va
lues decreased with decrease in strain rate. Serrated flow, a characte
ristic of dynamic strain ageing, was observed in the temperature range
523-673 K. The upper end temperature of serrated yielding decreased w
ith decrease in strain rate. A detailed analysis of the dependence of
critical strain for the onset of serrations on temperature and strain
rate yielded an apparent activation energy of 83 kJ mol-1 for serrated
flow at temperatures between 523 and 623 K. Ductility measured in ter
ms of percentage elongation and reduction in area after fracture showe
d a gradual decrease up to about 673 K and a general increase at high
temperatures at all the strain rates, exhibiting a ductility minima in
the intermediate temperature range. The alloy has undergone predomina
ntly transgranular ductile fracture at all strain rates and temperatur
es investigated. Yield and tensile strength of the forged tube plate m
aterial is consistently lower than the thin section bar material data.
However, the strength values were still higher than the minimum value
s proposed in the ISO specification for the thin section material. Low
er strength values of the forged tube plate material have been attribu
ted to its coarse grain size compared to that of thin section bar mate
rial.