Study On The Effects Of Trace Cerium On Microstructures And Mechanical Properties Of Rebars Used In Constructions

In order to improve the comprehensive mechanical properties of rebars,decrease the consumption of rebars and economize on steels,the development of new-type high-strength rebars has become an essential research trend.In this study,the effects of trace cerium on the microstructures and mechanical properties of rebars used in constructions have been investigated,aiming at ameliorating microstructures of rebars and enhancing their mechanical performance.Three groups of 0.23C-0.36Si-0.56Mn steel samples with various cerium additions were prepared in the medium frequency vacuum induction furnace in an attempt to contribute basic experimental data for developing new-type rebars used in constructions and improving their strength and toughness.As an elementary section of metallurgical research,the following jobs were conducted in the study:(1)Thermodynamic conditions for the formation of rare earth inclusions were obtained according to the thermodynamic calculation.(2)Three groups of specimens with different content of cerium were melted and cast in a vacuum induction furmace.(3)Chemical compositions of the specimens were examined.Metallographic microscope and scanning electron microscope as well as energy dispersive spectrometer were employed to characterize the variation of microstructures and non-metallic inclusions with cerium additions in the specimens.(4)The variation of specimens’ mechanical properties with cerium additions was investigated via a series testing such as static tensile tests,static impact tests and dynamic impact tests.(5)The mechanisms of cerium affecting the chemical composition and microstructure as well as the mechanical performance of the specimens were analyzed and discussed.The conclusions were drawn and shown as follows.1.Cerium can deeply purify the molten steel.Compared to the steel without cerium,when the steel contains Ce=0.01%,the oxygen and sulfur contents can be reduced by 52%and 57%,respectively.And the area percentage is reduced by 51.7%.2.When the cerium content was within the range of 0-0.01%,the grain size of ferrites remarkably decreased by 50.9%,from 19.65μm to 9.65μm.3.When the cerium content was 0.01%,most of the angular alumina inclusions with a size of about 10 μm and long strip-like MnS inclusions were transformed into spherical cerium containing complex inclusions with a size of about 1 μm.The size of inclusions was dramatically decreased and their morphologies were notably improved.4.The mechanical properties of steels with cerium addition were enhanced obviously.When the cerium content reached 0.01%,the specimens’ tensile strength and yield strength increased by 16.95%and 20.81%respectively compared to those of specimens without cerium.The impact energy increased by 91.94%,and the elongation to failure exceeded that of HRB400 standards.5.Under the similar strain rate of 1000 s-1,the dynamic impact yield strength of steel with 0.010%cerium addition increased by 180MPa compared to that of steel without cerium.