| Duplex Stainless Steel (DSS) has both the characteristic of the ferrite and austenite, DSS has a fine comprehensive mechanical and corrosion resistance properties and it is widely applied in the construction of seawater pump.However, there are some difficulties during the process of DSS, the main points of these difficulties are:It is difficult to control the ratio of two phases in organization of DSS, this may cause the precipitating of the third phase (a-phase and so on) and lead to decrease mechanical and corrosion resistance properties of the welding joint; the high strength, serious cold hardening effects of DSS and the structural characteristics of the overflowing parts of pump may result in the difficult machining and easy-deformation of the parts and components of DSS.Super Duplex Stainless Steel UNS S32760has the optimized proportion ration of ferrite and austenite (50%a-phase and50%y-phase), the content of Mo is increased and a small quantity of W and Cu is adding to improve the local corrosion resistance.Compare with normal austenitic stainless steel (304L,316L), UNS S32760has better resistance to Cl" and H2S stress corrosion, pitting corrosion, crevice corrosion and intergranular corrosion; Its yield strength is about2times of the normal austenitic stainless steel’s, this can greatly decrease the size of the structure of the equipment. There is very few applications of Super DSS UNS S32760on the equipments in our country, the welding and machining technology for this Super DSS are not mature.UNS S32760super duplex stainless steel is mainly used in parts or components of seawater pumps which will directly contact with seawater, this paper studied the two important manufacturing processes of welding and turning. The parts contacted with seawater will in a strong corrosive environment, the requirements of welding quality would be very high for these parts.In this paper, samples of welding parts of UNS S32760which were adopted TIG according to the analyzed welding process parameters and measures were taken and undergone a welding procedure qualification in accordance with ASME standard. These samples were also go through the corresponding mechanical properties test and G48A pitting corrosion resistance test, all results shown that the welding joint has good mechanical properties and corrosion resistance which meet the requirements of the project.The machinability of UNS S32760is also analyzed in this paper. The lathe, cutting tool, cutting tool geometry and cutting parameters were preliminary set according to the existing cutting theory of duplex stainless steel and stainless steel and combined with the actual situation of the factory and the structure characteristics of the seawater pump parts. The problems occurring during the machining process were analyzed and the cutting parameters, the clamping methods and processing sequence were adjusted, the machining results meet the requirements of the project. Finally, a reasonable turning processing for the parts of UNS S32760of seawater pump was summarized. |
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