QPT处理高强钢碳分配的定量调控机制

Quenching & Partitioning treated steel is the representative of third generation advanced high strength steels based on the transformation induced plasticity(TRIP) effect. Baosteel of China takes the lead in implementation of industrialization globally to achieve product of strength and elongation(PSE) of 20GPa%. However, quantitative regulation of carbon partitioning is not yet implemented, while carbide precipitation strengthening effect was not utilized. .The project firstly synergizes the metastable austenite TRIP effect and nano-carbide dispersion strengthened on the basis of theories of stability mechanism of sub-micro scale metastable austenite and strengthening mechanism of nano carbides. To set the PSE of 30GPa% as a goal, a series of high tech analysis methods such as EBSD and TEP thermal electrical power, analytic electron microscopy and synchrotron source X-ray diffraction etc. will be applied for in situ and quantitative studies of the microstructure evolution of multi-scale multi-phase microstructure consisting of submicron metastable austenite and nano carbides. Reasonable target microstructure for third generation high strength automobile steels will be proposed. Combined with the theory of simulation, elements design, novel QPT (T-Tempering) heat treatment will be investigated to achieve the quantitative distribution of carbon among segregation surrounding dislocations, nano carbide precipitation and in metastable austenite. Kinetics of aforementioned correlated processes and factors influencing these processes will be elucidated. .The above studies will enrich the multiphase organization design theory, for the optimization of QP steel, an achievement of new technology of QPT, the theoretical foundation for the realization of the three generation Chinese automobile steel from implementation to the invention.

QP处理高强钢是基于相变诱发塑性（TRIP效应）三代汽车用钢的代表，率先在宝钢实现全球工业化首发（强塑积20GPa%），但碳分配的定量调控尚未实现，碳化物沉淀强化作用并没有利用。本课题在亚微米尺度亚稳奥氏体稳定性机制和纳米碳化物析出强化原理基础上，以研发强塑积30GPa%碳配分钢为目标，研究亚稳奥氏体TRIP效应和纳米碳化物弥散强化的协同作用；采用EBSD、TEP热电工和消球差电镜等多种表征技术，原位研究含亚微米亚稳奥氏体和纳米碳化物的多尺度多相组织在载荷和温变情况下的演变规律；提出高强汽车用钢的合理目标组织；结合模拟和成分设计，采用QPT（Tempering）新工艺，实现碳在位错附近偏聚、纳米碳化物析出和在亚稳奥氏体相中的定量分配；阐明上述竞争又关联过程的动力学及其影响因素。上述研究将丰富多相组织设计理论，为QP钢优化，创成QPT新工艺，实现中国三代汽车高强钢从首发到首创奠定理论基础。

本项目通过模型钢实验研究结合计算模拟，研究了淬火-配分-回火（QPT）处理高强钢的组织调控机制及其与力学性能之间的相关性规律，重点研究了碳配分后形成碳化物，元素在位错、内部界面（主要为晶界和相界）偏聚，以及配分到奥氏体相等部分的定量调控机制。..运用热电功、TEM、3DAPT和XRD衍射分析等先进表征手段，研究了QPT（淬火-配分-回火）过程中碳在马氏体基体及马奥两相组织间的定量调控规律，理清了低温配分-回火阶段依赖于温度高低及时长，碳可扩散至马氏体中的位错处、在马氏体板条界面或晶界处偏聚，以及形成过渡碳化物甚至析出稳定纳米弥散分布碳化物的动力学特征。碳在马奥两相中的配分提高奥氏体稳定性并影响相界面结构，有助于TRIP效应的持续作用而显著提高强塑性。通过有限元方法、相场方法等计算模拟了碳在两相中配分的动力学特征。由模拟结果可以得到碳元素在马氏体与奥氏体间配分的整个定量演化过程。碳元素在马氏体与奥氏体间配分的定量模拟将为工艺设计提供有益的参考。..通过研究MnB-SiV钢的QPT过程，解释了V纳米碳化物析出和碳在亚稳奥氏体相中的定量分配这两个既竞争又关联过程间的影响规律。通过成分设计（QP-10NiNb钢）获得新型QPT钢（马奥组织+NbC弥散析出相），运用亚微米亚稳奥氏体和纳米碳化物的多尺度多相增强增塑原理，QPT模型钢的强度达到了2GPa,延伸率21.4%，远超目标强塑积30GPa%。..通过项目研究，丰富了多相组织设计精准调控理论，为QP钢优化，创成QPT新工艺，部分成果应用到工程实践，为我国三代汽车高强钢从首发到首创奠定理论基础。发表标注基金资助的学术论文29篇，其中SCI检索论文28篇，结合项目培养博士和硕士各3名，参与国际学术交流6次，国内学术交流2次。取得了项目预期成果和效果。