Effect Of Niobium On The Microstrures And Properties Of High Carbon Steel

Niobium is one of the important alloy element in steel industry and its role in the steelis stronger than the Cr, V. Niobium is abundant, cheap, and has a great application prospectin our country. Many researches about niobium in the functional mechanism of low carbonsteel has been reported a group of international and domestic academics, however, theresearch on niobium in the functional mechanism of high carbon steel is relative less andreserves and grade of niobium are low in our country. So directly micro alloying smeltingniobium alloy steel can reduce the waste of niobium resources, and improve utilization ofthe niobium resource. China’s economic development makes the surge in demand forhigh-carbon steel, especially as a large consumer of railway. For the study of niobium inthe high carbon steel, in particular, the role of heavy rail steel, this article chooses U74steel which has lower alloy elements as the research object, studies the influence ofniobium on the microstructure and mechanical properties of the high carbon steel.Baogang molten iron containing niobium was used as raw material at this experiment,using the intermediate frequency furnace and20kg multi-function avoidances thecombined-blowing vacuum induction furnace to smelt by selective oxidation and directalloying steel containing niobium. After, the test element in steel was determined, the effectof Nb on the microstructure and inclusion of test steel was analyzed by means ofmetallographic microscope, scanning electron microscope (SEM) and energy spectrum(EDS). The properties of test steel after adding Nb was determined through mechanicalproperties test, wear test, determination of total immersion and electrochemical corrosiontest.Ferrite and pearlite were got by rolling U74steel samples. Along with the increase ofthe content of Nb, grain size was refined in steel, the tensile and impact fracturemorphology were improved, and dimples distribution was more uniform. The molten steelwas purified and the size and the number of false debris is reduced through proper smelting and refining process.Nb was joined in the high carbon steel, which influence on the comprehensivemechanical properties. With the change in content of niobium in steel from0.012%to0.02%, hardness and microhardness of U74steel were improved obviously. Tensilestrength was increased by15%~20%, which was not very obvious to increase.The wearability of steel was improved by joining Nb into the high carbon steel.Wear-resisting degree was improved18.75%adding0.012%Nb, and wear-resisting degreewas improved32.75%adding0.02%Nb.U74Nb steel corrosion rate was less than ordinary U74steel. U74steel was mainlypitting corrosion, and U74Nb was mainly uniform corrosion, which pitting corrosion wasless, by observing from the macro rust layer.The rust layer that is black and not easy to fall off could be got easily fromU74Nb.The corrosion products of XRD analysis were mainly hydroxyl iron and iron oxide.U74Nb corrosion rate decreases with the increase of corrosion time, through fullimmersion corrosion and electrochemical corrosion test. U74Nb steel corrosion productswere more uniform density, higher up of the pit corrosion potential, smaller of pit corrosioncurrent and current density increased slowly by contrast. The corrosion resistance of U74steel was improved by adding Nb.