Corrosion And Fatigue Properties Of 301L Stainless Steel For Rail Vehicles And The Mechanism Of Its Structure

With the continuous develop ment of rail vehic les at ho me and abroad,lightwe ight has become an inevitab le trend in the developme nt of ra il vehic les.The301L stainless steel,as the ma in mater ia l of the rail car body,is a metastable austenitic stainless steel.It can produce strain-ind uced marte nsitic transfor mation through p lastic defor mation at room temperature,resulting in greatly improved strength and hardness,and ma inta ining a certain plastic ity.However,consider ing the comp licated work ing environment o f the ra il vehic le and the continuo us reciprocating wear between the vehic le body and the track,it is high require ments for mater ials.Corrosio n and fatigue,two of the most serio us fa ilure modes of ra il vehic les,have always been a prob lem that needs to be solved urgently.In this paper,ma inly stud ied the effects of the type and quantity of inc lus io ns in 301L austenitic sta inless steel and the marte ns itic trans formatio n dur ing ro lling o n pitting and intergra nular corrosion o f301L austenitic stainless steel.The different sens itization te mperatures are set to find the most sens itive te mperature point o f intergra nular corrosion o f 301L stainless steel through intergra nular corrosio n test,and ensure this temperature is avoided dur ing process ing or heat treatment.At the same time,the fatigue perfor mance of 301L austenitic sta inless steel DLT grade plate,used as the ma in beam o f the ra il vehic le under frame,was stud ied.The fa ilure mode was determined by fracture ana lys is,which provided experime nta l basis and theoretical support for the deve lopme nt of stainless steel rail vehicles in China.（1）The meta llographic method shows that the inc lus ions in five strength grades of the 301L auste nitic sta inless steel are a ll spher ical oxides.As the rolling reduction rate increases,the inc lus io ns break up and become smaller.The rating results show that Except for the MT leve l board,whic h is 1.0 leve l,the other leve l boards are all0.5 le ve l.In add ition,the FMP30 ma gnetic saturation meter measured that some of the austenite phase changed to the martens ite phase dur ing cold rolling,and the greater the reduction ratio,the more the martensite content.（2）The immers ion experiments of 6%FeCl3 solution showed that pitting corrosion occurred in the 301L austenitic sta inless steel o f five strength grades after immers ion for 72 h,and the pitting rate of the LT grade plate calc ulated by the we ight loss method was the largest,and the pitting rate of the MT grade p late was the sma llest.The stud y of potentiodyna mic polarization c urves shows that the self-corros ion current dens ity and the blunt curre nt density o f the LT grade plate are the largest.The self-corrosion curre nt density and the blunt curre nt dens ity o f the MT grade plate are the sma llest,and the se lf-corrosio n potentia l is the largest,ind icating that the LT grade plate has poor pitting corrosion res istance and the MT grade plate has better pitting corrosion resistance.（3）The 10%oxa lic acid solutio n etch test showed that intergranular corrosion occurred in the 301L austenitic stainless steel after sensitizatio n.As the sens itization temperature increases,the intergra nular corrosion degree of 301L austenitic stainless stee l first increases and then weakens.When the sens itization temperature is 650℃,there is a continuous and deeper grain boundary on the grain boundary,and the intergranular corrosion degree is the highest,ind icating that 650℃ is the"nose tip temperature"of 301L austenitic stainless steel.The time to stay at this temperature should be avoided or reduced as muc h as poss ib le dur ing the heat treatment.In additio n,the inter granular corrosio n sens itivity o f 301L austenitic stainless steel increases as the grain size becomes smaller.（4）The 65%nitr ic acid boiling exper iment showed that the 301L austenitic stainless steel of five strength grades had intergranular corrosion along the grain boundary after boiling for 48 h,and there were etch pits on the crystal gra ins.Count the width of the gra in boundary a fter corrosio n found that the corrosion groove o f the ST grade plate was widest,which was 5.74μm,and the intergra nular corrosion rate ca lculated by the we ight loss method was the lar gest,indicating that the ST grade plate was the most severely corroded and the intergranular cor rosion resistance was the worst.The DLT grade plate has the narrowest corrosion groove of 3.82μm;the MT grade plate is 4.26μm,but its grain surface corrosion is lighter and the intergranular corros ion rate is the s ma llest,indicating that the MT grade plate has the best resistance to intergranular corrosion.（5）The single point fatigue test estimated that the fatigue limit of 301L austenitic stainless steel DLT grade sheet is 395 MP.The S-N curve of the DLT grade plate was fitted by least squares method,and the power function equation of the S-N curve with a surviva l rate of 50%was obtained as follows:N^45.045=3.085×10¹²³.Fatigue fracture ana lys is can c learly observe the fatigue source zone,fatigue crack growth zone and insta ntaneous fracture zone.The fina l fracture mode is plastic fracture,which provides a certain experimenta l basis for the pro duction of stainless steel rail vehicles in China.