The effect of aging at 700 T for 0 ~ 3 000 h on ambient tensile properties of Φ57 mm x 9. 7 mm seamless tube steel S31042 （% : 0.06C

0. 35Si

1. 18Mn

24. 50Cr

20. 54Ni

0.40Nb

0.23N） has been studied. Results show that as aging for 0 - 1 000 h

with increasing aging time the yield strength （R

p0.2

） and tensile strength （ R

m

） of steel S31042 rapidly increase

but the elongation （A） and reduction of area （Z） of steel quick decrease； as aging for more than 1 000 h

the variation of each property index is tending slow； with increasing aging time

the morphology of ambient tensile fracture gradually transforms from tough fracture with enriching dimples to brittle intercrystalline fracture ； as aging for 0 ~ 1 000 h

with increasing aging time the amount of Cr

23

C

6

phase at grain boundary rapidl

y increases

and as aging time more than 1 000 h

the change of amount of precipitates at grain boundary is not obvious.