316H堆焊UNS N10003合金参数优化、组织和硬度的研究

研究异种合金焊接可以降低熔盐堆结构材料的成本并确保其安全性,本文采用钨极氩弧焊(GTAW)工艺,在316H不锈钢表面堆焊一层耐高温熔盐腐蚀的UNS N10003合金,优化了焊接工艺参数,通过光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、维氏硬度计等研究了堆焊层及界面的形貌、组织和硬度,为进一步研究多层、多道堆焊提供理论依据。研究结果表明:当电流一定时,稀释率随送丝速度的增加而减小,堆焊层高度随送丝速度的增加而增加,当送丝速度一定时,改变电流大小,堆焊层高度的变化范围为0.2~0.5 mm。堆焊层界面处可以细分为对流混合区(WM)、非对流混合区(UZ)和热影响基体区(BM)。堆焊层主要为奥氏体组织,在WM区有大量富Mo的M2C碳化物析出,UZ区的析出相主要是δ铁素体;316H基体区和WM区硬度分别为(160±10)HV和(202±11)HV,在γ基体的枝晶界上分布着尺寸细小的骨架状碳化物导致WM区硬度升高。

Investigation on microstructure and hardness of UNS N10003 weld cladding on 316H with optimization of process parameters

Studying dissimilar alloy welding can reduce cost and ensure the safety of the molten salt reactor structural material.In this work,a cladding layer of UNS N10003 alloy which is resistant to the corrosion of molten salts was deposited on 316H stainless steel substrate using Gas Tungsten Arc Weld(GTAW)process.The welding parameters were optimized.The microstructure and hardness of the cladding layer and cladding-matrix interface were systematically characterized by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and Vickers hardness tester.It provides a theoretical basis for further research on multi-layer and multi-channel surfacing.The results show when the current was constant,the dilution rate decreased with the increase of the wire feeding,but the layer height increased with the increase of the wire feeding speed.When the wire feeding speed was constant,the layer height varied from 0.2 mm to 0.5 mm with the changing of current.The cladding interface was divided into welding zone(WZ),unmixed zone(UZ),and base material(BM).The microstructure in surfacing layer is mainly austenite.The eutectic carbide of M2C type with molybdenum was precipitated in WZ and a fewδ-ferrite precipitates could be found in UZ.The hardness of the cladding layer was relatively uniform and the hardness of UZ reached(202±11)HV,and the hardness of BM was(160±10)HV.The greater hardness of the cladding layer should be caused by the numerous tiny carbides distributed in the dendrite boundaries.