Effects Of Welding And Rolling On The Microstructure And Mechanical Properties Of High Strength Low Alloy Steel

High strength low alloy steel is developed based on the carbon steel,and this steel has high strength,high plasticity and good low temperature impact toughness.It can effectively prevent the crack initiation and expansion to meet the requirement of freighter.In addition the steel also needs good welding performance and mechanical properties.Based on this,this paper will focus on the effects of welding and rolling process on the microstructure of high strength low alloy steel.In this study,a kind of high strength low alloy steel was designed.The effects of welding and rolling process on the microstructure of high strength low alloy steel were investigated by changing the welding cycle parameters and rolling process parameters.In this paper,the heat cycle of welding with different welding heat inputs and different peak temperatures is carried out on the high strength low alloy test steel using the Gleeble-1500 simulation test machine,and the high strength low alloy steel is thermo-mechanically treated according to the rolling principle.The HAZ of high strength low alloy steel can be divided into four zones: CGHAZ,FGHAZ,ICHAZ,and SCHAZ according to the peak temperature.After the welding thermal cycle,the microstructure of the heat-affected zone will be softened.The degree of softening in the coarse-grained zone of HAZ is the lowest,and the degree of softening in the fine-grained zone of HAZ is the highest.With the gradual increase of the peak temperature of welding heat cycle,the impact toughness of HAZ microstructure decreases with the decrease of peak temperature.By controlling the rolling technology of high strength low alloy steels,microstructures containing a large amount of acicular ferrite can be obtained,which promotes excellent ductility and toughness of the high strength low alloy steels.The toughness of hot rolled test steel at 930 ? is better than that of hot rolled test steel at 800 ? under the condition of the same deformation.According to the drawing condition,the elongation at break of 930 ? hot rolled test steel is better than that of 800 ? hot rolling,which agreeswith the general laws of mechanical properties.The ductile-brittle transition temperature of the hot-rolled test steel at930 ?was between-80 ? and-40 ?,and the ductile-brittle transition temperature of thehot-rolled steel at 800 ? was between-40 ? and room temperature.By observing the fracture pictures of the hot rolling test steel,it is found that the temperature of the test steel decreases,the fracture of the hot rolling test steel specimen changes from the dimple to the cleavage fracture,indicating that the low temperature is an important factor that affects the impact toughness of the test steel.