The mechanism of effect of isothermal temperature on banded structure is delved by calculation of ferrite incubation period and nucleation rate

and the evolution of banded structure in sample of gear steel SAE8822H (/% : 0. 22C

0. 20Si

0. 98Mn

0. 60Cr

0. 46Ni

0. 36Mo) heated in tube furnace at 930 ℃ for 10 min and isothermal-treated at 703 -579 ℃ for 1 h

air cooling

or isothermal-treated at 710 ~ 570℃ for 2 h

furnace cooling is observed. Results show that the difference of incubation period and difference of nucleation rate of ferrite between solute-depleted zone and solute-richened zone are the causes to produce banded structure ； with decreasing the isothermal temperature

the difference of incubation period between solute-depleted and solute-richened zone reduces and the relative nucleation rate also decreases

lead to relieving the banded structure of steel； for steel SAE8822H

isothermal treatment at 570 ℃ is available to e- laminate banded structure

in this case the relative nucleation rate is 6.3%.