奥氏体变形对低碳Mn-B-Nb-Ti钢连续冷却相变的影响

EFFECT OF AUSTENITE DEFORMATION ON CONTINUOUS COOLING TRANSFORMATION FOR A LOW CARBON Mn-B-Nb-Ti STEEL

采用热模拟实验技术、结合维氏硬度测试结果建立了一种低碳Mn-B-Nb-Ti钢的未变形奥氏体CCT曲线和在850℃经50％变形的变形奥氏体CCT曲线．利用光学显微镜、金属薄膜电子显微分析技术研究了冷却速度、变形对显微组织的影响结果表明，微量硼提高了过冷奥氏体的稳定性；随着冷却速度逐渐降低，未变形试样的组织由型贝氏体向型贝氏体变化；变形诱发Nb的用-碳-氮化物析出，提高贝氏体相变温度，促进型贝氏体转变；变形奥氏体的位错缠结抑制贝氏体长大，从而细化转变后的显微组织.

The continuous cooling transformation (CCT) diagrams of austenite non-deformation and 50% compressively deformed at 850 ℃ were constructed by means of a combined method of dilatometryand Vickers hardness measurement for a low carbon Mn-B-Nb-Ti steel. OM and TEM were employed to investigate the induence of cooling rate and deformation process on the transformation behavior and microstructure. The hardenability of austenite is enhanced by the addition of boron. The microstructure changes from Bc2 type bainite(upper bainite) to Bp3 type bainite in non-deformed austenite with decreasing the cooling rate. Plastic deformation on austenite induced niobium borocarbonittide precipitation and promoted both bainite transformation at higher temperature than that in undeformed austenite inducing Bm3/a type bainite formation and stifled the growth of bainitic ferrite by tangled dislocations resulting the refinement of microstructure.