烧结-硬化时冷却速率的影响

烧结-硬化正在成为应用范围较广的生产高强度粉末冶金零件的生产工艺。这种工艺能够使钢件在烧结炉中直接形成马氏体,使得用这种工艺生产的零件性能接近于淬火-回火钢件的性能。也省掉了单独的热处理作业,经济效益也很高。因为烧结-硬化的成功取决于烧结后加速冷却时,钢件稳定地形成高含量马氏体显微组织的能力。所以本文将研究从烧结温度开始冷却速率的变化对粉末冶金钢的显微组织、硬度及性能的影响。也将进一步说明如何利用比较设备末端淬火与烧结炉的冷却曲线来改进烧结-硬化工艺。     

粉末冶金铁基零件的烧结-硬化处理

粉末冶金铁基零件材料的力学性能都直接与其密度和显微组织相关。许多粉末冶金零件,为了在表面层或整个零件形成回火马氏体显微组织,都要进行热处理。可用"烧结-硬化"处理替代后续的淬火硬化作业。淬透性足够高的铁基粉末冶金材料,在烧结状态都可形成马氏体的百分含量相当高的显微组织。已开发出了烧结炉的加速冷却技术,其使用可对较大的零件进行"烧结-硬化"处理或用淬透性较低的材料生产横断面较小的"烧结-硬化"零件。将说明硬度与淬透性间的差异,阐述铁基粉末冶金材料的合金化方法是如何影响淬透性的。将介绍现有的"烧结-硬化"材料标准和讨论"烧结-硬化"工艺的优势与缺欠。     

烧结硬化钢高速高扭矩齿轮的开发

烧结硬化使粉末冶金零件可在一般烧结炉的冷却带进行硬化，而不需要在烧结后进行热处理。为开发用于可再充电的电动工具用的高速、高扭矩齿输，试验了掺加有2．0％Cu与0．90％石墨的预合金化粉末ATOMET 4701(0．45Mn-0．45Cr-0．9Ni-1．0Mo)。将零件生坯压制到密度6．85g／cm^3，在1120℃下于吸热性煤气气氛中烧结30min。烧结态零件(密度6．80g／cm^3)的表观硬度为37HRC。显微组织分析表明，在烧结炉冷却带充分产生了马氏体相变。随后，零件在180～210℃下回火0．5～4h。在180℃回火2h后，烧结硬化材料的力学性能与齿输齿的精度处于最佳结合状态，优于经热处理的烧结低合金钢材。     

机油泵传动链轮粉末冶金制造及感应热处理的工艺探讨

粉末冶金是一种高效低耗、节约材料的绿色制造技术。但粉末冶金零件因存在孔隙,密度不均匀,强度硬度相对较低,限制了其使用范围。本文主要研究了机油泵传动机构中链轮的粉末冶金成形、烧结工艺流程,以及该链轮感应淬火工艺中的感应器设计和感应淬火处理工艺的关键参数。结果表明,制备的链轮压坯密度高于6.7 g/cm³,经过1 100~1 120℃渗铜烧结后硬度达到76HRB,60 kW功率感应淬火热处理后齿部形成一层均匀的硬化层,硬度达到71HRA,满足产品性能要求,有效延长了链轮的使用寿命。     

现行烧结-硬化工艺回顾

烧结-硬化工艺,因为不需要再进行热处理,已发展成制造淬硬粉末冶金零件非常有效的一种减低成本的生产方法.最近几年,在烧结-硬化材料系统和烧结炉技术方面都取得了进展.这篇论文将评述这些进展和制造优质烧结-硬化零件所需要的一些关键工艺参数.涉及的具体内容有:合金选择,力学与疲劳性能,显微组织改进,烧结炉冷却速率最佳化及正确的回火周期.     

硬化烧结

正硬化烧结是将粉末冶金材料的烧结和热处理结合成一道工序。与粉末冶金常规的淬火-回火工艺相比,具有显著的优点。省掉了烧结后的一道单独淬火工序,消除了与热处理淬火相关的一些缺陷,缩短了零件的生产周期,降低了生产成本,节省了能源,尤其是对于处理大批量零件更为经济有效。     

低成本高比重细长钨钉配重零件的研制

本文采用传统的粉末冶金压制成形工艺,通过混料、压制、脱胶、烧结和机加工,可生产出完全符合要求的高比重细长钨钉零件。与注射成形工艺相比,简化了生产工艺,提高了生产效率,大大降低了生产成本,取得了良好的经济效益。     

