用分析电镜、扫描电镜等手段研究了稀土7075铝合金中粗大块状化合物的成分、结构和形成规律。研究表明，在铸态稀土7075合金中出现的粗大块状化合物是一种（Cr，TI）2RE（Al，X）20型稀土化合物，其中X为Mg、Cu、Zn等元素。该化合物具有体心立方结构，晶体常数为1.453～1.458nm，显微硬度为4000～5600MPa，计算密度为3.4g/cm3。合金中（Ti+Cr）含量的减少和凝固时冷却速度的提高均可抑制这种块状化合物的形成。

The effects of silicon additions up to 3.5wt% on the mechanical properties and microstructure of high speed steels 6W3Mo2Cr4v. W3Mo2Cr4V and W9Mo3Cr4V and W9Mo3Cr4V have been investigatied. In order to understand these effiects further, a Fe-16Mo-0.9C alloy is also used. The results show that silicon additions can increase the temper hardness of steels Fe-16Mo-0.9C, 6W3Mo2Cr4V and W3Mo2Cr4V, but yield an opposite influence on the temper hardness in W9Mo3Cr4V steel. A critical tempering temperature aeistsfor the bending strength of high speed steels containing silicon. If tempering is carried out at temperatureslower than the critical temperature, the bending strength of the high speed steels can be improved by the addition of silicon, otherwise their bending strength is decrcased. Transmission electron microscopyreveals that silicon addition can obviously refine secondary hardening carbides and inhibit the formationof M3C cementite at peak temperature. However, they are also found to accelerate both the depletion of martensite and the formation of coarse M6C precipites during temping. The mechanism wherebysilicon additions affect the secondary hardness of high speed steels is discussed in detail, and the types of high speed steel in which silicon additions can be used are suggested.

The effects of silicon additions up to 3.5 wt% on the as-cast carbides, as-quenched carbides and as-tempered carbides of high-speed steels W3Mo2Cr4V, W6Mo5Cr4V2 and W9Mo3Cr4V have been investigated. In order to further understand these effects, a Fe-16Mo-0.9C alloy was also studied. The results show that a critical content of silicon exists for the effects of silicon on the types and amount of eutectic carbides in the high-speed steels, which is about 3wt%, 2wt% and 1wt% for W3Mo2Cr4V, W6Mo5Cr4V2 and W9Mo3Cr4V, respectively. When the silicon content exceeds the critical value, the M2C eutectie carbide almost disappears in the tested high-speed steels. Silicon additions were fotmd to raise the precipitate temperature of primary MC carbide in the melt of high-speed steels that contained δ-ferrite, and hence increased the size of primary MC carbide. The precipitate temperature of primary MC carbide in the high-speed steels without δ-ferrite, bowever, was almost not affected by the addition of silicon. It is found that silicon additions increase the amount of undissolved M6C carbide very obviously. The higher the tungsten content in the high speed steels, the more apparent is the effect of silicon additions on the undissolved M6C carbides. The amount of MC and M2C temper precipitates is decreased in the W6Mo5Cr4V and WgMo3Cr4V steels by the addition of silicon, but in the W3Mo2Cr4V steel it rises up to about 2.3wt%.

The thin strip casting of high speed steels W3Mo2Cr4VSi and W6MoSCr4V2 has been investigated. The as-cast strips are of 2.5-4mm thickness, reduced by hot rolling to 1.8-2mm thickness. The steel sheets are used to make power hacksaw blades. The experimental results show that the metallurgical quality of the as-cast strips is now at an acceptable level, and the as-cast carbides in the strips are very free although the eutectic carbide network still exists. However, most of the eutectic carbide network in the strips can be broken up by post-treatment. Cutting test reveals that the performance of these hacksaw blades is satisfactory, compared with that of hacksaw blades made of conventionally produced steel sheets.

Mechanical activation has been found to be a very effective method of inducing reaction. In this paper, a mixture of ilmenite and graphite with a molar ratio of I to 3～4 was ball milled at room temperature and subsequently annealed. The enhanced carbothermic reactions were monitored by thermogravimetric analysis and X-ray diffraction analysis. A series of reduction reactions occurs with a higher reaction rate in a temperature range lower than that without pre-milling. A longer milling time leaded to a lower reaction temperature and less intermediate phases. When the milled powder was heated in a tube furnace to a temperature range between 1300℃ and 1400℃ for 2～6hours under a cheap mixed gas containing nitrogen, the composite powder of iron and Ti (C, N) without intermediate phases was achieved.