烧结硬化粉末冶金钢在高性能零件中的应用

粉末冶金烧结硬化是一种经济有效的生产高强度零件工艺过程。但是,其后续机加工相对困难和昂贵,因此尺寸公差控制也是烧结硬化过程中关注的重要目标。本文基于MPIF标准制备了多种烧结硬化材料,并对比了它们在同等压制压力下的测试试棒以及同等密度下工业粉末冶金零件上的强度、延伸率及尺寸稳定性表现。结果表明在工业生产条件下,所有材料都得到了有效烧结硬化并表现出了优秀的尺寸稳定性。在工业零件生产中,Cr M作为一种预合金无铜添加的经济有效的烧结硬化材料,由于它的高淬透性,在0.5%C(质量分数)添加时,表现出高的尺寸稳定性及极佳的性能。     

可烧结硬化组成合金的开发

粉末冶金产业市场力量正在挑战粉末冶金合金中通常使用的传统组成.Mo、Ni及Cu因和氧亲和力低,是铁基粉末冶金使用的主要合金化元素.另外,Mo对压缩性的影响很小,和Cu在烧结温度下通过液相可快速熔成合金.这三种元素也都增高钢的淬透性,用这些元素的混合物生产的零件可进行烧结硬化.价格压力迫使对采用这些元素的粉末组成重新进行...     

粉末冶金零件生产用石墨粉的选择

粉末冶金零件应用领域的扩大,在于和其他各种制造工艺与材料的竞争。这种竞争实质上是粉末冶金零件生产中的3个关键变量:使用性能(力学性能)、价格及精度(尺寸变化与其稳定性)和其他制造工艺与材料的竞争。而原材料价格的易变性强烈影响了其第4个变量:生产的利润率。在粉末冶金结构零件生产中,石墨的主要作用是烧结时使碳扩散到纯铁粉或预合金化铁粉颗粒中,以使钢基体硬化。石墨有2种:天然石墨和初生合成石墨,这2种石墨在烧结时的性状是不同的。本文介绍了最近一些实验室与规模生产的试验结果,通过选择最合适的石墨粉得到粉末冶金零件生产中的上述3个关键变量的最佳值,以提高粉末冶金零件的生产竞争力。     

粉末冶金Fe-2Cu-0.8C合金零件尺寸变化的分析与控制

Fe-Cu-C合金,特别是Fe-2Cu-0.8C合金,是粉末冶金零件生产中应用最广的一类合金材料.这种材料的力学性能与烧结性优异,成本具有竞争性,但是,用于生产尺寸精密与形状复杂的零件时,尺寸变化不易控制.本文分析了影响这种合金材料尺寸变化的因素,特别是烧结时的尺寸变化.介绍了一些添加铜的方式对烧结Fe-2Cu-0.8...     

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。     

优异烧结硬化材料(Ancorsteel737SH)的研发

烧结硬化技术能够帮助粉末冶金零件制造商改善生产效率和降低生产成本。但是,新型高性能烧结硬化材料和设备的缺少,已成为烧结硬化工艺发展的障碍。对材料的研究的重点是提高硬化性能和改善压缩性。最近一种具有高的烧结硬化性和高压缩性的新型烧结硬化材料已被研发出来,其性能超越之前的FLC-4608.这项改进可以让制造商在正常的烧结条件和压制条件下获得高的密度和高的性能。本文全面介绍了该材料的基粉在添加不同成分下,常规压制密度所对应的机械性能,同时也介绍了在生产过程中通过添加其它添加剂来获得高密度和高性能的方法。     

低合金钢粉的烧结硬化与性能研究

对粉末冶金公司生产的低合金含量的水雾化预合金钢粉Fe-1．8Ni-0．5Mo进行了烧结硬化工艺的研究，探讨了在较高密度条件下，以低合金钢粉为基础的材料体系的烧结硬化性能和影响因素。     

美国金属粉末工业联合会(MPIF)粉末冶金零件设计竞赛获奖MIM零件介绍(连载)

10阀体组合件生产厂商:Advanced Materials Technology获奖年份:2000奖项:大奖市场部门:工业马达/控制装置说明:该零件是测量化学物质与石油流量的仪器传感器控制阀中的阀体组合件。这个形状很复杂的零件替代了由2个普通粉末冶金零件和2个切削加工零件组成的组合件。MIM零件是由50Fe-50Ni合金材料制作的,最终烧结件密度为8.05g/cm3,硬度为     

