Large heat-input welding steel is widely used in shipbuilding, ocean engineering, bridge manufacturing, crude oil storage tanks and other fields. Large heat-input welding technology of thick plates effectively saves costs and improves production efficiency, which is a key research direction that attracts much attention in the welding field at present. The welding joint is the weakest link and the performance of HAZ, especially CGHAZ, is one of the important indexes to evaluate the welding performance. Therefore, the control of CGHAZ miscrostructure and performance is an important research direction in this field. Acicular ferrite is the main microstructure in the coarse grain heat affected zone (CGHAZ) of large heat-input welding steels based on oxide metallurgy process. The interlocking microstructure of acicular ferrite effectively ensures the toughness of CGHAZ. How to effectively control the formation of acicular ferrite is the key to the development of steels for large heat-input welding. The formation mechanism of acicular ferrite has not been unified and the influencing factors are complex. The formation mechanism of acicular ferrite is different and the combination of multiple nucleation mechanisms is possible. The main influence factors of the formation of acicular ferrite are directly related to the characteristics of inclusions in steels. By improving the size, morphologies and distribution of inclusions in steels, the nucleation rate of acicular ferrite could be improved. The interlock microstructure of acicular ferrite effectively guarantees the toughness of CGHAZ. The effective control technology of acicular ferrite formation process is not only the key to the continuous improvement of toughness in CGHAZ, but also the critical factors of the development of high-strength easily welded plate products. In additon, it is closely related to the deve-lopment of non-preheating supporting welding materials, which becomes the main research direction in this fields. Based on the key information of many references in this related fields, the development process of acicular ferrite control technology in CGHAZ for large heat-input welding is summarized in this paper, the nucleation mechanism and influence factors of acicular ferrite in CGHAZ are discussed and the main research results in related fields are listed. This paper provides useful reference data for technical research and product development of large heat-input welding steels. © 2022, Materials Review Magazine. All right reserved.
