EFFECT OF POROSITY ON THE FATIGUE BEHAVIOUR OF SINTERED PRECIPITATED NICKEL POWDER

Abstract

Groups of specimens with nominally 4% and 12% porosity have been prepared from fine (?240 + 300), medium (?200 + 240), and coarse (?150 ? 200) mesh sieve fractions of Sherritt-Gordon nickel powder by die compaction, preliminary sintering, re-pressing, and finally sintering at 1573K (1300°C). Irrespective of porosity content and the powder fraction from which they were prepared, all specimens exhibited a mixture of rounded and film-like porosity. The film-like porosity was more extensive in the more porous specimens, but in all specimens markedly influenced the fatigue behaviour. The development of persistent film-like porosity is attributed to the botryoidal form of the powder particles. The endurance limits of the less-porous specimens were almost identical, irrespective of the powder fractions from which they were prepared. However, the endurance limits of the more-porous specimens made from the coarse powder fraction were significantly lower than those made from the fine and medium powder fractions. The endurance limits of the less-porous specimens were much higher than those of the more-porous specimens and the endurance ratios were significantly higher. In all specimens, fatigue fractures were intergranular. The influence of film-like porosity on the fatigue behaviour is discussed.     

Fe-P-C-Cu-Mo系粉末合金的组织、性能及断口

研究了Fe-P-C-Cu-Mo系铁基粉末冶金材料中合金元素、烧结温度对合金组织及性能的影响,以及不同回火温度下磷的分布及其对合金断裂方式的影响。
通过研究得出:Fe-0.60%P-0-44%C-1.0%Cu-0.50%Mo合金在1160-1240℃烧结,保温1-2小时,可以获得较好的性能;若进一步经过850-900℃淬火,200℃或600℃回火,则合金的综合机械性能可以显著提高。通过试验发现:合金在200℃回火后,固溶在基体中的铝能抑制磷向晶界偏聚,使合垒断裂时呈现为穿晶断裂;400℃回火后,由于钼以碳化物形式析出,磷主要偏聚在晶界,造成合金沿晶断裂;600℃回火后,磷主要偏聚在孔隙表面,合金断口呈韧窝状。     

Fe—P—C—Cu合金的成分、组织与性能

在铁基粉末合金中,采取铁磷合金化,是改善和提高铁基粉末冶金制品的强度和韧性的有效方法之一。在Fe-P-C三元系合金的基础上添加一定量的铜元素,不仅可以减少合金的烧结收缩,而且能够进一步提高合金的机械性能。
本文着重讨论了Fe-P-C-Cu合金的成分、组织与性能之间的关系,研究了不同的铜含量、碳含量和烧结温度对合金的组织、机械性能及烧结收缩的影响规律。     

烧结金属过滤管法兰焊接强度测试

本文介绍了一种新型方法———“T”型支撑杆式测试多孔金属过滤管法兰焊缝强度 ,并从理论上推算出满足焊接强度要求的最小熔深值 ,结合强度测试结果和理论上溶深的最小值 ,判断焊缝质量 ,为焊接工艺和焊后处理工艺提供了参考     

SINTERED IRON-COBALT-MOLYBDENUM ALLOYS

Abstract

The magnetic properties and certain physical properties of sintered iron-cobalt-molybdenum alloys have been investigated, and a study made of the effect of processing variables, i.e. particle size, compacting pressure, sintering temperature and time. The compacting and sintering conditions which result in optimum properties have been determined. Consideration is also given to the influence on magnetic properties of variations in heat-treatment procedure, involving such factors as quenching temperature and media, ageing time and temperature, &c.

The substitution of ferro-molybdenum powder for elemental molybdenum powder reduces the cost of raw materials substantially without greatly diminishing the magnetic properties. Commercial powders with a normal particle-size distribution give good properties.

It was found that the alloys had somewhat better qualities than those made by casting.     

铝电解用铜基连杆材料的烧结致密化及其抗氧化性

为了获得致密的铝电解用铜基连杆材料,采用粉末冶金方法制备了Cu-Ni-Fe-Co合金材料,研究了该合金的烧结致密化过程及最佳致密度下该合金的抗氧化性能.结果表明:该合金的致密度随烧结温度的提高而提高,较低的烧结温度1 050℃难以实现致密化,但过高的烧结温度1 280℃容易使样品发生变形,烧结温度为1 250℃时能实现致密化且样品不发生变形;该合金的致密度随压制压力的增大有所提高,但超过600 MPa后,增幅趋于平缓.在较优的条件下可以制备出致密度为95.2%,晶粒尺寸为20～30 μm的合金,该合金力学性能良好,且在850℃空气中氧化动力学遵循抛物线规律,这证明合金表面形成了致密的复合氧化膜,随着反应时间的增加氧化膜具有保护作用.     

