石化容器用2.25Cr-1Mo-0.25V钢的CMT电弧熔丝增材制造工艺及组织性能研究

为探索大型石化筒体根部止口的制造新工艺，采用新研发的2.25Cr-1Mo-0.25V合金丝材，使用CMT电弧熔丝增材制造技术首次堆积2.25Cr-1Mo-0.25V直壁墙，探索增材后的最佳热处理工艺，以改善沉积态显微组织与力学性能。实验发现：增材成形的直壁件内部微观组织主要为板条贝氏体、粒状贝氏体和部分马氏体，堆积方向组织差异明显，显微硬度浮动剧烈，拉伸强度远高于母材，但断裂延伸率较低。对增材后的直壁件施加“消氢处理+去应力处理”和“模拟最小焊后热处理”，发现后者能将其塑性提升至与母材相当。根据显微组织分析，经过“最小焊后热处理”，沉积态的板条贝氏体和部分马氏体可转变成均匀分布的粒状贝氏体，组织间的各向异性显著降低。实验证明，应用新研发的2.25Cr-1Mo-0.25V丝材在最佳的CMT电弧熔丝增材工艺参数下成形直壁件并结合“最小焊后热处理”能够最大程度地改善显微组织和力学性能，最终满足石化容器筒体根部止口的服役指标。相比浇铸-锻造成形止口的工艺，开发的CMT电弧熔丝增材新工艺有望大幅节约生产成本，提高制造效率。

Study on Microstructure and Mechanics Properties of 2.25Cr-1Mo-0.25V Steel Fabricated by CMT Wire ARC Additive Manufacturing for Petrochemical Vessels

In order to explore the new manufacturing processes of large petrochemical cylinder root edges， a newly self-developed 2.25Cr-1Mo-0.25V flux-cored wire was firstly used to deposit 2.25Cr-1Mo-0.25V straight-walls based on cold metal transfer and wire arc additive manufacturing（CMT-WAAM）， and the best post-weld heat treatment was explored to improve microstructure and mechanics properties. The experimental results show that the internal microstructure of the straight-walls deposited by CMT-WAAM are mainly composed of lathy bainite， granular bainite and some martensites， with obvious differences in the building direction， dramatic floating micro-hardness and much higher tensile strength than that of the base metal， but lower fracture elongation. After applying “hydrogen elimination treatment+stress relief treatment” and “simulated minimum post-weld heat treatment” on the deposited walls， the latter was found to increase the plasticity to a level comparable to the base metal. Microstructure observations reveal that original lathy-bainite and partial martensite may be transformed into the uniformly distributed granular bainite after the “minimum post-weld heat treatment”， and the microstructural anisotropy may be significantly reduced. The experiments prove that the newly developed 2.25Cr-1Mo-0.25V wire may be used to deposit straight-walls under the optimal parameters， the subsequent “minimum post-weld heat treatment” may improve microstructure and mechanics properties to the greatest extent， which finally meet the service specifications of petrochemical vessel root edges. Compared with the casting-forging processes， CMT-WAAM is expected to significantly save production costs and improve manufacturing efficiency.