Interfacial Microstructure And Mechanical Properties Of Rolled Composite Thick Steel Plates

Heavy plates are widely used in heavy machinery,large ships,offshore oil platforms,dams and gates.They are generally produced by ingot casting or continuous casting billet.The traditional production method has many shortcomings,and the heavy plate produced by rolling clad using casting slab can not only fully exploit the advantages of high continuous casting billet production efficiency and good finished product quality,but also abandon the center shrinkage and shrinkage of large ingots.The disadvantages of serious segregation,low yield,and low-cost production of thick plates and extra-thick plates have attracted widespread attention.Due to the research on the blanking process of the composite thick steel plate,the quality control of the composite interface and the bonding mechanism of the rolling composite interface,further research is needed.In this paper,Q235 steel was used as raw material,and thick plate was prepared by multi-pass hot rolling composite method under protective atmosphere.The microstructure of composite interface was observed by metallographic microscope.The interface shear strength was measured by MTS810 test machine.The test,the interface bonding phenomenon of the composite steel plate was analyzed and studied,and the effects of parameters such as rolling deformation rate and rolling composite temperature on the interface bonding were discussed.The results show that when the rolling temperature is the same,the number of interfacial voids decreases with the increase of the cumulative reduction.Under the same cumulative reduction ratio,the number of composite interface pores decreases significantly with the increase of rolling temperature,but the internal matrix crystal The particle size gradually increases.The shear bond test proves that the composite bond plate prepared by rolling composite under protective atmosphere increases the interfacial bond strength with the increase of cumulative deformation rate and rolling temperature.In order to further explore the interface bonding of composite thick plates,a 55 mm thick plate was prepared by using Q345 steel as raw material,and the microstructure of the interface was observed by metallographic microscope and scanning electron microscope.The results showed that the matrix was observed.Both the composite interface and the microstructure are pearlite + ferrite,and the effect of recrystallizing and grain refining is remarkable.With the increase of the cumulative reduction ratio,the interface defects are reduced and the interface bonding strength is improved.When the cumulative reduction ratio reaches 66.0%,the interface shear strength reaches 321 MPa,the Z-direction tensile strength reaches 520 MPa,and the elongation after fracture reaches the highest 39.5.%,meet the requirements of GB/T 1591-2008 "low alloy high strength steel".The results of strong acid deep corrosion composite interface show that even after multi-pass rolling deformation,the composite interface still has traces of strong acid corrosion.At the same time,the impact test results show that the impact energy of the composite interface is lower than that of the base metal.