ULCB钢焊缝相及组织控制研究

For the reason of obtaining by thermomechanical of welding procedures, the mis-matched weldment and its mechanical properties, which is used to 21st century new type ultra low carbon bainite steel (ULCB), is difficult to fit to the base steel. However, concetrating on the properties of the matched weldment that is matched to ULCB base steel, considering to the nonuniform temperature field of submerged arc welding and the particularity of welded microstructure solidification, the project will try to propose and design one kind of welded microstructure and polyphase as lath bainite (LB), acicular ferrite (AF), granular bainite (GB) in dispersion distrbution form and low carbon martensite (M) as the welded microstructure. Forther more, with the aim at internal nature of science of fortitude refining, the acquisition path of the complex polyphase will be analysed deeply to disclose which is combined with welding heat simulation technology and cellular automaton method. With that bases, the interse relation rule among the polyphase choice of different microstructure and fortitude refining mechanism of weldment, compound mode of different complex polyphase and its proportion, different transition alloy elements of welding material and its content with macroscopic mechanical properties will be clarified. And more, the mathematical relation model and choice of polyphase and servo control of microstructure in welded seam of ULCB steel will be realized and established also. As an important purpose, the theoretical basis and technologic support, which is given to choice of polyphase and control of microstructure in welded seam, alloy design of welding materials and the prediction of mechanical property, will be provided for the project accomplishment.

21世纪新型控轧控冷超低碳贝氏体钢（ULCB）焊态条件下的焊缝组织及其力学性能无法匹配母材基体是一个亟待解决的重要课题。本项目以ULCB钢为载体，从埋弧焊非均匀温度场与焊缝组织凝固过程的特殊性出发，提出板条贝氏体（LB）、针状铁素体（AF）、弥散分布粒状贝氏体（GB）及低碳马氏体（M）多元复合相作为焊缝微观组织设计相，结合焊接热模拟技术和元胞自动机方法，对所提出复合相获得途径进行深入分析，揭示复合相强、韧/细化的内在科学本质。在此基础上，进一步澄清不同焊缝组织相选择及强、韧/细化机理、不同微观复合相组合方式及相比例、不同焊材合金过渡元素及含量与宏观力学性能之间的相互影响关系规律，并建立相应的数学关系模型，最终实现ULCB钢焊缝相选择及组织的伺服控制。项目的完成将为ULCB钢的焊缝相选择与组织调控、焊材合金系设计及力学性能预测提供理论依据和技术支撑。

21世纪新型控轧控冷超低碳贝氏体钢（ULCB）焊态条件下的焊缝组织及其力学性能无法匹配母材基体是一个亟待解决的重要课题。本项目以ULCB钢为载体，从埋弧焊非均匀温度场与焊缝组织凝固过程的特殊性出发，提出板条贝氏体（LB）、针状铁素体（AF）、弥散分布粒状贝氏体（GB）及低碳马氏体（M）多元复合相作为焊缝微观组织设计相，结合焊接热模拟技术和元胞自动机方法，利用MATLAB软件得到了焊接接头瞬时温度场的二维、三维视图，分析了焊接热源功率和焊接速度对温度场分布的影响，得出了晶体生长与温度场之间的关系，并提出复合相的获得途径，初步总结了贝氏体相变的演化机理。.对焊接接头相组织、相比例进行了分析，研究表明：当焊缝中AF含量达到30%时，韧性发生突变，有较大的增幅；当AF大于30%时，焊缝的冲击韧性随着AF比例的增大而增大。随GB含量的增加，抗拉强度呈先上升后降低的趋势。根据分布图拟合出GB与抗拉强度的关系式：y=507.153+11.875x-0.12x2。焊缝针状铁素体晶粒取向在某些晶体学方向上存在取向择优，各针状铁素体之间呈大角度晶界，具有较强的抗裂纹扩展能力，是主要的韧性相。粒状贝氏体作为强化相，则通过组织强化、固溶强化、位错强化、析出强化和细晶强化来增加焊缝强度。.分析了焊缝中合金元素对组织及性能的影响，结果表明：随B的升高，接头抗拉强度呈先急剧增加后缓慢增加的趋势；随Mn当量的增加，接头强度先呈现出增大后不变的趋势；随Al的增加，焊缝中的针状铁素体含量呈先增大再降低的趋势。.自主研发了ULCB用CaF2-MgO-Al2O3-CaO-MnO2渣系焊剂和Mn-Ni-Mo-Re-B合金系焊丝。实际施焊后，获得以AF和GB为主，以及少量LB和多边形铁素体（QF）的复合焊缝组织。焊接接头最高抗拉强度达853.7MPa，为母材的94.71%，冲击功大于120J，剪切面积百分比平均值为85%。焊缝区和HAZ的冲击吸收功和剪切面积随热输入的增加而减小。.本项目澄清了不同焊缝组织相选择及强、韧/细化机理、不同微观复合相组合方式及相比例、不同焊材合金过渡元素及含量与宏观力学性能之间的相互影响关系规律，并建立了相应的数学关系模型，最终实现了ULCB钢焊缝相选择及组织的伺服控制。本项目的完成将为ULCB钢的焊缝相选择与组织调控、焊材合金系设计及力学性能预测提供理论依据和技术支撑。