高钨铸造合金已用于铸造大型模具, 由于大量初生M6C碳化物的形成使模具变脆, 需探明初M6C的形成条件。实验表明当含碳量超过0.15%时, 合金中易析出初生M6C, 而10%Co起有效的抑制作用. 初生M6C是在1375 ℃时形成的, 它对通过固-液范围的冷却速度十分敏感, 快冷抑制它的形成.铸件中M6C的形成存在明显的尺寸效应, 枝晶间距大于150m时的较厚截面极易形成毫米量级的M6C, 严重的损伤合金的高温强度。 因此对大截面的模具合金, 为防止初生M6C的析出, 合金中最好保持0.04%---0.07%C和10%---15%Co。
Nickel based superalloys with high content of tungsten (W) have been applied to cast the large size die. Because the formation of large amount of primary M 6 C phase embrittles the die, it is necessary to explore the forming condition of primary M 6 C. The experiments prove that the alloys containing carbon content higher than 0.15% (mass fraction) tend to precipitate primary M 6 Ccarbide and 10% Co can restrict the formation of M 6 C effectively. The primary M 6 C forms at 1375℃. The cooling rate between the solid and liquid temperature range can influence the precipitation of this phase sensitively. Rapid cooling retard the formation of M 6 C obviously. The section size effect of the formation of M 6 C exists in castings. For a heavy section possessing dendrite spacing higher than 150m, it is very easy to form M 6 C with a millimeter magnitude, which damages the high temperature strength of alloys. To prevent the precipitation of M 6 C in large size section die, the composition of alloy is recommended to maintain at the level of 0.04%---0.07% C and 10%---15% Co.
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