通过热力学软件计算、组织观察以及显微硬度测定,研究固溶温度为850～1200℃时403Nb耐热钢中析出相的溶解与析出行为。结果表明：该耐热钢在高温下主要存在M23C6和MX两种类型碳化物;其中,M23C6型碳化物在900℃左右就完全溶解,而MX型碳化物则相对较稳定,在固溶温度超过1000℃时才开始缓慢溶解。随着固溶温度的升高,MX型碳化物颗粒逐渐减少且颗粒平均尺寸不断长大,但其中非平衡成分的低Nb含量MX型碳化物不断溶解,而平衡成分的高Nb含量MX型碳化物则不断长大。在固溶温度为1150℃时,403Nb钢中开始析出对性能不利的δ铁素体,且随固溶温度的升高,δ铁素体含量逐渐增多。
The dissolving and precipitation behaviors of precipitated phases in a martensitic heat-resistant steel 403Nb were investigated at the solution temperature ranging from 850 ℃ to 1200 ℃ by thermodynamic calculation,microstructural observation and micro-hardness test.The results show that two kinds of carbides exist in the steel at elevated temperatures,i.e.M23C6(M=Cr,Fe) and MX(M=Nb,Cr,Fe and X=C).The carbide M23C6 is completely dissolved at solution temperature of about 900 ℃.The MX carbide is more stable than M23C6 and begins to dissolve slowly at the solution temperature higher than 1000 ℃.The number of MX particles decreases and the average size increases with increasing solution temperature.When the solution temperature increases,the non-equilibrium MX carbide with low concentration of Nb is gradually dissolved,whereas the equilibrium MX particles with high Nb concentration are coarsened.Delta ferrite is observed to be precipitated in 403Nb alloy solution-treated at 1150 ℃ and the amount of precipitated delta ferrite increases with increasing solution temperature.Delta ferrite is detrimental to the mechanical properties and should be strictly controlled in 403Nb alloy.
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