Effect Of Alloying Treatment On The Microstructure And Properties Of Hadfield Steel

As a wear-resistant material, Hadfield steel has good toughness and wearresistance and is widely used in machinery, mining, metallurgy, railway and so on.Alloying treatment will improve the strength, toughness and wear resistance ofHadfield steel and expand its scope of application. In this paper, Hadfield steels withadding Cr-V-Ti-RE, Cr-V-Ti, Cr-RE and V-Ti-Nb-RE were prepared by adjusting thecomponents of the alloys. The investigation was carried out to study the effect ofdifferent alloying treatment on the microstructure, tensile properties, impact toughness,hardness, wear property and work hardening property.This thesis not only optimizedthe alloying treatment, but also analysed the wear mechanisms of Hadfield steel duringthe impact abrasive wear conditions. The main conclusions are shown as follows:(1) The microstructure of Hadfield steel is austenite after water treatment. Thealloying treatment has no a significant effect on phase composition of Hadfield steel,but affect the grain size and the size, shape and distribution of the impurities. Withalloying treatment, the vanadium, titanium and niobium elements will react with thecarbon and nitrogen elements so that carbon and nitrogen compounds are formed.Meanwhile, the rare earth element will react with carbon and nitrogen element so thatrare earth oxides and rare earth sulfides are formed. These tiny particles can be used asheterogeneous nucleation in liquid steel. Meanwhile, rare earth elements will promotefusing, dissociating and multiplication of dendritic crystal. With these factors，thegrains of Hadfield steel has been significantly refined. The alloying treatment isbeneficial to reduce the number and size of impurities, and improve the distribution ofimpurities in the matrix. When adding rare earth elements, the types of impurities willchange from main form of MnS and Al2O3to Ce2O2S.(2) The results indicate that the tensile properties, impact toughness, hardness，work hardening property and wear property of Hadfield steel increase due to alloyingtreatment. Meanwhile, the specimen with adding Cr-V-Ti-RE owns optimalcomprehensive performances, its tensile strength, yield strength, elongation, hardnessand impact toughness are respectively802MPa,446MPa,28.6%,217HBS and155J·cm-2, compare to the unalloyed, increase respectively by7.4%，14.7%，9.2%，12.4%and32.5%, work hardening parameter H increases by28.6%and wear propertyincreases by13.9%~45.4%. (3) The wear mechanism of Hadfield steel is drilling, cutting and spalling fatigueunder the working condition of impact abrasive wear. The wear mechanism will changewith the vary of the impact energy. Under low impact energy (1J), the wear surfacetopography of steel is mainly furrow and the wear mechanism is drilling and cutting.Under middle impact energy (2J,3J), the deformation of chisel pit mitigates and thenumber of furrows reduces, and the wear mechanism is also small drilling and cutting.Under middle impact energy (4J), the wear surface appears spalling fatigue, and thewear mechanism is spalling fatigue.