Research On Preparation And Microstructure Properties Of TiB₂ Particle Reinforced Steel

TiB₂ particle reinforced steel is a new composite material with high specific strength,high specific stiffness and low density.It is a potential lightweight material in automobiles.However,during solidification of TiB₂ particle reinforced steel,there are some problems such as agglomeration and floatation of TiB₂ particles.It is of great value and practical significance to study and analyze the motion mechanism and control methods of TiB₂ particles to improve the mechanical properties of steel.In this paper,TiB₂ particle reinforced steel was prepared by in-situ formation of TiB₂ particles in iron matrix.The distribution,morphology and mechanical properties of primary and eutectic TiB₂ particles in steel reinforced with TiB₂ particles at different cooling rates(step-shaped copper mould)were studied.The effects of rare earth elements on the distribution,morphology and mechanical properties of primary and eutectic TiB₂ particles in TiB₂ particulate reinforced steel were studied,and the effects of electromagnetic stirring on the distribution,morphology and mechanical properties of primary and eutectic TiB₂ particles in TiB₂ particulate reinforced steel were studied.The main conclusions are as follows:(1)The effect of different cooling rates on the distribution of primary TiB₂ particles in iron matrix were studied by designing a step-shaped copper mold to solidify at different cooling rates.When the ingot thickness was 1 mm,the primary TiB₂ particles size were about 3 ?m and distributed in the iron matrix,and when the ingot thickness was 5 mm,the primary TiB₂ particles size were about 8 ?m and the agglomeration occured.When the ingot thickness was 40 mm,the primary TiB₂ particles size were about 15 ?m and the agglomeration was serious.(2)The addition of 1wt%rare earth elements(Ce and La)can effectively refined the primary TiB₂ particles in the TiB₂ particle reinforced steel,increased the number of primary TiB₂ particles and inhibited the segregation of primary TiB₂ particles;In TiB₂ particles,the rare earth elements Ce and La existed in the form of oxides,which made the morphology of TiB₂ particles changeing obviously.The rare earth elements Ce made TiB₂ particles appeared as polygonal and aggregated together to form circular aggregates;the rare earth elements La led to spherical TiB₂ particles.The hardness of the samples without rare earth were about 52.5 HRC.After the addition of rare earth elements Ce,the hardness of the samples were 56.3 HRC.When the rare earth elements La was added,the hardness of the samples were 55.7 HRC.(3)A large number of cleavage steps were found in the tensile fracture morphology of TiB₂ particles reinforced steel before forging.The tensile strength of the samples were 520MPa and the elongation of the samples were about 3%;there were a large number of dimples with different depth in the tensile fracture of the forged samples.The tensile strength and the post-fracture elongation of the samples were obviously increased.The tensile strength and the post-break elongation of the samples were improved by adding rare earth elements Ce and La.(4)Electromagnetic stirring can effectively refined the primary and eutectic TiB₂ particles in the TiB₂ particles reinforced steel.without electromagnetic stirring,the size of the primary TiB₂ particles were about 35 ?m and the agglomeration was more serious,and the hardness of the samples were about 52 HRC.When the current intensity was over 300 A,the size of the primary TiB₂ particles were about 18 ?m and the distribution was uniform,and the hardness of the samples were about 55 HRC.