用PTA法研究了Fe-30％Nj合金中硼在晶界的偏聚行为.实验表明,在550—1200℃保温后,用不同方式冷却的试样中存在有平衡与非平衡两类硼偏聚,其形成机制各不相同,而且试验条件的影响亦不同.保温时形成的平衡偏聚在低温淬火试样中起主要作用.在高温加热后,用通常冷速冷却时,晶界偏聚主要来源于冷却过程中产生的非平衡偏聚.实际试样中观察到的硼偏聚是这两类偏聚的叠加,主要偏聚方式的转折温度区受冷却速度影响,在中等冷速下,这个转折温度在650—750℃之间。
It has been considered that the boron segregation at austenite grain boundaries is responsible for the effect of boron addition on the properties of the steel, such as hardenability, creep fracture, etc. By means of particle tracking autoradiograph(PTA) the grain boundary segregation of boron has been investigated in Fe-30% Ni alley, quenched from 550—1200℃ at different cooling rates. It is shown that two kinds of grain boundary segregation, equilibrium and nonequilibrium segregation, caused by different mechanisms take place. The nonequilibrium grain boundary segregation during cooling with boron depleted zone adjacent to the grain boundary is very sensitive to the cooling rate, and can be inhibited by rapid quenching. The temperature effect on these two kinds of grain boundary segregation are different, As the quenching temperature increases, the grain boundary segregation of boron due to equilibrium adsorption decreases, while the nonequilibrium segregation kinetically increases. The nonequilibrium segregation therefore dominates in the specimens quenched from high temperatures; and the equilibrium segregation in those cooled from low temperatures. In this work, the transition temperature lies in the range of 650—750℃, increasing with enhancing cooling rate.
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