摘要
针对常规激光熔覆在修复微小损伤Cr12MoV冷轧工作辊过程中存在的修复层表面硬度均匀性差和冶金缺陷问题,本文提出了一种8字形摆动激光同步送粉增材制造修复工艺。该工艺借助8字形摆动激光改变熔池运动轨迹来影响熔池的温度梯度和凝固速率,从而改善修复层的微观组织、表面硬度均匀性和冶金缺陷,最终达到了提高修复层耐磨性的目的。结果表明:在常规激光修复模式下,修复层表面色泽暗淡,界面结合区出现了裂纹,组织结构为粗大的柱状枝晶和等轴枝晶的混合组织,表面硬度极差为185.0 HV,硬度波动系数高达35.8,摩擦磨损过程中修复层出现了较大的剥落坑;在8字形摆动激光模式下,修复层形貌得到显著改善,其表面产生了金属光泽,界面结合区裂纹消失;8字形摆动激光的搅拌作用增强了熔池的对流,打断了柱状枝晶的生长,使得组织结构转变为单一的细小等轴枝晶,进而使得修复层表面硬度极差降低到61.1 HV,硬度波动系数降低到13.2,表面硬度均匀性得到明显改善,摩擦因数降低到0.56,磨痕宽度和深度均明显下降。最后,结合微观组织、数值模拟和元素分布等探讨了8字形摆动激光对修复层表面硬度均匀性的影响机理。
Objective Cr12MoV cold work die steel is widely used in the roll industry owing to its advantages such as low deformation,high abrasion resistance,and large bearing capacity.However,Cr12MoV rolls exhibit high hardness and brittleness,making them prone to spalling,pitting,cracking,and other microarea damage under service conditions.The harsh operational environment of rolls often involves substantial impact,extrusion,and external friction,leading to localized damage such as largearea spalling and cracking,ultimately resulting in roll scrap.Laser repair is a key method for restoring damaged rolls.This technique enables the formation of dense microstructures and metallurgical bonds at the interface,making it an important technology for repairing damaged Cr12MoV rolls.However,the surface hardness of the repaired layer exhibits fluctuations under the conventional laser mode,particularly in the interfacial transition zone.These variations negatively affect the rolling accuracy of highprecision plates and shorten the service life of rolls.This study explores the application of swing laser beams in welding to promote the transformation of columnar crystals to equiaxed crystals,addressing issues related to nonuniform surface hardness in repaired Cr12MoV rolls.This method aims to minimize hardness fluctuations in the interfacial transition zone,reduce metallurgical defects,and establish a framework for highquality surface repair of Cr12MoV rolls.Methods The surface of a Cr12MoV roll was machined into a trapezoidal damage repair groove using fine engraving technology.The damaged area was then repaired at conventional laser and figure8 swing laser modes.The following steps were undertaken:1)comparing the repair layer molding quality at two laser modes;2)analyzing and comparing the microstructure of the crosssection at the same depth of the repair layer using metallographic microscopy;3)analyzing and comparing the phase composition of the repair layer via Xray diffraction;4)examining the distribution of main elements(Fe and Cr)in the repair layer via energydispersive spectroscopy line scanning;5)testing the microhardness and wear resistance of the repair layer at different laser modes.By combining microstructural analysis,elemental distribution,and other findings,this study explored the mechanism through which the figure8 swing laser influences the surface microhardness uniformity of the repair layer.Results and Discussions At conventional laser mode,the surface color of the repair layer is dull,and cracks are observed in the interface bonding zone(Fig.7).The microstructure comprises a mixture of coarse columnar dendrites and equiaxed dendrites(Fig.8,Fig.9,and Fig.10).The difference between the maximum and minimum surface microhardness values is 185.0 HV,with a microhardness fluctuation coefficient of 35.8(Fig.13).Large spalling pits are found in the repair layer after friction and wear tests(Fig.16 and Fig.17).Furthermore,the figure8 swing laser considerably improves the appearance of the repair layer,imparting a metallic luster to the surface and eliminating cracks in the interface bonding zone(Fig.7).The figure8 swing increases convection in the molten pool,interrupts the growth of columnar dendrites,and transforms the microstructure into a uniform pattern of fine equiaxed dendrites(Fig.8,Fig.9,and Fig.10).The difference between the maximum and minimum surface microhardness values is 61.1 HV,with the microhardness fluctuation coefficient reducing to 13.2(Fig.13).Surface microhardness uniformity is improved considerably,while the friction coefficient decreases from 0.66 to 0.56.In addition,the width and depth of the wear marks decrease considerably(Fig.16 and Fig.17).Conclusions The study compared the effects of conventional laser and figure8 swing laser modes on the repair layer and found that the figure8 swing laser substantially can enhance the morphology and quality of the repair layer.The surface displays a metallic luster,and cracks in the interface bonding zone are eliminated,resulting in a smooth and defectfree repair layer.Additionally,Fe and Cr are more uniformly distributed in the repair layer.Furthermore,the figure8 swing laser reduces the temperature gradient and improves the solidification rate.These factors provide a stable grain growth environment,collectively promoting the transformation of columnar dendrites into equiaxed dendrites and reducing structural heterogeneity in the repair layer.The microhardness uniformity of the repair layer is improved,and as a result,the width and depth of the abrasion marks decrease considerably.These changes lead to an increase in wear resistance.
作者
林英华
黄桌
刘俊峰
康新
王开明
彭龙生
王新林
Lin Yinghua;Huang Zhuo;Liu Junfeng;Kang Xin;Wang Kaiming;Peng Longsheng;Wang Xinlin(College of Mechanical Engineering,University of South China,Hengyang 421001,Hunan,China;Hunan Key Laboratory of UltraFast Micro Technology and Advanced Laser Manufacturing,Hengyang 421001,Hunan,China;School of Mechanical,Electrical and Information Engineering,Putian University,Putian 351100,Fujian,China;School of Automobile and Mechanical Engineering,Changsha University of Science and Technology,Changsha 410114,Hunan,China;Hunan Lifang Roller Co.,Ltd.,Hengyang 421681,Hunan,China)
出处
《中国激光》
北大核心
2025年第8期137-153,共17页
Chinese Journal of Lasers
基金
湖南省教育厅科学研究优秀青年项目(24B0399)
福建省技术创新重点攻关及产业化项目(2023XQ017)
湖南省自然科学基金-省市联合基金(2022JJ50019)
南华大学人才引进项目(210XQD017)
湖南省自然科学基金(2024JJ5336)。
