| This paper selects the low carbon-medium boron alloy and medium carbon-medium boron alloy in the two ingredients series alloy as master alloy, adding the single alloy element into it. The effect of chromium, silicium and manganese content on microstructure, properties and wear-resistance of Fe-C-B hypoeutectic alloy were mainly studied. The results show that the type of the solidification structure does not change in the condition of sand casting of hypoeutectic Fe-C-B alloy by chromium, silicium or manganese alloying, which presents the typical solidification organization characteristics of hypoeutectic white cast iron. But they can accelerate precipitation of primary austenite, decrease volume of eutectic carboboride, improve the distribution of hard-phases, and improve the hardenability of alloy. The effect of Si is most prominent, the effect of Mn is the worst.The study also shows that alloying element of Cr, Si and Mn may cause solid solution strengthening when they dissolve into the matrix, decrease volume of hard phases, thus increasing the hardness of cast alloy. The impact toughness of alloy increases with the addition of Cr, which is up to5J/cm2. The main reason for improvement of the impact toughness is that the addition of Cr can reduce the intrinsic brittle of the hard phase, improve the distribution of hard phase and decrease volume of hard phase and restrain its grain growth. The effect of Si and Mn for the impact toughness of cast alloy is not ideal.The alloy is heated to1000℃for austenitizing and after quenching in water, then tempering at200℃. Ater heat treatment, their properties are all increased at different levels. The study shows that the order of the effect on the three elements is that Si>Cr>Mn. Two ingredients series of alloy with the adding of Si can significantly improve the comprehensive mechanical property, which has good hardness and impact toughness. When the content of Si is1.98%in the medium-carbon alloy, its hardness can maintain at59.9HRC, at the same time, its impact toughness is up to8.6J/cm2. When the content of Si is not more than1.65%in the low-carbon alloy, the impact toughness is up to10.8-11.6J/cm2. But the impact toughness decreases with the silicium addition increasing. The effect of Cr addition in the medium-caron alloy and the low-carbon alloy is different. The higher the Cr content of the low-carbon alloy, and its comprehensive mechanical property better. When the content of Cr is1.08%in the low-carbon alloy, its comprehensive mechanical property is best. The hardness of alloy maintains unchanged and its impact toughness decreases with Cr addition increasing, which due to the reduction in the number of hard phase. Another negative factor for property of alloy is that some obvious directive eutectic carboboride appears in the the microstructure of alloy with the excessive amount of Cr addition, which reduce the impact toughness of alloy. In the medium-carbon alloy, the addition of Mn content almost does not affect the mechanical properties of alloy; But in the medium-carbon alloy, only when the content of Mn is up to1.29%, its hardness reduces slightly, and its impact toughness increases from6.9J/cm2to9.5J/cm2.The results of impact abrasion test indicate that, the abrasive resistance of the medium-carbon master alloy is comparable to that of high chromium cast iron. Because of the content of carbon in the low-carbon alloy is too low, which results of the decreasing of hardness, and hence decreases its wear resistance remarkably. Si, Cr and Mn element can further improve the wear resistance in both of the alloys, which is up to1.07-1.31times higher than that of high chromium cast iron. Cr has better enhancing effect than Si, Mn has the worst effect. The wear resisitant of low-carbon alloy is higher than that of medium-carbon alloy by alloying. During the process of impacting abrasive wearing, the modes of wear are main presented as cutting furrow, micro-cutting, fatigue flaking and brittle flaking. |
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