Effect Of Rolling Process Temperature On Microstructure And Properties Of Steel

Hot-rolled H-beam is a metal material with high efficiency,high strength,good low-temperature impact toughness,and reasonable cross-section design.It is widely used in oil platform,railway and bridge construction.In recent years,with the scarcity of terrestrial natural resources,people have began to exploit marine resources,especially the Arctic region is rich in oil and natural gas,and its geographical environment determines low temperature.Therefore,in addition to its high strength,the steel structure for energy exploitation in the Arctic needs high low temperature toughness.At present,low temperature toughness of structural steels is mainly improved by adding alloy element Ni.Because Ni is a precious metal element,the cost of steel increases,and it is also a strategic resource.Therefore,how to improve the low temperature toughness of structural steels by process optimization without adding Ni is of great significance.Grain refinement is a common method of material strengthening,which can improve the strength and low temperature toughness of steel at the same time.In this paper,the effect of rolling temperature on average grain size,grain size distribution,phase composition and grain size difference between flange and web of hot rolled H-section steel Q345 E was studied,and the relationship between structure and properties was discussed.The above experimental results are analyzed from the deformation and recrystallization behavior of austenite.It is helpful to optimize the rolling process temperature system and improve the strength and low temperature toughness of hot rolled Q345 EH section steel.In this paper,hot-rolled Q345 EH section steel was set at six different rolling process temperatures: 990,970,950,930,910 and 890?.The grain sizes of flange head and center,web head and center were analyzed respectively.The changes of microstructures of materials after different rolling temperatures at different sampling sites were studied,and the changes of average ferrite grain diameter and grain size distribution in the microstructures of experimental samples under different sampling sites and rolling temperatures were statistically analyzed.The average ferrite grain diameter and its size distribution were measured by metallographic analysis method through EBSD surface scanning analysis.Accuracy,the changes of mechanical properties such as tensile strength and yield strength of experimental steel were studied by tensile test at room temperature,and the changes of impact absorption energy of experimental steel at-60?were explored by impact test.Based on the experimental results,the effects of different rolling temperatures on the grain size and distribution,phase composition and mechanical properties of the samples were analyzed.According to the research results in this paper,it can be found that the rolling temperature is set to 910 ~890?and the flange head and center,web head and center have good comprehensive mechanical properties.When the rolling temperature is 910?,it has the best comprehensive mechanical properties.The low temperature impact toughness of other specimens may be unqualified at different rolling temperatures or different sampling sites.The impact toughness at low temperature is related not only to the size of grain size,but also to the distribution of grain size,in which the effect of grain size distribution is more significant.However,within the scope of this experiment,the effect of the phase composition seems not obvious.Hot-rolled H-beam has different properties in different parts.The mechanical properties of web are better than flange.This is because web and flange deform in different parts during the actual rolling process of H-beam.Because of the large reduction of web in the rolling process,the deformation of web is also larger,resulting in the formation of fine grains,resulting in the mechanical properties of web due to flange.