等温温度对低碳齿轮钢带状组织的影响

通过计算铁素体形核孕育期和形核率探讨了等温温度对带状组织的影响机理,并观察了齿轮钢SAE8822H(/%:0.22C、0.20Si、0.98Mn、0.60Cr、0.46Ni、0.36Mo)在管式炉经930℃10 min降至703～579℃等温1h空冷,或710～570℃等温处理2 h炉冷后钢中带状组织演变。结果表明,贫、富溶质区铁素体形核孕育时间差和铁素体形核率差异是造成等温转变时产生带状的原因;等温温度降低时,贫、富溶质区的孕育期时间差缩短,相对形核率减少,带状减轻;齿轮钢SAE8822H在570℃等温可使带状组织消失,这时相对形核率为6.3%。

Effect of Isothermal Temperature on Banded Structure in Low Carbon Gear Steel

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 eliminate banded structure,in this case the relative nucleation rate is 6.3%.