Effects Of RE On Niobium Precipitation And Static Softening Behavior Of High Niobium Steel

In recent years, the organic combination of niobium microalloying and controlledrolling and cooling technology is the main development direction of high strength andhigh toughness steel. At the same time, the application of rare earth in high Nb steel hasgot great progress. In steel, the effect of Rare earth on the niobium solidsolution/precipitation behavior and the interaction between precipitation and the staticrecrystallization behavior are still difficult and hot problems for materials researchscholars. In this article, the effect of rare earth on Nb precipitation and static softeningbehavior in high Nb steel is researched by the experiment. The researches provideexperimental basis and theoretical reference for the development of rare earthmicroalloying high Nb steel.In this article, the compression test of low carbon high Nb steel with and without Lawas tested by using Gleeble1500D thermal simulation machine, and the stress relaxationcurves and the true stress-strain curve after three pass deformation at900℃ofExperiment steel were obtained. The solid solubility, second phase precipitated withniobium, microstructure and hardness variation after one/two pass deformation fordifferent holding time after quenching were studied by using Spectrometer, scanningelectron microscopy, transmission electron microscopy, laser scanning confocalmicroscope, and vickers hardness tester.The experimental results show that: rare earth La inhibits the precipitation kineticsprocess of second phase with Nb at900℃(austenite) after single pass deformation andextends second phase with Nb strain induced precipitation start time about14secondsand end time about36seconds. When the heating temperature is1250℃, rare earth Laincreases the solution of Nb percentage by30.6%. After single pass isothermal relaxation480seconds at900℃, rare earth La increases the percentage of niobium precipitation by29.6%and coarses the precipitation size. Solid dissolved and precipitated Nb in steel with and without La restrain staticsoftening behavior in1～2pass at900℃. The experimental steel were in the staticrecovery phase and the effect of La on the static recovery was little. At900℃, therecrystallization happens while the precipitation happens at the same time when the2～3pass gap time100seconds under the condition of1~2pass gap time10seconds, staticsoftening rate increased by8.7%of tested steel with rare earth La compared with testedsteel without rare earth La; The precipitation happens first (precipitated phase has notcoarsened) and recrystallization happens later when the2～3pass gap time100secondsunder the condition of1~2pass gap time244seconds, static softening rate increased by10.1%of tested steel with rare earth La compared with tested steel without rare earth La.