新型汽车用Q&P钢的研究现状与发展趋势

Research Status and Development Trend of New Automotive Q&P Steel

随着大气环境问题的日益加剧且全球范围面临着能源危机,在未来的几十年里,节能减排仍然是全球性的研究主题。汽车行业被要求在不降低安全性的前提下减轻车身质量,以达到节能减排的目的。汽车的轻量化推动先进高强钢从第一代发展到如今的第三代。先进高强钢主要通过合金成分设计、热轧、冷轧、热处理等工艺的配合对其微观结构进行调控来实现轻量化和安全性,且其内部变形机制研究更有助于把握性能调控过程。第一代、第二代汽车用钢的弊端主要有以下两方面:一方面,主要以铁素体等软相作为基体,导致钢的综合力学性能差,难以实现真正的轻量化;另一方面,第二代汽车钢性能的提升是以大量合金元素的添加为代价,生产成本较高,而且在商业化大生产当中铸造、热处理等工艺难以精细控制,存在诸多弊端。因此,第三代汽车钢得到良性的发展,其综合力学性能填补了第一代与第二代汽车钢之间的空白。Q&P钢作为典型代表,利用淬火-配分工艺,对多相、亚稳态和多尺度的微结构进行精细控制,可以获得马氏体、铁素体和奥氏体的混合组织。与第二代相比,第三代汽车钢的合金元素含量更低,满足了降低成本的要求。面心立方(FCC)与体心立方(BCC)的混合结构使得第三代汽车钢具有高强塑积(抗拉强度×延伸率)的特点,它的性能已接近时代汽车用钢的目标水平。本文概述了新型汽车用Q&P钢的发展历程,介绍了合金元素的作用、成型时的回弹,按照热处理工艺参数顺序(加热温度、淬火温度、配分温度、配分时间)阐述了工艺优化的内在原理。总结了塑性变形的强韧机制——“四种效应、两种机制”,思考了Q&P钢动态力学性能对工程实际应用的重要性,根据重大研究成果提出新的Q&P钢强化建议——晶界相变强化。最后描述了当前Q&P钢基础理论研究和工业化发展所面临的问题,并对该领域进行了展望。

With the increasing of atmospheric environmental problems and the global energy crisis,energy conservation and emission reduction will remain a global theme in the coming decades.The automotive industry is required to reduce body weight without reducing safety in order to achieve the goal of energy saving and emission reduction.The lightweight of automobiles has promoted the development of advanced high-strength steel from the first generation to the third generation today.Advanced high-strength steel is mainly through the combination of alloy composition design,hot rolling,cold rolling,heat treatment and other processes to adjust its microstructure to achieve lightweight and safety,and its internal deformation mechanism research is more helpful to grasp the performance control process.The disadvantages of the first and second generation automobile steels mainly include the following two aspects:On the one hand,the main use of ferrite and other soft phases as the matrix leads to poor comprehensive mechanical properties,making it difficult to achieve true weight reduction;on the other hand,the second the improvement of the performance of the automotive steel is at the expense of the addition of a large number of alloying elements,which increases the production cost,and it is difficult to finely control the casting and heat treatment processes in the commercial production,and there are many disadvantages.Therefore,the third-generation automotive steel has achieved sound development,and its comprehensive mechanical properties have filled the gap between the first and second-generation automotive steels.As a typical representative,Q&P steel uses the quenching-partitioning process to finely control the multi-phase,metastable and multi-scale microstructure,and obtain a mixed structure of martensite,ferrite and austenite.Compared with the second generation,the third generation automobile steel has a lower alloying element content,which meets the requirements of reducing costs.The hybrid structure of FCC and BCC brings the characteristics of high-strength plastic product(tensile strength×elongation),which makes the performance of the third-generation automobile steel close to the target level of the times.This article summarizes the development history of new Q&P steels for automobiles,introduces the role of alloying elements,springback during forming,and explains the internal principles of process optimization according to the order of heat treatment process parameters(heating temperature,quenching temperature,distribution temperature,distribution time).Summarized the toughness mechanism of plastic deformation-“four effects,two mechanisms”,considered the importance of dynamic mechanical properties to practical engineering applications,and put forward new Q&P steel strengthening recommendations based on major research results-grain boundary phase transformation strengthen.Finally,it describes the problems facing the current development and looks forward to the field.