The Effects Of Rare Earth On Recrystallization In High Niobium Steel

With the development of steel and iron industry, the requirement to quality of iron is morestrict. In recent years, oil and natural gas demand is gradually rising, thus, the oil and gasexploitation also gradually tend to the remote and environment worse area. In order to meet thelong distance transportation of petroleum and natural gas, more high performance pipeline steelproducts must be developed.The HTP process with the excellent technical characteristics can significantly improve theperformance of steel, so it is an important technological means to produce a new generation ofhigh Nb pipeline steel. Meanwhile, due to its unique physical and chemical properties. The rareearth has been widely used in the field of materials research, addition of rare earth canmetamorphose inclusions in the steel, purify the liquid steel and play the effect of microalloying.Study on the effect of niobium content in0.044%steel shows that, adding rare earth canpromote niobium in austenite of solid solution, promote the precipitation of niobium in ferriteregion. In the paper, the influence of rare earth on static recrystallization process and the rule ofmicrostructure evolution were studied by adding rare earth elements in the high Nb steel.Gleeble1500D was used respectively on two experimental steels. The composition anddistribution of inclusions was studied in experimental steel, the grain size of austenite and thesecond phase particles of solid solution in rare earth high Nb steel at1250℃for differentholding time was annlysed and static recrystallization process was researched. Meanwhile, themicrostructure of the material was obtained and the Microstructure was analysed by using theZeiss microscope and scanning electron microscope in the paper.The experimental results show that rare-earth can obviously inhibit the growth of austenitegrain to high Nb steel in the high temperature insulation process, promote solid solution ofsecond phase particle at the austenitizing temperature and significantly delay the process ofstatic recrystallization. The calculation by thermodynamics show that addition of rare earthin steel increased static recrystallization activation energy by37kJ/mol.That means the processing of static recrystallization of high Nb steel can be pushed to a highertemperature.At the same time, the kinetic equation of rare earth high static recrystallization wasfigured out. In addition, the amount of pearlite were reduced and the formation of acicularferrite and bainite were promoted by using rare earth in steel. Moreover, the pearlitemorphology was changed which pearlite interlamellar spacing was broken and the Fe3Cwas gradually changed into short flake. The result can provide the experimental basis fordeveloping the rare earth high Nb steel of the high performance in our country.