Mo含量对激光熔覆316L组织和耐蚀性能的影响

董刚; 曾宇; 胡健东; 庞靖凯; 杨高林; 石岳林; 张群莉; 姚建华

DONG Gang,ZENG Yu,HU Jiandong,PANG Jingkai,YANG Gaolin,SHI Yuelin,ZHANG Qunli,YAO Jianhua.Influence of Mo Content on Microstructure and Corrosion Resistance of Laser-cladded 316L[J],53(23):204-215

Influence of Mo Content on Microstructure and Corrosion Resistance of Laser-cladded 316L

Received:January 29, 2024 Revised:April 09, 2024

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DOI：10.16490/j.cnki.issn.1001-3660.2024.23.018

KeyWord:laser cladding 316L Mo element corrosion resistance performance grain size grain orientation

Author	Institution
DONG Gang	Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Special Equipment Manufacturing and Advanced Processing Technology Key Laboratory of the Ministry of Education/Zhejiang Province, Hangzhou , China
ZENG Yu	Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Special Equipment Manufacturing and Advanced Processing Technology Key Laboratory of the Ministry of Education/Zhejiang Province, Hangzhou , China
HU Jiandong	Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Special Equipment Manufacturing and Advanced Processing Technology Key Laboratory of the Ministry of Education/Zhejiang Province, Hangzhou , China
PANG Jingkai	Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Special Equipment Manufacturing and Advanced Processing Technology Key Laboratory of the Ministry of Education/Zhejiang Province, Hangzhou , China
YANG Gaolin	Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Special Equipment Manufacturing and Advanced Processing Technology Key Laboratory of the Ministry of Education/Zhejiang Province, Hangzhou , China
SHI Yuelin	Zhoushan Dingzun Technology Co., Ltd., Zhejiang Zhoushan , China
ZHANG Qunli	Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Special Equipment Manufacturing and Advanced Processing Technology Key Laboratory of the Ministry of Education/Zhejiang Province, Hangzhou , China
YAO Jianhua	Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Special Equipment Manufacturing and Advanced Processing Technology Key Laboratory of the Ministry of Education/Zhejiang Province, Hangzhou , China

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Abstract:

To achieve high-quality laser remanufacturing of 316L components, alloying element Molybdenum (Mo) is added during the laser cladding of 316L stainless steel powder to further enhance the corrosion resistance of 316L stainless steel in environments containing chloride ions, such as seawater. In order to study the effects of varying Mo content on the microstructure and corrosion resistance of the 316L cladding layer, laser cladding technology was utilized to fabricate 316L cladding layers with different Mo additions (2wt.%, 4wt.%, 6wt.%) on a 316L stainless steel substrate. The macroscopic morphology, microstructure, phase composition, elemental distribution, grain orientation, and corrosion resistance of the cladding layers were characterized by metallographic microscopy, scanning electron microscopy, laser confocal microscopy, X-ray diffraction, and an electrochemical workstation. The results indicated that when the addition of Mo element did not exceed 4%, the phase within the cladding layer remained unchanged, still comprising austenitic phases. However, when the Mo addition reached 6%, the substantial incorporation of Mo reduced the stability of austenite in the stainless steel. The increased undercooling altered the solidification conditions of the alloy, causing partial transformation of austenite into martensite, while a significant amount of un-melted Mo particles appeared in the cladding layer. With the increased content of Mo, the texture strength of grains in the <001> direction decreased, showing a tendency to grow towards the <111> direction. Moreover, the grains became refined, with the average grain size in the cladding layer reducing from 235.59 µm to 184.35 µm. The higher proportion of smaller-sized grains increased the grain boundary area, resulting in the accumulation of dislocations within the grains and enhancing the dislocation density of the cladding layer. The smaller grain size, with its larger grain boundary area, provided more nucleation sites for the growth of the passivation layer and could promote the formation of a uniform and dense passivation film, which significantly impacted the corrosion resistance. Additionally, as the content of Mo element increased, the number of pitting sites decreased, resulting in a significant improvement in the cladding layer's corrosion resistance. When the Mo addition was at 4%, the self-corrosion current density reduced from 8.253×10–6 A/cm2 in the untreated group to 4.540×10–7 A/cm2, and the passivation resistance increased from 4 927 Ω.cm2 to 8 702 Ω.cm2, an enhancement of approximately 75%. With a Mo addition of 6%, the self-corrosion current density and the passivation resistance value started to decline but still performed better than the untreated group. The reason for this was the presence of un-melted Mo particles in the cladding layer at the 6% addition level, which lead to an uneven distribution of elements. Localized regions with elevated content of Mo could form galvanic cells with other areas, with the Mo-rich regions acting as anodes, thereby exacerbating corrosion in the other areas and causing an overall decline in the cladding layer's corrosion resistance. Chloride ions, being a highly penetrative substance, are capable of penetrating the passivation film, leading to pitting and intergranular corrosion. The addition of Mo enhances the performance of the passivation film, rendering the surface passivation layer of the cladding denser and more stable against the attack of chloride ions. This further improves the resistance of the 316L cladding layer to corrosive agents present in marine environments.