| The hot roll’s working life mainly was decided by the thermal fatigue resistance and the friction and wear performance. The development of these roll materials is from the Chilled cast iron, the high chromium cast iron, the semi high speed steel, the high speed steel to the Cemented carbide. However, these kinds of materials have some problems, such as short life and high cost, which can’t meet the market requirement. So developing a new roll is an important subject. In recent years, composite roll because of its excellent performance have draw the public attention. This is expected to gradually replace the current widely used cemented carbide roll.Using the squeeze casting method, we have successfully prepared the Al2O3p/20Cr25Ni20composites. Using scanning electron microscopy (SEM), metallographic microscope, energy spectrometer, X-ray diffract meter, type hardness tester, friction and wear testing machine, etc studied on microstructure and hardness of the material. Especially analyzed the thermal fatigue resistance and the friction and wear performance of the composite material, then had the contrast test with other roll materials. In addition, analyzed the mechanism of crack initiation and propagation.The experimental results showed that:Al2O3particles uniformly distributed in the Al2O3p/20Cr25Ni20composites, grain is fine and structure is compact, no shrinkage and loose, good mechanical combination of Al2O3particles and matrix. As-cast Al2O3p/20Cr25Ni20composite tissue was mainly made of [Fe, Ni] compound, Cr7C3. But in heat treatment state, in addition to the above group, also generated the Fe2O3products. The hardness of As-cast Al2O3p/20Cr25Ni20composites from composite layer to the substrate decreased. And hardness raised significantly after heat treatment.The test used one circle way by firstly heating5minutes under the temperature650℃and then by water quenching5minutes. Such repeated cycle thermal shock30times only to appear tiny crack. However, Al2O3p/steel base gradient composite material thermal shock30times in the same conditions did not appear micro cracks. Therefore, the latter anti-fatigue performance was superior to the former. But the anti-fatigue performance of Al2O3p/20Cr25Ni20composites was superior to Al2O3p/steel matrix composites, high speed steel and high chromium cast iron and hard alloy.This paper studied the high temperature oxidation behavior of Al2O3p/20Cr25Ni20composites,Under the condition of weak mechanical bond, Due to oxygen and iron generated oxide, didn’t match the thermal expansion coefficient and elastic properties of the substrate, firstly, crack initiated in the oxide layer. With the increase of the thickness of oxide layer, accelerated the growth of cracks. And the cracks from all directions met, which would lap together to form larger macro crack.Under the same test parameters the condition, Al2O3p/20Cr25Ni20composites wear-resisting performance is poorer than cemented carbide. But it was superior to Al2O3p/steel matrix composites, high speed steel and high chromium cast iron and hard alloy.Therefore, in order to improve the high temperature thermal fatigue resistance and the friction and wear performance of the composite material. We should choose better oxidation resistance ceramic particles and heat resistant steel substrate material. And as far as possible select two kinds of materials whose thermal expansion coefficient closes to each other, which can decrease the thermal stress when it work at high temperature and improve the thermal fatigue resistance. Also can choose appropriate ceramic particles volume fraction, and optimize the wear-resisting performance of the composite material at high temperature. |
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