Design Of Microstructure And Investigation Of Properties Of The Reinforced Phases In Wear-resistant Steel

The strengthening phases(hard phases)play an important role in the performance of anti-abrasive steel.Because of the complex structure and composition and small size of the hard phases in the anti-wear steel,their physico-chemical properties are difficult to obtain quantitatively,leading to the inability to select the appropriate phase and control the composition.Therefore,based on the typical strengthening phases in the advanced wear-resistant steel,this paper adopts first-principles calculation combined with advanced microstructure and performance characterization method to investigate the mechanical and thermal properties of the multielement strengthening phase.The aims are to provide some valuable data for the database of structure and properties of hard phases.It can also provide some guidance for the selection and performance control of hard phase.It is helpful to improve the performance and design new anti-wear steels.The content and results are as following:(1)The experimental results show that the M7C3 carbides in Fe-12Cr-4.5C hypereutectic high chromium cast iron are hexagonal structures with a=b=13.842 A,c=4.495 A,a=?=90°,?=120°.The atomic ratio Fe:Cr=4.9:2.1.The carbides in W6 high speed steel are mainly M6C,but also contain V8C7 and M23C6.The stoichiometric ratio of M6C is Fe2.39W1.14Mo1.57Cro.54V0.36C1.09.The carbides in W18 high speed steel are M6C,and the stoichiometric ratio is Fe3.01 W2.33Cro.38V0.28C1.06.The related data can be used as the basis of theoretical model.(2)According to the formation and evolution of the strengthening phases,Fe-C phases are the most primitive strengthening phases in steel.Fe-C phases have good toughness and the mechanical properties increase with the carbon content increasing.?-Fe3C has very strong anisotropy and at high temperature,thermal expansion coefficient of ?-Fe2C is largest,Which can reach 4.5 ×10-5/K.(3)B or W doping can improve the thermal expansion coefficients of the orthorhombic CrC3 type multielement carbides to 5 ×10-5/K.B can improve the oxidation resistance of hexagonal Cr7C3 type multielement carbides.Mo,W and W+B co-doping improve the toughness of h-Cr7C3 type multielement carbides.Cr3Fe3Moo.5W0.5C2B has good mechanical properties and high thermal expansion coefficient as 8 ×10-5/K,matching the thermal expansion of steel matrix.(4)When the ordered carbon vacancy concentration is lower than 16.7%in VCi1-x phases,the stability is strengthened,but the mechanical modulus is degraded.VC0.875 has largest intrinsic hardness,but compared with VC,its high temperature mechanical properties is worse.Young's modulus of VC,VC0.875 and VC0.750 obtain the maximum value along the principal axis.Thermal expansion coefficient of VC0.875 is 2.8 ×10-5/K under high temperature.(5)For ternary Fe6-xMxC(M=W/Mo)phases,when the atomic ratio Fe/(Fe+M)is greater than 50%,the elastic modulus decreases sharply.The mechanical properties of Fe2W4C and Fe3Mo3C are better than Fe2Mo4C and Fe3W3C under high temperature.The thermal expansion coefficients are 0.6 × 10-5/K for Fe2Mo4C and Fe3W3C.For the quaternary(Fe,W,Mo)6C phases,when the atomic ratio is 16.7%<Fe/(Fe+Mo 4+W)<50%,the overall chemical bondings are strong,results in the higher elastic modulus and melting point.(6)The experiments validate that the doping of tungsten can improve the fracture toughness of primary carbides in hypereutectic high chromium cast iron.The nano indentation tests show that Young's modulus and hardness on the transverse section are slightly larger than the Young's modulus and hardness on the longitudinal section,which is consistent with the calculated results.The two-dimensional distribution of Young's modulus and hardness of W6 and W18 high-speed steel are obtained by NanoBlitz 3D method as well as the statistical values along the x-axis direction.The results are compared with theoretical results and the reason of the difference is analyzed.