高强韧中锰钢的变形机理及成型性研究

  工业的发展离不开钢铁材料的支撑。然而，我国的高端特种钢材仍然依赖于进口。作为第三代汽车用先进高强钢的一种，中锰钢因其优异的综合力学性能，已成为近年来钢铁材料领域的研究热点。对于高强韧中锰钢的研发是补齐我国工业短板，助力我国经济高质量发展的重要一环。针对高强韧中锰钢变形机理及成型性的研究，有助于更好开发下一代高强韧钢以及服务于其应用。

  本论文使用两种中锰钢材料分别分析了其强化机制和成型性。合金设计基于位错工程理念，即高位错密度可以同时引起高强度高延展性，以及马氏体时效钢中纳米析出相强化的理念。通过优化合金元素比例和价格，开发了一种质量分数为Fe-12Mn-3Ni-3Al-4Mo-0.01B的中锰钢。设计了一系列工艺路线，通过轧制工艺调控中锰钢的奥氏体体积分数。冷轧提高了中锰钢的位错密度，固溶处理和时效工艺获得高密度的纳米析出相从而产生强化效果。拉伸测试结果表明，温轧、冷轧工艺及480°C的6小时时效处理的钢获得了较优的力学性能，其马氏体的体积分数高达86.3%。马氏体基体中可以观察到大量纳米析出相，促进其屈服强度和极限抗拉强度分别达到了1845 MPa和2030 MPa。基于同步辐射XRD的测试结果，计算了样品时效前后马氏体基体中的位错密度，定量分析了不同强化机制对中锰钢屈服强度的贡献。结果表明，轧制工艺之后高密度位错是该中锰钢的主要强化机制，而时效后析出强化成为了该中锰钢中的主要强化机制，对屈服强度贡献了约917 MPa。

  基于质量分数Fe-10Mn-0.2C-2Al-0.1V的中锰钢，开展了双相区退火、双相区退火-淬火配分两种工艺热处理并研究其成型性。通过组织演变和拉伸测试得到的力学性能指标，包括强度、延伸率、应变硬化系数及塑性应变比等，从多个角度评估了其成型性。实验结果表明，双相区退火中锰钢在保持相似各向异性性能的同时具有更好的加工硬化能力和更高的延伸率，因而具有更好的成型性，为今后的工业化生产提供了参考。

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