Complex study of the phase composition of powdered stock for high-speed steel ROM2F3

Conclusions By a complex of methods we succeeded in determining the phase composition of powders intended for the production of high-speed steel ROM2F3 by the method of powder metallurgy. By chemical differentiation of the carbides and solid solutions (-Fe, -Fe) we established qualitatively the prescribed composition of the carbides MC and M₂C, and in monoliths the composition of M₆C. The distribution of elements between the carbides MC and M₂C was demonstrated, and their quantities and composition determined. The energy spectra obtained from carbide particles showed that in vanadium base MC and in molybdenum M₂C a very small amount of iron is dissolved (in the form of impurities).It was the first time that x-ray microspectrometric analysis was used in combination with investigations of carbides in the powders of high-speed steels in the regime of secondary emission and with emission spectroscopy with a plasma source of excitation (in determining some elements).Translated from Poroshkovaya Metallurgiya, No. 4(280), pp. 48–51, April, 1986.     

The mechanism of sintering of copper-aluminum powder alloys in the presence of a liquid phase

Summary The investigation has demonstrated that, when mixtures of copper and aluminum powders are sintered at temperatures exceeding the eutectic point, an increase in the specimen volume is observed; the higher the aluminum content of the alloys, the greater is this increase. The specimen growth is associated with the swelling of the copper particles as a result of the penetration of aluminum into them and the formation of voids at the sites of the aluminum particles.     

Structure formation during activated sintering of high-speed steel

Features of structure formation during activated sintering of high-speed steel using a boron-containing additive as an activator are studied. It is shown that presence of an activating additive, its composition and content in the charge, determine features of structure formation compared with sintering without an additive. In the temperature range for solid-phase sintering the content of additive in the charge and the ratio of its components have little effect on the average carbide component size. As temperature increases and there is an increase in boron content in the charge sintering is accompanied by both some increase in austenite grain size and development of a significant difference in carbide grain size. The effect of nickel on size reduction of sintered steel structural components is established.     

Formation and solid-phase sintering of high-speed steel powders

Translated from Poroshkovaya Metallurgiya, No. 4(328), pp. 52–55, April, 1990.     

Pore filling process in liquid phase sintering

Models for liquid flow into isolated pores during liquid phase sintering are described qualitatively. The grains are assumed to maintain an equilibrium shape determined by a balance between their tendency to become spherical and a negative capillary pressure in the liquid due to menisci at the specimen surface and the pore. With an increase of grain size, the grain sphering force decreases while the radius of liquid menisci increases to maintain the force equilibrium. When grain growth reaches a critical point, the liquid menisci around a pore become spherical and the driving force for filling the pore rapidly increases as liquid flows into it. The critical grain size required for filling a pore increases linearly with pore size. Experimentally, filling of isolated pores has been investigated in Fe-Cu powder mixture after liquid phase sintering treatment and after dipping into a molten matrix alloy. The observed pore filling behaviors agree with the qualitative predictions based on the models. In Fe-Cu alloy, pore filling is terminated by gas bubbles formed in liquid pockets. This paper is based on a presentation delivered at the symposium “Activated and Liquid Phase Sintering of Refractory Metals and Their Compounds” held at the annual meeting of the AIME in Atlanta, Georgia on March 9, 1983, under the sponsorship of the TMS Refractory Metals Committee of AIME.     

Special features of formation of the ring-shaped structure in solid- and liquid-phase sintering alloys of the TiC-Ni-Mo system

Translated from Poroshkovaya Metallurgiya, No. 6(354), pp. 75–79, June, 1992.     

Effect of charge fractional composition on high-speed steel powder sintering

The fractional composition of gas-atomized high-speed steel R6M5K5 is studied for its effect on the main features of activated sintering of compacts. A mixture consisting of nickel powder and 30% (wt.) boron is used as an activating addition. It is established that a reduction in average particle size increases shrinkage after sintering, but the dependence of compact shrinkage on fractional composition is different for monodispersed and polydispersed compositions. The maximum size of powder particles for polydispersed compositions has little effect on shrinkage, whereas in the case of monodispersed mixtures there is a marked increase in compact density after sintering with a reduction in particle size. There is a marked increase in density providing closed porosity (90–93%) with a sintering temperature of 1200C, whereas in order to achieve a similar density in the mixture without activator the sintering temperature should be at least 1230C.Translated from Poroshkovaya Metallurgiya, No. 10, pp. 15–20, October, 1992.     

