| The application of invar alloy has been restricted by the poor weldability,low strength,weak rust resistance,etc.Therefore,the research on the influence of different alloying elements on the weld structure,mechanical properties and corrosion resistance of invar alloy has a positive role in promoting the development of invar alloy.Taking Fe-36Ni as the research object in this paper,invar alloys with the addition of 0?1.0wt.%Ti,Ti-Nb,Ce,Ce+Ti,Ce+Bi or RE-magnesium-ferrosilicon alloy were prepared by arc melting to explore the changes of their microstructure and corrosion resistance.Selecting the components of invar alloy with excellent comprehensive properties to prepare welding materials,and the tungsten gas arc welding was used for practical welding to explore the influence of alloying elements on the structure and properties of invar alloy weld.The results show that:(1)With the increase of addition amount of Ti,the grain of invar alloy becomes coarse and uniform,meanwhile,the cellular structure is gradually refined.Therefore,the minimum average size of cellular structure is about 6.5?m,with the refinement rate is about 72%in invar alloy with the addition of 1.0%Ti.And,the microstructure of invar alloys with the addition of Ti-Nb are uniform,both grain and cellular structure are refined with the increase of the added amount of Ti-Nb,which means the comprehensive refining effect of invar alloy with the addition of 1.0%Ti-Nb is the best,the refining rate of grain and cellular structure is 43.9%and 57.8%,respectively.In addition,the grain size and its homogeneity are decreased,the cellular structure is decreased first and then increased with the increase of addition amount of Ce,Ce+Ti,Ce+Bi or RE-magnesium-ferrosilicon alloy.What's more,because of the refinement of the structure and the precipitation of the strengthening phase,the average hardness of the invar alloy with the addition of 1.0%Ti-Nb is the highest,which is 193 HV,increasing by nearly 30%.(2)The self-corrosion current density of invar alloy decreases first and then increases with the increase of addition amount of Ti,Ti-Nb,Ce or Ce+Ti,and gradually decreases with the increase of addition amount of Ce+Bi or RE-magnesium-ferrosilicon alloy.In each system,the invar alloys with 0.2%Ti,0.2%Ti-Nb,0.2%Ce,0.5%Ce+Ti,1.0%Ce+Bi and1.0%RE-magnesium-ferrosilicon have the lowest corrosion current density,which decreases about 4.7%,72.4%,87.5%,46.1%,28.9%and 25%,respectively.In addition,add alloying elements to invar alloy promote the formation of?-Fe OOH,which is conducive to the improvement of rust layer stability.The volume fraction of?-Fe OOH in the outer rust layer of invar alloy with the addition of 0.1%Ce is the largest and densest,which is contributed to the best protection of the rust layer.(3)All the welds welding with wires with the addition of 0.5%Ti,1.0%Ti-Nb,0.5%Ce+Ti,0.5%Ce+Bi and 0.5%RE-magnesium-ferrosilicon alloy are formed beautifully without obvious defects,and the microstructure of each weld is also refined,which was consistent with the preliminary test results.Weanwhile,the thermal expansion coefficient of each weld conforms to?25?<1.5×10-6/?.(4)The hardness and tensile strength of invar alloy weld with 1.0%Ti-Nb or0.5%RE-magnesium-ferrosilicon alloy are significantly increased,with the hardness increased by nearly 14.5%and 10.4%,respectively,the tensile strength increased by 53.8%and 32.0%,respectively,and the elongation after fracture was 42.9%and 23.2%,respectively.Also,the hardness and tensile strength of invar alloy weld with the addition of0.5%Ti or 0.5%Ce+Ti are improved,but the elongation after fracture is not obviously improved.In addition,the impact test results show that the normal temperature impact toughness of the invar alloy weld with the addition of 0.5%Ti or 1.0%Ti-Nb is increased by14.9%and 31.2%,respectively,and the low temperature impact toughness is increased by6%and 7.8%,respectively.However,due to the influence of rare earth inclusions,the normal and low temperature impact toughness of invar alloy weld welding with wire with addition of 0.5%Ce+Ti or 0.5%RE-magnesium-ferrosilicon alloy has not been improved. |
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