The Effect Of Re On Microstructure And Properties Of The Q345B Steel

Low-alloy high-strength steel Q345 B is widely used in shipbuilding,engineering machinery parts,bridges,oil production platforms,etc.due to its high strength,good low temperature impact toughness and excellent welding performance.With the development of microalloy technology and controlled rolling and controlled cooling technology,microalloying and TMCP technology are widely used at home and abroad to produce low alloy high strength steel.However,TMCP technology cannot control the amount of reduction and cooling rate indefinitely,and its grain refinement can only be limited to a certain range.The addition of microalloying elements to steel improves the performance of low alloy steels with fine grain strengthening and precipitation strengthening,but increases production costs.Baotou Steel utilizes the natural advantages of its rare earth symbiotic ore in the Baiyun Obo Mine,and fully exerts its effects on the deterioration,purification and microalloying of rare earth elements in steel.This paper takes Q345 B as the research object,based on the advanced steelmaking equipment and 2250 hot rolling production line of Baotou Steel Rare Earth Steel Sheet Plant to produce Q345 B steel containing rare earth.The effect of RE element on the low-magnification structure of low-alloy high-strength steel Q345 B slab was analyzed by metallographic microscope,scanning electron microscope,tensile tester and Charpy impact tester.The influence of segregation of slab composition,the influence of inclusions in steel and rolling State of the structure,the effects of tensile mechanical properties and the effects of Charpy impact energy and section shear area.Through research,it is concluded that rare earth RE element can significantly improve the segregation phenomenon of structural steel Q345 B,and the quality of slab is improved from center segregation C class 3.0 to C class 1.5.After adding rare earth elements to Q345 B steel,it can effectively purify molten steel and refine grains.The rare earth RE element can significantly improve the segregation zone of the core of thestrip,which increases the ferrite content of the Q345 B steel.Through the Q345 B hotrolled strip tensile test,it is concluded that 0.0016% of the rare earth element can improve the Q345 B hot-rolled strip,the yield strength is about 20 MPa,and the tensile strength is about 10 MPa.At the same time,with the increase of strength,the elongation rate also increased,and the average elongation after fracture increased from 24% to31%.The rare earth RE element can significantly improve the Charpy impact energy and port shear area of the Q345 B hot rolled strip.Under the same process,the Q345 B Charpy impact energy of rare earth-containing RE can reach the effect of Q345E(standard requirement longitudinal-40 °C Charpy impact energy ? 34J).The results show that under the same industrial conditions,rare earth elements improve the microstructure of Q345 B steel,improve the mechanical properties,and improve the economic benefits of enterprise products.