烧结后热处理对烧结硬化粉末冶金钢零件尺寸精度与力学性能的影响

在铁基粉末冶金零件的最终形生产中尺寸精度是一个关键参数.粉末冶金零件生产厂商一直在追求较大的零件,但终端用户规定的绝对公差一般并不随零件尺寸而改变.因此,对较大的零件,尺寸变化或尺寸变化的偏差必须减小.除了与常用低合金粉末冶金钢的压制与烧结相关的尺寸变化外,烧结硬化合金对粉末冶金零件生产还提出了一些独特挑战与机遇.在烧结炉中能淬硬的零件,就不要后续淬火作业了.可是,形成的未回火的马氏体显微结构对尺寸稳定性与力学性能来说并不理想.回火的淬硬钢由于马氏体转变成了密度较高的较稳定的铁素体与碳化物显微结构,从而改善了力学性能并使尺寸产生收缩.另外,许多铜及碳含量高的烧结硬化钢牌号都会导致残留奥氏体的含量较高.残留奥氏体可改进冲击性能与延展性,但是,由于热波动残余奥氏体可转变成密度较低的贝氏体和/或马氏体从而影响尺寸的稳定性.为得到最好的力学性能与尺寸控制组合,烧结硬化钢需要进行适当的热处理.本文考察不同的烧结后热处理对烧结硬化粉末冶金钢尺寸、显微结构以及力学性能的影响.     

合金化Fe-Mo-Ni-Cu-C烧结硬化钢性能研究

以Fe-Mo预合金粉为基粉,通过添加合金元素Ni、Cu,经820℃部分扩散制成Fe-Mo-Ni-Cu部分扩散合金粉,应用粉末冶金技术制备了Fe-Mo-Ni-Cu-C烧结硬化钢,对该材料的组织结构和物理机械性能进行了研究。实验结果表明:烧结硬化钢材料在烧结后期于氢气保护下直接冷却,不需要单独淬火,随冷却速度不同,Fe-Mo-Ni-Cu-C烧结硬化钢的主要金相组织为回火马氏体、珠光体和下贝氏体。合金元素Mo、Ni、Cu的加入改善了材料的组织,大幅度提高了材料的强度和硬度。材料硬度:HRC 50,拉伸强度:σb936 MPa,冲击韧性:23.6 J/cm2,密度:7.23 g/cm3。     

Leaner alloys for the PM industry

Abstract

Numerous lean alloy systems are now available to the PM parts manufacturer as potential lower cost solutions without sacrificing part performance. More recently, steels containing 0·3 and 0·5% prealloyed molybdenum have been introduced which can be tailored with reduced Ni and/or Cu additions to meet specific properties for use in press and sinter applications or as quench and temper grades. These reduced Mo prealloys complement the already familiar 0·85 and 1·5%Mo grades to provide a full range of prealloyed molybdenum steels. Another method to reduce susceptibility to market pricing has been through incorporating manganese, which is historically inexpensive yet highly beneficial to steel properties. Combining Mn with moderate levels of Mo in specially designed alloy grades provides a lean alternative to Ni and Cu containing hybrid alloy steels. This study will examine these lean alloys and explore where there may be opportunity to use them in place of traditional PM grades.     

烧结钢生产过程中的尺寸变化及其控制(1)

烧结零件的尺寸变化及控制对其生产过程及成本至关重要，尤其是近几年烧结硬化技术的发展，减少了烧结后精整（sizing）的可能性，对烧结过程中零件的尺寸变化及其控制提出了更高的要求，本文结合烧结钢零件的生产过程综述了影响尺寸变化的各种因素，并阐述如何协调这些因素以便最有效地控制尺寸变化。并结合烧结钢最常用的几个合金体系举例说明。     

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。     

世界粉末冶金工业一瞥

简介了国外与国内的粉末冶金工业发展现状;详述了近年来出现的温压、流动温压、高速压制、动磁压制、AncorMax D压制的新技术以及选择表面致密化方法;并对烧结硬化材料、软磁复合材料、磁致热材料等粉末冶金新材料进行了评述.     

