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噴射成形含鈮M3型高速鋼的組織和耐磨性

Microstructure and wear resistance of spray-formed M3 high speed steel with niobium addition

  • 摘要: 采用噴射成形技術制備了M3型高速鋼和以Nb替代V的M3型高速鋼.利用掃描電鏡、X射線衍射、差示掃描量熱儀和金相顯微鏡研究了Nb對M3型高速鋼組織的影響.噴射成形能有效消除宏觀偏析,細化組織.以Nb代V,提高了MC型碳化物開始析出溫度,大量MC相先于共晶反應析出,呈獨立的近球形分布于晶界,同時其尺寸減小.由于消耗大量C,抑制了共晶反應,M2C片層數量減少且厚度變薄,其在熱變形過程中更易于分解,進一步增加了組織均勻性.低溫低載荷時含鈮的M3型高速鋼抗磨損性能顯著優于M3高速鋼,溫度升高到500℃時磨損機制逐漸以氧化磨損為主,兩合金的抗磨損性能差距減小,主要原因是大量呈彌散球形分布的含鈮MC型碳化物能有效提高高速鋼的磨粒磨損抗性,而其對抗氧化性能并無明顯作用.

     

    Abstract: M3 high speed steel (HSS) with or without niobium addition was prepared by spray forming, and the effect of niobium on the microstructure of M3 HSS was investigated by scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD) analysis, differential scanning calorimetry (DSC) and optical microscopy (OM). Finer and uniformly-distributed grains without maerosegregation appear in the as-deposited HSS, and the addition of niobium tends to shift the precipitation of primary MC-type carbides to a higher temperature. Plenty of refined niobium-containing MC carbides precipitate as isolated sphere particles in the grain boundaries before onset of eutectic reaction. Niobium mainly appears in primary MC-type carbides by consuming carbon, which suppresses the degree of eutectic reaction to a large extent, leading to the decrease in both amount and size of M2C lamella carbides. The refined metastable M2C carbides in Nb-containing HSS can be completely decomposed easily during hot deformation, and the homogeneity of carbides in Nb-containing HSS is improved. The wear-resistant property of Nbcontaining HSS is superior to that of M3 HSS at a lower load or temperature. But this gap is reduced with temperature rise. The main reason is that the large number of refined primary MC carbides can improve the abrasive wear resistance of HSS, but have no effect on its oxidation resistance.

     

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