Study On New Carbon Steel/Stainless Steel Corrosion Resistant Steel Rebar

Stainless steel clad rebar is a new type of corrosion resistant steel bar which has both high corrosion resistance of stainless steel bar and high strength,ductility of carbon steel.It has high cost performance and good market prospect.At present,the production technology of stainless steel clad rebar still exists in cases where the cladding layer and the carbon steel core cannot achieve metallurgical bonding and the thickness of the coating layer is not uniform.Developing new process technologies is the key to solve these problems.In this paper,the cold-drawing-high temperature brazing technology is used to prepare stainless steel clad rebar.Stainless steel clad rebars were prepared using copper,brass,and electroplated copper as brazing filler metal.The effects of brazing temperature and holding time on the corrosion resistance,hardness of stainless steel layer and brazing seam structure were investigated using optical microscopy,scanning electron microscopy(SEM),Rockwell hardness tester and electrochemical workstation.The results show that metallurgical bonding cannot be achieved with electroplated copper as the brazing filler metal.When copper and brass were used as the brazing filler metal,there forms a continuous metallurgical bond with the base metal.During the brazing process,FeCrNi bubble solid solution is formed in the brazing seam zone between carbon steel and brazing filler metal area.As the brazing temperature and holding time increase,the number of irregular peak-like solid solution increases and gradually grows toward the brazing filler metal layer and the stainless steel side.At 1200 ? for 1.5 h,there was no obvious interface between the brazing seam area and the base metal,and the diffusion degree was more thorough.The composition has basically reached the same level.At the same time,the grain size of Q235 carbon steel increases with the increase of brazing temperature and holding time.Electrochemical tests show that the austenite grains grow and coarsen as the brazing temperature increase,and the amount of carbides gradually decreases.The corrosion resistance of 304 stainless steel coating increases first and then weakens.The corrosion resistance of the stainless steel coating was the worst at 950?,0.5h and 1..at 1200?,and the best corrosion resistance was obtained when it was at 1100? for 1.0h.The hardness of stainless steel coating decreases with the increase of brazing temperature and the holding time.Using Cu/Fe as a diffusion couple to establish the relationship model between Cu diffusion concentration distribution and brazing temperature and holding time.The effect of brazing temperature and holding time on the diffusion distance of Cu in y-Fe was studied,which lays a foundation for optimizing the parameters of brazing process.The results show that the diffusion distance of Cu in ?-Fe increases with the increase of brazing temperature and holding time.The measured results of diffusion distance line scanning are in good agreement with the theoretical results.According to the relationship between brazing temperature and holding time under the condition of Cu diffusion distance of 21.16 ?m,the brazing temperature and holding time can be reasonably selected to form sufficient solid solution,and the austenitic grain growth of the base metal can be controlled.Thus the brazing joint with the best shear strength can be obtained.The effects of brazing temperature,the thickness of brazing filler metal,the material of brazing filler metal and the thickness of stainless steel cladding on residual stress of Q235/Cu/304 brazing joint were studied by finite element simulation technique.The results show that the carbon steel is subjected to axial compressive stress,and the stainless steel side is tensile stress.The side of the copper brazing material layer near the carbon steel is compressive stress,and the tensile strength is close to the stainless steel side.Brazing temperature has little effect on axial residual stress.The increase of the thickness of the copper solder layer and the thickness of the stainless steel cladding layer can increase the axial residual stress.When Ni is used as the brazing layer,the entire brazing layer is subjected to a large axial compressive stress.The calculation results show that the smaller thickness filler metal layer and stainless steel cladding layer should be chosen as far as possible in order to reduce the compressive stress of carbon steel/copper boundary and improve the shear strength of the joint.