先进的烧结-硬化材料在汽车齿轮、凸轮及链轮等中的应用

最近的汽车产业应用,要求具有高表观硬度、高淬透性及高力学性能的粉末冶金零件材料。这些要求往往是相互矛盾的,因此需要开发烧结态具有高表观硬度、良好静态动态力学性能又不会增加后续热处理费用的新材料。传统上,烧结硬化材料具有适用的表观硬度,但力学性能与烧结体密度差。这里将用资料证明具有良好压缩性,高表观硬度及提高力学性能的一系列烧结硬化材料的力学性能。集中讨论这些材料在汽车发动机与变速器中的应用,诸如齿轮、凸轮及链轮等,这些零件目前都是由压制-烧结及热处理工艺或由铸件或锻造材料用常规切削加工生产的。也将讨论用高温烧结来增强其工艺过程。     

用一次压制-一次烧结达到高密度

利用一次压制-一次烧结高密度工艺可使铁基粉末冶金材料的生产减低生产成本及制造性能较高的零件。用一次压制-一次烧结达到高密度是一个系统方法,需要制备原料粉的预混合粉和随后进行压制与烧结。这篇论文将说明有助于用一次压制-一次烧结达到密度7.5g/cm3所使用的粉末与生产工艺方法。烧结体密度达到这个水平的粉末冶金零件,与用现行压制工艺生产的相比,力学性能有显著改进,已接近锻钢的使用性能。     

高使用性能粉末冶金零件的表面致密化

为保证机构的可靠性,历史上一直在用锻钢合金批量生产高转矩变速器零件,诸如变速器齿轮、高性能链轮、单向离合器座圈及滚珠轴承座圈。虽然用粉末冶金工艺生产的零件成本低廉,但常规粉末冶金钢的静态、疲劳及耐磨性能的局限性,使粉末冶金零件不能应用于上述领域。为解决这些缺欠,近年来,一直在研发用选择性表面致密化(SSD)改进粉末冶金钢性能的各种生产工艺。特别是,PMG集团开发出了一种拥有专利权的表面致密化工艺——DensiForm。利用这种工艺可使零件表面关键部分形成深度达1mm的完全致密化表面层,而零件心部仍然是多孔性的。这种结合与粉末冶金材料合金化的灵活性,使生产的烧结钢零件的使用性能可与在高应力下使用的锻钢性能相比拟。本文将介绍2个例子,即变速器中应用的表面致密化螺旋齿轮和直齿链条的驱动链轮。本文说明了螺旋齿轮和驱动链轮的生产工艺与显微组织,介绍了轿车变速器用螺旋齿轮的性能(其中包括在三轴总成的成对试验台架上得到的滚动接触疲劳的数据)和表面致密化链轮的材料性能与使用性能。     

固体燃料种类和配比对烧结矿质量的影响

为了合理利用燃料资源和降低生产成本,以混匀矿为主要含铁原料,系统研究了焦粉和2种煤粉对烧结矿化学成分、矿物结构和矿物组成以及烧结矿冶金性能的影响。结果表明,在等热值条件下,焦粉有利于改善烧结矿的中温还原性能,但会恶化其低温还原粉化性能;而2种煤粉做固体燃料可以增加烧结矿总的交织-熔蚀结构,对改善烧结矿的冷态强度和低温还原粉化性能比较有利。     

Formation and Sintering Behavior of Nanocrystalline Fe-Ni Powder by Mechanical Alloying

Thepotentialapplicationofnanostructuredma terialsusedasnovelstructuralorfunctionalengi neeringmaterialslargelydependsontheconsolida tionofpowdersbywhichthebulknanostructuredsolidsaremade .Theretentionofthemetastablemi crostructureintheconsolidationprocessismandato ryforpreservingthesuperiormechanical,electricalorcatalyticpropertiesofthematerial.Severalau thorsshowedthatthepressure assistedsinteringisadequateforbothreachingfulldensityandprevent inggraingrowth ,besidesthenanostructuredmateri als…     

Turning and drilling of parts made from sinter hardenable steel powders

Abstract

The constant demand for improved mechanical properties and lower production costs of PM parts has lead to the development of sinter hardenable steel powders. These powders produce fully martensitic microstructures by appropriately controlling the cooling rate during the sintering operation. Thus, the heat treatment operation (oil quenching) that would generally be required to obtain hardened parts can be eliminated. However, machining of the relatively hard sinter hardened parts is difficult.It then becomes critical to optimise the tool selection and the machining conditions, such as surface speed and feed. This paper presents guidelines for the turning and drilling of parts made with sinter hardenable powders, as well as a discussion on the effect of manganese sulphide particles and chip formation during turning.     