细粒级铁矿粉对烧结液相和矿结构的影响

利用基础烧结设备检测了细粒级铁矿粉同化速度、流动能力,并通过微型烧结杯模拟料层下部单元点烧结过程的方法来研究配加15%细粒级矿粉的烧结矿结构变化,有效分析了3种细粒级矿粉在烧结时的液相行为及对烧结矿结构和性能的影响。通过比较生产用混匀矿与配加质量分数为15%的A、B、C粉的烧结矿结构表明:A粉有利于减少烧结矿内部孔洞的尺寸,减少核颗粒和液相间较大孔洞的数量,并能促进针铁矿发展;B粉会增加烧结矿内部大孔洞,增加柱状或片状铁酸钙的生成;C粉同化速度慢,液相流动能力差,粘结效果差,会使液相与核颗粒间孔洞尺寸和数量增加。烧结杯试验结果表明:在生产用混匀矿中使用质量分数为15%的A粉,烧结矿的转鼓指数提高2.94%,低温还原粉化指数(RDI)降低3.37%。     

Structuring on sintering in the presence of liquid phase in Cr-Cu-iron group metal systems. I. Cr-Cu system

Structuring has been examined for Cr-Cu composites under conditions of impregnation and subsequent liquid-phase sintering at 1200°C in a vacuum of (2–4) · 10⁻³ Pa with reduced and electrolytic chromium powders. The size distribution for the particles of the refractory component in the microstructure containing the reduced chromium on liquid-phase sintering for 60 min corresponds to a logarithmic normal distribution; the distribution parameters are sensitive to the volume fraction of refractory particles. The calculated values for the dihedral angle are close to one of the modes of the distribution for the dihedral angles in the microstructure for specimens made of electrolytic chromium (115°). At 1200°C, the equilibrium Cr_s-Cu_l system obeys the condition . This indicates the probability of formation or preservation of framework structure elements during the liquid-phase sintering, which are observed by experiment in specimens containing reduced chromium. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 3–9, May–June, 2006.     

铁矿粉烧结液相流动特性

在铁矿粉烧结过程中,铁矿粉与CaO反应生成的液相的流动特性,是衡量烧结混合料能否有效粘结的重要指标之一.采用微型烧结法和基于流动面积的粘度测量法,以10种常用进口铁矿粉为对象,研究其液相流动特性及其影响因素.分析了铁矿粉的液相流动特性对实际烧结过程的影响.结果表明:不同种类的铁矿粉由于其自身特性的不同,所生成的液相的流动能力及其随温度、碱度的变化规律有很大差异.     

Specific features of the use of unconventional carbon-containing components in the technology of powdered steels: Report 2. The influence of unconventional carbon-containing components on the sintering processes in the technology of powdered steel

The processes of sintering powdered carbon steels with the introduction of unconventional carbon-containing components into the charge (special artificial low-ash graphite, pyrocarbon, and high-temperature coal-tar pitch) are considered. It is shown that the features of the chemical and granulometric compositions and the crystalline structure of these components (to a greater extent than the conventionally used pencil lead) determine the acceleration of material homogenization during sintering, improve its structural characteristics, and increase its mechanical properties.     

Densification kinetics of W-Fe-Sn pseudoalloys in liquid phase sintering

The densification kinetics in liquid phase sintering of W-Fe-Sn powder composites containing 90 wt.% of a refractory component and 10 wt.% of a low-melting component is strongly dependent on the iron content in the melt. As the iron content in composites increases, the concentration dependence of their densification shows a maximum. Samples containing more than 1.5 wt.% Fe grow intensively because of the formation of W₆Fe₇ intermetallide whose decomposition temperature is higher than that of liquid phase sintering. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 22–29, 2007.