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首页> 外文会议>International Conference on Microalloying for New Steel Processes and Applications; 20050907-09; Basque Country(ES) >Microstructure Evolution in Fine-Grained Microalloyed Steels
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Microstructure Evolution in Fine-Grained Microalloyed Steels

机译：细晶粒微合金钢的组织演变

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摘要

There is an increasing emphasis to develop novel hot-rolled high strength steels with fine and ultra fine grain sizes for structural and other applications. Traditionally the concept of microalloying has been employed to refine microstructures thereby obtaining increased strength levels. For example, employing an alloying strategy with Nb, Ti and Mo is promising to attain yield strength levels of 700MPa and beyond. In the present study, the transformation behaviour is investigated for a HSLA steel containing 0.05wt%C-1.65wt%Mn-0.20wt%Mo-0.07wt%Nb-0.02wt%Ti. The ferrite formation from work-hardened austenite has been studied for simulated run-out table cooling conditions employing a Gleeble 3500 thermomechanical simulator equipped with a dilatometer. The effects of cooling rate and initial austenite microstructure, i.e. austenite grain size and degree of work hardening, on the austenite decomposition kinetics and resulting ferrite grain size have been quantified. Based on the experimental results, a phenomenological transformation and ferrite grain size model is proposed for run-out table cooling conditions. The transformation model includes submodels for transformation start and ferrite growth. The latter is described using a Johnson-Mehl-Avrarni-Kolmogorov approach. The degree of work hardening is incorporated by introducing an effective austenite grain size as a function of the strain applied under no-recrystallization condition. The ferrite grain size can be predicted as a function of the transformation start temperature. Increasing both cooling rate and amount of work hardening can optimize ferrite grain refinement. In the present steel, ferrite grain sizes of as low as 2μm have been obtained in this way. The results observed for the present steel are compared to the transformation behaviour in previously studied Nb-Ti HSLA steels of similar strength levels.
机译：人们越来越重视开发具有细晶粒和超细晶粒尺寸的新型热轧高强度钢，以用于结构和其他应用。传统上，已经采用微合金化的概念来细化微结构，从而获得提高的强度水平。例如，采用与Nb，Ti和Mo的合金化策略有望达到700MPa甚至更高的屈服强度水平。在本研究中，研究了含有0.05wt％C-1.65wt％Mn-0.20wt％Mo-0.07wt％Nb-0.02wt％Ti的HSLA钢的相变行为。已经使用配备了膨胀计的Gleeble 3500热机械模拟器对模拟淬火工作台冷却条件研究了由加工硬化奥氏体形成的铁素体。已经量化了冷却速度和初始奥氏体组织，即奥氏体晶粒尺寸和加工硬化程度对奥氏体分解动力学和所得铁素体晶粒尺寸的影响。根据实验结果，提出了一种用于跳动台冷却条件的现象学转变和铁素体晶粒尺寸模型。转换模型包括用于转换开始和铁素体生长的子模型。使用Johnson-Mehl-Avrarni-Kolmogorov方法描述了后者。通过引入有效的奥氏体晶粒尺寸，作为在无再结晶条件下施加的应变的函数，可以引入加工硬化程度。铁素体晶粒尺寸可以根据转变开始温度来预测。增加冷却速率和加工硬化量可以优化铁素体晶粒细化。在这种钢中，以此方式获得了低至2μm的铁素体晶粒尺寸。将本钢观察到的结果与强度相似的先前研究的Nb-Ti HSLA钢的相变行为进行了比较。

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