用烧结硬化工艺生产汽车分动箱链轮

烧结硬化工艺可利用通过烧结炉一次烧结生产强度与表观硬度高的粉末冶金零件。烧结硬化工艺省掉了烧结后的热处理，从而消除了与热处理相关的一些缺陷，诸如零件的扭曲变形、油污染及增大生产成本。为烧结硬化应用开发了低合金钢粉。这些低合金钢粉与可利用的装备有强化冷却能力的装置的烧结炉相结合，使烧结硬化对于因大小或形状难以淬火的零件特别有吸引力。Masco Tech Sintered Components最近开发的汽车分动箱链轮，就是成功应用低合金钢粉与烧结硬化工艺的一个范例。这篇论文阐述了粉末混合料配方与烧结参数对选择的可烧结硬化材料的力学性能的影响，和将链轮的主要生产线从传统的成形、烧结、精整及淬火的生产工艺改造成生产成本较低的成形与烧结硬化生产工艺采取的方法。     

Characterisation of machinability of sintered steels during drilling operations

Abstract

This study deals with the quantitative evaluation of the machinability of sintered steels during drilling operations. A characterisation technique using scanning electron microscopy and image analysis was developed to characterise quantitatively the amount of flank wear on drillbits. It was shown experimentally, using a drilling test bench, that the evolution of flank wear was proportional to the rate of variation of the thrust force as measured during drilling. Thus, the results show that the slope of the linear region measured on the curve of the thrust force v. the amount of material removed is a more accurate criterion to characterise the machinability of PM products than the average thrust force, which is often suggested in the literature.

Furthermore, the effect of the technique used to add MnS to PM powders was investigated. Quantitative characterisation of machinability during drilling operations showed that parts made with steel powders of the type FC–0208 + 0·5 wt-%MnS machine better when the manganese sulphide particles are pre-alloyed rather than admixed. Finally, machinability of parts made with two sinter hardening powders was characterised including a pre-alloyed MnS powder. The results showed that the ‘drillability’ of this type of part is improved when they are in the presintered state rather than when they are in the green state, i.e. unsintered. Moreover, parts made with the sinter hardening powder pre-alloyed with manganese sulphide particles (MnS) showed superior machinability characteristics.     

Influence of magnesia on iron ore sinter properties and productivity

Abstract

Dolomite and other MgO bearing materials are being increasingly used as basic flux constituents for production of fluxed sinters. Addition of flux materials in sinter influences the resultant sinter microstructure and chemical properties. The physical and metallurgical properties of sinter mainly depend on mineralogy of the sinter. Dolomite is the source of double carbonate of calcium and magnesium. Recent studies reveal that, apart from the additional fuel needed, the addition of dolomite and MgO bearing material greatly influences the magnetite content and the properties of the sinter produced. The increasing use of MgO bearing fluxes in the blast furnace burden, and the trend to incorporate a major part of fluxes in the sinter mix led to an investigation of the influence of MgO on sinter properties and productivity. In this study, the systematic investigation has been made on the influence of MgO% (1·4 to 2·6) on sinter mineralogy and sinter properties with dolomite. Microstructural examination of dolomite sinter revealed that hematite and calcium ferrite phases decreased whereas magnetite phase increased with increase in MgO percentage in sinter. From the laboratory pot grate sintering results it was found that sinter reduction degradation index improved whereas tumbler index and reducibility decreased with increase in MgO%.     

THE FABRICATION OF HIGH-SPEED TOOL STEEL BY ULTRAFINE POWDER METALLURGY

Abstract

Various powder-metallurgy techniques have been developed during recent years to avoid segregation effects associated with the conventional methods of casting and forming high-speed steels. These techniques have generally involved the consolidation of hot working or hot pressing of 50–500μm prealloyed powders into dense billets or rods.