含镁、碱土金属复合合金的开发与炼钢应用（Ⅰ）

研究了镁、碱土金属与各化学元素的相互作用机理，含镁、碱土含量复合合金的制取因素，合金的制取条件和方法。比较了含镁、碱土含量复合合金冶炼的几种工艺流程和热力学，动力学因素，并指出了各自存在的缺点与优点。得到了开发含镁，碱土金属复合合金的最佳工艺和参数。     

THE MECHANICAL PROPERTIES OF HOT-RECOMPACTED IRON-NICKEL SINTERED ALLOYS

Abstract

Powder-metallurgy components which are to withstand high dynamic stress are frequently required to possess both high strength and great toughness. This combination of properties can best be achieved by increasing the density of the sintered component and one method of doing so is bot pressing.

This paper deals with the mechanical properties of sintered iron–nickel alloys produced by hot compacting in six stages, as follows:

(1) Preparation of the powder mix.

(2) Production of compacts under a pressure of 8 Mp/cm²

(3) Heating the compacts to 1000°C (1275 K).

(4) Re-pressing the hot compacts in a die heated to 300°C (575 K).

(5) Cooling in air.

(6) Sintering at optimum temperature and time under optimum furnace conditions.

The investigation covered the dependence of tensile strength, elongation at fracture, and Brinell hardness of alloys with Ni contents of 1–10% on the sintering temperature and time, on the furnace conditions, and on raw-material variables.

It was found that Fe–Ni powder-metallurgy parts with a maximum tensile strength of ～60 kp/cm² could be produced. The Brinell hardness reached 190 kp/mm² with 10% Ni content. Elongation at fracture was in the region of 45% with 1% Ni and remained comparatively satisfactory even with high Ni contents if very pure raw materials were used. Powder-metallurgy materials with a tensile strength of 60 kp/cm² and an elongation at fracture of 17% can be obtained by the process.     

烧结钕铁硼的力学性能研究现状

分析了烧结钕铁硼呈脆性的原因，介绍了烧结钕铁硼的力学性能研究现状以及研究烧结钕铁硼力学性能的重要性。     

钼顶头破坏行为及强韧化分析

通过对钼顶头破坏行为的分析，说明了钼顶头破坏的主要原因。并进一步通过对钼顶头强韧化的分析，阐述了钼顶头延长使用寿命的措施，并制定了钼顶头生产工艺。     

DIMENSIONAL CHANGES OF SINTERED Fe-Ni,Fe-Cu,Fe-Ni-Cu ALLOYS

Abstract

Sintered alloys of the Fe-Ni, Fe-Cu, and Fe-Ni-Cu systems have been investigated by using single-pressing, double-pressing and hot-forging techniques. Different iron powders containing 0-6 wt.-% nickel or 0-5 wt.-% copper, also (for the ternary system) 0-5 wt.-% of both nickel and copper, were compacted and sintered and the effect of the additions on dimensional changes was studied. The influence of particlesize, compacting pressure, sintering temperatures, and furnace type on dimensions has been determined.     

SINTERED IRON-BASE ALLOYS WITH HIGH STRENGTH USING SELECTED NITRIDES AND SILICIDES

Abstract

The techniques used in alloying in iron powder metallurgy have been extended by employing special compounds. The introduction of the alloying elements in this form and the decomposition of selected nitrides and silicides are described. Elements that oxidize readily at high temperatures (e.g. Cr, Si) can be added in a relatively pure and homogeneous state. These elements stabilize the α phase and thus improve the sintering behaviour.

The paper deals mainly with the preparation of binary Fe-Cr, Fe-Si, and also ternary Fe-Cr-Si alloys obtained by ‘in situ’ decomposition of Si₃N₄, Cr₂N, and CrSi₂ in an iron matrix (WP-150).

The study covers the properties of the powders and their mixtures, the pressing and sintering conditions, the sintering behaviour in the range 1000–1300°C with varying alloying additions, for different sintering times and atmospheres. The tensile strengths observed are ～525 N/mm² at a densityof 6·7 g/cm³, with ～3% elongation at fracture. With respect to the low density and the carbon free state of the alloys, the strength values may be considered as rather high. A study of the homogenization process is being carried out.     

