低碳高强Q&P钢制备过程中的合金元素配分控制及组织演变规律研究

In recent years, in order to answer the environmental problem of automobile making and enhance the safety properties of car crash, the researcher at home and abroad put forward a new technology for heating processing that Quenching and Partitioning to product third generation high-strength steel, and studied the partion mechanism of C alloy. However, it is very important that alloying elements to microstructures and mechanical properties of Q&P steel. At present， the study is not systematic that the influence of the partion mechanism of alloying elements on the mechnical stability of retained austenite at room temperature. It is the require immediately solution scientific problem that study on the influence mechanism of materials microstructure, grain size, feature and dislocation configuration the alloying elements spread partition in two-phase boundary，and the study on which alloying element is improtant to partitioning and the relation between the alloying and C element partitioning in prodution technology and heating processing technology of Q&P steel. Thus, there are important theoretical significance and practical value that the study on alloying elements partitioning technology and microstructure controlled to enhance the content of retained austenite and mechanical stability of low carbon high-strength steel is suitable for research welding performance and high-strength and high-obdurability of Q&P steel.

为应对汽车制造和使用过程中的环境和安全问题，近年来，国内外研究者提出了一种新颖的热处理工艺-淬火（Quenching）+碳配分（Partitioning）生产第三代高强钢，并对碳配分机制进行了研究，但对合金元素在高强钢中的配分机制及其对室温残余奥氏体机械稳定性的影响，目前尚未有系统性的研究。合金元素对于高强钢中的显微组织和力学性能具有重要影响，因此，结合新一代高强钢的生产工艺与热处理制度，研究合金元素配分机制以及合金元素配分与碳配分二者间的相互影响规律，探索材料显微组织结构、晶粒尺寸、形貌以及位错组态等对合金元素在两相界面间进行扩散配分的影响机理，揭示何种合金元素能够在其中发挥最佳的配分作用，都是亟待解决的科学问题。围绕提高低碳高强钢显微组织中残余奥氏体含量及机械稳定性等关键问题，开展合金元素配分工艺及显微组织控制研究，对开发具有良好焊接性能和高强韧性的Q&P钢具有重要理论意义和应用价值。

高强钢中的碳含量必须控制在较低的水平以保证良好的焊接性能，但是，这会影响碳配分的作用和残余奥氏体稳定性，导致强塑积的降低。因此，本工作提出采用合金元素（如锰）配分作用来部分代替碳配分，以提高高强钢的残余奥氏体稳定性和焊接性能。针对低碳硅锰钢，采用在双相区保温、奥氏体化、淬火配分等新热处理工艺：I&Q&P，研究高强钢的Mn配分行为及对残余奥氏体和力学性能影响。结果表明，试验用钢经双相区保温时，Mn元素随着保温时间的延长，从铁素体向奥氏体中的配分含量不断增加，Mn元素在720℃和760℃达到化学势平衡所需的保温时间分别为1500s和1300s。与传统Q&P工艺对比，利用I&Q&P热处理工艺得到的高强钢的伸长率提高了4%，强塑积提高了20%，钢中残余奥氏体由富Mn的残余奥氏体和经C配分作用稳定的残余奥氏体组成，显著提高室温下钢中残余奥氏体的含量和机械稳定性。当实验用钢经I&Q&P二步法处理时，室温组织中二次淬火马氏体含量几乎全部消失，富锰的残余奥氏体能稳定到室温，而经该工艺处理后钢的抗拉强度为1240~1480MPa，伸长率12.9%~23.3%，强塑积高达25000MPa•%以上。