Production and properties of brass-base P/M constructional materials. A review

Conclusions The best processing properties are exhibited by brass powders manufactured by the diffusional impregnation technique, using a zinc powder, brass swarf, or a copper-zinc master alloy as a point source. However, as this is a very labor-intensive process, normally preference should be given to melt atomization as a method of manufacture of brass powders. Brass P/M parts produced by the conventional method consisting of pressing a powder and sintering the resultant compacts have porosities of not less than 7–10%, and consequently this method is not widely used for the production of constructional brass parts. The sintering of compacts from copper and copper-zinc master alloy powders gives more stable zinc contents compared with the sintering of compacts from copper and zinc powders; the greatest stability of chemical composition is exhibited by sintered compacts from a homogenized brass powder. The formation of diffusional porosity accompanying the evaporation of zinc may be prevented by performing sintering in the presence of a liquid phase (which appears in the presence of a phosphorus or lead addition), saturating the sintering atmosphere with zinc vapor, and adding carbonates or halides of alkali and rare-earth metals to starting powders. The mechanical properties of materials can be markedly improved by eliminating their porosity. This may be achieved by subjecting porous preforms to hot forging, which enables brass P/M parts to be obtained whose mechanical properties are comparable to those of cast parts.Translated from Eoroshkovaya Metallurgiya, No. 3(255), pp. 56–64, March, 1984.     

Sintering and tribological properties of lead-free bronze alloy for friction materials

Abstract

A lead-free bronze alloy powder with a dispersed sulphide solid lubricant phase has been produced by atomisation as a substitute for lead bronze friction materials. The powder has been processed to produce a bronze/steel bimetal strip by a sinter/roll/sinter process route, via both solid state and liquid phase sintering. Friction properties of the developed materials and a sintered bronze were compared in pin-on-disc tests; the Cu–Sn–S material shows excellent properties, equivalent to those of a lead bronze, and is being assessed for use in high pressure bushes.     

Mo-La合金棒烧结密度的影响因素浅析

选取6种Mo-La粉,考察费氏粒度、粒度分布、形貌以及不同烧结温度对Mo-La合金棒烧结密度的影响,结果表明;相同烧结工艺下,随着钼粉费氏粒度的增大,Mo-La合金棒的烧结密度在减小;费氏粒度相同,粒度曲线偏左的钼粉,Mo-La合金棒烧结密度高;颗粒大小均匀的钼粉,Mo-La合金棒烧结密度接近理论密度,而颗粒大小不均匀...     

铜粉对MIM钨铜合金组织和性能的影响

采用金属注射成形（MIM）技术制备了钨铜合金,定量表征了铜粉的粉末粒度和粒形,重点研究了铜粉粒度和粒形对MIM钨铜合金组织与性能的影响。通过对比铜粉的粒径、粒度分布宽度、长宽比、粗糙度、赘生物指数和钝度等特征参数,破碎铜粉与水雾化铜粉颗粒呈枝晶状,粒径远小于还原铜粉,但破碎铜粉粒度分布宽,微观结构上的规则度、表面光滑程度以及分散程度最佳。破碎铜粉混合钨粉为原料,通过MIM技术制备钨铜注射生坯致密度高、缺陷少,烧结后钨铜合金的组织与性能最优,致密度为96.2%,硬度为235HV,抗弯强度为1 200 MPa,热导率为128 W/(m·K),电导率为30%IACS。     

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.     

Comprehensive Investigations of the Supersolidus Liquid-Phase Sintering of Two Plastic Mold Steels

The processing of plastics, particularly reinforced composites, necessitates the use of corrosion- and wear-resistant materials for tools that come into contact with the polymer. For such applications, plastic mold steels were developed that offer not only a good wear resistance due to the presence of carbides in a martensitic matrix, but also good corrosion resistance provided primarily by a sufficient amount of dissolved chromium. The common processing route for these high-alloyed materials is the hot isostatic pressing (HIP) of gas-atomized powders (PM-HIP). In this context, sintering plays an insignificant role, except for the processing of metal-matrix composites (MMCs). The development of novel wear- and corrosion-resistant MMCs based on plastic mold steels requires knowledge of the sintering behavior of prealloyed powders of such tool steels. It is well known that alloyed powders can be processed by supersolidus liquid-phase sintering (SLPS), a method leading to almost full densification and to microstructures without significant coarsening effects. In this work, two different gas-atomized powders of plastic mold steels were investigated by computational thermodynamics, thermal analysis, sintering experiments, and microstructural characterization. The results show that both powders can be sintered to almost full density (1 to 3 pct porosity) by SLPS in a vacuum or a nitrogen atmosphere. Experimental findings on the densification behavior, nitrogen uptake, and carbide volume fractions are in good agreement with calculations performed by computational thermodynamics.     

CONTINUOUS COMPACTION BY CYCLIC PRESSING

Abstract

A process recently developed produces wide, thick bars of unlimited length from powder, granular, or sponge raw materials by a cyclic pressing operation. The process can be adapted readily for laboratory study or for large-scale production.

Many materials have been pressed by this technique, and in all cases compaction was similar to that experienced in conventional pressing. Work on the pressing, sintering, and subsequent working of various nickel powders and of a nickel-iron-molybdenum magnetic alloy has been carried out. Carbonyl nickel powder produces nickel strip of high quality. A high-permeability alloy containing nickel 79, iron 17, and molybdenum 4% can be made into strip with good magnetic properties by compacting the powders with the cyclic-pressing technique and then sintering and rolling the pressed bar into strip.