High temperature deformation of oxidized β-Zr-Mo alloys

The flow properties of β-phase Zr-Mo alloys were investigated by means of compression testing in a nominally pure (10 ppm O₂) argon atmosphere. Experiments were carried out in the strain rate range 10^-1 to 10^-5 s^-1 and from 900 to 1000°C. The stress-strain curves were unusual in that they exhibited a continuous decrease in flow stress with strain, after little or no work hardening. A further unusual feature of the data was that the flow stress in interrupted tests increased with delay time in all the alloys. By contrast, crystal bar Zr, tested under the same atmosphere, exhibited neither flow softening nor significant interruption hardening, but deformed in a conventional manner. The results obtained from X-ray investigations, as well as from interrupted tests and from tests carried out in a more purified atmosphere, indicated that the occurrence of both interruption hardening and flow softening was associated with the formation of an oxygen stabilized a-layer on the outer surface of the β-sample. Growth of the hard α-layer during annealing produces strengthening while its decrease in volume during deformation produces softening. A model, based on the assumption that the hard α-phase shares the load applied to the sample, was developed, and its predictions agree satisfactorily with the experimental observations. The extreme sensitivity of Zr-Mo alloys to trace amounts of oxygen is attributed to the presence of liquid molybdenum oxides in the surface scale, which leads to rapid oxygen transport. The stress sensitivity of the strain rate in these alloys decreases from 4.0 to 3.4 as the molybdenum concentration is increased from 0 to 6 pct, for both the yield and the steady-state regimes of flow. The alloy flow stress increases with molybdenum concentration approximately as C^0.4, and it is apparent that the molybdenum atoms do not act as individual obstacles to flow, but are likely to lead to strengthening by indirect means.     

Hundred years of precipitation hardening

About 100 years ago, precipitation hardening was discovered and the first structural aluminum alloys with considerable strength were developed. Our present understanding of the phenomenon in based on the application of dislocation theory as well as reaction kinetics, especially the role of metastable phases and lattice defects in nucleation from supersaturated solids. The prerequisites for optimum precipitation hardening can be precisely defined. However, the progress in the development of new alloys has been slow in the recent years. The original alloy is still in use today.     

粉末冶金法制取低铼钼合金的研究

研究了用粉末冶金法制取Mo－3％Re合金的工艺．结果表明．粉末冶金法可以制得性能良好的Mo－3％Re合金．在混和料的制备中采用湿混或干湿混合．有利于Re的均匀分布；且3％Re的加入，可大大细化钼合金的晶粒．     

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.     

钼合金粉末冶金研究进展

钼及其合金具有优异的高温力学性能，被广泛应用于冶金、机械、化工、航空和核工业等领域。粉末冶金是钼合金的主要制备方法。通过固溶强化、第二相强化、细晶强化等多种强化手段可以提高钼合金的力学性能，从而拓宽钼合金的应用范围。本文介绍了粉末冶金制备钼合金的研究进展，包括粉体制备方法、压制工艺及坯体烧结工艺等，讨论了钼合金的强韧化方法及其机理，并展望了粉末冶金法制备钼合金的发展方向，以期对钼合金的设计和制备提供一些思路。     

The Fracture Toughness and Toughening Mechanism of Commercially Available Unalloyed Molybdenum and Oxide Dispersion Strengthened Molybdenum with an Equiaxed,Large Grain Structure

Commercially available molybdenum and oxide dispersion strengthened (ODS) molybdenum produced by powder metallurgy (PM) methods were subjected to tensile testing, fracture toughness testing, and examination of the toughening mechanism. Both PM and ODS molybdenum have an equiaxed grain size that is larger in scale than comparable wrought products. This results in lower tensile strength and a higher tensile ductile-to-brittle transition temperature (DBTT) for PM and ODS molybdenum compared to wrought product forms. Although the grain size for PM molybdenum is large and the oxygen content is relatively high, both attributes tending to embrittle molybdenum, the transition temperature and fracture toughness values are comparable to those observed for wrought molybdenum. Crack initiation at grain boundaries and the center of grains where pores are present were observed to leave ligaments for the PM molybdenum that are similar in scale to those observed for wrought molybdenum. This is a similar toughening mechanism to the ductile laminate mechanism observed for wrought molybdenum. The larger oxide particle size for PM ODS molybdenum produces larger cracks that result in lower fracture toughness values and a higher DBTT in comparison to PM molybdenum. The impact of the grain size, grain shape, and oxide particles on the toughening mechanism and resulting properties is discussed.