The work described has demonstrated that much finer, 0·5–5μm, powders of M2 and M50 steels may be cold pressed and sintered to produce bodies with densities of 99% theoretical containing uniformly distributed 1–2μm particles of carbides. It is anticipated that the method will have application for the manufacture of complex-shaped parts with very small material losses and little machining.

An account is given of the preparation of the fine powders by ball-milling and their subsequent compaction, sintering, and microstructure. The control of carbon and oxygen levels by carbon addition to the powders is described.     

Recycling of steel plant mill scale via iron ore pelletisation process

Abstract

Mill scale is an iron oxide waste generated during steelmaking, casting and rolling. Total generation of mill scale at JSWSL is around 150 t/day and contains 60–70%FeO and 30–35%Fe₂O₃. To recover the iron, the mill scale must be smelted in a blast furnace or other reduction furnace; however, it is usually too fine to use without previous agglomeration such as via pellet or sinter mix. JSWSL operates a 4·2 Mtpa pellet plant to produce pellets for Corex and BF ironmaking units. The aim of this study is to determine the effect of mill scale on pellet properties. Detailed laboratory basket trials were conducted using up to 40% of mill scale in the pellet mix. The addition of mill scale up to 10% is considered to provide the optimum balance of chemical, physical and metallurgical properties of the pellet.     

Structure and mechanical properties of sintered Ni free structural parts

Abstract

Ni, Cu and in some cases Mo are the alloying elements which have traditionally been used in sintered steels. High performance of powder metallurgy (PM) structural parts from Fe powders is reached mainly by alloying of Ni. The use of Mn in Fe base PM structural parts has been avoided because of its high affinity to oxygen. It is difficult to sinter Mn steel, without oxidation, in industrial atmospheres. However, the PM industry follows also possibilities in order to develop Ni free sintered steels which render as high mechanical properties as diffusion alloyed Ni containing sintered steels and further fulfil the requirements of health protection. In recent years Mn have been introduced as alloying element in Fe based structural parts, on laboratory scale and also for pilot scale production. In this paper the factors that contribute to the structure and mechanical properties of sintered Mn steels are summarised.     

Optimisation study of ironmaking using biomass

Abstract

The economic advantage of using biomass as partial substitute for fossil reductants in the blast furnace (BF) process was studied by simulation. A thermodynamic model of the BF was used in combination with simple models of the coke plant, sinter plant, hot stoves, basic oxygen furnace and power plant. Pretreatment of the biomass before its injection in the BF is considered in a pyrolysis unit where the carbon content and heating value are raised and the oxygen content is lowered, which is beneficial for the BF. The system was optimised with respect to the price of raw steel, considering costs of raw materials, energy and CO₂ emissions of the unit processes. The study demonstrates that biomass in partially pyrolysed form is a potential auxiliary reductant and that the optimal states of operation within certain regions depend strongly on the price structure of the raw materials and emissions.     

PM Nickel Alloys for Thermionic Emitters

Abstract

An introduction explains the principles for substrates of oxide thermionic emitters. A method of fabrication, alternative to the traditional fusion processes, is described, employing roll compaction of mixed metal powders, with the recognized advantages over conventional ingot pressing and sintering for medium-scale production with modest equipment investment. Especially valuable is the capability to sinter continuously, rapidly, and at relatively low temperatures, which confers extra control over contents of volatile and reactive additives. Protection of these additives during sintering and preliminary fabrication is effected by prealloying and coating the alloy powders with a layer of the matrix metal-nickel. The equipment and process is described with attention to controlling uniformity of thickness and density transversely and along the strip length, which is essential in minimizing edge cracking during the early rolling stages. Purity and compositional control is held to much tighter tolerances than for cast alloys, but a microheterogeneity obtains: a method for demonstrating this feature is illustrated. This microinhomogeneity modifies the diffusion characteristics of the additives and is a factor in restricting grain growth during fabrication and operation. PM/0240     

DETERMINATION OF HOOP STRESSES INDUCED IN A CYLINDRICAL STEEL DIE BY COMPACTING METAL POWDERS

Abstract

Because of the lack of stress data, steel dies for compacting metal powders were designed in the past on the assumption of hydraulic pressure transmission by powders.