对粉冶TZC合金钼顶头高温强度影响因素分析

着重从粉冶ＴＺＭ及ＴＺＣ合金钙顶头的合金化元素及热处理制度方面进行了分析和探讨，以便进一步提高粉冶ＴＺＭ及ＴＺＣ合金钼头的耐高温强度。     

粉末冶金高强度烧结钢的疲劳特性

通过测定N-110烧结钢旋转弯曲疲劳下的S-N曲线、疲劳裂纹扩展速率da/dN以及疲劳门坎△K_th,对烧结材料的疲劳特性进行了探讨,初步阐明了孔隙的存在对各种疲劳性能的影响规律以及热处理状态与疲劳性能之间的关系。     

在分解氨气氛中烧结Fe-C系时反应的热力学分析

本文通过热力学分析得出:在烧结过程中H₂与石墨难以形成CH₄,但易从Fe₃C中夺取C;分解氨作为烧结铁基材料的保护气氛是一种脱碳性气氛。
本文试图通过热力学分析,弄清分解氨作为铁基粉末冶金烧结保护气氛在烧结过程中可能发生的化学反应及其对烧结材料的影响,从而进一步认识分解氨气体的特性。     

表面滚压强化对粉末冶金烧结钢疲劳强度的影响

表面强化是提高粉末冶金烧结钢疲劳性能的有效途径。对N-110高强度烧结钢进行表面滚压强化后的疲劳试验结果表明,表面滚压强化可以大幅度提高疲劳极限。     

ON THE BEHAVIOUR OF SOME SULPHUR COMPOUNDS ADDED TO SINTERED IRON-BASED FRICTION MATERIALS

Abstract

The results of previous studies of frictional properties of sintered iron-based brake linings containing additions of graphite, molybdenum disulphide, lead, corundum (Al₂O₃), and barytes (BaSO₄) are summarized.

Interpretation of qualitative topography and of quantitative analysis by means of electron-microprobe analysis supports the idea of the formation of BaAl₂O₄ in the regions of direct contact between BaSO₄ and Al₂O₃.

Further results concerning the behaviour of sulphur, obtained by means of electron-microprobe analysis, are also discussed.     

HIGH-STRENGTH SINTERED IRON-BASE ALLOYS BY USING TRANSITION METAL CARBIDES

Abstract

A simple method of producing alloy steels by mixing, pressing, and sintering iron powder with carbides of transition metals is described. The carbides must have a high carbon content and be soluble in iron. These characteristics are found in the carbides of chromium, tungsten, molybdenum, and vanadium. Tensile strengths of ～800 N/mm² have been achieved in annealed specimens having carbide additions of 1–12 wt.-%, depending on the carbide. The additions produce steels with partly air-hardening properties.

The effects of concentration and particle size of the carbides, sintered density, sintering conditions, and cooling rate on mechanical properties have been determined. The alloys are not very sensitive to the sintering atmosphere. The effect of heat-treatment on the mechanical properties of Fe-Cr₃C₂ alloys is reported. A tensile strength >1300 N/mm² was observed with 4 wt.-% Cr₃C₂. Dilatometric measurements were conducted with different carbide concentrations and heating conditions to study the sintering process. The important process of homogenization was investigated by electron microprobe analysis.     

TURNING AND DRILLING OF SOME TYPICAL SINTERED STEELS

Abstract

Turning and drilling tests have been carried out on nine different materials.

The most critical factor in turning is the breakouts at the corners of the test-specimen, especially at low densities. These can be eliminated by adopting a lower feed and smaller depth of cut. The best surface finish is achieved with the highest possible speed and low cut depth. Alloying iron with 0·5% sulphur resulted in the lowest recorded specific cutting force, a good surface finish, and the longest tool life attained. The density had no influence on the tool wear.

Tool life in drilling can be improved considerably by using: (a) a 40° helix angle for soft power-metallurgy materials; (b) extra-short drills. Burrs can be eliminated by shortening the chisel edge or increasing the point angle to 185°. The use of sulphur-alloyed iron resulted in a tool life many times higher than that for plain iron of the same density.

Machining recommendations are given for turning and drilling the various materials.     

铝活化烧结钨的组织形貌和性能分析

本文通过实验探讨了铝对钨的活化烧结行为,并应用扫描电镜(SEM)分析了样品组织形貌,结果表明,由于Al的加入使钨的致密度得到显著提高。