摘要
Cr12MoV冷轧工作辊用于轧制高精度板材时,其表面硬度均匀性和耐磨性面临较高要求。然而,在Cr12MoV冷轧工作辊表面直接采用激光熔覆Fe90合金粉末制备增材层,可能会导致表面硬度不均匀的问题。因此,研究了制造层表面平整对Fe90增材层组织结构和表面硬度均匀性的影响,并基于数学标准差方法表征了增材层表面硬度均匀性。结果表明:制造层表面处理前,增材层表面成形质量差,组织结构为柱状晶和等轴晶混合组织,表面显微硬度极差为178.1 HV,硬度波动系数为45.7,试样磨损量和摩擦系数分别为1.10 mg和0.65;制造层表面处理后,增材层表面成形质量变好,组织结构转变为单一形态树枝晶,表面显微硬度极差为97.5 HV,硬度波动系数降低到23.9,试样磨损量和摩擦系数分别为0.32 mg和0.48。结合增材层显微组织和硬度波动分析,揭示了制造层表面平整对Fe90增材层表面硬度均匀性的影响机理,为表面硬度均匀的激光增材层的制造提供了新的思路。
Objective Cr12MoV cold work die steel is widely used in the roll industry due to its advantages,such as minimal deformation,high abrasion resistance,and large bearing capacity.Cr12MoV rolls have high hardness and brittleness and are prone to spalling,pitting,cracking,and other microarea damage during service.The service conditions of rolls are harsh,as they are often subjected to significant impact,extrusion,and external friction.This makes them highly susceptible to localized damage,such as largearea spalling and cracking defects,ultimately leading to Cr12MoV roll failure.Laser repair is a method used to restore damaged rolls,producing a dense structure and metallurgical bonding at the interface.It has become an important technology for repairing Cr12MoV rolls.However,under conventional laser processing,the surface hardness of the repair layer fluctuates significantly,and the hardness variation in the interface transition zone is pronounced.This negatively affects the repair of cold rolling work rolls used in rolling highprecision plates,severely impacting both rolling accuracy and roll service life.This paper introduces the application of laser beam oscillation in welding to promote the transformation of columnar crystals into equiaxial crystals.This technique addresses issues such as poor surface hardness uniformity in repaired Cr12MoV rolls,large hardness fluctuations in the interface transition zone,and metallurgical defects.The findings provide a valuable reference for achieving highquality surface repair of Cr12MoV rolls.Methods Laser cladding of Fe90 alloy powder is applied to the surface of Cr12MoV cold rolling work rolls to create additive layers.A subsequent layer is then deposited on both the conventional manufactured layer and the single manufactured layer.Initially,the forming quality of the additive layers under the two different surface conditions of the manufactured layers is compared.Next,the microstructural features of the crosssections and longitudinal sections of the additive layers are examined using a metallographic microscope,followed by a comparative analysis of the microstructures at the same depths within the additive layers.Xray diffraction is then used to analyze the phase compositions of the additive layers.Additionally,the energy dispersive spectrometer(EDS)line scanning is conducted to examine the distribution of the primary elements,Fe and Cr,in the repair layers.Finally,the hardness and wear resistance of the additive layers under different manufactured layer surface conditions are tested.By combining microstructural analysis,element distribution,and other evaluations,the impact mechanism of manufactured layer surface grinding on the uniformity of surface hardness in the additive layers is explored.Results and Discussions Before manufactured layer surface grinding,the additive layer surface is uneven,with an average surface roughness of 24.41μm(Fig.3).The microstructure of the crosssectional and longitudinal sections of the additive layer consists of a mixture of columnar and equiaxed crystals.The surface hardness varies widely,reaching as low as 178.1 HV,with a hardness fluctuation coefficient of 45.7.Additionally,extensive delamination pits are observed under friction wear(Figs.12 and 14).After manufactured layer surface grinding,the additive layer surface becomes flatter,with an average surface roughness reduced to 15.50μm(Fig.3).Furthermore,the manufactured layer enhances the consistency of laser energy absorption on its surface,improving the uniformity of the melt pool temperature and flow field.This stabilization of grain growth conditions transforms the microstructure into a uniform dendritic crystal form(Figs.11 and 12).The range of surface hardness decreases to 97.5 HV,with the hardness fluctuation coefficient reduced to 23.9,significantly improving surface hardness uniformity.The friction coefficient decreases from 0.65 to 0.47,and both the width and depth of the wear tracks are significantly reduced(Figs.12 and 13).Conclusions In this study,an Fe90 alloy additive layer is prepared on the surface of Cr12MoV cold rolling work rolls using laser cladding technology,and the effect of manufactured layer surface grinding on the additive layer is studied.Surface grinding of the manufacturing layer improves the forming quality of the additive layer,reduces surface roughness,decreases the temperature gradient between the center and edges of the melt pool,and increases the solidification rate.It also results in a more uniform distribution of Fe and Cr elements within the additive layer,enhances the consistency of the crystal growth environment,and promotes a transition to a uniform microstructure,thereby suppressing microstructural variations in the additive layer.Overall,this study demonstrates that incorporating a surface grinding process into the laser cladding procedure enhances the forming quality,hardness uniformity,and wear resistance of the additive layer.
作者
王志龙
林英华
张为峰
康新
彭龙生
王新林
Wang Zhilong;Lin Yinghua;Zhang Weifeng;Kang Xin;Peng Longsheng;Wang Xinlin(Hunan Provincial Key Laboratory of Ultrafast MicroNano Technology and Laser Advanced Manufacturing,School of Mechanical Engineering,University of South China,Hengyang 421001,Hunan,China;School of Mechanical,Electrical and Information Engineering,Putian University,Putian 351100,Fujian,China;Hunan Lifang Roller Co.,Ltd.,Hengyang 421681,Hunan,China;Hunan High Wear Resistant Alloy Material Advanced Manufacturing Engineering Technology Research Center,Hengyang 421681,Hunan,China)
出处
《中国激光》
北大核心
2025年第12期84-98,共15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)。