True die stresses existing in a hardened steel die during the compacting of various lubricated and non-lubricated powders have been measured by mounting strain-gauges on the periphery of the die at numerous points along its length.

Values of the hoop stress varied from approximately 0·05 to 0·40 of the calculated and measured hydraulic fluid stress. For a particular metal powder, the stress was a function of the average particle size, the powder height, and the amount of lubrication.     

A neural network based model of sinter quality and sinter plant performance indices

Abstract

A prerequisite of a smooth operation of the ironmaking blast furnace is that the quality of the burden is stable. In blast furnaces where sinter is used as the (main) iron bearing material, its quality plays a crucial role in productivity and fuel economy. Simultaneously the corresponding factors must be considered for the sinter plant. The present paper studies the influence of three variables characterising the bedding piles and five sinter plant operation variables on sinter quality, sinter plant productivity, specific fuel consumption and share of cold return fines. Daily mean values for a period of five years of operation were used in the data driven modelling based on feedforward neural networks. The resulting models were found to describe the major changes in the outputs well. The input–output relations captured by the models were analysed by perturbing one input variable of the networks at a time and analysing the predicted behaviour of the outputs.     

THE PRESSING AND SINTERING PROPERTIES OF IRON POWDERS

Abstract

Some twenty different iron powders are available in Europe for the manufacture of sintered bearings and structural parts. These powders can be grouped under four headings: reduced, atomized, comminuted, and electrolytic. Details are given of the experience gained in testing these types of powder by the methods in common use in the metal-powder industry.

The influence of the data thus obtained on the processing, in particular the pressing and sintering conditions, of iron powders is discussed in detail. Consideration is given to the way in which the properties of the powders affect their sinterability, the pressing operation and tool design, and also the physical characteristics of the finished product.     

PM processing of elemental and prealloyed 6061 aluminium alloy with and without common lubricants and sintering aids

Abstract

A comparison has been made between compaction, sintering, microstructural and mechanical properties of the 6061 aluminium alloy prepared via premixed elemental (EL) and prealloyed (PA) powders (as received and degassed) with and without additions of sintering aids and various solid and/or liquid lubricants. Both EL and PA powders were cold pressed at different pressures, ranging from 250 to 770 MPa, and sintered under vacuum in the range 580–640^°C for 30–120 min. and then under pure nitrogen atmosphere for comparison. Vacuum degassing of the PA powder provided better compressibility and thus higher green densities than those for the as received PA or the premixed EL powder compacts pressed at compaction pressures ≥340 MPa. Near full sintered densities of , ～98%TD were obtained for both EL and PA 6061 Al alloys. Degassed PA Al with 0·6 wt-% paraffin wax (PW) or with only 0·12 wt-%Pb addition as sintering aid and no lubricant, and premixed EL with only 0·12 wt-%Pb addition and no lubricant gave the best optimum properties. It became apparent that additions of some solid lubricants such as lithium stearate (LS) and acrawax to both the premixed EL and PA powders provided reasonable green densities, but had deleterious effect on sintered densities and microstructures, particularly under vacuum sintering. Heating data curves during the sintering cycle, revealed formation of both transient and persistent liquid phases for the EL and mainly supersolidus liquid phase sintering (SLPS) mechanism for the PA. Tensile properties of the degassed, vacuum or nitrogen sintered PA Al alloy in T6 condition were higher than those of the equivalent alloy prepared by EL mixing with the former giving a tensile strength of 330 MPa and 6–8% elongation to failure, which are similar to those of the commercial (wrought) 6061 Al alloys.     

