Research On Boride Reinforced High Boron Casting Steels And Their Tribo-corrosion Mechanism In Molten Aluminium

In the aluminium processing industry,which includes die casting,semi-solid processing and the hot dip aluminizing production process,the relative components?such as the dies,shot sleeve and plunger?contact molten aluminium and thus suffer from static corrosion,dynamitic erosion-corrosion and even tribo-corrosion,causing the components to have shortened lifetimes and even fail.Moreover,the sustained deterioration is unpredictable and uncontrollable,thereby leading to the large costs of maintaining and replacing the corroded parts.Therefore,it is necessary to produce a cast steel with excellent tribo-corrosion resistance.Aiming at corrosion and tribo-corrosion issues of steel in liquid aluminium,this work mainly focus on alloying elements of Cr,Mo,B,Ti controlling M₂B?M=Fe,Cr,Mo?,Ti B₂ and high contends of Al/B enhanced high boron casting steels and their microstructures,mechanical properties,corrosion and tribo-corrosion resistances.Additionally,the tribo-corrosion mechanism was also systematically analyzed.The main results were obtained as followes:?1?The contents of B and Cr could significantly change the morphology and crystal structure of boride.Thereinto,with the change of B?1.0?1.5wt.%?3.5?4.0wt.%?and Cr?16.5?17.0wt.%?14.0?14.5wt.%?,the crystal of M₂B boride changed from tetragonal?Fe,Cr?₂B to orthorhombic?Cr,Fe?₂B.?2?Compared to Fe-rich M₂B boride and Cr₂B,only the orthorhombic?Cr,Fe?₂B could react with liquid aluminium forming the periodic layered structures?PLSs?corrosion products.It benefitted from the?Cr,Fe?₂B and its corrosion production of PLSs,the static corrosion volume loss rates of Fe-14.0?14.5wt.%Cr-3.5?4.0wt.%B cast steel under the static corrosion for 8h and tribo-corrosion condition of 10N-150mm?s^-1-30min was 78%and 70%lower than H13 steel,respectively.?3?Coarse primary Cr-rich M₂B boride,irregular hypereutectic blocky Mo-rich M₂B borides and their corrosion products?such as protrusion?could resist the liquid aluminium diffusion and reduce the spallation rate of corrosion products effectively.The tribo-corrosion volume loss rate of Fe-4.0?4.5wt.%B-14.5?16.0wt.%Cr-8.0?8.5wt.%Mo-2.0?3.5wt.%Al high content boron casting steel was 88%lower than H13 steel.?4?With the adding of Ti element,the toughness of high boron cast steel improves remarkably which benefits from the formation of Ti B₂ phase making the the M₂B borides broken net and refined and high boron cast steel still kept the good corrosion resistance.?5?The mass loss of the tribo-corrosion process of boride reinforced high boron casting steel mainly depends on the interaction of corrosion and wear.In addition,with the load,rotating speed and test time increasing,the high boron casting steel suffered a big mass/volume loss under the intensified interaction of corrosion and wear.The tribo-corrosion process consists of the corrosion of matrix,degradation of M₂B borides and exfoliation of corrosion products.