微量元素和变形条件对超细晶中厚板显微组织的影响

Effects of microalloying element and deformation condition on microstructure of ultrafine-grained medium and heavy plate

通过对3种不同铌、钒含量的低碳钢进行多道次热压缩变形以模拟中厚板的超细晶轧制工艺，考察了显微组织演变过程、微合金元素和变形条件对组织演变的影响。结果表明：变形过程中有部分奥氏体通过形变诱导相变转变为铁素体；变形并快速冷却后得到平均晶粒尺寸为3～6μm的超细晶组织．铌促进、钒抑制形变诱导铁素体相变，铌、钒微合金化均有较好的细化作用，铌的作用优于钒．再结晶温度以上进行的粗轧有利于精轧时形变诱导铁素体的形成；在精轧温度范围内，增加变形道次、降低道次应变率有利于获得细化的显微组织；降低终轧变形温度对组织细化是最有效的．

Microstructure evolution, effects of deformation condition and microalloying element on microstructure were investigated through multi - pass hot compression on three mild steels with Nb or V doped to simulate the rolling process of medium and heavy plate. The experimental result showed part of austenitic transformed into ferrite during deformation through deformation induced ferrite transformation （DIFT） , and ultafine - grained microstructures of 3 - 6 μm in grain sizes were achieved after multi-pass deformation and fast cooling. The DIFT was expedited by Nb - doping and inhibited by V-doping. The microstructures were refined by both Nb and V microalloying, and the gain refinement effect of Nb was better than that of V. The DIFT took place during finish rolling was promoted by rough rolling undertaken at elevated temperature. Grain refinement can be achieved by increasing the deformation pass and reducing the pass strain during finish rolling. The most effective approach for grain refinement is to lower the finish rolling temperature.