Study On Microstructure And Mechanical Properties Of AL6XN/Q345R Clad Plate By Vacuum Hot-Rolling Process

AL6XN super austenitic stainless steel(UNS N08367)is a kind of low-carbon,high-purity,nitrogen-reinforced austenitic stainless steel.Due to its excellent mechanical properties and corrosion resistance,good formability and welding performance,it can replace the traditional duplex stainless steel and expensive nickel-based alloys in some fields.However,the high cost of AL6XN has become an important reason for limiting its application.AL6XN/Q345R clad plate has excellent corrosion resistance and lower cost.Compared with the traditional explosive cladding,the vacuum rolling cladding(VRC)process is simpler,environmentally friendlier and has a higher interface bonding rate.It can be used to manufacture high-quality AL6XN/Q345R clad plates.In this paper,the process of manufacturing the AL6XN/Q345R clad plates by the vacuum rolling cladding method is studied.It mainly includes the method of forming blanks of clad plates,and the effects of rolling heating temperature,rolling reduction ratios,heat treatment process and cooling method after rolling on the microstructure and properties of the clad plates;the mechanism of element diffusion at the clad interface,the microstructure of the recombination region of interface,the types of interface inclusions,and the formation mechanism were investigated,and the main research contents and conclusions are as follows:(1)In order to ensure the coordinated deformation between stainless steel and vessel steel,prevent the weld cracking during rolling,and keep the interface in a high vacuum state,a 4-layer symmetrical forming mode of vessel steel-stainless steel-stainless steel-vessel steel was designed.(2)Under the laboratory conditions,the stainless steel/vessel steel clad plates produced by vacuum rolling cladding have achieved good metallurgical combination without uncomplicated area.Due to the diffusion of Cr,Ni,Mo and C elements near the clad interface,it can be divided into four areas:stainless steel matrix,recombination region of interface,decarburization area and carbon steel matrix.Al2O3 and Al-Si-Mn-O composite oxides are dispersely distributed near the interface.(3)The influence of heating temperature on the interface microstructure and mechanical properties of stainless steel/vessel steel clad plates were studied.The results show that when the heating temperature is 1150,1200,1250?,and the reduction ratio is 80%,the diffusion of elements increases with the increasing of temperature.The shear strength of three kinds of clad plates with different heating temperature are 349,362 and 347 MPa,which is far beyond the national standard.The fracture mode of clad interface is ductile fracture with good plasticity.The yield strength of the base material of clad plates under the three heating temperatures is not meeting the national standard,which needs to be further optimized.(4)The influence of the reduction ratios on the microstructure and mechanical properties of the stainless steel/vessel steel clad plates interface was studied.The results show that the clad plates achieve good metallurgical bonding at 60%and 80%reduction ratios,when the heating temperature is 1200?.The number and size of oxides near the 60%reduction ratios interface are larger,and the diffusion distance of elements is longer.The shear strength of clad plates under different reduction ratios are 289 MPa and 362 MPa,which met the national standard requirements.The bonding performance of clad plates under 80%reduction ratios was significantly better than 60%reduction ratios.(5)The effects of different heat treatment and cooling methods after rolling on the interface structure and mechanical properties of stainless steel/vessel steel clad plates are studied.The results show that the bonding performance of the composite plate manufacture by 910? quenching+650? tempering heat treatment or online cooling is far beyond the national standard,and the mechanical properties of base material is optimized to meet the national standard requirements.Through preliminary estimation of the Schaeffler phase diagram,EBSD analysis of the recombination region of interface,and hardness test,the microstructure in the recombination region of interface was determined to be martensite.(6)Based on the results of laboratory research,an industrial trial production of AL6XN/Q345R clad plates was performed at NANJING IRON&STEEL CO,and clad plates with good shape and specifications of 23 × 2400 × 12000mm were manufactured.The clad plates were tested for properties such as shear,tensile,impact,and bending,and the intergranular corrosion resistance tests of the multi-layer material were tested.Trial production of AL6XN/Q345R clad plates meet the requirements of various standards.