Research On Room Temperature Forming Behavior Of Q235 Carbon Steel/410/304 Stainless Steel Composite Plate

With the development of modern industrial technology,the performance requirements of materials are increasing day by day,and a single material has been unable to meet the requirements.Therefore,the research and preparation of new composites has become an important development direction.As an important part of composites,metal matrix composites have become one of the most popular scientific research topics.Carbon steel has the advantages of high strength,low cost and excellent processability,while stainless steel has high surface properties and good corrosion resistance.Carbon steel/stainless steel clad plate has both excellent properties.It can save a lot of precious metals such as Cr and Ni,and is widely used in petroleum,chemical industry,food,water conservancy facilities and other important fields.In the whole industrial chain of carbon steel/stainless steel clad plate,especially in the processing and application of its thin plate,deep processing is a key step in its industrial application.However,the research on plastic processing methods such as bulging,deep drawing and bending of composite plate is rarely reported in domestic and foreign journals.Few scholars have been involved in the research on the forming limit diagram(FLD)of metal clad sheet.The main reason is that the deformation resistance of component metal plates is different,and the deformation coordination between carbon steel and stainless steel is poor.In addition,the microstructure of the component plate in the carbon steel / stainless steel composite plate,the bonding strength at the interface and the rolling and stamping process of the sheet will directly affect its formability.Therefore,the study of the formability of carbon steel/stainless steel composite sheet has important theoretical significance and practical application value for its application in the industrial field.Firstly,the Q235 carbon stee/410/304 stainless steel clad plate with good bonding and no cracking was prepared by symmetrical hot rolling,and part of the rolled clad plate was annealed at 900 ? for 2 h.It was found that the grain size of carbon steel increases after annealing and 410 stainless steel changes from martensite to sorbite.Although the grain size of 304 stainless steel was refined to a certain extent,the twins were reduced,the work hardening was eliminated,and the deformation resistance was weakened.So,the overall plasticity of the composite plate was enhanced and the elongation was improved.Moreover,after annealing,the hardness of the base plate decreases,and only the hardness of the two interface layers increased.Then,based on Nakazima experimental method and Aramis computer vision technology,the strain of composite plate under different strain states in the process of bulging deformation was tested.The data points were fitted by high-order polynomials,and the nonlinear fitting of high-order polynomials was transformed into a multivariate linear regression problem by the substitution method.The FLD data points were fitted by the least square method.FLD with lower order and simpler form of quadratic polynomial fitting was selected as the final result.The law and causes of thickness distribution in all directions under different strain states were further analyzed,and the mechanism of crack initiation and diffusion on the interface compound layer caused by deformation incompatibility and local strong stress was explored.Next,using the original rolled sheet and annealed sheet,the deep drawing experiments were carried out when different surfaces contact the die.The fluctuation curve of limit drawing ratio(LDR)of stainless steel clad plate under different experimental parameters was drawn.For the original rolled sheet,the LDR of stainless steel contacting with die was higher than that of carbon steel contacting die.Due to the improvement of plasticity and interfacial bonding strength and the elimination of residual stress after annealing,and the limit drawing ratio of the samples with different sides of the composite plate contacting the die was 1.92.The thickness strain distribution curve and force-displacement curve of cylinder under different experimental parameters were drawn in this paper.The bottom,corner and wall area of the cylinder were selected,and the microstructure changes of the interface between Q235 carbon steel and 410 stainless steel were observed.Finally,the numerical simulation model of rigid punch bulging experiment was established in ABAQUS,and the reasonable meshing and forming parameters were set.Five criteria for judging plate instability in finite element simulation based on shell element were analyzed,and the maximum punch force criterion,strain gradient change criterion and strain rate change criterion were simulated and verified.The Q235 carbon steel/410/304 stainless steel clad plate was regarded as an integral plate,and its FLD prediction simulation was carried out.The results showed that using the standard of strain rate change at the maximum deformation grid of sheet was more accurate than the other two methods.For the maximum punch force criterion and the strain gradient change criterion,the instability time determined by the former was earlier than the real instability,while the instability time determined by the latter lagged behind the real instability.