Study On Welding Performance Of TA2 Pure Titanium Pipe

Titanium and titanium alloy have excellent properties such as high strength and good plastic toughness,which are widely used in shipbuilding,aerospace and chemical industries.Therefore,the progress of research on welding technology of titanium and titanium alloy has great engineering application value.In this paper,the welding test of TA2 pure titanium tube is carried out by manual TIGwelding.Appearance inspection,X-ray flaw detection amalysis,mechanical property detection analysis,XRD test analysis,microstructure and fracture morphology analysis and corrosion resistance research are carried out on weiding joint.The research results provide theoretical support for the application of TA2 pure titanium pipe connection on ships.The main research contents completed in this paper are as follows:(1)Study the influence of weiding current on weld formation;through the appearance inspection and X-ray flaw detection analysis of the welded jiont,the results show that the color of the weld and the base metal are the same silver white,which conforms to GB/T463 standard.The weld has no defects such as cracks,incomplete penetration,inclusions and pores.The weld belong to class B weld and meets the requirements of international standard ISO 5817:2014.(2)The mechanical properties and microstructure of the welded joint were tested and analyzed.The results showed that the tensile specimens had plastic fracture at the weld joint.The tensile strength of the two specimens were 424.91 MPa and 409.98MPa,which were 0.9 times higher than the specified tensile strenghth of 430MPa(measured value of base metal).The normal bending and back bending reached 180 without cracking,which was in line with the national standard GB/T 3634-2010.The hardness values of parent metal,heat affected zone and weld vary from 176 to 184 HV,170 to 178HV and 168 to 173 HV respectively,the overall hardness values show the trend of parent metal>heat affected zone>weld.The XRD pattern shows that when the diffraction angle 20 is about 40,the highest diffraction peak appears,which coincides with the diffraction peak of Ti.Ti exists as the main phase,and then the intensity of diffraction peak gradually weakens with the increase of diffraction angle.Through comparative analysis,TiO2,Ti 3N 2,TiH 2 and S,P compounds are partially present in the titanium tube,but the content is less,and they are dispersed and distributed in the titanium tube.From the macroscopic organization,the distribution of base metal area,heat affected area and weld area can be clearly seen.In terms of microstructure,the microstructure of the base metal region is a equiaxed crystal with fine grains.The structure of the heat affected zone is a combination of a large number of equiaxed crystals and a small number of elongated strip crystals,which are found to be martensite structures by analysis.There are also a few equiaxed grains in the weld zone,and a large number of elongated crystals,i.e.acicular martensite structures,can be seen.(3)Through salt spray corrosion and electrochemical corrosion,the corrosion resistance of weld zone and base metal samples of titanium pipe were tested and compared.The corrosion resistance of welded joint and base metal was studied from the aspects of weight loss,corrosion morphology and corrosion rate.The results show that TA2 pure titanium and weld have good salt spray corrosion resistance.In 3.5%HCl solution,the self-corrosion potentials of TA2 pure titanium tube,heat affected zone and weld are-0.623V,-0.756V and-0.774V respectively,and the self-corrosion currents are 9.451e-6A,9.688e-6A and 1.536e-5A respectively,through comparison,it can be seen that the corrosion resistance performance is as follows:parent metal>heat affected zone>weld;In 3.5%NaCl solution,the corrosion potentials of base metal,heat affected zone and weld are-1.378V,-1.386V,-1.303V respectively,and the corrosion currents are 1.077e-5A,2.339e-5A and 7.561e-6A respectively,through comparison,it can be seen that the corrosion resistance performance is as follows:weld>base metal>heat affected zone.(4)The titanium tube obtained from the welding test has been tested and is in good condition and can be applied to the pipeline system on ships.