Tensile and fatigue properties of cold and warm compacted Alumix 431 alloy

Abstract

In this experimental study, tensile and fatigue properties of the Alumix 431 alloy (Al, Zn, Mg and Cu alloys) produced using the conventional press and sinter processes in different pressures and temperatures are investigated. The results clearly showed that the warm compacted specimens can reach the mechanical properties of the cold compacted ones under less pressure. In the fatigue tests it was observed that fracture started from large pores as shown in all scanning electron microscope (SEM) examinations and ductile fracture occurred. 85% of the 180 MPa/80°C and 77% of the 230 MPa/RT specimens fractured at the machined surface. Tensile and fatigue properties of warm compacted (180 MPa/80°C) and cold (230 MPa/RT) compacted specimens are almost equal at these same densities. This result indicates the economic benefit of warm compaction by the much lower applied compaction pressure.     

Sintering Characteristics of Indian Chrome Ore Fines

Chrome ore concentrate consists of high-temperature melting oxides such as Cr₂O₃, MgO, and Al₂O₃. The presence of these refractory constituents makes the ore a very high melting mineral. Hence, it is difficult to produce sinter from chrome ore by a pyrometallurgical route. Currently, chrome ore is ground to below 75 μm, pelletized, heat hardened through carbothermic reaction at 1300 °C to 1400 °C, and then charged into a submerged electric arc furnace (EAF), along with lumpy ore for ferrochrome/charge-chrome production. Electricity is a major cost element in this extraction process. This work explores the sinterability of chrome ore. The objective of this study was to: (1) determine whether chrome ore is sinterable and, if so, (2) ascertain ways of achieving satisfactory properties at a low temperature of sintering. Sintering of the raw material feed could be a way to reduce electricity consumption, because during sintering a partial reduction of minerals is expected along with agglomeration. Studies carried out by the authors show that it is possible to agglomerate chrome ore fines through sintering. The chrome ore sinter thus produced was found to be inferior in strength, comparable to that of an iron ore sinter, but strength requirements may not be the same for both. Because the heat generation during chrome ore sintering is high owing to some exothermic reactions, compared with iron ore, and because chrome ore contains a high amount of fines, shallow-bed-depth sinter cake production was attempted in the laboratory-scale pot-sintering machine. The sintered product was found to be a good conductor of electricity because of the presence of phases such as magnetite and maghemite. This characteristic of the chrome ore sinter will subsequently have a favorable impact in terms of power consumption during the production of ferrochrome in a submerged EAF. The sinter made was melted in the arc furnace and it was found that the specific melting energy is comparable to that of heat-hardened chrome ore pellets but lower than briquettes and lump ore.     

A REVIEW OF SINTERED METAL BEARINGS: THEIR PRODUCTION,PROPERTIES, AND PERFORMANCE

Abstract

Five classes of sinter-based bearings are identified: steel-backed materials with compacted non-porous sintered linings for engine bearings and wrapped bushes; steel-backed materials with porous sintered linings impregnated with a plastic, intended for operation dry or with sparse lubrication; unbacked porous sintered-metal parts impregnated with oil to form self-lubricating bearings; unbacked non-porous sintered metal parts incorporating graphite; sintered polytetrafluoroethylene parts incorporating powdered metals. Methods of manufacture are outlined.

Techniques of bearing evaluation are described, the most useful being sophisticated, flexible test-rigs which approach closely the conditions of actual bearing applications.

The relative fatigue strengths of sintered engine-bearing linings are given and sintered copper-lead is shown to be equivalent in fatigue strength to cast linings.

The impregnation of sintered bronze linings with PTFE and lead yields a material with good un lubricated wear-resistance. The effect of load, rubbing speed, and other variables is described. A polyacetal lining bonded to a steel backing via a porous bronze interlayer gives a bearing material with good performance under conditions of sparse lubrication.

The relative merits of oil-impregnated porous metal bearings obtained by the pressing and sintering of copper, iron, or aluminium alloy powders are described. For optimum performance the bearing conditions should favour the formation of a hydrodynamic film of oil over the bearing surface.

