Study On The Microstructure And Properties Of 12% CR Ferritic Stainless Steel Welded Pipe

12%Cr ferritic stainless steel is a kind of hyperpure,low-carbon,low-chromium,economy ferritic stainless steel,not only has it good weldability,but also the price is low,studying the weldability of this kind of steel is meaningful to improve the production efficiency of steel and iron manufacturing industry in our country.This research is using HFW on 12%Cr ferritic stainless steel,and researching the influence on macro-morphology and microstructure.Change the welding speed,the welding gas protection condition and heat treatment process after welding to get different welding result and do mechanical property experiment on microhardness,strength of extension,impact toughness and frictional wear property.Research the relationship in welding process,microstructure and mechanical property,find the regularity of HFW on 12%Cr ferritic stainless steel and provide theoretical guidance for practical production.Analysis the morphology and structure of welded joint,the welding heat affected zone presents drum type form,the width hn is 0.6?0.75mm,it is around 1/4?1/3 of pipe thickness 3mm,ho?hi?1.3?-2.2hn,fo?fi?1.3?3fn,which are in the perfect value range of weld structure parameters.With the increasing of welding speed,the width of HAZ is decreasing.12%Cr ferritic stainless steel base metal is single phase ferrite and grain size is around 30?m.After HFW process,weld-fusion line consists of ?-ferrite,coarse grain Martensite and remaining Austenite,grain size is 80?100?m;HAZ area consists of equally distributed Martensite and ferrit,grain size is 20?50?m.The area where temperature is lower than 850? does not have phase change process even it is affected by the heat source and the texture is nearly same as base metal.Some alloying elements appear in welding process with the form of educt which will impact the quality of welding joint,so the content of alloying elements should be strictly controlled.The result of mechanics performance testing on welded joint shows that,a good deal of high hardness Martensite will be produced during welding process.Martensite improves hardness,strength and wear resistance,increases regional hardenability and decrease impact toughness of welded joint.Grain in HAZ is in large size compared with other area and there are some educts existing in HAZ.These factors also make a harmful influence to the service character of material.Welding speed will have an impact on HAZ width,and also on high-hardness and low-toughness area.Heat treatment process after welding can decrease grain size,homogenize texture and improve overall performance of the material.Welding gas protection condition can prevent large quantity of oxide inclusion in order to avoid hot crack and other related weld defect.HFW process of 12%Cr ferritic stainless steel should be provided good gas protection condition and heat treatment process after welding.While ensuring getting good weld structure parameters,welding speed is as faster as better.Simultaneously,we should strictly control alloying elements content and add proper elements to get a better welded joint.