Effect Of Quenching Process On Microstructure And Properties Of Cu Age-hardening Flat Bulb Steel

Copper-bearing low alloy steel has become the key structural material of modern marine bull steels,and plays an important role in the development of marine economy.So far,the reports on microstructure change and behavior of solid solution and precipitation of copper-rich precipitates of copper-bearing low alloy steel in different quenching processes(electromagnetic induction quenching and traditional furnace quenching)are very few.It is well known that different quenching ways not only affect microstructure characteristics and the behavior of solid solution and precipitation of copper-rich precipitates,but also have an important impact on its mechanical and processing property.Therefore,the paper is forward to investigate the behavior of solid solution and precipitation of copper-rich precipitates,and comparison of microstructure characteristics and strengthening and toughening mechanisms in different quenching process.The conclusion of this study can be drawn as follows:The prior austenite grain size of flat bulb steel in electromagnetic induction quenching process is finer than that of traditional furnace quenching.The microstructure of Copper-bearing low alloy flat bulb steel is bainite.The result is that the lath size of steel in electromagnetic induction quenching process is smaller,using SEM.In the meanwhile,the analyses by EBSD show that compared with quenched steel in traditional furnace quenching process,the effective grain size of quenched steel in electromagnetic induction quenching process is finer,and grain boundary density of large and smaller angle of those is significantly increased.After tempering,the tempered samples under different quenching processes respectively retain the microstructure characteristics of quenched samples in different quenching ways.In addition,the phenomenon of recovery and recrystallization occurs in tempering process.The results of mechanical experiments show that the yield strength and tensile strength of quenched and tempered flat bulb steel of induction quenching are respectively higher than those of traditional furnace quenching.There are differences in the properties of low-alloy copper-bearing tempering steels in different heat treatment processes.The strengthening mechanism shows that in different quenching process,fine-grained strengthening plays an important roles in strengthening mechanism.Compared with tempered samples of traditional furnace quenching process,the dislocation strengthening and the fine grain strengthening of tempered samples in electromagnetic induction quenching process are increased,and its precipitation strengthening is weakened because of the coarsen of copper-rich precipitates.Toughening mechanism shows that with EBSD analyses,the density of lager-angle grain boundary in electromagnetic induction quenching process is higher than that of the traditional furnace quenching process,and the proportion is also higher than those.The reason of differences in toughness is the density of lager-angle grain boundary in different heat treatment process and the crack propagation direction is greatly deflected at the large-angle grain boundary.The study of the change rule of copper-rich precipitates in experimental steel is simplified into three processes: air-cooling precipitation,quenching solid solution,and tempering precipitation.With DICTRA and TC-PRISMA simulating the solid solution and precipitation behaviors respectively,their results show that during the electromagnetic induction quenching process,the copper-rich precipitates are not completely dissolved.It was observed that the copper precipitates of the tempered steel in different quenching processes and hot-rolled steel are elliptical or spherical,often distributing near dislocations or slab boundaries.The diameter of the hot-rolled copper-rich particles is in the range of 6-12 nm.The average diameter of the copper-rich particles of the tempered steel in induction quenching is 36.7nm,while that of the tempered steel in traditional quenching is 25.7nm,in accordance with the simulation.