The incorporation of graphite into fully compacted powder-metallurgy parts gives improved wear-resistance under dry and sparsely lubricated rubbing conditions.

PTFE parts incorporating metal powders can be moulded to finished size by powder-metallurgy techniques.     

Abrasive power of titanium carbide and carbonitride

Conclusions In comparisons of the abrasive powers of powders it is necessary to consider their production technology. Only those results are comparable which have been obtained in grinding tests on the same material. In the choice of a powder as an abrasive it is necessary to know its dynamic abrasive power. The character of variation of this property enables optimum abrasive machining conditions to be determined. In the grinding of steels at pressure of up to 75 kN/m² titanium carbide and carbonitride (5 wt. % N) powders surpass electrocorundum in abrasive power during the first 300–500 sec of operation and give a better surface finish. They can therefore be successfully used as grinding powders and micropowders for the preparation of pastes intended for the abrasive machining of steels.Translated from Poroshkovaya Metallurgiya, No. 6(222), pp. 78–81, June, 1981.     

MECHANICAL PROPERTIES OF SINTER/FORGED LOW-ALLOY STEELS

Abstract

The paper describes preliminary work on sinter/forged low-alloy steels. The mechanical properties and structures of both atomized and blended alloys were investigated. By using a good-quality atomized powder of the SAE 4600 type, tensile and fatigue properties equivalent to those of wrought steels could be obtained. Atomized alloy powders with higher oxygen contents had poor ductility and impact values because of surface oxides on the powder particles.

Blended iron alloys gave tensile strengths up to 72 tonf/in² (1112 MN/m²) with much higher ductility and impact-resistance than would be obtained with conventionally pressed and sintered alloys.     

Influence of powder characteristics on sintering behaviour and properties of PM Ti alloys produced from prealloyed powder and master alloy

Abstract

The use and development of titanium and titanium alloys have been strongly correlated to high technology industries where costs are not the most important aspect. Titanium could see its market grow by the application of lower cost and more efficient processing methods such as powder metallurgy. This work deals with the characterisation of two types of powders: commercial prealloyed powder and powder produced from master alloy combining mechanical milling and conventional blending to adjust the particle size. The characteristics of the powders, sintering behaviour and final properties of the parts indicate that the master alloy approach leads to better compressibility than the prealloyed powders and, therefore, to lower dimensional change during sintering. The most important result is that it is possible to obtain Ti alloys with properties similar to or better than alloys from prealloyed powders and to obtain homogeneous microstructures, which allows the composition to be adjusted to requirements.     

Microstructural Investigations of the White and Deformed Layers Close to the Turned Surface of Ti-6Al-4V

In the aircraft industry, along with geometrical and dimensional integrity, the surface integrity of manufactured parts is a necessity. In fact, severe anomalies generated during machining may have a substantial impact on the lifetime of the parts. Nevertheless, these anomalies are not well known in terms of microstructures such as the white layer in titanium alloys. Based on this observation, the present paper deals with microstructural investigations performed on Ti-6Al-4V white and deformed layers generated during turning with a round uncoated carbide insert. The aim of this study is to characterize these anomalies in terms of microstructure and phases. In particular, this study provides a better understanding of metallurgical transformations in the sublayer of machined surfaces through qualitative models.

     

MODERN ATOMIZING TECHNIQUES

Abstract

Reduced iron, copper-base, and refractory metal powders have dominated the raw-material field during the rapid growth of the PM industry in the last 30 years. Emphasis has been on the economic mass production of structural parts, rather than on properties. New material concepts have brought about the need for new and improved powders possessing enhanced properties and performance reliability, i.e. atomized powders. Modern atomizing techniques and parameters are reviewed in terms of their economics and influence on powder properties, chemistry, ultimate structural control, property reliability, and alloy and process flexibility, especially with materials difficult to fabricate.