The effect of solution treatment at 1 050 - 1 150℃ on structure and mechanical properties of 1. 0 mm cold rolled plate of nickel base alloy 690 (% ： 0. 020C

29. 93Cr

9. 82Fe

0. 19A1

0. 25Ti

0. 023Nb

0. 012Mo

0. 004 2N) melted by a 20 kg vacuum induction furnace has been studied. Results show that with increasing temperature of solution treatment from 1 050 Y to 1 100 ℃ the average grain size of steel linearly increases from 12 μm to 29 μm

with the temperature being more than 1 100 °C

the grain size increases rapidly and the average grain size is up to 58 at 1 150 ℃； as solution treatment temperature is more than 1 090 °C

the chromium-rich carbides in alloy dissolve completely; the fine grained strengthening is main strengthening mechanism of alloy 690

with increasing solution temperature

the ambient tensile and yield strength of alloy decrease respectively from 780 MPa and 400 MPa to 662. 5 MPa and 250 MPa

while the elongation of alloy increases from 40% to 51. 75%.