預變形溫度對納米貝氏體相變動力學及組織的影響

預變形溫度對納米貝氏體相變動力學及組織的影響Effects of Pre-deformation Temperature on Nanobainitic Transformation Kinetics and Microstructure

采用熱模擬試驗機在300~850℃施加20%的壓縮預變形后進行300℃等溫相變實驗，研究了預變形溫度對中碳納米貝氏體鋼等溫相變動力學及組織的影響。結果表明，預變形工藝使貝氏體相變孕育期顯著縮短；低溫預變形工藝使貝氏體相變在整個等溫區間內均得到加速，高溫預變形工藝使貝氏體相變僅在等溫初期得到加速，等溫后期相變速率明顯減緩；隨預變形溫度的降低，貝氏體鐵素體板條厚度逐漸增加；預變形工藝增加了貝氏體相變組織小角度晶界的頻率，低溫預變形試樣的小角度晶界頻率高于高溫預變形試樣。利用解析相變模型計算了貝氏體等溫相變過程中的相變動力學參數n，并對貝氏體相變過程中的形核長大方式進行了判定，發現預變形工藝改變了貝氏體相變的形核位置，低溫預變形試樣主要以晶隅形核為主，高溫預變形試樣主要以晶棱、晶面形核為主。

As a new steel, nanobainitic steel has favourable strength and good plasticity, but the bainitic transformation needs a longer time, so as to severely slow production efficiency down. So, the research of acceleration methods of bainitic transformation is of significance. In our work, in order to accelerate the bainitic transformation rate, the 20% compression pre-deformation at 300~850℃ and isothermal transformation at 300℃ were conducted on a thermal simulator. The effects of pre-deformation temperature on nanobainitic transformation kinetics and microstructure of the medium carbon nanobainitic steel were investigated. The results showed that pre-deformation process obviously shortened the incubation time of bainitic transformation. Low pre-deformation temperature could accelerate bainitic transformation at whole isothermal region, while high pre-deformation temperature accelerated bainitic transformation at the initial stage, and hindered bainitic transformation at later stage. Bainitic ferrite lath thickness was increased with decreasing pre-deformation temperature. The pre-deformation process increased the frequency of small angle grain boundary of bainitic transformation microstructure, and the frequency of small angle grain boundary of low pre-deformation temperature was higher than that of high pre-deformation temperature. The kinetic parameters n of bainitic transformation was calculated by the analytical model, the model of nucleation and growth were identified, the pre-deformation process changed the nucleation position of bainitic transformation. The crystal corner nucleation was mainly obtained through low pre-deformation temperature, and the crystal edge and the crystal face nucleation were mainly obtained through high pre-deformation temperature.

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