超低碳贝氏体高强钢焊接熔敷金属复相分割微观结构及强韧化机理研究

The new generation of high strength steel has evolved to ultra-fine grain with high cleanliness, high uniformity, and high strength and toughness. However, its development and application are restricted due to the lack of the corresponding welding consumables with the equal strength and toughness match. The main reason is that the current strengthening and toughening mechanism of weld deposited metal of welding consumables has been unable to meet the development of high strength steel. This project focuses on the theory of the strengthening and toughening mechanism of weld deposited metal of new welding consumables, that is, the multiphase segmentation and control of microstructure. The alloy system of weld deposited metal will be optimal designed with Design-Expert soft. The effects of alloy elements on the multiphase segmentation microstructure, and the formation and evolution of microstructure will be investigated. Moreover, the effects of welding processes with or without extra energy on the microstructure of weld deposited metal will be investigated during the crystallization, solidification and solid-state phase transformation of welding pool. The role of multiphase segmentation microstructure and its effect on the strengthening and toughening of weld deposited metal for high strength steel will be discussed. In addition, the effect of the formation of coalesced bainite on the strengthening and toughening mechanism of weld deposited metal will also studied. This project will provide the new theoretical basis and experiment instruction to design various welding consumables, and strengthen and toughen weld deposited metals for 690-1200 MPa grade ultra low carbon bainitic high strength steels. It is of significance to promote the development of basic theory of welding metallurgy, and enlarge its application of high strength steel.

新一代高强钢具有超细晶、高洁净度、高均匀性和高强韧性等特性，但由于缺乏与之配套的等强韧性焊材，使其发展和应用受到限制。其根本原因是现有焊材熔敷金属强韧化机制已不能适应高强钢的发展。本项目就新型焊材焊接熔敷金属强韧化理论，即微观结构的复相分割与控制机制进行研究：1）采用Design-Expert对焊接熔敷金属合金系优化设计，搞清合金元素交互作用及对复相分割微观结构及其组织形成与演变规律；2）研究焊接熔敷金属在焊接自身工艺和外加能量及其耦合条件下对熔池结晶凝固和固态相变过程中微观组织演变的影响，探讨其复相分割微观结构的作用及对强韧性的影响；3）研究焊接熔敷金属中复合贝氏体的产生条件、影响因素及其对强韧性的影响。本项目为解决制约690-1200 MPa超低碳贝氏体高强钢应用急需配套的焊材设计及其焊接熔敷金属强韧化提供新的理论依据和实验指导，对促进焊接冶金基础理论发展及扩大高强钢应用具有重要意义。

专用于焊接690MPa级以上超低碳贝氏体高强钢焊接材料的缺乏已成为制约新一代高强钢结构发展和应用的瓶颈。其根本原因是现有焊材熔敷金属强韧化冶金机理的研究已不能适应当代高强钢的发展。.本项目开展超低碳贝氏体高强钢焊接熔敷金属复相分割微观结构及其强韧化机理研究，获得以下成果：（1）采用Design-Expert对焊接熔敷金属合金系优化设计，搞清了合金元素交互作用及对复相分割微观结构及其组织演化规律，获得了主合金系（C、Mn、Si等）、次合金系（Cr、Ni、Mo等）和微合金元素（Zr、Ti、Ce等）对熔敷金属力学性能的影响规律。结果表明：降低C含量并优化Mn、Si、Cr等合金元素配比可提高熔敷金属的强韧性。配方（C0.02wt.%，Mn1.94wt.%，Si0.64wt.%），（Cr0.20wt.%，Mo0.54wt.%，Ni2.46wt.%）和（Zr0.077wt.%，Ti0.040wt.%，Ce0.033wt.%）具有最佳的强韧性匹配。（2）开展调节焊接工艺参数和外加能量场条件下，熔池结晶凝固和固态相变过程中微观组织演变影响的研究，研究了“复相分割微观结构”的形成机制和作用及其对熔敷金属强韧性的影响。结果表明：90%Ar+10%CO2和75%Ar+25%CO2两种保护气体条件下，熔敷金属中均获得了复相分割微观组织，降低热输入，可以避免晶粒粗化，获得较高的强韧性；当t8/5处于6~12s时，模拟粗晶区冲击韧性优良；采用外加超声振动可以有效的细化晶粒，提高熔敷金属冲击韧性。（3）研究了熔敷金属中复合贝氏体的产生条件、影响因素及其对强韧性的影响。结果表明：Ni、Mn元素以及其他固溶原子元素的偏析会促进联合贝氏体形成，粗大的微观组织会显著降低熔敷金属韧性。在对安全性要求极其高的690MPa级以上高强钢焊接结构中，应尽量避免联合贝氏体的出现。.项目研究凝练了超低碳贝氏体高强钢熔敷金属强韧化冶金机理，填补690-1200MPa级别焊装钢结构专用焊材空白。相应的成果为超低碳贝氏体高强钢焊材设计提供理论依据和工程应用参考，对促进焊接冶金基础理论发展及拓展高强钢焊装结构更广泛的工程应用具有重要意义。