Study On Forming Mechanism And Deformation Behavior Of 2507 Duplex Stainless Steel

2507 duplex stainless steel is a kind of duplex stainless steel with low carbon content and high chromium,nickel,molybdenum,nitrogen and other elements.Due to the difference in the crystal structures and properties of the austenite and ferrite phases,duplex stainless steels have a more complex plastic deformation behavior than single-phase stainless steels.With the popularization of duplex stainless steel applications,the research on its forming properties is extremely urgent.However,the lack of exploration of the forming mechanism and deformation behavior limits the secondary processing of duplex stainless steel sheets.Therefore,this paper takes 2507 duplex stainless steel as the research object.Based on the experimental duplex stainless steel sheet mechanical properties and forming performance,using OM,EBSD,TEM and other analysis methods,through planar anisotropy,macro texture,microstructure and micro-grain orientation,the forming performance and two-phase deformation behavior are deeply discussed;and the cold rolling direction is changed during the cold rolling process to weaken the influence of unfavorable texture on the forming performance.The r-value is increased,which provides a new possibility for improving the forming performance of the sheet.Through various forming experiments and tensile tests in different directions,the basic forming properties are understood.The mechanical properties of different directions are different.The tensile strength along 90°is the largest,which is about 6.3%higher than the tensile strength along 45° direction.The Lankford coefficients(r-values)are in an inverted V-shaped distribution.The r-value in the RD is the smallest,only 0.45.The r-value in the 45° direction reaches the peak value of 1.05,which is about 2.3 times than the r-value in the RD.The r-value along TD is between the other two directions and is 0.88.The conical cup test shows that the experimental plate has a larger cone cup value.The earing test shows that the stamped products are easy to produce 45° ears.The Erichsen cupping test under different test conditions shows that the cupping value is affected by the deformation speed and lubrication conditions.Through the Swift deep drawing test research,the a-fiber texture(<110>//RD)is the main texture component in ferrite,concentrated in {001}<110>to{112}<110>.The grain orientation in the austenite is mainly concentrated near theβ orientation line,and a certain amount of recrystallized R texture.The thickness of the deep drawing cup in different directions is unevenly distributed,and the rounded corners at the bottom are easily broken areas.The folding crack at the cup edgy is caused by the lack of blank holder force and the unevenness of the two-phase deformation.Through the texture analysis of the different thickness layers of the experimental plate,there is an obvious texture gradient in the thickness direction.During the tensile deformation process,the {001}<110>oriented grains in the 45°direction are deflected and become {115}<110>oriented grains,resulting in the largest {111}/{001} volume ratio and the largest r-value in the 45°direction.Through the different strain rates tensile test,the experimental plate is not sensitive to the tensile rate.Through the change of the microhardness values of the two phases under different strains,it is found that the microhardness of the ferrite phase is smaller than that of the austenite phase.The softer ferrite accommodates greater deformation in the initial stage of deformation.As the amount of deformation increases,the deformation begins to be transferred to the harder austenite phase,and the two phases deform in coordinate.At the same time,by observing the microscopic deformation morphology of the two phases,the study found that the strain is unevenly distributed in the ferrite and austenite phases,the dislocations are plugged at the phase boundary,and the movement of the dislocations is hindered by the phase interface,which reduces the ability of coordinated deformation between austenite and ferrite phases.By comparing the research of different cold rolling directions on the forming properties,the influence of different rolling processes on the forming properties is revealed.Under the same total reduction ratio,changing the direction of cold rolling has little effect on the strength,but it has a significant impact on the r-value.After transverse rolling,the r-value is increased to 0.98,which is 8.9%higher than that after conventional rolling.The transverse rolling can effectively weaken the rolling texture in the ferrite,especially the {001}<110>.The{001}<110>strength is reduced by 41.7%,which greatly reduced the influence of unfavorable texture on the formability of the plate,thereby increasing the r-value and the formability.